Modular Synthesizer - Types of Modules

Types of Modules

Modular synthesizers fall into two broad categories, analog, and digital. The analog modular synthesizer is a type of synthesizer consisting of separate specialized modules connected by wires (patch cords) to create a so-called patch. There are three basic kinds of modules: source, processor and logic. The basic modular functions are as: signal, control, logic/timing. Outputs are an electric voltage.

There exist many different types and sub-types of modules – even modules with the same basic function will have different inputs, outputs and controls on various models. There are some standards which manufacturers followed for their range of synthesizers, such as 1V/oct; however, connecting synthesizers from different manufacturers may require cables with different kinds of jacks.

Some standard modules found on almost any modular synth are: SOURCEs - characterized by an output, but no signal input; it may have control inputs:

• VCO – Voltage Controlled Oscillator, a continuous voltage source, which will output a signal whose frequency is a function of the settings. In its basic form these maybe simple waveforms (most usually a square wave or a sawtooth wave, but also includes pulse, triangle and sine waves), however these can be dynamically changed through such controls as sync, frequency modulation, and self-modulation.
• Noise source - A source that outputs a random voltage. Common types of noise offered by modular synthesizers include white, pink, and low frequency noise.
• LFO - A Low Frequency Oscillator may or may not be voltage-controlled. It may be operated with a period anywhere from a fortieth of a second to several minutes. It is generally used as a control voltage for another module. For example, modulating a VCO may create vibrato while modulating a VCA may create tremolo. The pulse wave can be used as a timing / trigger function.
• EG - is a transient voltage source. A trigger in the presence of a gate, applied to an Envelope Generator produces a single, shaped voltage. Often configured as ADSR (Attack, Decay, Sustain, Release) it provides a transient voltage that rises and falls. It can be triggered by a keyboard or by another module in the system that produces a rapidly rising trigger in the presence of a gate. Usually it controls the output of a VCA or VCF, but the patchable structure of the synthesizer makes it possible to use the envelope generator to modulate other parameters such as the frequency or pulse width of the VCO. Simpler EGs (AD or AR) or more complex (DADSR—Delay, Attack, Decay, Sustain, Release) are sometimes available.

PROCESSORs - characterized by a signal input and an output; it may have control inputs.

• VCF - Voltage Controlled Filter, which attenuates frequencies below (high-pass), above (low-pass) or both below and above (band-pass) a certain frequency. VCFs can also be configured to provide band-reject (notch), whereby the high and low frequencies remain while the middle frequencies are removed. Most VCFs have variable "q" (resonance), often voltage-controlled.
• VCA - Voltage Controlled Amplifier, is usually a unity-gain amplifier which varies the amplitude of a signal in response to an applied control voltage. The response curve may be linear or exponential. Also called a two-quadrant multiplier.
• RM - Ring modulator - Two audio inputs are utilized to create sum and difference frequencies while suppressing the original signals. Also called a four-quadrant multiplier.
• Mixer - a module that combines multiple signals.
• Slew limiter - is a very-low frequency lowpass filter. This can be used to create glide or portamento between notes.
• S&H - Sample and hold, is usually used as a control-voltage processor. Depending upon the design, usually an ascending edge (trigger), captures the value of the voltage at the input, and outputs this voltage.
• Sequencer, is a compound module which produces a sequence of voltages, usually set by adjusting values on front panel knobs. Basic sequencers will be stepped by a trigger being applied to the trigger input. More complex designs may have the sequencer step forwards or backwards, or only run for a limited number of stages.
• Custom Control Inputs - It is possible to connect any kind of voltage to a modular synthesizer as long as it remains in the usable voltage range of the instrument, usually -15V to +15V.

Modular synthesizers can be bulky and expensive. Reproducing an exact patch can be difficult or next to impossible. In the late 1970s, modular synthesizers started to be largely supplanted in pop music by highly integrated keyboard synthesizers, racks of MIDI-connected gear, and samplers. However, there continues to be a loyal following of musicians who prefer the physically patched approach, the flexibility and the sound of traditional modulars. Since the late 1990s, there has been a resurgence in the popularity of analog synthesizers spurred on by physical standardization practices, an increase in 'retro' gear and interest, decreased production costs and increased electronic reliability and stability, the rediscovered ability of modules to control things other than sound, and a generally heightened education through the development of virtual synthesis systems such as MAX/MSP and Pd.