What All Those Knobs on Your Synthesizer Do

A synthesizer (or software designed to look like a synthesizer) often has a wall of knobs and sliders with weird, arcane labels. Without knowing what these do, it’s hard to make sounds other than by trial and error. This article tries to demystify them so that hopefully your synthesizer makes more sense.

VCO – Voltage Controlled Oscillator

This is where everything begins. An oscillator generates an electrical signal such as a sine wave, square wave, saw wave, or triangle wave. This electrical signal is eventually sent to speakers where it turns into a sound wave that you can hear. By itself, an oscillator will produce a simple sound, but when combined with the other controls such as a VCA, VCF, LFO, or ADSR envelope you can get more interesting noises.

Often this control will be labeled with the acronym VCO, for voltage controlled oscillator. The term voltage controlled is a fancy way of saying that the oscillator’s output frequency can be changed. Inside a synth, a VCO has a voltage coming in which determines the frequency (i.e. pitch) of the sound it produces. Change the voltage, and you change the output frequency. Pressing a key on the synthesizer keyboard causes a particular voltage to be fed into the oscillator, causing the pitch you hear to match the key you pressed.

Here’s an example of an oscillator in action. Notice how when you move the frequency slider the pitch changes:

Your browser does not appear to support WebAudio. Please use a more recent version of Safari, Chrome, or Firefox to see these examples. Power On Off VCO Wave Form Sine

Square

Sawtooth

Triangle Frequency

Pro Tip To hear sound switch the “Power” button to “On”.

Now, instead of a frequency slider, here’s a more realistic example with a piano keyboard. Each time you press a key, it changes the frequency that the oscillator emits:

Your browser does not appear to support WebAudio. Please use a more recent version of Safari, Chrome, or Firefox to see these examples. Power On Off VCO Sine

Square

Sawtooth

Triangle ← C1 C♯1 D♭1 D1 D♯1 E♭1 E1 F1 F♯1 G♭1 G1 G♯1 A♭1 A1 A♯1 B♭1 B1 C2 C♯2 D♭2 D2 D♯2 E♭2 E2 F2 F♯2 G♭2 G2 G♯2 A♭2 A2 A♯2 B♭2 B2 C3 C♯3 D♭3 D3 D♯3 E♭3 E3 F3 F♯3 G♭3 G3 G♯3 A♭3 A3 A♯3 B♭3 B3 C4 C♯4 D♭4 D4 D♯4 E♭4 E4 F4 F♯4 G♭4 G4 G♯4 A♭4 A4 A♯4 B♭4 B4 C5 C♯5 D♭5 D5 D♯5 E♭5 E5 F5 F♯5 G♭5 G5 G♯5 A♭5 A5 A♯5 B♭5 B5 C6 C♯6 D♭6 D6 D♯6 E♭6 E6 F6 F♯6 G♭6 G6 G♯6 A♭6 A6 A♯6 B♭6 B6 C7 →

Notice that after playing a note the sound never stops until you turn the synth off. We’ll see why in the next section.

Often a synth will have multiple oscillators that can produce sound at the same time, which allows creating more interesting sounds. You can sometimes also change the octave the oscillator emits. This will often be labeled with numbers like 2’, 4’, 8’, 16’, etc. The lower the number, the higher the pitch.

VCA – Voltage Controlled Amplifier

Think of this as a volume knob. The electrical signal that comes from an oscillator is fed into a VCA to be amplified, before being sent out of the synth to some sort of speaker.

Since it is a voltage controlled amplifier, the amount of amplification it performs can be changed. Typically this is not controlled directly by knob or slider on the synth, but by another component such as an LFO or ADSR envelope (both of which we’ll talk about below).

Another important use of a VCA is to act as a gate. Notice how in the oscillator examples above notes played forever (until you turned the synth off). A VCA lets you stop the sound when you let go of a key. Each time you press a key, the synthesizer will send a gate signal turning the VCA on (and letting sound from the oscillator through), and when you let go of the key, another gate signal is sent to turn the VCA off.

In the example below you can control the VCA volume by moving the slider[1]. Also, notice how each time you let go of a key the sound now stops, due to a gate signal being sent to the VCA.

Your browser does not appear to support WebAudio. Please use a more recent version of Safari, Chrome, or Firefox to see these examples. VCO Wave Sine

Square

Saw

Triangle VCA Amplitude ← C1 C♯1 D♭1 D1 D♯1 E♭1 E1 F1 F♯1 G♭1 G1 G♯1 A♭1 A1 A♯1 B♭1 B1 C2 C♯2 D♭2 D2 D♯2 E♭2 E2 F2 F♯2 G♭2 G2 G♯2 A♭2 A2 A♯2 B♭2 B2 C3 C♯3 D♭3 D3 D♯3 E♭3 E3 F3 F♯3 G♭3 G3 G♯3 A♭3 A3 A♯3 B♭3 B3 C4 C♯4 D♭4 D4 D♯4 E♭4 E4 F4 F♯4 G♭4 G4 G♯4 A♭4 A4 A♯4 B♭4 B4 C5 C♯5 D♭5 D5 D♯5 E♭5 E5 F5 F♯5 G♭5 G5 G♯5 A♭5 A5 A♯5 B♭5 B5 C6 C♯6 D♭6 D6 D♯6 E♭6 E6 F6 F♯6 G♭6 G6 G♯6 A♭6 A6 A♯6 B♭6 B6 C7 →

VCF – Voltage Controlled Filter

Sitting in between a VCO and a VCA is a voltage controlled filter. A filter removes frequencies that occur above or below a certain frequency, or within a certain range. Since it is voltage controlled, you can change which frequencies the filter removes, either with a knob or slider, or indirectly via a different component such as an LFO or ADSR envelope.

Although the typical base sounds generated by a VCO (square wave, sawtooth wave, triangle wave) might seem simple, they actually consist of many different frequencies combined together. Think of the sound created by a VCO like a block of marble. Similar to how selectively removing parts of a marble block will reveal a sculpture underneath, selectively filtering some of the frequencies from a VCO’s output lets you create many different types of sound.

A synth will typically have a knob or slider that controls the filter’s cutoff frequency. Any frequencies above this will be removed[2]. When this is set to a low value, the sound will be muffled like it is coming from the next room. A separate knob or slider will usually control the amount of resonance. Resonance means that frequencies near the cutoff frequency will be amplified, and this slider controls how pronounced they are.

In this example, you can see how changing the cutoff frequency and resonance affects sound coming from an oscillator:

Your browser does not appear to support WebAudio. Please use a more recent version of Safari, Chrome, or Firefox to see these examples. Power On Off VCO Wave Sine

Square

Saw

Triangle VCF Cutoff Frequency Resonance

Pro Tip For a wah-wah effect, maximize the resonance and move the cutoff slider up and down quickly.

ADSR Envelope

Stands for Attack, Decay, Sustain, and Release Envelope. An envelope allows changing a parameter over time while a key is pressed. Most commonly an envelope can be connected to the VCA volume or VCF cutoff frequency. For example, when connected to the VCA volume the 4 parameters have this meaning:

Attack After a key is pressed the rate at which the volume goes from silence to full volume. Decay The rate at which the full attack volume fades to the sustain volume after the attack is complete. Sustain The volume that is held after decay ends, until the key is released. Release The rate at which time the sustain volume fades to silence after the key is released.

When you press or key, the attack and then decay portions of the envelope will take effect, until the sustain volume is reached. The sustain volume will then be held as long as the key is pressed. When the key is released, the release portion of the envelope will take effect until the volume drops down to zero.

Different ADSR envelopes allow creating sounds reminiscent of traditional musical instruments. For example, when simulating a struck instrument such as a piano or bell you’d want a quick attack, whereas a bowed instrument such as a violin would have a slower attack.

Your browser does not appear to support WebAudio. Please use a more recent version of Safari, Chrome, or Firefox to see these examples. Envelope Attack Decay Sustain Release VCA Amplitude ← C1 C♯1 D♭1 D1 D♯1 E♭1 E1 F1 F♯1 G♭1 G1 G♯1 A♭1 A1 A♯1 B♭1 B1 C2 C♯2 D♭2 D2 D♯2 E♭2 E2 F2 F♯2 G♭2 G2 G♯2 A♭2 A2 A♯2 B♭2 B2 C3 C♯3 D♭3 D3 D♯3 E♭3 E3 F3 F♯3 G♭3 G3 G♯3 A♭3 A3 A♯3 B♭3 B3 C4 C♯4 D♭4 D4 D♯4 E♭4 E4 F4 F♯4 G♭4 G4 G♯4 A♭4 A4 A♯4 B♭4 B4 C5 C♯5 D♭5 D5 D♯5 E♭5 E5 F5 F♯5 G♭5 G5 G♯5 A♭5 A5 A♯5 B♭5 B5 C6 C♯6 D♭6 D6 D♯6 E♭6 E6 F6 F♯6 G♭6 G6 G♯6 A♭6 A6 A♯6 B♭6 B6 C7 →

The envelope can sometimes be turned on or off by a toggle under the “VCA” header: gate or hold (for off), and “env” for on.

LFO – Low Frequency Oscillator

A low frequency oscillator is like a regular VCO, except that it’s normally used to modulate another parameter, instead of directly producing sound itself. In fact, it wouldn’t be very useful for producing sound, because often the frequencies it outputs are lower than what humans can hear (hence why it is called a low frequency oscillator). Along with an ADSR envelope, an LFO allows for parameter values to change over time while a key is pressed.

For example, if a LFO produces a signal whose amplitude goes up and down, like a sine wave, and is connected to a VCO, the frequency of the VCO will go up and down in a sine wave. This sounds like vibrato. When connected to a VCA, it will cause the sound to become louder and quieter in a regular pattern, like tremolo.

In the example below, notice how changing the wave type of the LFO changes the sound coming out of the VCO:

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VCO LFO Wave Sine

Square

Sawtooth

Triangle Frequency Amount VCO Wave Sine

Square

Sawtooth

Triangle ← C1 C♯1 D♭1 D1 D♯1 E♭1 E1 F1 F♯1 G♭1 G1 G♯1 A♭1 A1 A♯1 B♭1 B1 C2 C♯2 D♭2 D2 D♯2 E♭2 E2 F2 F♯2 G♭2 G2 G♯2 A♭2 A2 A♯2 B♭2 B2 C3 C♯3 D♭3 D3 D♯3 E♭3 E3 F3 F♯3 G♭3 G3 G♯3 A♭3 A3 A♯3 B♭3 B3 C4 C♯4 D♭4 D4 D♯4 E♭4 E4 F4 F♯4 G♭4 G4 G♯4 A♭4 A4 A♯4 B♭4 B4 C5 C♯5 D♭5 D5 D♯5 E♭5 E5 F5 F♯5 G♭5 G5 G♯5 A♭5 A5 A♯5 B♭5 B5 C6 C♯6 D♭6 D6 D♯6 E♭6 E6 F6 F♯6 G♭6 G6 G♯6 A♭6 A6 A♯6 B♭6 B6 C7 →

An LFO can sometimes be connected to a VCA or VCF. When connected to a filter’s cutoff frequency you can get some interesting effects. Try playing around with the cutoff frequency and resonance sliders:

Your browser does not appear to support WebAudio. Please use a more recent version of Safari, Chrome, or Firefox to see these examples. LFO

VCF LFO Wave Sine

Square

Sawtooth

Triangle Frequency Amount VCF Cutoff Frequency Resonance ← C1 C♯1 D♭1 D1 D♯1 E♭1 E1 F1 F♯1 G♭1 G1 G♯1 A♭1 A1 A♯1 B♭1 B1 C2 C♯2 D♭2 D2 D♯2 E♭2 E2 F2 F♯2 G♭2 G2 G♯2 A♭2 A2 A♯2 B♭2 B2 C3 C♯3 D♭3 D3 D♯3 E♭3 E3 F3 F♯3 G♭3 G3 G♯3 A♭3 A3 A♯3 B♭3 B3 C4 C♯4 D♭4 D4 D♯4 E♭4 E4 F4 F♯4 G♭4 G4 G♯4 A♭4 A4 A♯4 B♭4 B4 C5 C♯5 D♭5 D5 D♯5 E♭5 E5 F5 F♯5 G♭5 G5 G♯5 A♭5 A5 A♯5 B♭5 B5 C6 C♯6 D♭6 D6 D♯6 E♭6 E6 F6 F♯6 G♭6 G6 G♯6 A♭6 A6 A♯6 B♭6 B6 C7 →

Pro Tip Use this with low notes to get the signature “wobbly” dubstep bass sound.

Although it’s called a low frequency oscillator, a synth will sometimes allow an LFO to output higher frequencies as well. When frequencies get high enough and are connected to the VCO pitch, they stop causing a vibrato effect and instead start changing the timbre of the sound. This is the basis of FM Synthesis (which is beyond the scope of this article).