[LAU] Octaver or fuzztone effect

[Folderol]

On Sat, 26 May 2007 11:09:49 -0700
Ken Restivo <ken at restivo.org> wrote:

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> On Sat, May 26, 2007 at 04:38:46PM +0200, Georg Holzmann wrote:
> > Hallo!
> > 
> > >http://www.geocities.com/CollegePark/Library/1355/tonemachine.gif
> > >http://www.geofex.com/FX_images/foxxfuzz.gif
> > 
> > Okay, I did not mean the circuit, but a schema of the mathematic behind 
> > it ... ;)
> > Then it should be easy to build in software ...
> > 
> 
> Maybe model the circuit in something like SPICE, and have a look at what the modelled circuit does to a sine-wave input, or, and impulse?
> 
> http://www.linuxjournal.com/article/2169
> 
> Hmm. An interesting project might be hacking SPICE into being a kind of a deconvolution engine, to build a WAV impulse response file of a circuit. Then you could use that IR to "play" through the circuit using JACE or similar.
> 
> The maths involved in such a thing would be way beyond my meager skills, however.
> 
> - -ken

The preamp stage gives some filtering that seems to lift at around 3kHz
(fairly typical 'brightness').

The funny bit is a variation on a full-wave rectifier which has the
effect of crude frequency doubling. Instead of a switch it is better to
make the 'bottom' half variable so you can control the amplitude of the
doubled effect. Don't know quite how you'd do this is software, you
need to sort of 'fold' the signal so the negative bits go positive
instead.

That is followed by a single amplifier giving the drive to an
ordinary 2 diode limiter (fuzz). This kind of limiter doesn't give
a hard cutoff, but a slightly rounded waveform - sounds smoother. The
'sustain' control is simply drive level. More drive = more distortion
and longer before it comes out of limiting.

Followed by a slightly unusual tone control - quite interesting - and
a final buffer amp.


-- 
Will J G