Audio Rate Filter Modulation
Hello folks, excuse me for my silly questions, but I'm a noob and I don't know how to achieve my idea.
How can I modulate the cutoff frequency of a filter at audio rate without artifacts? Also is it possible to make a filter self oscillate?
Thanks in advance! :)
PS: I have a feeling I might have to use gen~ or poly~, but I've never used them.
if you think it to the end, self oscillation (or high resonance) and artefact-free audio rate modulation is never really possible. (well, to be exact, even without resonance artefact can occur when the frequency of whatever jumps across the spectrum.)
there are some propertional answers though.
for example you can modulate the filterfrequency with a very high velocity in audio rate when you use the slide~ object as your filter brick(s).
of course slide~ does not know how to spell "resonance" at all, but it allows any input for freq without moaning.
if your interest is not envelopes but only quick jumps for different note on events, you could implement a little delay in a generator to give a biquad~ or sfv~ type of filter time to reach the goal frequency before the next musical event starts to play. this little trick can make sound your filters a bit different. ;)
Thank you for your reply. I tried slide~ but I didn't manage to make it work. I run audio through the first inlet and cycle~ --> snapshot~ to modulate the 2nd or 3rd inlet of slide~ but it didn't have any effect. I checked biquad~ 's help and its self-oscillation only works just as an oscillator, it doesn't accept input in that mode, so it's not really useful for me. Unfortunately slide~ won't work for me, because of the lack of resonance.
Excuse me, but my explaination could be too bad or generic. What I want with self-oscillation is something similar to Live's Operator's.
Regarding the filter modulation, I want to approach the fm feature of (and generally the entire) Sherman Filterbank 2
slide~ 2. 2. will interpolate between 5 samples and that makes a onepole filter at sampligrate/4.
try this, then you can feed it frequency in hertz.
(example is with !/, replace that with !/~ )
i think i got you regarding self oscillation... that kind of self oscillation which some analog filters can serve in live performances... but i am afraid you guessed right and building a proper ladder filter emulations should be done in gen~.
biquad~ can have a high resonance level and you could trigger a ringing from it by sending some low noise into it, but you cant modulate it fast enough to get what you are looking for.
The [filtercoeff~] is designed to do just that.
This solved my problem. filtercoeff~ is exactly what I needed. Thank you!
what will that helper utility change? biquad will still interpolate internally and tend to explode on frequency modulation.
The problem is that I don't have a clue how filters work, and if I have to study about them and then learn gen~, I will just opt for vst~ and use a ready-made solution. Thanks again.
one could roughly distinguish between "digital filters" (biquad/poles and zeros, chamberlin/svf, FFT, FIR/IIR, comb) and "digital emulations" of (analog) filters ("moog filter" ect.)
and of course @jfc is right that filtercoeff~ is the easiest way to control biquad~s (because filtergraph~ does not allow signal input and calculating filter coefficients on your own is CPU-intense and not necessarily a beginner level task)
however, that biquad allows you to control everything with audio rate, does not mean that it will always work like you wish.
it is still a start though, sfv~ for example does not even allow signal input. btw, vst plug-ins dont do, either. ;)
so let filtercoeff~ and biquad~ be your friends for a few days and see how it goes.
I was thinking about about using u-he Zebra2 or even Reaktor that have audiorate filters AFAIK inside vst~.