I've done a nice job plotting the frequency response of both bp~ and vcf~ and exposing their formulas,
see https://github.com/porres/Live-Electronics-Tutorial/tree/v1.0-beta-17/Examples/Vol.2/Part.05-Filters(Basic)/22-Filters.types/2.Filter.Types/2.Resonant/2.Bandpass and https://github.com/porres/Live-Electronics-Tutorial/tree/v1.0-beta-17/Examples/Vol.2/Part.09-Filters-Reverb-Karplus/31-Filters(Advanced)/3.Z-plane Em dom., 8 de mar. de 2020 às 19:59, Miller Puckette via Pd-list < [email protected]> escreveu: > > > > 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. > > > Aha - yes, my (Q+!) fix aims to allow changing Q without much affecting > the perceived loudness, but doesn't account for varying the center > frequency. > > To loudness-balance filtered white noise, you'd want to aim to get the > same signal power as the noise has in a one-bark-wide band. Above 500Hz > this increases linearly with frequency. So you'd want a 10-dB increase > in the signal for a 10x increase in center frequency. However, for > frequencies > below 500hz you'd want the result to be roughly independent of center > frequency. So what you're seeing looks OK except that it should be > corrected > below 500 Hz. > > OTOH if you want to balance with the whole of the white-spectrum noise (not > just the slice that's in your local bark) then you have to go look at > equal-loudness coutours (since in that case we're comparing loudnesses of > sounds at different frequencies). At that point I just give up and use my > ears :) > > > > 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~? > > > That's how I normalize in the patch. Example (but ignore the Hilbert > stuff): > > http://msp.ucsd.edu/syllabi/171.20w/patches/7.e.graphing-resonant-filter.pd > > > > 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??? > > > > Shouldn't the bandwidth of the filter let the same signal enery pass > > regardless of center frequency? > > > Yeah, depends on whether you want to match power ( roughly dividing by > sqrt(f/Q) for "reasonable" f/Q values) or "sound good" (as I think Q+1 does > fairly well). > > Also, the result for white noise isn't necessarily representative of what > you > get filtering real signals - all sorts of things happen then. > > cheers > Miller > > Sorry if I skipped this part of my DSP classes... > > > > thanks! > > P > > > > > > > > _______________________________________________ > > [email protected] mailing list > > UNSUBSCRIBE and account-management -> > https://lists.puredata.info/listinfo/pd-list > > > > _______________________________________________ > [email protected] mailing list > UNSUBSCRIBE and account-management -> > https://lists.puredata.info/listinfo/pd-list >
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