- Miller Puckette via Pd-list pd-list@lists.iem.at [2020-03-04 16:49]:
vcf~ aims for an approximate peak gain of 1 (although this is _very_ approximate for low values of Q).
Thanks for the info Miller!
Measuring vcf~ with a Q of 5 and noise~ I do get different results depending on the center frequency. For 100Hz the filter output is 26dBRMS softer than its input signal, at 1000Hz it is 16dBRMS softer, and at 10000Hz it is 5dB softer. Raising the Q to 15 softenes all three levels accordingly.
Me, I use Q+1 to normalize filtered white noise.
Is that the way how you do it in vcf~'s code or how you would do it to normalize after bp~?
But theory would suggest the output power should be proportional to bandwidth (= f/Q) - with the bandwidth limited to Nyquist frequency - so one would divide by sqrt(min(f/Q, SR/2)) . I'll stick with multiplying by Q+1 for myself :)
I can't seem to get around the fact that sqrt(f/Q) changes with center frequency, and Q+1 does not. Is that part of the simplification?ยด
Shouldn't the bandwidth of the filter let the same signal enery pass regardless of center frequency?
Sorry if I skipped this part of my DSP classes...
thanks! P