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

[Tim Goetze]

Steve Harris wrote:

>On Mon, Oct 21, 2002 at 02:39:05 +0200, Tim Goetze wrote:
>> pleased to announce the release of 'unmatched'.
>> 
>> 'unmatched' is a simple effort to recreate some aspects of
>> the tone shaping of a real instrument amplifier. unlike
>
>Excellent. Can I ask how you did the FIR -> IIR mapping? Is it neccesary
>or significantly better to use doubles for the coefficents?

a quick test (%s/double/float/g) shows the cpu usage doubling,
but i'm unsure what may cause this huge performance drop.

doubles should, on average, mean we seldom hit the denormal number
bounds, or at least less frequently than with floats. i also expect
doubles to be beneficial to the filter stability by minimizing
round-off error, though i may be wrong here. lastly, x87 uses 80 bits
of precision internally, so it hardly means a performance penalty,
unless the cpu D-cache has problems keeping the filter history in
reach.

the converger program is at http://quitte.de/Converger.py --
it won't run without the mandala module, but it hopefully 
serves well to explain the algorithm (and probably better 
than my distorted translation into human language.)

>Have you experimented with adding a delay line and LP filter to simulate
>reflections off the back wall of the cabinet?

actually the next thing i'd have done do to come closer to the
original impulse would be an added IIR operating behind a delay 
line, yes. the current plugin response does not capture the later
parts of the original response so well (now that you mention it, 
i think it must be those reflections). however personally i'll
probably do more research on nonlinear effects before refining
this method.

tim