[LAU] [LAD] [ANN] CAPS 0.9.12

Fons Adriaensen fons at linuxaudio.org
Sat Aug 24 21:48:13 UTC 2013

On Sat, Aug 24, 2013 at 09:56:47PM +0200, Tim Goetze wrote:
> Thanks a lot for the evaluation and the problem report; I hope this
> hasn't caused damage to your ears (which I value highly!) or
> equipment.

I've learned to mute monitoring while doing such tests...

> It adds to the evidence that implementing thorough control
> smoothening is inevitable in the long run.

That may or not solve the problem. You have 3 input parameters
(P), and 5 biquad coefficients (C). Interpolating the C can
make a biquad unstable, and if this happens it doesn't matter
how fast or slow you do it. The only solution is to interpolate
the C only between sets of values that correspond to values of
the P that are not too far apart. So you need two levels, first
on the P to limit the rate of change of the parameters, then on
the C to avoid zipper noise.

> >Apart from this, it also produces multiplicative LF noise
> >at some low frequency settings. This is typical for type of
> >filter used.
> I haven't been able to measure such noise at anywhere near audible
> levels, not even when followed by high-gain saturation.  If you have,
> can you point out an input signal and settings that can provoke it?

The noise remains below audible levels in this case (there
are some plugins that are much worse). But it is still much
higher than it should be. The reason is that a biquad is not
the right filter for this job, at least not at low frequencies.



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It's also a pipe-dream, founded on self-delusion, nerd hubris
and hysterically inflated market opportunities. (Cory Doctorow)

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