Synthesizers modify sound waves and create unique sounds. Since modular synthesizers allow a user near infinite variations for modifying sound waves, we’ve chosen to focus on a simple, basic system to show how they work.

Doepfer A-100 Mini System

1 Power supply The power supply includes the transformer on the outside of the system as well as the circuit board on the inside of the case. The external piece can be disconnected for easy transportation while also using a minimal amount of space inside the case.

2 Input Most contemporary modular systems have MIDI, which lets them interface with electronic keyboards, controllers, or computers.

3 Bus board The bus board distributes power from the power supply to multiple modules.

4 Power cables

5 Modules Almost any combination of modules can be put into the case and mounted to the rails, so long as they fit within the width of the case.

6 Patch cables The Eurorack system uses 3.5mm phone connecter leads to connect or “patch” modules together.

7 Case Cases are measured vertically in Rack Units (U or RU, where 1U ≈ 1.75” or 133.35mm) and horizontally in Horizontal Pitch units (HP, where 1 HP ≈ 1/5” or 5.08mm). Dieter Doepfer created the “Eurorack” system in the A-100 around 1995, which refers to cases & modules that are 3U tall (about 5.25”) and multiples of 2HP wide.

8 Mounting rails The mounting rails have threaded holes that are 1HP apart. This allows the modules to be moved along the rails in any location and then secured to the mounting rail with a screw.

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Sound Wave Basics

Wave types 1 Sine 2 Triangle 3 Square 4 Sawtooth

Attack, Decay, Sustain, and Release (ADSR) An envelope can be generated around a sound wave to help define how that sound wave acts when initiated. If pressing a keyboard key, the period between when a key is first pressed and when it reaches full volume is called the attack . After the sound reaches full volume, it may decay or lower in volume until it reaches the sustain level, which is held until the key is released. Once the key is released, the release determines how long the sound will fade out until completely gone.

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Basic Types of Modules

1 MIDI interface The MIDI interface module converts digital signals from keyboards, controllers, or computers into analogue signals that the system can use. Pressing a key on a keyboard and then letting go also tells the system when to start or stop the sound; this is referred to as a “gate.”

2 Voltage control oscillator (VCO) Oscillators generate sound waves. The higher the voltage, the higher the note will be; most oscillators will increase one octave for each additional volt of power. Most oscillators can produce sawtooth, square, triangle, and sine shaped sound waves.

3 Attenuator Attenuators decrease the amplitude of the sound, making it quieter.

4 Low pass filter (LPF) Low pass filters allow the lower or bass portions of the sound to “pass” through and block out the higher parts of the sound. The point at which that happens – the cut-off point – is adjustable.

5 Voltage controlled amplifier (VCA) Amplifiers increase the amplitude of the sound, making it louder.

6 Envelope generator (EG or ADSR) Envelope generators modify the Attack, Decay, Sustain, and Release of the sound wave.

7 Low frequency oscillator (LFO) Low frequency oscillators usually operate at a frequency that is too low for human ears to hear. They are mainly used to modify other sound waves in the modular system; for example, an LFO could add vibrato to the sound. Similar to VCO’s, they can usually produce sawtooth, square, triangle, and sine shaped sound waves.

A Simple Patch

Here is an example of a patch that could be made on this system; even with just this simple patch, adjusting the nobs on the modules could produce thousands of different kinds of sounds.

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