[linux-audio-dev] [ann] unmatched - a LADSPA amp tone

Steve Harris S.W.Harris at ecs.soton.ac.uk
Wed Oct 30 13:17:00 UTC 2002


On Wed, Oct 30, 2002 at 06:11:11 +0100, Tim Goetze wrote:
> Steve Harris wrote:
> 
> >Thanks for doing that, I haven't had the time. Can you produce a spectrum
> >plot for the current s/w chain?
> 
> http://quitte.de/sine-spectrum.gif
> http://quitte.de/straight-spectrum.gif

The sine spectrum looks pretty close to me, except that some of the low
harmonics are too high, probasbly cutting back some of the parameters to
the valve would fix this.

I would guess that if we can fix the low harmonics the right thing to do
is to modulate the strength of the sin shaper with incoming amplitude.
 
> >It would be more efficient to just calculate the corect chebyshev in
> >realtime, the problem is that they have lienar CPU cost with the number of
> >harmonics, 20 harmonics for example will be pretty expensive. As we are
> >building on the existing harmonics generated by the valve sim though we
> >shouldn't need that many.
> 
> there's one problem i see: if we employ a chebyshev, it is going
> to create harmonics no matter what amplitude our incoming signal
> is iiutc. this is unlike the real thing, which will produce a
> different spectrum if one is playing softly, or with the volume 

I was planning to vary the generated harmonics with incoming
amplitude, but it doesn't look like this is the right appraoch, there are
allready plenty of strong harmonics, a cheby would just make it muddier.

The strong presence of low harmonics is probably the cause of the
softness.

- Steve



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