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  • Writer's pictureJoe Chris

Synthesizers III: Control Voltages – Gates, Triggers, and Envelopes

In the previous post, we built a basic voice in VCV rack with an oscillator, a filter and an amplifier. In this post, we will look at how gates, triggers, and envelopes and how they work both in a modular and non-modular enviornment to create interest in synth voices.

In any synth you control with a keyboard, when you press down a key the sound starts and when you let go the sound stops. This is a “gate”. Think of gates as a sort of binary switch - the sound is either on or off. When no key is pressed, the voltage is set to 0. When a key is pressed the voltage is set to whatever the max of the system is.

In VCV rack, load an LFO (low frequency oscillator) and a “scope” (oscilloscope) module to your patch. We will use a square wave as a gate for this example.

Connect the square wave of the LFO to the CV input on your amplifier*. Also connect it to the X-In on your oscilloscope. You will notice that as the square wave switches “on”, the amplifier switches on as well. But when the voltage of the square wave is at 0 (as seen by the oscilloscope or the red light on the LFO module) the amplifier is turned off as well.

LFO on
LFO off

*The CV input on your amplifier stands for “Control Voltage Input”. Control voltages are a way we can control modules using the output of other modules, rather than having to manipulate every parameter by hand. In modular formats especially, this is incredibly useful.

A trigger is a gate, but instead of being a constant signal at max voltage, it is just a single short spike. Triggers are commonly used “trigger” the next action of a module, rather than that module being a continuos action. So for example a step sequencer, a trigger can be used to tell it when to switch to the next note. Clocks modules send out triggers at regular intervals, but we can also create this effect by using a square wave LFO with the pulse width set to the minimum.

What’s cool about achieving it this way, is you start to see how many things in programming synths can be accomplished in a multitude of ways just by having an understanding of how things work and how to work with what you have.

The final piece of the puzzle that you need to get up and running with synthesizers is envelopes. Envelopes are similar to a gate, but instead of being an on-off switch they are LFO’s that can be adjusted in a variety of ways to modulate the sound. The classic being a modified form of a square wave, with 4 “Stages” denoted by the letters ADSR. A for Attack, D for Decay, S for Sustain, and R for release. This wave form that you dial in is used as a control voltage, which we will dive deeper into in the future. But for now, just understand that control voltages (or CVs). We can use an envelope on many things, but most synths will use at least one on the Amplifier to control the volume of the sound.

Load up Envelope ADSR. ADSR stands for Attack, Decay, Sustain, and release. You will find an envelope on every synthesizer you come across, and are the key part of creating different sounds ranging from sweeping string pads to percussive drum kits. As such, they are one of the most important aspects of sound design to understand.

A – how long a sound takes to reach full volume

D – how long it takes from peak volume of attack to volume of S (sustain level)

S – the dynamic level at which the sound sustains

R – how long a sound takes to return to silence after the gate is off

So with the ADSR module in our patch, lets connect the output of it to the CV in on the amplifier and send a gate (LFO square wave, larger pulse width) to the gate in on the ADSR. Experiment with the dials on this module, and hear how it affects the sound.

So with that, we have an understanding of how many synths work and operate. Though the examples we used were in a modular enviorment, all of this applies with any synth even if you are unaware of it happening. In the next post, we will take a look at the GUI’s of various soft synths and identify where all of these important functions can be found, without needing to resort to a modular enviornment to explain.


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