[PD] bandpass makeup gain formula?

Miller Puckette msp at ucsd.edu
Wed Mar 4 16:48:45 CET 2020


vcf~ aims for an approximate peak gain of 1 (although this is _very_
approximate for low values of Q).

Me, I use Q+1 to normalize filtered white noise.  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 :)

Miller

On Wed, Mar 04, 2020 at 12:58:09PM +0000, Claude Heiland-Allen wrote:
> Hi Peter,
> 
> On 2020-03-04 11:18, Peter P. wrote:
> > I am trying to calculate a makeup gain factor for white noise sent into
> > [bp~] and [vcf~] bandpass objects depending on the center frequency and
> > the Q (width) so that it measures the same in dBRMS before and after the
> > filter. I am currently measuring it but am wondering if
> > a.) this has been done before
> 
> Not quite the same, but maybe useful:
> https://lists.puredata.info/pipermail/pd-list/2010-08/082104.html
> 
> > and
> > b.) if there is an analytical solution to it already
> 
> vcf~ code has a gain adjuster in it, but I don't know the theory behind it.
> 
> 
> Claude
> -- 
> https://mathr.co.uk
> 
> 
> 
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