I'm just starting to design a modular synth and i have a beginners question. Is it possible to use an Audio signal as a control voltage? Essentially all I want is to be able to use a standard oscillator as a modulator to control cutoff frequency, like you can do on the Pro-1 or EMS synth. I presume it is possible, but I realize that Audio is AC voltage and CV is DC voltage. So is it safe to mix these signals? Maybe someone brave can just try it and see if it works...


...I want is to be able to use a standard oscillator as a modulator to control cutoff frequency, ...
-- Plurnstyle

Short answer: Yes you can use adio as CV.
Not sure what you are getting at though. To ''use a standard oscillator as a modulator to control cutoff frequency" you don't require audio as CV?


So you can plug audio signal into cv input even though it's AC to DC?
I just want to use an a basic oscillator as an LFO, it should be simple...

So how would you set up an Oscillator with no cv output, as an LFO? Presumably you just slow down the Oscillator and plug it's audio output into a cv input, right??


So how would you set up an Oscillator with no cv output, as an LFO? Presumably you just slow down the Oscillator and plug it's audio output into a cv input, right??

-- Plurnstyle

Yep. Any OSC that can go slow enough can work as an LFO.
Likewise, an audio OSC with square output and adjustible pulse width can produce triggers and gates.


Amazing, so there's no issue with mixing AC and DC signals?


Amazing, so there's no issue with mixing AC and DC signals?
-- Plurnstyle

As long as you respect the expectations on the receiving side, no. (As in most cases in life ;-)
Meaning most audio gear - like PA systems or studio gear - will get upset when your modular output has DC in it. Such gear usually has steep filters to prevent anything below 20Hz to ever reach a speaker. Power amps often shut down when they sense DC. At the very least it will lessen your headroom. But inside a modular often mixing of AC and DC ist required for CV, such as shifting a LFO signal (AC) swinging between -3V and +3V into unipolar so it moves between 0 and +6V by adding +3V offset (DC). Even audio gets hefty DC applied to it in some distortion units.


Very interesting, and how would you add the offset to make the voltage above zero?


By using a CV conditioner like the Ladik M-120 . It can mix two channels of audio/CV (and invert them) and add a negative or positive offset to the mix. It is 'DC coupled' meaning it will not filter out DC (as opposed to audio/hi-fi gear).


Nice, that sounds very useful. But to use an oscillator as a modulator it doesn't actually need the offset, right?


Not necessarily. But you will want an attenuater/verter. Unless you prefer a vibrato spanning multiple octaves ;-))
Put it however you like, a attenuverter/scaler/shifter is one of your most basic modular needs.


Ah, of course, you need some way to control the depth. Thanks for being so informative, I'm learning a lot here
Ok slightly different train of thought: What would happen if you plug an Oscillator's output into it's own cv input making a loop? Would it make a complex wave shape, or just break the module?
Haha, sorry, just trying to learn how these things behave...


Feedback frequency modulation. Unless you carefully control the fb level you will get some disgusting noise.