Subject: Re: [linux-audio-dev] [ann] unmatched - a LADSPA amp tone
From: Steve Harris (S.W.Harris_AT_ecs.soton.ac.uk)
Date: Mon Oct 28 2002 - 16:13:24 EET
On Mon, Oct 28, 2002 at 01:30:49 +0100, Tim Goetze wrote:
> it's an interesting pov though, in fact i've been thinking
> about algorithms that work like IIR filters (that are often
> used for HP/BP/LP) with the addition of nonlinear terms for
> recreating the tube distortion. the maths of such a thing are
> not easy to grasp though.
In my (limited) experince its really hard to make them stable. But you can
make interesting non-linear filters by using different parameters for the
different halves of the wave cycle. This is what makes the gong sound
gongy (waveguide_nl.h). It could also apply to cone modelling, as the
characteristics of the deflection in the positive and negative directions
will be a bit different.
<rambling>
To make a nonlienar cone filter you could either use different IIR
parameters for signal sign, or you could us different parameters for
different amplitudes (or both).
Different amplitudes would be equivalent to how you model nonliear systems
with FIR impulses - I can't believe I didn't think of it before.
- Steve
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