What Does a VCA Do? (Modular Synth 101 | Part 2)

Continuing with this series on modular synthesizers, I take a look at the VCA (Voltage Controlled Attenuator). It is said to be one of the most valuable parts of a synthesizer and I use a simple example to illustrate what a VCA does.
See more Modular Synth 101 videos here: • Modular Synth 101

[@id.unknown1283]

I'm always trying to explain my setup to my wife and always get stumped when it comes to modules like a VCA. Great explanation

[@musicalmiscellany]

Thanks man. This is a new series. I'll post another episode each Monday for the next couple months. Each one will be around 2 min long so it should make it easy for someone to just get the foundations.

[@bearshield7138]

Thank you so much There is so much t learn and I do not even know where to start

[@musicalmiscellany]

I think this series will help a lot. Tune in every Monday for the next episode.

[@HoneyWindbutton]

I was confused because I thought VCA stood for voltage controlled amplifier. Which is the opposite of an attenuator.

[@musicalmiscellany]

A lot of companies say it stands for voltage controlled amplifier but in reality very few actually boost a signal past unity gain. So they’re not “amplifiers” at all. VCAs typically adjust a signal between 0 and unity gain. This makes them more of an attenuator than an amplifier.

[@HoneyWindbutton]

@@musicalmiscellany thanks for the reply. Boosting it from zero to unity would make it an amplifier though, wouldn’t it?

[@musicalmiscellany]

@@HoneyWindbutton Boost implies greater than unity. So, what a VCA is typically doing is turning a signal down from unity to 0 (or somewhere in between) making it an attenuator. Keep the keyboard paradigm in your mind's eye... when you let off the key, the sound should stop (be at 0). When you press a key, the sound should appear (be at unity gain). In contrast, a basic amplifier/boost circuit would take a signal from unity to +6db or +10db or whatever. There are some VCAs on the market that can boost a signal beyond unity gain but their primary function is still to attenuate a signal when no CV is applied.

[@harryyes1527]

I understand that you can use an attenuator to control the strength of a modulation signal, but can you use a vca for the same thing?

[@musicalmiscellany]

Great question. You can. However, a VCA works best when you want the signal to rise and fall in intensity over time. If you want to attenuate something to a fixed level and not change it, an attenuator would work better (though you could still do it with a VCA). If you wanted to attenuate a signal to a certain level, then boost (or cut) it slightly, then go back to the same level, that's where a VCA shines. Hopefully that made sense. Essentially, an attenuator is better for a fixed position where a VCA simply adds voltage control to that attenuation.

[@harryyes1527]

@@musicalmiscellany Ok that makes total sense now. thanks for taking the time to reply!

[@musicalmiscellany]

@@harryyes1527 I'm glad that helped. Another way to think about it... with an attenuator you set the knob and the incoming signal will stay at that level (until you grab the knob and turn it). With a VCA you can continuously vary the signal level with a so-called invisible hand that constantly turns the knob (control voltage).

[@harryyes1527]

@@musicalmiscellany And this explains why im coming across VCA's both with knobs and without, the ones without are just being modulated by cv and the ones with knobs are also attenuators?

[@musicalmiscellany]

@@harryyes1527 You're on the right track. However, this is where the modules vary a bit by brand. If you see a VCA that just has 3 jacks... that is very straightforward (input, CV, output). Not all of them are that simple though. With the ALM Tangle Quartet I used in this video, it has a knob to attenuate the incoming CV (which is being used to attenuate the incoming audio). However, if you don't have a cable present in the CV jack... the module just functions as a standard attenuator (input/output jack). Not all VCAs work this way though. Some may do nothing if there's not a plug in the CV jack. Others have 2 knobs, one to control the CV and one to control the original signal. I know... it's complicated. All of that said, it sounds like you've got the concept.