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 >
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