[linux-audio-dev] Diode wave shaper (LADSPA plugin)?

Jens M Andreasen jens.andreasen at chello.se
Mon Aug 16 08:43:14 EDT 2004


On mån, 2004-08-16 at 12:45, Erik de Castro Lopo wrote:
> On Mon, 16 Aug 2004 12:13:51 +0200
> Alfons Adriaensen <fons.adriaensen at alcatel.be> wrote:
> 
> > This is a bit too simple. The diode circuit does not perform hard
> > clipping when driven at moderate levels.
> > 
> > Something like 
> > 
> >   out = tanh (in)       (or tanhf() if available)
> > 
> > or
> > 
> >   out = in / sqrt (1 + in * in) 
> 
> Both of those would probably sound better than what I posted,
> but the original circuit had a 12k source impedance. As soon
> as the the input overcomes the forward voltage drop of the
> diodes the impedance of the diodes drops to the low hundreds 
> of ohms.

Wouldn't the current be limited by the 12k resistor, so that the
impedance of the diode won't drop as fast as you suggest?

Anyways, here is a variation on the same theme, supposedly synthesizing
tape saturation:

http://home3.netcarrier.com/~lxh2/tapesat.html
http://home3.netcarrier.com/~lxh2/tapesat2.gif

/jens

> 
> If you Spice the given circuit I think you'll find that the
> output looks a lot more like what I posted than either of
> the above.
> 
> Erik



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