–10 dB Most consumer and lower-cost professional audio equipment use a signal level reference known as line level or –10dBV (decibel volts). The most common connectors are RCA (phono) or 3.5mm , although 1/4” is also used; the signal is “unbalanced” (it uses two wires: signal and ground). In the line level standard, a sine wave that varies between +/–0.447 volts is considered to be at –10dBV. By contrast, a typical oscillator signal in a modular synthesizer is +/–5 to +/–8 volts. As a result, you will need either an output module in your modular synth or one heckuva input attenuator on your mixer or recorder to plug your synth into equipment that runs at line level. Similarly, you will need to substantially boost a line level signal to get it up to modular standards to process in your modular synth.

(Normalized) The power of modular synthesizers is that you can patch a signal to flow the way you prefer through your system. This can also be a time-consuming bummer when you’re just trying to patch a “typical” signal flow. Therefore, some manufacturers have created “ semi-modular ” synths that have all of these typical connections pre-wired for you, with the important feature that many of these wirings can be overridden by inserting patch cables into the correct jacks. These pre-wired connections are often referred to as being normalled . For example: An internal noise source may normally be connected to one channel of a mixer that appears before the filter , but if you insert a patch cable into a jack usually labeled external input, this “normalled” connection is broken and replaced by your external connection.

0–5v Denotes a range of 0 to 5 volts, which is common for gates, triggers, and modulation control voltages in modular synthesizers. Gates and triggers – which initiate events such as new notes – typically rise from 0v to 5v (0 to 10v is also common), with roughly the middle of that onset starting the event. Gates are considered high when held at 5v (or 10v), and then low when they return to 0v. Click for more details.

1/8” Often used to incorrectly describe the connector size commonly used in Eurorack format modules, as well as Buchla audio signals. In fact, Eurorack modules use 3.5mm jacks and plugs (slightly larger than 1/8” ); Buchla uses Switchcraft Tini-Jax connectors. Tini-Jax are 3.5mm in diameter, but are slightly different physically from a common 3.5 mm jack. 1/8” plugs would be loose in both of these jacks, so make sure you get 3.5mm connectors ordering parts or cables for these formats.

1 ppqn The most common sequencer clock division forwards it one step pulse ) per quarter note. This is often the core sync pulse that is distributed in a modular system, and is either multiplied or divided to create other musical divisions.

1 v/oct The most common standard for controlling pitch in a modular synthesizer. Under the system, increasing the voltage going into a VCO (Voltage Controlled Oscillator) 1 volt – say, from 0.5v to 1.5v – would raise its pitch by one octave . Click for more detail.

1/4” The most common connector size used for 5U Moog format) modular synthesizers. These are TS (tip/sleeve) jacks and plugs, similar to guitar and other instrument cables.

1 pole This format of numbers and abbreviations (dB/oct = decibels per octave) is often used to refer to the frequency response behavior of a filter. A filter typically has a cutoff or corner frequency it is tuned to. It then reduces (filters) the frequency spectrum of a signal going through it so that its loudness is multiples of 6 decibels weaker for each octave further away you get from the cutoff frequency. A 6dB/octave filter is often referred to as a “ one pole ” filter (as each pole of a filter’s design results in 6dB of attenuation), and has a relatively weak effect on the signal going through it. Low Pass Gates ( LPGs ) typically – but not always – use 1 pole low pass filters, reducing the strength of higher harmonics by 6 decibels for every octave above its cutoff frequency.

2’ Sometimes seen on octave selector switches for oscillators. It refers to the length of an organ pipe. Shorter pipes = higher pitches; 2’ is rarely seen on modular oscillators as it’s rather high in pitch – two octaves above middle C as a starting point. A pipe or setting twice as long ( 4’ ) is one octave lower; a pipe twice as long again ( 8’ ) is two octaves lower; etc.

2 Pole This format of numbers and abbreviations (dB/oct = decibels per octave) is often used to refer to the frequency response behavior of a filter. A filter typically has a cutoff or corner frequency it is tuned to. It then reduces (filters) the frequency spectrum of a signal going through it so that its loudness is multiples of 12 decibels weaker for each octave further away you get from the cutoff frequency. A 12dB/octave filter is often referred to as a “ two pole ” filter (as each pole of a filter’s design results in 6dB of attenuation). Vintage Arp, Korg, and Oberheim instruments often featured 2-pole filters, often resulting in brighter sounds when compared to those with 4-pole instruments.

2.5 mm A common screw thread size used to mount Eurorack modules. This size is most common when using a system of loose nuts that slide along the rails that the modules are attached to.

3 Pole This format of numbers and abbreviations (dB/oct = decibels per octave) is often used to refer to the frequency response behavior of a filter. A filter typically has a cutoff or corner frequency it is tuned to. It then reduces (filters) the frequency spectrum of a signal going through it so that its loudness is multiples of 18 decibels weaker for each octave further away you get from the cutoff frequency. It is often used a coded shorthand for when someone wants to refer to acid-type bass lines from a TB- 303 without mentioning the instrument by name. Click for more details.

3 mm A common screw thread size used to mount Eurorack modules. This size is most common when using module mounting rails that have been pre-drilled.

3U Refers to modules that are 3 rack units ( U ) high – the Eurorack standard, which is by far the most common modular format today, even though it’s one of the youngest formats.

3.5 mm The standard connector size used for jacks and cables in Eurorack format modular synthesizers. Note that this is slightly larger that 1/8”. Click for more details.

4’ Sometimes seen on octave selector switches on oscillators. It refers to the length of an organ pipe. Shorter pipes = higher pitches; 4’ is the highest octave setting you will see on most oscillators. A pipe or setting twice as long (8’) is one octave lower; a pipe twice as long again ( 16’ ) is two octaves lower; etc.

+4 dB This describes the reference used for professional level audio signals. Although it is higher than the more common line level (3.473 volts peak to peak compared to 0.895 volts), it is still not as high as the level used inside many modular synthesizers these days (10 volts ore more peak to peak). As a result, you will often need to attenuate (turn down) a modular signal plugged into a +4dB input, and turn up a +4dB audio signal fed into a modular synth – by a large amount.

4-40 A screw thread size occasionally used to mount Eurorack modules. This size is used by Pittsburgh Modular for their cases, for example.

4U Refers to modules that are 4U (rack units) high – namely, Buchla and Serge systems, as well as do-it-yourself clones of these modules. Both Buchla and Serge lean toward a more experimental approach to synthesis and music, so some users wear “4U” as a badge of honor that they’re non-conformist and cool. (And they are.)

4 Pole This format of numbers and abbreviations (dB/oct = decibels per octave) is often used to refer to the frequency response behavior of a filter. A filter typically has a cutoff or corner frequency it is tuned to. It then reduces (filters) the frequency spectrum of a signal going through it so that its loudness is multiples of 24 decibels weaker for each octave further away you get from the cutoff frequency. This design is often used in vintage Moog and Roland synths. 4-pole filters are often associated with subjectively fatter, more “round” sounds than 2-pole filters – but generalizations are always dangerous.

5U Refers to modules that are 5U (rack units) or 8.75” (22.2 cm) high, which is most often associated with the vintage Moog standard and those who have followed in their footsteps, including Synthesizers.com (Dotcom) and Moon Modular. You will sometimes hear this used interchangeably with MU for Moog Units, which also refers to a standardized width of 2.125” (5.4 cm) wide per MU. Given that this standard is both historical and physically large, some users “5U” as a badge of honor that they’re traditional and cool. (And the are.) There was also a briefly popular 5U format from MOTM that used a different width and power connection. It has since been discontinued, but there are still diehard MOTM format users today.

6 dB/oct This format of numbers and abbreviations (dB/oct = decibels per octave) is often used to refer to the frequency response behavior of a filter. A filter typically has a cutoff or corner frequency it is tuned to. It then reduces (filters) the frequency spectrum of a signal going through it so that its loudness is multiples of 6 decibels weaker for each octave further away you get from the cutoff frequency. A 6dB/octave filter is often referred to as a “one pole” filter (as each pole of a filter’s design results in 6dB of attenuation), and has a relatively weak effect on the signal going through it. Low Pass Gates (LPGs) typically – but not always – use 1 pole low pass filters, reducing the strength of higher harmonics by 6 decibels for every octave above its cutoff frequency.

6P1 Korg collaborated with Noritake Itron Corporation to repurpose a compact fluorescent display into a micro-sized triode tube . Click through for a link to learn more.

8’ Sometimes seen on octave selector switches on oscillators. It refers to the length of an organ pipe. Shorter pipes = higher pitches; 8’ is typically associated with middle C. A pipe or setting half as long (4’) is one octave higher; a pipe or setting twice as long (16’) is one octave lower.

10 vpp An abbreviation for " 10 volts peak to peak " with peak to peak being the difference between the lowest and highest voltage reached during a signal's travels. This is a common voltage range for both audio and modulation signals in a modular synthesizer. The actual range is between –5 and +5 volts. See my diatribe above in the definition of 0–5v : The precise range may be varied to change the depth of their effect, so don’t get too hung up on specific voltage ranges. Pay more attention to whether they vary between 0v and some value, or swing in roughly equal amounts both above and below 0v (as 10vpp does).

12 dB/oct This format of numbers and abbreviations (dB/oct = decibels per octave) is often used to refer to the frequency response behavior of a filter. A filter typically has a cutoff or corner frequency it is tuned to. It then reduces (filters) the frequency spectrum of a signal going through it so that its loudness is multiples of 12 decibels weaker for each octave further away you get from the cutoff frequency. A 12dB/octave filter is often referred to as a “two pole” filter (as each pole of a filter’s design results in 6dB of attenuation). Vintage Arp, Korg, and Oberheim instruments often featured 2-pole filters, often resulting in brighter sounds when compared to those with 4-pole instruments.

16’ Sometimes seen on octave selector switches on oscillators. It refers to the length of an organ pipe. Longer pipes = lower pitches; 16’ is in the mid-bass range. A pipe or setting half as long (8’) is one octave higher; a pipe half as long again (4’) is two octaves higher; etc.

18 dB/oct This format of numbers and abbreviations (dB/oct = decibels per octave) is often used to refer to the frequency response behavior of a filter. A filter typically has a cutoff or corner frequency it is tuned to. It then reduces (filters) the frequency spectrum of a signal going through it so that its loudness is multiples of 18 decibels weaker for each octave further away you get from the cutoff frequency. It is often used a coded shorthand for when someone wants to refer to acid-type bass lines from a TB-303 without mentioning the instrument by name. Click for more details.

24 ppqn A common master clock division used in MIDI DIN sync , and other systems common to electronic music and synthesizers. It means internally, 24 subdivisions of time are counted for every quarter note at the current tempo. This fast internal clock can then be divided down to create sixteenth notes (÷6), eighth notes (÷12), eight note triplets (÷8), etc.

24 dB/oct This format of numbers and abbreviations (dB/oct = decibels per octave) is often used to refer to the frequency response behavior of a filter. A filter typically has a cutoff or corner frequency it is tuned to. It then reduces (filters) the frequency spectrum of a signal going through it so that its loudness is multiples of 24 decibels weaker for each octave further away you get from the cutoff frequency. This design is often used in vintage Moog and Roland synths. 4-pole filters are often associated with subjectively fatter, more “round” sounds than 2-pole filters – but generalizations are always dangerous.

32’ Sometimes seen on octave selector switches on oscillators. It refers to the length of an organ pipe. Longer pipes = lower pitches; 32’ is the lowest setting you will see and is getting into earthquake territory. A pipe or setting half as long (16’) is one octave higher; a pipe half as long again (8’) is two octaves higher; etc.

A-440 This is the frequency in hertz (cycles per second) of the A above Middle C. It is often used as a tuning reference.

AC In modular terms, AC refers to a voltage that alternates between positive and negative values – such as the output of an oscillator.

AC Coupled An AC coupled input attempts to remove any constant DC voltage going through it. This is useful if have an audio signal (such as the output of an oscillator) which is AC in nature, and you want to remove any accidental DC offset that might have crept into it. These offsets can cause one half of the AC waveform to clip prematurely, or can cause clicks at the start and end of envelopes or mutes. However, this coupling can mildly distort a wave going through it, as in essence AC coupling is a high pass filter that is attempting to remove very low frequency components. Click through for a link to a good technical article on the subject.

Active Multiple Quite often you need to split or copy a signal to send to more than one destination. This is commonly done with a multiple, where you plug one source in, and then plug in additional patch cables to go off to multiple destinations. An active or buffered multiple is one that includes a buffer circuit between the input and output, making sure the signal does not lose its strength or integrity by being split too many times, and that no funny business happening on one of the outputs affects any of the other connections. Some modules have good buffering built into their outputs, and can drive multiple modules without issue. But if you try to use a passive mult to connect to, say, three oscillators, and you realize the tracking isn't very good (they quickly go out of tune as you go up and down the scale), then you need a buffered mult instead. Click through for more technical details.

AD Attack/ Shorthand for a two- stage Decay envelope. This simple envelope shape raises from 0 volts to its maximum level (typically 5, 8, or perhaps 10 volts) at a speed defined by its Attack parameter , and then immediately falls back to 0 volts at a rate defined by its Decay parameter. A variation on this is the AHD envelope: After finishing the Attack stage, it holds at the maximum level for a specified amount of time (in contrast to an AR envelope, which holds at the maximum level for as long as the note on gate is high), and then decays back to zero. I have heard there are some envelopes that a hybrid of AHD and AR in that they hold the maximum level for either the defined Hold time or the as long as the incoming gate is high; let me know in the comments if you have a specific example.

Additive Synthesis One of the main properties that make a sound unique is the mixture of harmonics – pure component frequencies – that it is built from. Additive synthesis is a technique that gives you direct control over each of those component harmonics, allowing you to directly dial in the mix you want. As immediate and intuitive as that sounds on paper (or on screen), in reality it takes a lot of work to craft the correct mixture to recreate another sound, especially since the strength of each harmonic usually varies over time. Additive synthesis oscillators are relatively rare in modular synths; two examples are the Verbos Harmonic Oscillator and the Make Noise tELHARMONIC.

ADSR An envelope generator with four stages: Attack, Decay, Sustain , and Release . When this envelope generator receives a gate input, it typically starts at 0 volts (which is the equivalent of silence when connected to a Voltage Controlled Amplifier , or the lowest frequency when connected to a voltage controlled filter or oscillator) and raises to the maximum voltage it can output (typically 5 to 10 volts depending on system; it can often be set with an output level control) over a time set by the Attack control. Once it reaches that level, the output voltage immediately starts dropping to speed set by the Decay control it until it reaches the voltage set by the Sustain control. If the input gate is still active, this level is maintained until the gate goes back to 0 volts (usually because you released the key on a controlling keyboard, etc.). At that time, the output voltage then starts dropping back to 0 volts at the rate set by the Release control. Click for more about variations in ADSR behaviors.

AFG The AFG (Audio Frequency Generator) is a very full-featured analog oscillator released by Livewire Electronics. It has since been discontinued, but refurbished B-stock units come up for sale every now and then. The expansion modules were, to the best of my knowledge, never released (at least not widely). Yes, it uses two power connectors. No, I haven't seen a manual for it yet.

Aftertouch Some keyboards measure how hard you press down on the keys, and convert this to a voltage (or other control signal such as MIDI, which can then be converted into a control voltage ) that you can use to add expression to a note, such as adding vibrato or opening the filter wider. Monophonic aftertouch measures one pressure value for the entire keyboard, regardless of which key(s) you are pressing; polyphonic aftertouch produces a signal for each individual key. Important trivia: Touch plate keyboards actually measure the surface area of the skin touching them rather than pressure or force – so you can increase or decrease the aftertouch amount by rolling between the tip and length of your finger.

AHDSR This is a slightly fancier ADSR envelope that holds the voltage typically at its maximum value for a specified time after the attack is done rising and before the decay starts falling.

Algorithm The different synthesis techniques that may be coded inside a software-based module is often referred to as the module's algorithms . Click through for a few examples.

Aliasing If you play back a digital audio file where half of the sample rate is an audible pitch, you will also hear a mirror image of the sound’s harmonic content reproduced started at that half-sample-rate pivot (unless some excellent filtering has taken place). Click for more details.

Alternating Current In modular terms, AC refers to a voltage that alternates between positive and negative values – such as the output of an oscillator.

AM Amplitude Modulation ( AM ) is the name given the to the technique of varying the amplitude or loudness of one signal known as the carrier (typically an audio signal, swinging both above and below 0 volts) with a second signal called the modulator . In the typical amplitude modulation (AM) scenario, a low frequency oscillator with a positive voltage (say, between 0v and 5v, or maybe something smaller such as between 1v and 2v) is fed into the control input of a voltage controlled amplifier to add vibrato to an audio signal passing through it. Technically, this is known as a two-quadrant multiplier or modulator, as any negative swings in the modulation signal are ignored; when patching tremolo , you may need to make sure an offset voltage is being added to your LFO to make sure the sound doesn’t cut out on the lower excursions of the LFO’s waveform. Click for more detail.

Amplitude Modulation Amplitude Modulation (AM) is the name given the to the technique of varying the amplitude or loudness of one signal known as the carrier (typically an audio signal, swinging both above and below 0 volts) with a second signal called the modulator. In the typical amplitude modulation (AM) scenario, a low frequency oscillator with a positive voltage (say, between 0v and 5v, or maybe something smaller such as between 1v and 2v) is fed into the control input of a voltage controlled amplifier to add vibrato to an audio signal passing through it. Technically, this is known as a two-quadrant multiplier or modulator, as any negative swings in the modulation signal are ignored; when patching tremolo, you may need to make sure an offset voltage is being added to your LFO to make sure the sound doesn’t cut out on the lower excursions of the LFO’s waveform. Click for more detail.

Analog The term analog implies a signal is continuously variable, compared to digital where a signal has been converted into discrete numbers. In the land of modular synthesizers, analog refers to a circuit design that has no digital (or at least, computer-based) components – instead, it does all of its processing using transistors, diodes, capacitors, and the such rather than CPUs and DSPs. Click for some editorializing.

Analog OR An “analog OR” or “maximum” circuit looks at one or more incoming control voltages, and outputs just the highest value. The output of an analog OR can never be higher than the highest of value of any incoming voltage. This is a particularly good way to combine two envelopes, such as one with a fast attack and decay, and one with a slow attack.

Analog Shift Register An Analog Shift Register (ASR) is a cross between a Sample & Hold module and a Bucket Brigade Delay (assuming you already know how those work). When initially triggered, it samples the incoming voltage, and presents that at its first output. On the second trigger , the incoming voltage is sampled again with this new voltage presented at the first output, while the original voltage is now moved to a second output. This game of "telephone" is passed along for as many stages as the ASR has – traditionally three or four. Click through for more history as well as links and sources.

AND function One of the most common Boolean or binary logic functions , AND says only output a gate on signal if all of the inputs see “high” gate signals (i.e. input 1 and input 2 etc. all have gate ons). A NAND function has an inverted output: The output would be low if both inputs were high, but otherwise would be high.

AR The two-stage Attack/Release envelope raises from 0 volts to its maximum level (usually 5, 8, or maybe even 10 volts) at a rate set by its Attack parameter, and then stays at that value for as long as the gate signal fed into the envelope generator stays high. Then when the gate signal goes back to zero, the envelope's output also falls back to zero at a rate set by its Release parameter. (There is a separate type of envelope known as an AHD – Attack/Hold/Decay – where you specify a fixed time for the level to stay at its maximum, rather than pay attention to the gate signal.)

Arpeggiator Putting on our music theory hat for a second, an arpeggio is a type of “broken chord” where the notes are played individually rather than all at once. An arpeggiator – usually built into a keyboard, or a device inserted between your keyboard and sound module – makes it easier for you to play arpeggios: You just hold down the notes of the chord, and it automatically plays the notes one at a time, over and over again, like a step sequencer you can program on the fly just by holding down a chord. Good arpeggiators have options for different patterns (up, down, back and forth, random , etc.), and even a latch or hold where it will keep doing this even after you’ve released the keys.

Articulate The details of playing a note – how forcefully you play it, as well as any inflections you may insert while playing that note – is known as how you " articulate " a note.

ASR An Analog Shift Register (ASR) is a cross between a Sample & Hold module and a Bucket Brigade Delay (assuming you already know how those work). When initially triggered, it samples the incoming voltage, and presents that at its first output. On the second trigger, the incoming voltage is sampled again with this new voltage presented at the first output, while the original voltage is now moved to a second output. This game of "telephone" is passed along for as many stages as the ASR has – traditionally three or four. Click through for more history as well as links and sources.

Attack This usually refers to the first stage of an envelope that occurs at the onset of a note, as it rises from 0 volts (silence when if controlling an amplifier module) to typically the value of maximum loudness. Percussive and plucked sounds have very fast attacks; slow, languid wind or string instrument phrases may have long attacks.

Attack/Decay Shorthand for a two-stage Attack/Decay envelope. This simple envelope shape raises from 0 volts to its maximum level (typically 5, 8, or perhaps 10 volts) at a speed defined by its Attack parameter, and then immediately falls back to 0 volts at a rate defined by its Decay parameter. A variation on this is the AHD envelope: After finishing the Attack stage, it holds at the maximum level for a specified amount of time (in contrast to an AR envelope, which holds at the maximum level for as long as the note on gate is high), and then decays back to zero. I have heard there are some envelopes that a hybrid of AHD and AR in that they hold the maximum level for either the defined Hold time or the as long as the incoming gate is high; let me know in the comments if you have a specific example.

Attack/Decay/Sustain/Release An envelope generator with four stages: Attack, Decay, Sustain, and Release. When this envelope generator receives a gate input, it typically starts at 0 volts (which is the equivalent of silence when connected to a Voltage Controlled Amplifier, or the lowest frequency when connected to a voltage controlled filter or oscillator) and raises to the maximum voltage it can output (typically 5 to 10 volts depending on system; it can often be set with an output level control) over a time set by the Attack control. Once it reaches that level, the output voltage immediately starts dropping to speed set by the Decay control it until it reaches the voltage set by the Sustain control. If the input gate is still active, this level is maintained until the gate goes back to 0 volts (usually because you released the key on a controlling keyboard, etc.). At that time, the output voltage then starts dropping back to 0 volts at the rate set by the Release control. Click for more about variations in ADSR behaviors.

Attack/Hold/Decay/Sustain/Release This is a slightly fancier ADSR envelope that holds the voltage typically at its maximum value for a specified time after the attack is done rising and before the decay starts falling.

Attack/Release The two-stage Attack/Release envelope raises from 0 volts to its maximum level (usually 5, 8, or maybe even 10 volts) at a rate set by its Attack parameter, and then stays at that value for as long as the gate signal fed into the envelope generator stays high. Then when the gate signal goes back to zero, the envelope's output also falls back to zero at a rate set by its Release parameter. (There is a separate type of envelope known as an AHD – Attack/Hold/Decay – where you specify a fixed time for the level to stay at its maximum, rather than pay attention to the gate signal.)

Attenuverter A special version of an attenuator that can also invert the polarity of the signal or voltage going through it. Most attenuverters use pass through no signal at their center position; as you turn them clockwise , you turn up the normal version of the signal; as you turn them counterclockwise, they turn up an inverted version of the signal. Some attenuverters are a normal attenuator with a polarity switch added on.

Audio Frequency Generator The AFG (Audio Frequency Generator) is a very full-featured analog oscillator released by Livewire Electronics. It has since been discontinued, but refurbished B-stock units come up for sale every now and then. The expansion modules were, to the best of my knowledge, never released (at least not widely). Yes, it uses two power connectors. No, I haven't seen a manual for it yet.

Balanced Audio This refers to a system where three wires are used to carry an audio signal: one is the ground (the 0 volt reference), the second carries the audio signal as it varies above and below 0v, and the third carries an inverted copy of the audio signal that goes negative while the original is going positive. Balanced audio usually implies a reference signal level of +4dB (higher than line level; still lower than most modular synths), although microphone signals – much weaker by comparison, and therefore more susceptible to outside noise – are almost always balanced as well. Modular synths tend to use unbalanced audio for their internal signals. If you require a balanced output (or input), you need a special module that converts between balanced and unbalanced audio, plus does any necessary level matching.

Balanced Modulator Balanced or ring modulation is a special type of amplitude modulation, where one bipolar (swinging both above and below 0 volts) signal – the modulator – is used to vary the amplitude of a second bipolar signal, known as the carrier. The modulator’s frequency is both added to and subtracted from the carrier’s frequency; the resulting harmonics replace the original carrier and modulator. Click for more details.

Banana An alternate type of connector (https://en.wikipedia.org/wiki/ Banana _connector) used by 4U systems such as Buchla (control voltages) and Serge (both control and audio). These cables have only one wire, so they carry only the signal, relying on the module panels and chassis of the system to provide the ground reference. Banana connectors have an advantage in that they are usually “ stackable ” meaning you can plug a one jack into the back of another, providing a passive multiple.

Bandpass Filter bandpass filter (BPF) leaves the harmonics around the center, corner or cutoff frequency untouched, and attenuates those above and below the center frequency. The further away you get from the center, the more they are attenuated, based on the number of poles in the filter, with each pole equalling 6 decibels of attenuation for each octave you get away from that center.

Bark Scale The human auditory (hearing) system can be thought of as consisting of a series of bandpass filters. Interestingly, the spacing of these filters do not strictly follow either a linear frequency scale or a logarithmic musical scale. The Bark Scale is an attempt to determine what the center frequency and bandwidth of those "hearing filters" are (known as critical bands). Click through for a few more details and technical links.

BBD An early design for an echo or delay effect where the input audio would be sampled as an analog voltage, and held for a brief moment. Then at the next above-audio sample rate clock pulse, this voltage would get passed to the next sample and hold (bucket) in the circuit, while a new level was sampled. Bucket brigade delays (BBDs) usually have numbers of stages or buckets that are powers of two (256, 512, 1024, 2048, etc.); the delay length is determined by the number of stages multiplied by the time interval between samples. Click for more about the downsides of BBDs.

Beating When two oscillators are tuned to very nearly – but not quite – the same frequency, the difference between them causes an interference pattern known as beating . When the difference in frequency is below the audio rate, this can sound like a tremolo applied to the loudness of the combined sound. Click for more.

Beats Per Minute BPM (beats per minute) is the most common way of stating tempo: How many beats (typically, quarter notes) should be counted every minute. A tempo of 120 beats per minute means there would be two beats every second (120 beats/minute x 1 minute/60 seconds = 2).

Berlin School A particular style of electronic music popularized by the likes of Tangerine Dream and Klaus Schulze based on analog synthesizers, heavy on repetitive sequences and floating chords or drones with solos played on top. More recent versions of Berlin School music can be heard from Node and Red Shift.

Bi-N-Tic filter In a switched capacitor design, capacitors are switched in and out of the circuit at high speeds to create the average "C" required in a typical RC filter circuit to produce the desired cutoff frequency. In some module designs, the frequency of the high speed clock used to switch the capacitors are in and out can be audible as its own pitch, creating aliasing -like artifacts.

Binary A cornerstone of digital systems is the binary counting method, where each digit can have only two different values: 0 or 1; off or on; low or high. A binary signal can only have one of these two states. Therefore, a gate or trigger signal in a modular synth – even if generated by analog circuitry – could be referred to as a binary type signal. See the entry for Boolean for things you can do with binary signals like gates and divided clocks.

Bipolar No, not a disorder that afflicts synthesists who have a love/hate relationship with their instrument! A voltage that can range both above and below zero is referred to as bipolar. Some modulation signals inside a modular synth – such as vibrato (varying the pitch of an oscillator both above and below the note it is supposed to be playing) – are bipolar in nature.

Blue Noise Technically, a type of noise whose power density (spectral loudness) increases 3 dB per octave with increasing frequency. It has a very “hissy” characteristic, lacking in bass. Click for a link with examples.

Boolean Boolean is a fancy way of saying binary. Boolean logic can have only two states: high or low; 1 or 0; on or off. Click for more details.

BPF A bandpass filter (BPF) leaves the harmonics around the center, corner or cutoff frequency untouched, and attenuates those above and below the center frequency. The further away you get from the center, the more they are attenuated, based on the number of poles in the filter, with each pole equalling 6 decibels of attenuation for each octave you get away from that center.

BPM BPM (beats per minute) is the most common way of stating tempo: How many beats (typically, quarter notes) should be counted every minute. A tempo of 120 beats per minute means there would be two beats every second (120 beats/minute x 1 minute/60 seconds = 2).

Brown Note Bass, how low can you go? The mythical brown note is so low (some say 5-9 Hz – well below human hearing) that it sets up a resonance in that body that causes a person to lose control of their bowels.

Brownian Noise Also referred to as brown noise , technically it’s a type of noise whose power density (spectral loudness) decreases 6 dB per octave with increasing frequency. It has a bass-heavy sound, akin to the sound of the surf at a distance. It can also be used a slowly changing random control voltage or modulation signal, instead of as an audio source.

Buchla Buchla (founded by Don Buchla) was one of the first manufacturers of modular synthesizers. They tend to be associated with a more experimental approach to synthesis and composition. For example, almost all of their instruments do not have a normal keyboard controller, replacing the keys with touch plates in various configurations that are often freely programmable rather than being assigned to triggering a specific note. Some refer to the “ West Coast Synthesis ” approach when talking about Buchla instruments. Morton Subotnick is one of the earliest composers to demonstrate the power of the Buchla instrument.

Buchla Bongos This is a classic patch where a complex sound source – such as one oscillator frequency modulating another – is sent through a Low Pass Gate with either just a trigger to “ strike ” the vactrol inside or otherwise an instant attack/fast decay envelope to create a nice percussive sound. The fact that the low pass gate reduces the higher harmonics as its volume dies away helps tame the harmonics coming from the complex source, and give it a decay similar to a struck percussive instrument.

Bucket Brigade Delay An early design for an echo or delay effect where the input audio would be sampled as an analog voltage, and held for a brief moment. Then at the next above-audio sample rate clock pulse, this voltage would get passed to the next sample and hold (bucket) in the circuit, while a new level was sampled. Bucket brigade delays (BBDs) usually have numbers of stages or buckets that are powers of two (256, 512, 1024, 2048, etc.); the delay length is determined by the number of stages multiplied by the time interval between samples. Click for more about the downsides of BBDs.

Buffered Multiple Quite often you need to split or copy a signal to send to more than one destination. This is commonly done with a multiple, where you plug one source in, and then plug in additional patch cables to go off to multiple destinations. An active or buffered multiple is one that includes a buffer circuit between the input and output, making sure the signal does not lose its strength or integrity by being split too many times, and that no funny business happening on one of the outputs affects any of the other connections. Some modules have good buffering built into their outputs, and can drive multiple modules without issue. But if you try to use a passive mult to connect to, say, three oscillators, and you realize the tracking isn't very good (they quickly go out of tune as you go up and down the scale), then you need a buffered mult instead. Click through for more technical details.

Burst Generator When you send this module a trigger, it outputs a stream or “burst” of triggers in response. You usually have control over the number of triggers, the spacing between them, and often the probability that individual trigger output will be sent or skipped (for random patterns). At its most tame, it can be use to create “double pluck” triggers in response to a normal note on; and its most extreme, it is used to trigger a high-energy, chaotic stream of drum hits that may or may not be in time with the music.

Bus Board This simple circuit board takes the output of your modular system's power supply and creates multiple copies of it, routed to connectors that go to your individual modules. Click through for advice on finding the best bus board designs, and how to connect them.

Carrier There are a few different synthesis techniques where one usually audio-rate signal varies another audio signal. For example, in frequency modulation , a second signal (called the modulator) varies the frequency (pitch) of the main signal, called the carrier. More specifics are described in the entries on frequency modulation and amplitude modulation.

CCW Counter-clockwise, usually in the context of rotating a control the left (in the opposite direction of how a clock's hands move).

Cent When tuning instruments, a semitone is divided into 100 units called cents; there are 1200 cents per octave (100 x 12 semitones). When one oscillator is detuned compared to another, the difference in their frequencies is sometimes measured in cents.

Chaotic Believe it or not, chaotic does not mean completely random to mathematicians. Chaos theory deals with systems that are random within certain boundaries – such as the path of a wobbling wheel or the frequency of a dripping faucet. Although they are not out of control, neither are they completely predictable. In synthesis, a chaotic system usually refers to a modulation generator that is similar to a low frequency oscillator, but which has unpredictable wobbles or glitches in an otherwise loosely or occasionally repetitive pattern. It can also refer to bursts of triggers that do not follow musical divisions.

Chorus A type of signal processor that makes a single audio signal sounds like multiple sources, playing in almost-unison with some slight detuning. This is done by delaying a copy of the original signal, and then varying the amount of delay to create animation in the final mix between the two.

Class Compliant This refers to a device that is "plug and play" – it can be plugged directly into a computer or other host and immediately be recognized without additional drivers needing to be installed. This comes up in the modular world with MIDI to CV/Gate interfaces that use USB: If your converter is a USB Host , and you plug a class compliant USB Device such as a controller keyboard or fader panel into it, the converter will recognize it. Click through for more on USB Hosts and Devices.

Clip All active electronic circuits have a limit on how strong of a signal can pass through them. These limits are often associated with the positive and negative power supply levels. If the signal attempts to go beyond these limits, they instead get chopped or clipped off at that limit. For example, an input voltage of +12 volts may get through without alteration, but +13 volts at the input would come out as 12 volts. This clipping causes distortion in the waveform, usually adding higher harmonics (such as a harsh buzz). Different circuits enter clipping in different ways – some may have a bit of rounding off before they reach that flat threshold ; this is referred to as soft clipping and is often desirable as it can be less harsh.

Clock Usually refers to the main rhythmic pulse in a system. Often, the clock pulse is much faster than anything it might drive, such as a sequencer or LFO. The most common clock rate is 24 ppqn (pulses per quarter note), as is the case with MIDI clocks and DIN Sync. However, a trigger that drives a sequencer forward one note at a time may also be called the “clock” in a system. Indeed, there are modules that create divisions and multiplications of the main clock to generate new clock signals with a relationship to the main clock.

Clockwise Clockwise, as in rotating a control the the right – in the same direction as a clock's hands move.

Comparator An electrical device that compares the level of one voltage to a second. That second voltage may be a second input on a comparator synth module, or may be set with a knob or internal reference voltage. Most often, a comparator outputs a gate signal that goes high when the first signal is higher than the second (or vice versa), and which goes low when the first signal is lower than the second. At audio rates, it converts an input waveform into a square or pulse wave, with the second signal setting when the new waveform goes high or low in voltage.

Complex Oscillator This module typically has a pair of oscillators behind one panel that is prewired where one oscillator modulates the other’s frequency (known as Frequency Modulation or FM synthesis); some also allow you to quickly switch them so that the first modulates the amplitude of the second, or some other variation. They may also have waveshapers built in. They are based on a popular module created by Buchla, which is a standard of the “West Coast” approach to synthesis.

Compound Module A module that has more than one common synthesis element behind the front panel. The most common Compound Module is a Complex Oscillator , which has two voltage controlled oscillators as well as typically wave shapers and VCAs. Other common compound modules are envelope generator + VCA, LFO + VCF, and noise + sample & hold.

Control Voltage The concept of control voltage (CV) is at the very root of modular synthesizer. The general idea is that analog voltage levels are used control functions and parameters of a module. For example, one control voltage may determine the pitch played by an oscillator; a second control voltage may determine how loud that signal is after it’s passed through a voltage-controlled amplifier. CV is the most common shorthand to refer to control voltage – for example, when a synthesizer module says it features “CV over the filter’s resonance,” that means there is a control voltage input to control the amount of resonance (feedback) – not just the customary knob on the front panel.

Control Voltage Processor CVP is the abbreviation for a module that allows processing of the voltage going through it – such as amplifying or attenuating it, offsetting it in a positive or negative direction, introducing slew (slurring of changes in voltage), and possibly other functions such as deriving a gate signal from an incoming voltage by running it through a comparator. Make Noise’s Maths is perhaps the most well known control voltage processor out there; you will also find some modules with CVP specifically in their name. Regardless, it’s good to have one or more of this type of module in your system to help massage voltages to get them to do what you want (or to teach them new tricks).

Corner Frequency The cutoff or corner frequency of a filter is the point at which is starts filtering. For example, if a low-pass filter has a corner frequency of 500 Hz (cycles per second), all harmonics or other sound components below 500 Hz will be allowed through untouched, and all harmonics above 500 Hz will be “filtered” – reduced in loudness – the further above 500Hz you go.

Counter Clockwise Counter-clockwise, usually in the context of rotating a control the left (in the opposite direction of how a clock's hands move).

Cutoff Frequency The cutoff or corner frequency of a filter is the point at which is starts filtering. For example, if a low-pass filter has a corner frequency of 500 Hz (cycles per second), all harmonics or other sound components below 500 Hz will be allowed through untouched, and all harmonics above 500 Hz will be “filtered” – reduced in loudness – the further above 500Hz you go.

CV The concept of control voltage (CV) is at the very root of modular synthesizer. The general idea is that analog voltage levels are used control functions and parameters of a module. For example, one control voltage may determine the pitch played by an oscillator; a second control voltage may determine how loud that signal is after it’s passed through a voltage-controlled amplifier. CV is the most common shorthand to refer to control voltage – for example, when a synthesizer module says it features “CV over the filter’s resonance,” that means there is a control voltage input to control the amount of resonance (feedback) – not just the customary knob on the front panel.

CV/Gate This is the shorthand to say a synthesizer may be controlled by voltages (see control voltage above) – usually for pitch – and gate signals to indicate when a note is “on.” An increasing number of controller keyboards are including CV/Gate output in addition to the customary MIDI (Musical Instrument Digital Interface), making them much easier to connect to a modular synthesizer, as no additional MIDI to CV interface is required.

CVP CVP is the abbreviation for a module that allows processing of the voltage going through it – such as amplifying or attenuating it, offsetting it in a positive or negative direction, introducing slew (slurring of changes in voltage), and possibly other functions such as deriving a gate signal from an incoming voltage by running it through a comparator. Make Noise’s Maths is perhaps the most well known control voltage processor out there; you will also find some modules with CVP specifically in their name. Regardless, it’s good to have one or more of this type of module in your system to help massage voltages to get them to do what you want (or to teach them new tricks).

CW Clockwise, as in rotating a control the the right – in the same direction as a clock's hands move.

DADSR This is a slightly fancier take on the standard ADSR envelope generator that introduces an initial timed delay before the initial attack stage (rising from 0 to a peak level) begins. One patch idea is to route this type of envelope to a low pass filter cutoff, so there’s initially a muted, filtered sound when the note starts, and then after a pause it starts to swell into a brighter, fuller sound.

DC In modular terms, DC refers to a voltage that tends to stay at one steady level for awhile, such as a gate output that switches between 0v when a note is off and 5 or 10v when a note is on. It can also refer to a slowly changing voltage, such as an envelope.

DC Coupled When a module says its inputs are DC Coupled , that means it can accept DC voltages (constant or slowly changing voltages) and pass them through unaltered. This is important if, for example, you want to use a VCA to control the amplitude of an envelope going through it: You would need one that was DC coupled, as an AC coupled input would try to remove the DC component of the signal (such as its sustain level) and return it to 0v. Click through for a link to a good technical article on the subject.

DCO DCO (Digitally Controlled Oscillator) is a hybrid design for an analog oscillator that – instead of using a voltage level to determine the pitch of the oscillator – uses a digital device such as a counter to determine the length of each waveform cycle and therefore the pitch. On the plus side, tuning is very stable, unlike some all-analog designs. On the minus side, there are no imperfections in pitch that cause subtle detuning (and therefore the perception of “fatness”) when using more than oscillator per voice . Click for more details.

Decay In general, decay refers to a voltage or overall level dropping down from some high point, such as the decay stage of an envelope generator. A real-world analogy is that after you initially strike a drum or pluck a string, it decays in volume from its initial loudness eventually all the way to silence. It can also refer to the tail of a reverb or echo effect where the sound dies away over time.

Delay You all know what the word delay means in the normal world; it can appear in different forms inside a modular synth. For example, it can refer to the spacing between repeats in an echo; that’s why an echo device is often known as a “delay” effect. It can also refer to a programmable amount of time you delay a signal, such as a gate, trigger, or initial stage of an envelope so a note would start later than it was actually played.

Delay/Attack/Decay/Sustain/Release This is a slightly fancier take on the standard ADSR envelope generator that introduces an initial timed delay before the initial attack stage (rising from 0 to a peak level) begins. One patch idea is to route this type of envelope to a low pass filter cutoff, so there’s initially a muted, filtered sound when the note starts, and then after a pause it starts to swell into a brighter, fuller sound.

Detune If you have two oscillators tuned to exactly the same frequency – and I mean, exactly the same frequency – there’s not much point in having more than one oscillator. However, when you change the tuning of one ever so slightly – in other words, detune it – you will start to hear interesting interactions between the two, often referred to as chorusing or beating. The result tends to be more interesting and “full” – and a bit more natural, as two singers or instruments can rarely hit exactly the same note.

Difference A fancy way of saying you subtracted on control voltage from another. It can also be applied to audio or harmonics.

Digital There was a time when digital (referring to circuitry based around binary logic, computers, and the such compared to the old-fashioned transistors, op amps, capacitors, and other bits that make up analog circuitry) was a dirty word among synthesists. The assumption was digital techniques created sounds that were more sterile, brittle, and abrasive – and just not as “authentic.” Today, digital circuitry is embraced in synthesizers, including modular systems. Although analog will always hold a special place in our hearts, a well-implemented digital circuit can sound just as good as an analog one, while digital signal processing and programming can create a wider range of sounds than most analog circuitry.

Digitally Controlled Oscillator A DCO (Digitally Controlled Oscillator) is a hybrid design for an analog oscillator that – instead of using a voltage level to determine the pitch of the oscillator – uses a digital device such as a counter to determine the length of each waveform cycle and therefore the pitch. On the plus side, tuning is very stable, unlike some all-analog designs. On the minus side, there are no imperfections in pitch that cause subtle detuning (and therefore the perception of “fatness”) when using more than oscillator per voice. Click for more details.

DIN Sync A clock signal for controlling the tempo of sequencers, arpeggiators, and drum machines, distributed using cables with DIN-style connectors (yes, just like old-fashioned MIDI connectors, but DIN Sync is even older). Roland pioneered this standard, which included sending 24 pulses per quarter note ( PPQN ), giving rise to the alternate name Sync24 . Korg equipment used a variation of this running at 48 pulses per quarter note, also known as Sync48. DIN Sync is still a popular way of sending a clock signal to a modular synth today, especially when interfacing with other vintage synthesizers, sequencers, and drum machines.

Diode Ladder Filter This is a filter design most often associated with the Roland TB-303 Bass Line, which is known for its rubbery sound with eager resonance.

Direct Current In modular terms, DC refers to a voltage that tends to stay at one steady level for awhile, such as a gate output that switches between 0v when a note is off and 5 or 10v when a note is on. It can also refer to a slowly changing voltage, such as an envelope.

Distortion When the shape of a waveform or other varying voltage has been changed, technically it has been distorted. When people say they hear distortion, they are often referring to an audio waveform that has been “clipped” (the top and bottom excursions get flattened out when the reach a certain limit) or when it has “entered saturation ” – it is being bent because it is getting close to clipping. Sometimes you will hear users talk about “overdriving” a module, which causes distortion. Distorting a waveform alters its harmonic structure, often adding higher harmonics.

Dry A sound with no effects is referred to as " dry "; a sound with effects (such as reverb) mixed is referred to as " wet ." Effects units or mixers often have wet/dry mix amounts that set the ratio between the original, unprocessed sound and the fully-effected sound.

Duophonic Duophonic means two "voices." Most early synths (including modular systems) are monophonic, which means they can play only one note at a time; some instruments have enough oscillators, filters, envelopes, and amplifiers that they could play two separate notes as once. Some MIDI interfaces for modular synths include duophonic modes so you can patch up and control two separate voices from your keyboard. Some users play fast and loose with terms such as duophonic, monophonic, and polyphonic; some really care about precise usage - click through for a link by an authoritative article by Marc Doty on the subject.

Duration Duration is another way of saying length. A clock pulse or a gate signal that is “high” for a certain amount of time – say, 100 msec – is said to have a duration of 100 msec. The length of time you hold a note down, or the length of a step in a sequence, is also called its duration.

East Coast Synthesis This blanket term is applied to most common synthesizer configuration pioneered by East Coast based companies such as Moog, Arp, and EML (as well as “Far East” companies such as Roland and Korg) where one or more oscillators producing waveforms with rich harmonic content (such as a sawtooth or square wave ) are fed into a filter that removes some of those harmonics, and then onto an amplifier to shape the loudness of a note. This approach is also often known as subtractive synthesis , as the filter reduces (subtracts) harmonics that came from the oscillators. East Coast synthesizers also regularly have organ-style black & white keyboards, and four stage ADSR type envelopes. Today it's common to mix both East Coast and West Coast approaches in the same system.

Effect Loop Sometimes you might want to send a signal outside your modular system, process it through an external effects device, and bring it back into your modular for more processing. This going out/coming back in is referred to as an effect loop . The trick with modular synths is that their internal signal levels tend to be much higher than those used by external effect equipment, so a modular effect loop will usually have level matching circuitry as well.

EG The envelope generator (EG) module is used to shape the loudness or dynamics of a note when connected to a VCA (Voltage Controlled Amplifier), as well as how its frequency content or timbre changes over time when connected to a VCF (Voltage Controlled Filter). To do this, and envelope generator creates a voltage that typically rises from zero volts to some maximum level, and back down again. You control how long this takes, usually in various stages: an attack stage as it goes from zero to max, a decay stage as if falls back down from maximum to either zero (in the case of an AD, or Attack/Decay envelope) or an intermediate level known as the sustain, and then (usually after a key has been released and the corresponding gate signal has gone back to zero) from the sustain level back to zero over a duration known as its release.

Emphasis This word can have two meanings. In a normal audio context, it usually means some form of high frequency boost, as emphasizing the higher harmonics can add clarity to a tone and help distinguish it from another. In synthesizers, emphasis usually means the Q or resonance setting on a filter, as increasing this setting boosts (emphasizes) the harmonics at the cutoff or corner frequency.

Envelope In general, the term envelope refers to the “shape” of a sound – the contour of how it gets louder and then softer over time. Sometimes envelope is used as shorthand for envelope generator. Envelopes are often described by the stages they have in them – for example, an ADSR envelope has attack, decay, sustain, and release stages. This glossary contains definitions for the most common envelope types.

Envelope Follower This module follows the loudness contour of a sound, and outputs a voltage that corresponds to how that loudness changes. They tend to perform some smoothing on this signal so that it’s not too nervous or jumpy in nature. Envelope followers often also have a gate output that goes high when the loudness of the input signal went over a certain level, and low when it falls back below that level. Click for what to look out for an envelope follower.

Envelope Generator The envelope generator (EG) module is used to shape the loudness or dynamics of a note when connected to a VCA (Voltage Controlled Amplifier), as well as how its frequency content or timbre changes over time when connected to a VCF (Voltage Controlled Filter). To do this, and envelope generator creates a voltage that typically rises from zero volts to some maximum level, and back down again. You control how long this takes, usually in various stages: an attack stage as it goes from zero to max, a decay stage as if falls back down from maximum to either zero (in the case of an AD, or Attack/Decay envelope) or an intermediate level known as the sustain, and then (usually after a key has been released and the corresponding gate signal has gone back to zero) from the sustain level back to zero over a duration known as its release.

Envelope Tracking This describes the main action of an envelope follower: a module or section of a module that follows the loudness of a signal and outputs a voltage that corresponds to – tracks – that input.

Euclidian Rhythms Euclidean rhythms are based on a math trick promoted by Godfried Toussaint at McGill University in Canada: If you take a pattern length (such as 16) and a number of beats (such as 6), and spread those beats out across the pattern using an algorithm based on mathematician Euclid’s Elements, the results are rhythmic patterns that closely or exactly matched many world music styles. Click through for more details, including links to the original paper and example modules. It is also discussed on page 300/301 of Patch & Tweak.

Eurorack Eurorack is arguably the most popular format of modular synthesizer today, with over 100 manufacturers and over 1000 modules available. It was created by Doepfer Musikelektronik in 1995, basing its size off the Eurorack format for lab equipment. Some users will try to tell you that Eurorack doesn’t “sound” as good as other formats, but that’s just based on a few substandard manufacturers or modules; there’s nothing inherent to the standard that makes a huge difference in the final sound (no; the difference between 12 and 15 volt power supplies is not enough to most ears).

Exponential In general terms, this is a mathematical curve that starts out relatively flat and then bends to climb steeply. In synthesizer terms, it most often refers to the control voltage scheme where a change of 1 volt corresponds to an increased pitch of one octave, which is doubling in cycles (vibrations) per second. This is in contrast to a linear system where 1 volt increase would always result in the same increase of cycles per second. Click through for more details.

Fader A control that can reduce the strength of a signal or voltage going through it.

Filter A module that reduced or removes certain frequencies and harmonics from the sound that is passed through it. In a synthesizer, the most typical filter types are low pass (passes all of the harmonics below its cutoff or corner frequency untouched, and then reduces the level of higher harmonics the further you go above that cutoff frequency), high pass (passes all harmonics above its cutoff frequency untouched, and reduces the level of progressively lower harmonics below the cutoff), bandpass (harmonics right around the cutoff are passed intact, and then reduced more in level the further away they are above or below the cutoff frequency), and notch (harmonics right around the cutoff frequency are reduced or cut out entirely; others above or below are allowed to live). Click through for a link to a nice demo video & article.

Flanger A signal processor often identified as the one that creates a “jet taking off” whoosh. What’s going on behind the panel is that a copy of the input signal is delayed by a very small amount (longer than a chorus effect; shorter than an echo effect) and mixed in with the original. When the delay is constant, the result is a “comb filter” where certain harmonics are cancelled out as they are mixed back on top of themselves out of phase . When the delay is varied over time, you get swooshes and sweeps. The effect was originally created by playing two tape reels of the same song, starting them in time with each other, and dragging your finger on the flange of one of the tape reels to delay it.

Flip-Flop In binary logic terms, a flip-flop toggles between high and low every time it receives an input trigger (i.e. the first trigger would set the output high, the second trigger sets it low again, and so on). In clock or audio terms, it divides the speed of an input clock or square wave by 2.

Flying Bus This is a very simple type of power distribution or bus board that typically uses a ribbon cable with multiple connectors along its length to take the output of your power supply and distribute it to your individual modules. They're cheap and easy to install and use, but in a few cases might be a cause of noise being shared between modules.

FM Frequency modulation (FM for short) refers to a synthesis technique where the pitch of an oscillator is varied (modulated) very quickly – at audio rates – by another oscillator. The result is a complex side of harmonics that may either be nicely in tune or clangorous and “out of tune” with the fundamental pitch of the main oscillator. Click through for more detail plus links to technical explanations.

Force-Sensing Resistor In modular systems, an FSR (Force-Sensing or -Sensitive Resistor) usually takes the form of a circular pad that you press on to vary a parameter. It acts as a resistor that decreases in resistance the harder you press.

Formant Many instruments based on vibrating tubes – including our own vocal tract – have certain frequencies that they like to vibrate or “resonate” at. When you send a sound down these tubes, they will accentuate the frequency of that sound (or some of its harmonics) to match these resonate frequencies. Each of these resonant frequencies is known as a formant of that instrument. A common way of synthesizing vocal-like sounds is to pass an oscillator through a filter or equalizer that has several formant peaks, spaced apart in ways that mimic certain vowels.

Four Quadrant Multiplier A Four-Quadrant Multiplier is a special case of Amplitude Modulation (AM). It is also referred to as ring or balanced modulation. One signal changes the level of – "multiplies" – the level of a second signal. A typical use is two VCOs running at audio rates fed into a ring modulator (a four-quadrant multiplier). The output is a complex set of component tones that don’t follow typical “musical” spacing based on octaves above the fundamental that harmonics usually follow. Namely, the modulation frequency is both added to and subtracted from the carrier’s frequency; the resulting harmonics replace the original carrier and modulator. Say the carrier was a sine wave (only the fundamental harmonic present) at 600Hz, and the modulator was a sine wave at 100Hz. The result would be a tone that had frequency components at 500 and 700Hz. Click through for more details and a useful link.

FracRack A less-common format of modular synthesizers put forward by PAiA and Blacet Research. It stands for Fractional Rack ; one unit is 1.5” (3.8 cm) wide by 3U , or 5.25” (13.3 cm) high. Click through for a link to technical details on the format.

Fractional Rack A less-common format of modular synthesizers put forward by PAiA and Blacet Research. It stands for Fractional Rack; one unit is 1.5” (3.8 cm) wide by 3U, or 5.25” (13.3 cm) high. Click through for a link to technical details on the format.

Frequency Modulation Frequency modulation (FM for short) refers to a synthesis technique where the pitch of an oscillator is varied (modulated) very quickly – at audio rates – by another oscillator. The result is a complex side of harmonics that may either be nicely in tune or clangorous and “out of tune” with the fundamental pitch of the main oscillator. Click through for more detail plus links to technical explanations.

FSR In modular systems, an FSR (Force-Sensing or -Sensitive Resistor) usually takes the form of a circular pad that you press on to vary a parameter. It acts as a resistor that decreases in resistance the harder you press.

Function Generator The term function generator can have two meanings in the world of synthesis. One, test equipment that generates waveforms such as sine or square waves are often called “function generators.” Two, envelope generators are sometimes referred to as “function generators.” In both cases, “function” means to execute an equation of some sort, such as creating a periodic waveform such as a sine or creating a rise & fall in response to a trigger.

GAS Many find modular synthesis addictive, succumbing to an uncontrollable urge to keep adding more modules to their systems. Modular addicts jokingly refer to this as having a case of severe GAS : Gear Acquisition Syndrome.

Gate This is one of the main signal types that are passed around inside a modular synthesizer. It jumps to high level – typically 5 volts – when a new note is supposed to start (such as when you press a key on a keyboard controller), or when a sequencer jumps to the next “stage” or note. A gate typically stays at that level for the duration of the note (i.e. while the key is being held down), and suddenly drops or “goes low” to its resting level – typically 0 volts, but sometimes –5 volts or another number – when the note ends (i.e. when the key is released). In practice, when a gate signal is sent to a typical envelope generator, the start of the gate (when it “goes high”) tells the envelope to go through its Attack and Decay stages; while the gate remains high, the envelope stays at its Sustain level, and when the gate goes low again, the envelope moves onto its Release stage.

Gate Detector A module or section of a module that looks at a varying input voltage or even an audio signal, and then sets a gate output “high” (see above) when that signal goes above a often user-settable level (often referred to as a threshold).

Gear Acquisition Syndrome Many find modular synthesis addictive, succumbing to an uncontrollable urge to keep adding more modules to their systems. Modular addicts jokingly refer to this as having a case of severe GAS: Gear Acquisition Syndrome.

Glide Refers to a note that glides from one pitch to another while it is still audible. The music term for this effect is portamento , which is a slurring between notes. In a synthesizer, this effect is created by causing the control voltage for the pitch of a note to slide from the pitch of the previous note rather than make a discrete jump. The module that creates this effect is sometimes known as a slew generator, slew limiter, slope generator, or lag. Some use the terms glide, glissando, and portamento interchangeably, but if you want to split musical hairs, a glissando (gliss) is a different effect where the intermediate notes are more distinct – such as played rapidly in order – rather than slurred through.

Granular Synthesis Granular synthesis can be thought of as particle theory applied to sound. The concept is that a sound can be broken down into very small “grains” – typically 1-50 or 100 msec in duration. These tiny snippets are then played back to reproduce the original sound, or to create new sounds by changing the speed, pitch, volume, playback order, and direction of the individual grains. You can crossfade between these modified grains, or layer more grains on top. The result can range from audio processing tricks such as changing speed without changing pitch and vice versa, to creating psychedelic “clouds” of sound (and indeed, there is a popular module called Clouds). Click through for links to a few articles on implementing granular synthesis.

Half-Wave Rectifier half-wave rectifier passes only positive voltages, and replaces anything negative with 0v. In other words, anything “below zero” is clipped off.

Hard Sync This is the most common type of oscillator sync where the slave oscillator will reset its waveform whenever it receives a sync pulse. If the type of sync is not specified, then it’s probably hard sync . For more details, see the entry for Sync and look at the section on oscillators.

Harmonic A single harmonic is the purest sound possible: It contains no overtones or other identifying characteristics aside from its pitch and loudness. The shape of its vibration – whether it be vibrating the air so you can hear it, or causing the electrical vibrations of a voltage going up and down – is a sine wave. Most of the time, overtones have a very specific pitch relationship to each other. The first or lowest harmonic – known as the ‘fundamental’ – is the pitch of the sound, just as the lowest note of a chord is its ‘root.’ The other harmonics are higher, and spaced out as integer multiples of the fundamental: two times its frequency, three times, four times, and so forth. The first few harmonics happen to have a nice musical spacing: an octave; an octave and a fifth; two octaves. But the higher they get, the less musical they may seem. Click on the term's name for how this relates to waveshapes and timbre.

Hertz/Volt A system where a change of 1 volt at the input results in a change in pitch of a fixed number of hertz (cycles per second), rather than a fixed musical interval. Click for more detail.

High (gate) When a gate signal is at the voltage level (typically 5 volts, although it can be more) that indicates it is “on” – such as when a note is being held down on a keyboard controller – it is said that the gate is high. (Admit it: Some of you were expecting a drug joke.)

High Pass Filter The high pass filter (HPF) design passes harmonics above its cutoff or corner frequency untouched, and reduces the level of lower harmonics depending on how far below the cutoff they are. In a 12dB/oct (decibel/octave) high pass filter, harmonics one octave below the cutoff frequency (in other words, one half the cutoff frequency) are reduced in level by 12 dB; harmonics two octaves below the cutoff (one quarter the frequency) are reduced by 24dB, and so forth. High pass filters are typically used to create bright sounds where the higher harmonics are much stronger than the fundamental and lower harmonics – for example, the sound of a harpsichord.

Horizontal Pitch HP = Horizontal Pitch. In the Eurorack format for synthesizer modules, the width of a module is defined as the number of hp (horizontal pitch) units. Each hp is 0.2” (0.5 cm). Most modules are even numbers of hp wide, although some are odd numbers. Also, modules tend to be ever so slightly less than exactly some multiple of 0.2” wide, just to make sure you don’t run into problems with ever so slightly too wide modules overlapping.

HP HP = Horizontal Pitch. In the Eurorack format for synthesizer modules, the width of a module is defined as the number of hp (horizontal pitch) units. Each hp is 0.2” (0.5 cm). Most modules are even numbers of hp wide, although some are odd numbers. Also, modules tend to be ever so slightly less than exactly some multiple of 0.2” wide, just to make sure you don’t run into problems with ever so slightly too wide modules overlapping.

HPF The high pass filter (HPF) design passes harmonics above its cutoff or corner frequency untouched, and reduces the level of lower harmonics depending on how far below the cutoff they are. In a 12dB/oct (decibel/octave) high pass filter, harmonics one octave below the cutoff frequency (in other words, one half the cutoff frequency) are reduced in level by 12 dB; harmonics two octaves below the cutoff (one quarter the frequency) are reduced by 24dB, and so forth. High pass filters are typically used to create bright sounds where the higher harmonics are much stronger than the fundamental and lower harmonics – for example, the sound of a harpsichord.

Hz/V A system where a change of 1 volt at the input results in a change in pitch of a fixed number of hertz (cycles per second), rather than a fixed musical interval. Click for more detail.

IADSR This is an Attack/Decay/Sustain/Release (ADSR) envelope generator that allows you to start the attack phase at an initial level – the “I” – rather than the customary 0 volts. The envelopes in the Prophet VS , as well as a module from Ladik, have this capability; IMHO more should adopt it.

Impedance Resistance it the measure we use in DC circuits; impedance is used to measure AC circuits as this value can change with frequency. Synth modules usually have their inputs and outputs defined as impedance. In general, you want a low output impedance and a high input impedance. The greater the difference between the two, the less chance the input is going to affect what’s being delivered by the output. Eurorack modules tend to have an input impedance of 100k (100,000 ohms); output impedances can vary from near zero to 1k.

Initial/Attack/Decay/Sustain/Release This is an Attack/Decay/Sustain/Release (ADSR) envelope generator that allows you to start the attack phase at an initial level – the “I” – rather than the customary 0 volts. The envelopes in the Prophet VS, as well as a module from Ladik, have this capability; IMHO more should adopt it.

Inrush Current Some modules need considerably more power than stated in their specifications when they are first starting up. This start-up burst is referred to as Inrush Current . Tube modules, as well as modules and bus boards that have more than a one or two electrolytic capacitors, are the most likely culprits when it comes to high start-up inrush demands. More sophisticated power supplies have protection against too high of a current demand, and will shut down the voltage rail where it senses too high of a demand.

Integrator This function smoothens out an incoming signal so that the change in voltage level. “ Integrator ” is the technical name for this math function; you are more likely to see this module called a slew limiter (where I go into more detail on its uses) or less often as a lag generator or processor.

Inverter An inverter multiplies an incoming control voltage by –1. In the case of a gate or logic inverter, it reverses the high and low states so that (for example) 0v becomes 5v and 5v becomes 0v. This is sometimes referred to as a polarizer, as it changes the polarity (+ versus –) of a signal. A control voltage inverter is often combined with an offset voltage to adjust the output voltage into the desired range. For example, if you had an envelope generator that had an output range of 0 to +8 volts, and you just inverted it, the result would be 0 to –8 volts. Since some modules such as voltage controlled amplifiers usually expect only positive voltages, you would then need to add 8 volts to that result to get an upside-down (inverted) envelope that still had an overall range of 0 to +8v.

Inverting Mixer Most signal mixers make an effort to keep the same polarity of a signal as it passes through the mixer. However, some mixers may invert the polarity or “phase” of a signal (as it’s a simpler design); other mixers may allow you to invert a signal on purpose so that you can experiment with tricks like adding one waveform or filter mode output out of phase with another coming from the same oscillator or filter.

IV Cable You often need to send one signal to multiple destinations. Options for doing this include using dedicated multiples, free-floating widgets with multiple jacks wired together, or fancy cables that allow you plug one or two extra cables into them. The IV cable is one the latter: Made by Erthenvar, it has an extra 3.5mm jack molded into the mid-point of the cable (loosely resembling an intravenous or “IV” drip), in addition to having 3.5mm plugs at either end.

Jack That hole you plug your patch cables into on the face of your synthesizer modules? That’s called a jack. The size and type of jack – 3.5mm, banana, or 1/4” – often is one of the defining features of different synth module formats: 3U/Eurorack, 4U, and 5U/MU respectively. (No, a plug is not called a Jill. Actually, it’s the other way around: A plug is sometimes referred to as a male connector, and a jack is referred to as a female connector.)

Karplus Strong This is a physical modeling synthesis algorithm designed to replicate the sound of plucked, vibrating strings – although it has also proven useful for some percussion sounds as well. A short sample – originally noise, although it can be a high frequency chirp or other sound – is sent to both the output, and to a delay line. The output of a delay line is connected to a filter – originally a one-pole low pass filter; changing the filter has a huge effect on the character of the sound – and then back to both the main output and the input of the delay line. A few modules implement Karplus Strong synthesis, although it is an interesting challenge to patch yourself and play with the results.

Keyboard Tracking Most modular synths follow a strict relationship between voltage and pitch, such as 1 volt per octave; any deviation would cause tuning errors. Because of this sensitivity, 1v/oct and similar signals and connections are sometimes specifically distinguished as keyboard tracking rather than just “CV” (control voltage) to make it clear they are not attenuated or otherwise modified when controlling a function on a module.

Keytar A strap-on, lightweight, portable keyboard meant to allow keyboardists the same freedom (not to mention posturing opportunities) as guitarists.

Krell Patch Recreating this patch is a challenge many modular musicians like to tackle. It is based on the 1959 movie Forbidden Planet, in a segment where they supposedly play the music of the ancient Krell race. In general terms, each note has a random pitch, envelope, and duration. Buchla expert Todd Barton is often pointed to as the reference on how to create this patch; he has a video on Vimeo explaining it (included in the links on the page for this definition).

Lag Generator This function smoothes out an incoming signal so that the change in voltage level cannot exceed a certain number of volts per second. This causes the result to “lag behind” changes in the input. It is sometimes called a slew limiter or technically as an integrator. Click through for some example applications.

LFO This module produces repetitive, cycling waves ranging in frequency from the low end of the audio spectrum to as slow as many seconds or even minutes per cycle. They are used to produce effects such as tremolo (when controlling the loudness of a signal), vibrato (when controlling the pitch of a signal), repetitive filter wah-wah effects, pulse width modulation to vary the waveshape of a pulse in an oscillator, and more.

Line Level Most consumer and lower-cost professional audio equipment use a signal level reference known as line level or –10dBV (decibel volts). The most common connectors are RCA (phono) or 3.5mm, although 1/4” is also used; the signal is “unbalanced” (it uses two wires: signal and ground). In the line level standard, a sine wave that varies between +/–0.447 volts is considered to be at –10dBV. By contrast, a typical oscillator signal in a modular synthesizer is +/–5 to +/–8 volts. As a result, you will need either an output module in your modular synth or one heckuva input attenuator on your mixer or recorder to plug your synth into equipment that runs at line level. Similarly, you will need to substantially boost a line level signal to get it up to modular standards to process in your modular synth.

Linear FM The short answer is: This is often the preferred input response for frequency modulating (FM’ing) an oscillator, as the result stays in tune while you change the modulator. Click through for the longer answer.

Linear Power Supply A linear power supply design takes a higher incoming voltage and reduces it to a lower voltage using components such as transformers. In very general terms, they tend to introduce less noise into the output power signal, at the cost of increased heat and weight (they're not very efficient). Many are moving to a hybrid power supply that combines a switcher with a small linear supply or regulator to get the best of both worlds.

Linear VCA A linear voltage-controlled amplifier (VCA) uses a simple mathematical relationship between control voltage input and signal level output – for example, 50% of nominal control voltage in would result in the output signal being at 50% of the level of the input signal. This, however, is not how our ears perceive loudness; a sound must be amplified by 10x in order to be perceived as twice as loud. This makes a linear VCA desirable for scaling control voltages, but perhaps less so for scaling audio signals. If you connect an envelope generator with an exponential output to a linear VCA, then you will get the desired aural result. Confusing? That’s why it’s great when an envelope generator or VCA has a switch or control to vary it between linear and exponential response. A linear mixer is similar to a linear VCA: “half” on the input level control equals the output having half the voltage swing as the input. Again, this is fine for altering control voltages, but not for mixing audio signals; in that case you want a mixer with exponential controls.

Linear VCO A linear voltage-controlled oscillator (VCO) follows the volts/hertz (v/Hz) standard; more common is the exponential volts/octave (v/oct) standard. The exception is frequency modulation (FM), where a linear control voltage input is often preferred to recreate classic style FM as it does not change the fundamental pitch of the carrier oscillator.

Logic Binary or Boolean logic is a way of combining gate signals (on or off voltages) to create new outputs. Each section of a logic module typically includes 1 to 3 inputs, with 2 being the most common. An OR function says if there is a gate on (or “high”) signal at any of the inputs (i.e. input 1 or input 2 or input 3, etc.), to output a gate on signal. An AND function says only output a gate on signal if all of the inputs see “high” gate signals (i.e. input 1 and input 2 etc. all have gate ons). Adding an “N” to the front of a function’s name says “not” this function – in other words, a NOR function would only output a high signal if all inputs were low (not input 1 nor input 2 are high). Click through for more information and a thorough reference.

Logic Functions In a modular synth, control voltages tend to be continuous in nature, while gate and trigger signals are binary: on or off; high or low. This is the same as logic signals in digital circuitry. Therefore, some make digital logic modules. A common logic function is OR: If either signal A or signal B is high (on), then output a high gate signal (on); otherwise output a low gate (off). Another is AND: If and only if signal A and signal B are both, then output a high gate (on); otherwise, output a low gate (off). These are great functions for combining beat triggers from different timing sources.

Looping Sometimes it’s useful to have a module loop or repeat its functions. For example, an envelope generator that can be set to loop becomes a low frequency oscillator: as it attacks to a maximum value and decays back to zero, it starts that attack phase again. Quite often you want a note sequencer to loop: When it reaches the last note in the sequence, it would be useful for it to then look back to or return to the first note and start over. Audio recorders with looping features are also popular for live performance.

Low (gate) Most often, this is shorthand for saying a gate or trigger signal is in its “off” condition (typically 0 or –5 volts, in contrast to a “high” or “on” signal of +5 volts). It’s also a rather intriguing, unusually synth-heavy album by David Bowie (RIP).

Low Frequency Oscillator This module produces repetitive, cycling waves ranging in frequency from the low end of the audio spectrum to as slow as many seconds or even minutes per cycle. They are used to produce effects such as tremolo (when controlling the loudness of a signal), vibrato (when controlling the pitch of a signal), repetitive filter wah-wah effects, pulse width modulation to vary the waveshape of a pulse in an oscillator, and more.

Low Pass Filter The low pass filter (LPF) design passes harmonics below its cutoff or corner frequency untouched, and reduces the level of lower harmonics depending on how far above the cutoff they are. In a 12dB/oct (decibel/octave) low pass filter, harmonics one octave above the cutoff frequency (in other words, double cutoff frequency) are reduced in level by 12 dB; harmonics two octaves above the cutoff (four times the frequency) are reduced by 24dB, and so forth. This is the most common type of filter used, as most natural sounds have stronger low harmonics and weaker high harmonics – especially as a note fades to silence. Click through for a link to a nice video that demonstrates using a low pass filter on classic waveforms.

Low Pass Gate By strict definition, a low pass gate (LPG) is a low pass filter whose cutoff frequency goes down into the subsonic range as its control voltage goes towards 0 volts, resulting in the input signal being filtered almost into silence. Some replicate this by combining a low pass filter and a voltage controlled amplifier into the same module, with both following the same control voltage. In either case, as an input envelope falls from a high level to 0 volts, the output gets duller (higher harmonics are filtered more) as it falls to silence. This mimics the way many natural sounds work. Click through for more details and examples, including a discussion of vactrols which are often used in low pass gates.

LPF The low pass filter (LPF) design passes harmonics below its cutoff or corner frequency untouched, and reduces the level of lower harmonics depending on how far above the cutoff they are. In a 12dB/oct (decibel/octave) low pass filter, harmonics one octave above the cutoff frequency (in other words, double cutoff frequency) are reduced in level by 12 dB; harmonics two octaves above the cutoff (four times the frequency) are reduced by 24dB, and so forth. This is the most common type of filter used, as most natural sounds have stronger low harmonics and weaker high harmonics – especially as a note fades to silence. Click through for a link to a nice video that demonstrates using a low pass filter on classic waveforms.

LPG By strict definition, a low pass gate (LPG) is a low pass filter whose cutoff frequency goes down into the subsonic range as its control voltage goes towards 0 volts, resulting in the input signal being filtered almost into silence. Some replicate this by combining a low pass filter and a voltage controlled amplifier into the same module, with both following the same control voltage. In either case, as an input envelope falls from a high level to 0 volts, the output gets duller (higher harmonics are filtered more) as it falls to silence. This mimics the way many natural sounds work. Click through for more details and examples, including a discussion of vactrols which are often used in low pass gates.

M2.5 A common screw thread size used to mount Eurorack modules. This size is most common when using a system of loose nuts that slide along the rails that the modules are attached to.

M3 A common screw thread size used to mount Eurorack modules. This size is most common when using module mounting rails that have been pre-drilled.

Magic Smoke Not many people realize this, but most modules are made from concentrated smoke. If some of that smoke is released, then most modules will no longer function properly, If at all. It is time to contact its manufacturer, beg forgiveness, and see if they can fix it. The most common reason for the Magic Smoke to escape is plugging in a power header backwards (or offset by a pin or two).

MArF The rare Buchla Model 248 MArF (Multiple Arbitrary Function Generator) is a cross between a sequencer and an envelope generator (both described elsewhere in this glossary) in that it typically contains 16 or 32 stages (sometimes referred to as “segments”), and a rate control to interpolate between these stages. This means very complex envelope shapes and other control voltage sequences can be created. Later on, Buchla used the term MARF to describe the multi-step envelopes in instruments such as the Buchla 400.

MIDI Short for Musical Instrument Digital Interface. MIDI is a common language to connect one synthesizer to another, and synthesizers to a computer. Although it is a digital language, it is easy to buy a MIDI to CV/Gate (control voltage and gate) converter module that handles both note events and MIDI clocks for driving sequencers and the such. The biggest thing to watch out for is what type of connector is required: the traditional 5-pin DIN, or a USB computer-style connection.

Mini Keys A number of keyboard controllers and even keyboard synths use a key size that is much smaller than a typical piano key. Mini keys is the term commonly used (sometimes derisively, although the space and cost savings can be quite significant) to refer to this hardware choice.

Minimum A “ minimum ” circuit works in the opposite way of a maximum (analog OR circuit): it looks at one or more incoming control voltage, and outputs the value of the lowest one.

Mixer This module combines signals together. You may use a mixer to combine audio signals, in which case you may want one with exponential level controls and perhaps stereo panning, or to combine control voltages, in which case you may want linear level controls plus additional functions to invert and offset the voltages going through it. Click through for a link to an article on choosing utility mixers

Modular A modular synth breaks down the main components of a synthesizer – the tone-generating oscillators, the tone-modifying filters, the amplitude-shaping VCAs, and the modulation sources that create envelopes, tremolos, and more – into individual modules you can purchase and install. At the most basic level, this allows you to play mix-and-match in building your own custom synth. Click through for more reasons to go modular.

Modulation When you vary a parameter of a synthesizer module using voltage control , it is said that you’re modulating that parameter. For example, when a low frequency oscillator (LFO) varies the cutoff frequency of a filter to create a wah-wah effect, it is said that the LFO is modulating the cutoff. When an envelope generator causes a voltage controlled amplifier (VCA) to open up to allow a sound to become suddenly loud, and then fades it back down to silence, you can also say the envelope is modulating the amp (although some like to restrict the term “modulate” to a repetitive action). Therefore, we call the sources of these changes modulators. Click through for a link to a nice introductory video on modulation.

Modulator We touched on the general subject of modulation and modulators in the definition above. However, quite often when someone uses the term modulator, they’re usually discussing a synthesis techniques where one usually audio-rate signal “modulates” (varies) another audio signal. For example, in frequency modulation (FM) synthesis, the modulator (or modulating oscillator) varies the frequency (pitch) of the main signal generator (oscillator), called the carrier. In ring, balanced, or amplitude modulation, the modulator is varying the loudness of the carrier signal. So the term modulator is a way to make it clear which component you’re talking about in one of these patches: not the main tone generator, but the module that is driving that generator crazy.

Monophonic A monophonic instrument is only capable of playing one note at a time. Common examples include brass and woodwind instruments as well as the human voice. A typical modular synthesizer voice is also monophonic, as it requires so much hardware and effort to patch together the components required to make that one note. Click through for more details.

Moog Moog (founded by Robert Moog) was one of the first manufacturers of modular synthesizers. Although they offered a wide variety of alternate musical interfaces over the years, they tend to be associated with using a normal keyboard controller to make it easier for musicians trained on traditional instruments such as the piano or organ to play a synthesizer. Indeed, one of the earliest and most famous albums created using a Moog modular synth was Switched On Bach by Wendy Carlos. Moog is often associated with the “East Cost Synthesis” approach.

Morphing In the context of a modular synth, morphing refers to an oscillator that can more or less smoothly change the shape of its output waveform – and therefore, the resulting sound – as you play it. This is usually the domain of digital oscillators which internally crossfade (or in some cases, switch) from one waveshape to another, although it is sometimes applied to analog oscillators that give you real time control over waveshapes.

Mother-32 A very popular semi-modular synthesizer by Moog. It comes in its own case, but can be mounted in a Eurorack-format case. It comes with one VCO (sawtooth and pulse waveforms), one LFO ( triangle and square waveforms), one Moog-style transistor ladder filter that can be low pass or high pass, and one AD or AR envelope generator. It also has a very capable step sequencer plus a miniature one-octave keyboard. What makes it a semi-modular is a nice patch panel that allows alternate routings for the way the synth voice is internally wired, and for it to be patched to external modules. As so many of these were sold, I’m using it as a representative of a typical semi-modular or “starter” synthesizer voice when discussing how to expand a basic modular system. I have an online introductory course to the Mother-32 coming out this spring, and will have a course plus ongoing weekly series on adding different modules to this starter system.

MU Refers to modules that are 5U (rack units) or 8.75” (22.2 cm) high, which is most often associated with the vintage Moog standard and those who have followed in their footsteps, including Synthesizers.com (Dotcom) and Moon Modular. You will sometimes hear this used interchangeably with MU for Moog Units, which also refers to a standardized width of 2.125” (5.4 cm) wide per MU. Given that this standard is both historical and physically large, some users “5U” as a badge of honor that they’re traditional and cool. (And the are.) There was also a briefly popular 5U format from MOTM that used a different width and power connection. It has since been discontinued, but there are still diehard MOTM format users today.

Multi-Tap Delay A delay works by in essence putting audio in one end of a pipe and grabbing it again when it comes out the other. A multi-tap delay says “Why wait until the audio snapshots go all the way through the pipe? Let’s grab it when it’s only part way through the pipe.” Those points where it’s prematurely grabbed are the “taps” – kind of like additional water taps added along a long pipe. Click on the name "multi-tap delay" for more details and background.

Multiple Quite often you need to split or copy a signal to send to more than one destination. This is commonly done with a multiple (“mult” for short) where you plug one source in, and then plug in additional patch cables to go off to multiple destinations. Click through for details on the different types of mults.

Multiple Arbitrary Function Generator The rare Buchla Model 248 MArF (Multiple Arbitrary Function Generator) is a cross between a sequencer and an envelope generator (both 