Subject: Re: [linux-audio-dev] [ann] unmatched - a LADSPA amp tone
From: Tim Goetze (tim_AT_quitte.de)
Date: Tue Oct 22 2002 - 22:38:26 EEST
Steve Harris wrote:
>On Tue, Oct 22, 2002 at 03:00:03PM +0200, Tim Goetze wrote:
>> i guess (don't know much about reverb design [yet]) that in
>> order to get a truly 'white' reverb the number of delay lines
>> approaches infinity. which turns a decent implementation into
>> a real programming challenge. :) nonetheless, one could start
>> with what we have -- usually people complain that there's not
>> enough 'color' in our digital reverbs ('gray'?).
>
>Also, 1 delay will give you white, so maybe its just the middleground that
>causes problems. Its possible that a linear waveguide based reverb will
>shift the frequencies less.
>
>You're right though, we should try an off the shelf reverb first.
the problem with converging IIR is that either the IIR or the
converging algorithm or both don't like impulses that are too
lively. the converger will simply fall dead when it sees an
exponentially decaying white noise impulse. it makes sense,
my understanding of its nature has it that the IIR really likes
to oscillate smoothly. i'd love to see the response of a good
concert hall, that will surely clear some questions on my part.
>> >PS "Steve's flat" was captured with a half knackered monitor and a three
>> >quarters knackered mic. I should probably do it again, as I have moved :)
>>
>> and i should really do the fender here and compare the original
>> to the convolved/iir-filtered emulation. but it's more important
>> to get the nonlinear parts right first i think.
>
>As a first cut, have you tried valve_1209 + valve_rec_1405 + [some LP
>filter] plugins? These make a fairly conventional tube model when applied
>in that order, and the rectifier includes some line sag effects which are
>the source of some of the compression effects (modulo my very basic
>knowledge of electronics).
what i don't get about the valve (the rect influence seems
negligible) is that it only shapes the negative portion of a
sine. without a LP, there's faint aliasing. it doesn't sound
so bad though, in fact i like it.
however i'm into harsh distortion now, and have fed the fender
three sines from zero to full gain (three octaves of 'c').
the shaping it does has some important properties that i'm only
beginning to understand, but it really does look fundamentally
different. it seems to self-oscillate at the zero-crossings,
and otherwise compresses the sine much like your valve does,
only the output signal is not a straight line where compressed,
but rather another irregular but smooth oscillation about a DC
value. a (realtime) electric circuit simulator would come in
handy here. i have a schematic of a tube amp circuit but i'm
not apt at drawing conclusions from it.
tim
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