[LAU] [LAD] [ANN] CAPS 0.9.12

Fons Adriaensen fons at linuxaudio.org
Sat Aug 24 23:05:37 UTC 2013

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. So you would
either have to 

* run the new filter (with the new parameters) for some
  time before crossfading, which will complicate the
  code, or

* copy the state of the old into the new filter, but
  with a biquad this can again produce quite heavy
  spikes wich may last much longer than your crossfade.
  This can happen even when both the  new and old filter
  are set to 0 dB gain.

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).



A world of exhaustive, reliable metadata would be an utopia.
It's also a pipe-dream, founded on self-delusion, nerd hubris
and hysterically inflated market opportunities. (Cory Doctorow)

More information about the Linux-audio-user mailing list