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

[Tim Goetze]

Steve Harris wrote:

>We'd also need to split up the incoming signal by frequency though, and
>that would make it expensive to run.

very much so.

>> been thinking about how to do a hard clipper with sinc some more
>> today, without real results though.
>
>Yeah, I think thats difficult, and probably not neccesary, the "hard clip"
>from a guitar amp doesn;t look very hard to me, so I recon you could just
>apply the shaper, plus a bit of oversampling, a LP filter and it'd be
>fine.

http://quitte.de/driven.gif
does look like hard clipping to me (sine, shaped at maximum gain).

>Remind me: what was the thing that put us off chains of models? Was it

* the harmonic mix didn't resemble the original
* too muddy
* aliasing when stacked (though oversampling might help)

>just the messy bottom end? Or was there more? I'm pretty sure I can fix
>the muddly low harmonics and it sounds like other people aren't modeling
>the variation in harmonic amplitude with signal amplitude, so maybe it
>isn't important.

went looking at some pod distortion. it seems you're right about
the harmonic mix not being influenced by signal amplitude, it
seems they just fade them in with more gain. an interesting fact is
that the harmonics it generates die away before they reach 11 kHz; a
high f sine input will cause relatively few harmonics, a low f will
have many. looks like they simply use a LP (albeit one with very good 
stop-band attenuation) to fight aliasing.

i'm puzzled how they do manage to come up with such a lot of
different distortion characters though.

tim