Editing Modular synthesizer (section)

== Types of module ==
The basic modular functions are: signal, control, logic and timing. Typically, inputs and outputs are an electric [[voltage]].

The difference between a synthesizer module and a stand-alone [[effects unit]] is that an effects unit will have connections for input and output of the audio signal and knobs or switches for users to control various parameters of the device (for example, the modulation rate for a chorus effect) while a synthesizer module may have connections for input and output, but will also have connections so that the device's parameters can be further controlled by other modules (for example, to connect a [[low-frequency oscillator]] module to the modulation input of a [[Delay (audio effect)|delay]] module to get the chorus effect.)

There exist many different types of modules.  Modules with the same basic functions may have different inputs, outputs and controls, depending on their degree of complexity. Some examples include the voltage-controlled oscillator (VCO), which may have options for sync (hard or soft), linear or exponential frequency modulation, and variable waveshape; the voltage-controlled filter (VCF) that may have both resonance and bandwidth controls; and the envelope generator which may provide outputs at each stage of the process. Examples of more complex modules include the frequency shifter, sequencer, and vocoder.

Modular synthesizers may be bulky and expensive. There are some standards that manufacturers follow for their range of physical synthesizers, such as {{nowrap|1 V/octave}} control voltages, and gate and trigger thresholds providing general compatibility; however, connecting synthesizers from different manufacturers may require cables with different kinds of plugs.

[[Image:Doepfer A-100.jpg|thumb|A [[Doepfer A-100]] (1995 to present)]]
German engineer [[Dieter Doepfer]] believed modular synthesizers could still be useful for creating unique sounds, and created a new, smaller modular system, the Doepfer A-100. This led to a new standard for modular systems, [[Eurorack]]; as of 2017, over 100 companies, including [[Moog Music|Moog]] and Roland, were developing Eurorack modules.<ref name="FactMag-201700921" />

=== Typical modules ===
Modules can usually be categorized as either sources or processors.<ref>Austin, Kevin. "[http://econtact.ca/17_4/austin_synthesis.html A Generalized Introduction to Modular Analogue Synthesis Concepts]." eContact! 17.4&nbsp; Analogue and Modular Synthesis: Resurgence and evolution (February 2016). Montréal: [[Canadian Electroacoustic Community|CEC]].</ref> Standard modules found in a modular synthesizer are:

''Sources'' - characterized by an output, but no signal input; it may have control inputs:
* VCO – [[Voltage-controlled oscillator]], outputs a signal whose frequency is a function of input control voltage and settings. In its basic form, these may be simple [[waveform]]s (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 - Common types of noise offered by modular synthesizers include [[white noise|white]], [[pink noise|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 will produce a frequency modulation perceived as [[vibrato]], while modulating a VCA will produce amplitude modulation perceived as [[tremolo]], depending on the control frequency. A rectangular wave output from an LFO can be used as a logic output for timing or trigger functions on other modules.
* EG - An [[envelope generator]] is a transient voltage source. A trigger control signal applied to an envelope generator produces a single, shaped voltage. Often configured as [[ADSR envelope|ADSR]] (attack, decay, sustain, release) it provides a control voltage that rises and falls. Usually it controls the amplitude of a VCA or the cutoff frequency of a 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.
* [[Music sequencer|Sequencer]] or [[analog sequencer]], is a family of compound module types that may be a source or a processor. As a source, depending upon the configuration, it may produce a sequence of voltages, usually set by adjusting values on front panel knobs. The sequencer may also output a trigger, or gate, at each step. Sequencers are stepped by a trigger being applied to the trigger input. Designs may allow for stepping forwards or backward, oscillating patterns, random order, or only using a limited number of steps. An example of an analog sequencer and controller with this level of complexity is the Doepfer A-154, A-155 combination.

''Processors'' - characterized by a signal input and an output and 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]].{{efn|Some VCFs can also be configured to provide band-reject (notch), whereby the high and low frequencies remain while the middle frequencies are attenuated.}} Most VCFs have variable resonance, sometimes voltage-controlled.
* VCA - [[Voltage-controlled amplifier]], 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]].
* LPG - Low-pass gate, is a compound module, similar to a VCA combined with a VCF. The circuit uses a [[resistive opto-isolator]] to respond to the control voltage, which also filters the sound, allowing more high-frequency information through at higher amplification.
* RM - [[Ring modulator]] - Two audio inputs are utilized to create sum and difference frequencies while suppressing the original signals. Also called an [[analog multiplier]] or [[frequency mixer]].
* Mixer - A module that adds voltages.
* Multiple - [[Fan out]] a voltage output to multiple inputs.
* Slew limiter - A sub-audio [[low-pass filter]]. When used in a control voltage path to an oscillator, produces a [[portamento]] effect.
* 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 until the trigger input reads another voltage and repeats the process.
* [[Music sequencer|Sequencer]], (see also above), as a processor, may have a signal input into each step, (location or stage), which is output, when stepped to. An example of this type of sequencer is the Doepfer A-155.
* 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.