From the original SynthMaker forum (2004–2014), with its members’ names and dates.
Tom7777 ·
I have made a quick example of what seems to be a resonance bug -
download/file.php?id=4
In the example mycos optimized SVF is used however it seems to happen with other filters that have been posted also and it seems to be a bug when certain keys are played it overdrives but others seem fine so im guessing this is a bug. Thanks
rl ·
Well, that's what people call 'resonance', isn't it. Excitation at certain frequencies cause the filter to 'scream'. I think MyCo's implementation is clean. Just plug it to an analyzer module and watch the impulse response.
At resonance=1 the filter makes a pretty nice sine oscillator oscillating at the cutoff frequency:
Note that a SVF filter is known to be a bit unstable at very high frequencies. The example shows a little notch above 20kHz
(I like that attachment feature)
Tom7777 ·
Well, that's what people call call 'resonance', isn't it. Excitation at certain frequencies cause the filter to 'scream'. I think MyCo's implementation is clean. Just plug it to an analyzer module and watch the impulse response.
Well i was expecting a reply like that, it seems fine with the other keys, myco said it seemed to be a bug himself, how do you get rid of the screaming on certain keys then? if it's the 'normal' thing that it sounds totally rubbish on certain keys.
MyCo ·
well, I said the same like rl, the SVF is not a stable filter. They use a "tripple pass fix", so the filter processes everything 3 times and add the results together with a scale factor.
The self oscillation is a different problem, you can get around it, by limiting the resonance input to 0.99, but the unstable character (crackles and overdrive sometimes) is still there. I found out, that you can avoid it, by scaling down the input signal to a range at -0.33 to 0.33, but then you'll also introduce aliasing when you scale it up again after the filter.
Tom7777 ·
So it's sort of a bug then but mainly with that filter ok, i thought it might have been a SM issue because i have noticed it with various other filters from the forum. Are you sure it's only at very high frequencys, i don't know too much about frequencys but when testing some higher notes than V can play fine and again its just a few keys where this happens which is odd but im probably wrong in thinking low notes = low frequencys, high notes = high freqs right? How would i apply the scaling on the SVF i changed floats MULTI and TSF3 values which im guessing are the ones to change? but it still happens.
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