Re: [linux-audio-dev] wcnt linear filters

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Subject: Re: [linux-audio-dev] wcnt linear filters
From: Steve Harris (S.W.Harris_AT_ecs.soton.ac.uk)
Date: Tue Feb 03 2004 - 16:34:24 EET


On Tue, Feb 03, 2004 at 03:13:54 +0100, Alfons Adriaensen wrote:
> On Tue, Feb 03, 2004 at 01:52:13PM +0000, Steve Harris wrote:
> > On Tue, Feb 03, 2004 at 02:21:53 +0100, Tim Goetze wrote:
> > > ps: the svf sounds better to me with the 'very slight waveshape for
> > > extra stability' removed.
> >
> > Yeah, but without it the filter tends to explode with highish cutoff
> > values (above fs/4 IIRC). I should probably move it to doubles and remove
> > the waveshape.
>
> Moving it to doubles will not help. The problem is that at high F, the
> simple mapping from the continuous time domain to the sampled domain breaks
> down. You need to modify the params as non-linear functions of F and Q
> in order to correct for this.

OK, thanks. Yes, that rings a bell now - I think I made it a bit better by
oversampling the input (2 or 4x). I'l have a look at your plugin to see
what you've done.

- Steve


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