[linux-audio-dev] Re: Cheby amp code

Steve Harris S.W.Harris at ecs.soton.ac.uk
Tue Nov 5 12:12:46 UTC 2002

On Mon, Nov 04, 2002 at 11:49:59 +0000, Steve Harris wrote:
> Just tried it, tested with a synthetic overdrive effect. The results look
> plausible. but I haven't tried shaping anything with them.

I mentioned our stumbling ardound in the dark on the music-dsp list, and
Jay Tomas came back with this:

hints for characterizing the amp:
1) don't try to characterize the whole amp at once with test signals..
characterize each preamp stage individually.  Attempting to characterize
the clip curve of the whole amp will yield a frequency dependent clip
curve which isn't much use to you in a software implementation.
2) start with trying to measure the pre and post clip EQ curves with
test signals and then
use this info to deduce the effective static non-linear clip curve that
would approximately model what you are seeing.

So, it sounds like f we can get a curve off the seperate stages they
wont need fancy filter mangling, and saws are the way to go (well, noone
pointed and laughed ;)

Point 2 is a good one, by applying the EQ effect of the amp in reverse we
can counter out the filtering that makes the saws hard to analyse.

The bad news is that it means going inside someones amp with a probe, I
would have a go myself, but I've allready killed my last amp, and my
electronics skills are bad enough that I would probably fry myself ;)

Brave and/or stupid volunteers welcome ;)

- Steve

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