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Here are a few basic must-know terms for analog synthesizers.
See our video tutorials.

Voltage Control

Voltage control is a basic concept used in modular synthesis that you must grasp to fully use the instrument. It's really very simple - if a module has a voltage-controllable parameter, that parameter can be controlled by other modules that produce voltages. This is a very powerful idea!


A gate signal is an on/off voltage produced by keyboard controllers and sequencers. Gate signals are typically used to fire envelope generators and start sequencers.

Pitch Voltage

Pitch voltage is a signal used to control the pitch (frequency) of an oscillator. Each volt equals one octave of change in the frequency.

Envelope Generator

An envelope generator produces a voltage that changes over time according to knob settings. This voltage is used to control module parameters such as filter cutoff frequency or amplitude via a VCA.

The envelope output begins when a gate signal is received. This gate signal may come from a keyboard controller, a sequencer or other module. The output may be short or may continue until the gate signal is removed then release slowly over a long period of time.

There are typically 4 phases to an envelope. The ATTACK phase begins when the gate is received by pressing a key. The voltage rises according to the speed set by the attack knob. After the Attack peak, the DECAY phase begins and the voltage decays according to the speed set by the decay knob down to the SUSTAIN level where the voltage is maintained as long as the gate is present. When the key is released, the RELEASE phase begins and the voltage returns to 0 according to the speed set by the release knob.

See our Q109 Envelope Generator which is a standard manually-controlled ADSR envelope generator. Also see our Q179 Voltage Controlled Envelope Generator which can use velocity signals to control the speed and amplitude of envelopes to add expression to your playing.

LFO - Low Frequency Oscillator

An LFO is a special type of oscillator that produces waveforms to modulate other parameters in a synthesizer. It's typically slower than an audio oscillator like the Q106. The Q167 LFO++ is a full-featured LFO with a built-in envelope generator and wave curver.


A sequencer produces a sequence of voltages that can be used to create melodies or control any module. Each step of the sequencer's output is set by a knob. Sequencers typically have their own internal clock to set their speeds. Sequencers can be activated and disabled by keypresses or other modules, even other sequencers.

See our Q119 24-step Sequencer and our Q960 8-step Moog-Style Sequencer.

VCA - Voltage Controlled Amplifier

A VCA controls the amplitude of a signal. Amplitude is a fancy word for volume. A VCA's amplitude is controlled with an external voltage, typically an envelope generator,

See our Q108 Amplifier Module for manual and voltage control of the amplitude of audio and control voltage signals. Also see our Q148 VCA++ Module which includes a left-right panner, tuner and headphone amplifier.

VCF - Voltage Controlled Filter

A filter removes frequencies in a waveform and is a critical component in a synthesizer voice. The cutoff frequency of a VCF can be changed with a control voltage. This control voltage is typically provided by an envelope generator. Frequencies can be emphasized using the Q or resonance control.

The Q107 State Variable Filter Module provides voltage controlled low-pass, high-pass, band-pass and notch outputs along with voltage control of resonance. Our Q150 Ladder Filter Module modeled after the Moog filter. We also offer the Q127 Fixed Filter Bank Module with 12 band-pass filters, a low-pass filter and a high-pass filter.

VCO - Voltage Controlled Oscillator

A VCO produces audio signals used to build a synthesizer voice. Most VCOs offer various waveforms like Sine, Square, Sawtooth which contain different harmonics. The pitch (frequency) of the VCO is determined by a control voltage - typically with a 1 volt per-octave response. This control voltage can be supplied by a keyboard, sequencer or other modules. An oscillator produces an output at all times. A VCA is typically used to turn the audio on and off.

See our Q106 Oscillator Module with Sine, Triangle, Ramp, Sawtooth, Square and Pulse waveform outputs along with adjustable range settings and a hard-sync input.

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