I use biquads in JSyn. The coefficients are calculated using RBJ's excellent biquad cookbook from the music-dsp archives.
I have found that I can recalculate and update the filter coefficients on the fly without unpleasant artifacts. I do NOT zero out or modify the internal state variables. I should think that setting them to zero would sound pretty bad. Generally the filter settings are changed gradually using a knob or driven by an LFO or envelope. Phil Burk On Tue, Mar 1, 2016 at 6:56 AM, Paul Stoffregen <p...@pjrc.com> wrote: > Does anyone have any suggestions or publications or references to best > practices for what to do with the state variables of a biquad filter when > changing the coefficients? > > For a bit of background, I implement a Biquad Direct Form 1 filter in this > audio library. It works well. > > https://github.com/PaulStoffregen/Audio/blob/master/filter_biquad.cpp#L94 > > There's a function which allows the user to change the 5 coefficients. > Lines 94 & 95 set the 4 filter state variables (which are 16 bits, packed > into two 32 bit integers) to zero. I did this clear-to-zero out of an > abundance of caution, for concern (maybe paranoia) that a stable filter > might do something unexpected or unstable if the 4 state variables are > initialized with non-zero values. > > The problem is people wish to change the coefficients in real time with as > little audible artifact as possible between the old and new filter > response. Clearing the state to zero usually results in a very noticeable > click or pop sound. > > https://github.com/PaulStoffregen/Audio/issues/171 > > Am I just being overly paranoid by setting all 4 state variables to zero? > If "bad things" could happen, are there any guidelines about how to manage > the filter state safely, but with with as graceful a transition as possible? > > > > _______________________________________________ > dupswapdrop: music-dsp mailing list > music-dsp@music.columbia.edu > https://lists.columbia.edu/mailman/listinfo/music-dsp > >
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