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

[Tim Goetze]

Steve Harris wrote:

>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

yep, that's what i expect, too.

>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.

it's interesting to know that valve preamp stages should have
a small bias (to + iirc), and you can in fact observe this in
the amp output i've recorded.

>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).

i'm still trying to model the hard-driven valve in the time
domain. the more i look at it, the more i think the 'building of
potentials' i've tried to describe comes near it. though it would
be nice to base it on hard facts about valve amp behaviour, too.

interestingly, the sine, shaped by the hard-driven amp, looks
a lot like the plots of 'ion conductivity' and 'Aktionspotential' 
from human heart analysis.

unfortunately they don't give a formula in the book i have on my
lap. any heart surgeons around? ;)

>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.

in fact you described something along these lines a few days
ago. ;)

tim