I guess I can get the coefficients and derive an overall gain parameter. I got objects in ELSE that do that [coeff2pz]. But if it also depends on the frequency I should calculate this all of the time which doesn't seem reasonable. Maybe just keeping a safe 0.5 q is fine...
You know, using something like lop~ is pretty stable, I am now wondering if I should just use if for the sake of simplicity and efficiency as well. Do I really need a 6db decay per octave instead of 3db? What do you people think? will make some tests... thanks Em qua., 27 de abr. de 2022 às 09:11, José de Abreu <[email protected]> escreveu: > sorry, but I'm very curious. Using a resonance filter implies phase > shifting right? (instead of using a non resonance linear phase filter) But > this means that the tuning of the KS will be affected only near the > resonance? i may not understand this fully, but I never thought about using > resonance inside KS > > Em qua., 27 de abr. de 2022 08:51, Claude Heiland-Allen < > [email protected]> escreveu: > >> Hi Alexandre, >> >> On 27/04/2022 06:01, Alexandre Torres Porres wrote: >> > hi list, I'm using a 2nd order lowpass resonant filter whose >> > coefficients I'm getting from the famous Eq-cookbook and using it >> > inside a feedback loop to implement karplus-strong. >> > >> > I also have a coded object for that (pluck~) and the 'q' parameter is >> > 0.5, which is a "safe" setting, i.e. the filter doesn't get unstable >> > and blows up. >> >> The filter in isolation should be stable for any positive 'q', but its >> gain might get bigger than 1 making the larger feedback loop explode. >> >> You can do some additional gain reduction if increasing the q factor >> increases the peak gain of the filter and makes the feedback loop explode. >> >> > I was now trying to find a higher 'q' coefficient but it's hard to >> > know where I can go "exactly" just under it could blow up. >> >> You want the total gain in the feedback loop for all frequencies to be >> less than 1, i.e. peak (over frequencies) gain less than 1. >> >> > Is there an easy way to know this other than trial and error? >> The filter gain probably depends on cut-off frequency as well as q, so >> the filter peak gain is a function of 2 parameters. Maybe gathering >> numerical data and surface-fitting a mathematical function could work, >> if the maths to do it analytically is too hard. >> >> If you modulate the filter parameters, it could still explode (the >> filter theory as per eq cookbook is only valid for fixed parameters, >> afaik). >> >> If you implement with insufficient accuracy inside the filter feedback >> (e.g. single precision floating point for 'y' in a biquad >> implementation), rounding errors can accumulate and can affect the >> actual gain (vs the theoretical gain you'd get from exact maths). >> >> >> Claude >> -- >> https://mathr.co.uk >> >> >> >> >> _______________________________________________ >> [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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