[Fons Adriaensen] >On Sun, Aug 25, 2013 at 12:21:52AM +0200, Tim Goetze wrote: > >> I'm planning to evade this problem by crossfading between two parallel >> static filters. Some phase mismatch issues can probably be expected >> when the parameter sweep covers a larger range, but I'm hopeful it >> will turn out not to be much of a problem in actual practice, and that >> we will find out soon. It really needs a fix. > >I doubt very much if that will provide a practiacal solution. >The state of the filter depends on signal history. Depending >on the parameters, this could be quite long. I think the question deciding the quality of the filter fade is, how big will the phase difference between the two filters be? Amplitude differences shouldn't matter when we crossfade, as long as we're not phase-canceling. These are very simple filters that don't take long to settle on a stable phase relationship. A reasonably small parameter change will not change their phase response by much, so my expectation is that there will be only little cancellation and the fade thus close to imperceptible; at most a slight attenuation of high-frequency content. Just theorising over a glass of wine though. >The simple solution is to smooth the input parameters, >limiting their rate of change. Nobody expects an EQ >section to change from 100 Hz to 10 kHz in less than >half a second (unless it's a synth VCF module, but then >you definitely need something else than a biquad). Yes, that is a very convenient way to solve it, perhaps the preferable one given the realities. Tim _______________________________________________ Linux-audio-user mailing list Linux-audio-user@xxxxxxxxxxxxxxxxxxxx http://lists.linuxaudio.org/listinfo/linux-audio-user
