[music-dsp] tube amp emulation

Steve Harris S.W.Harris at ecs.soton.ac.uk
Tue Apr 9 07:05:25 EDT 2002

On Tue, Apr 09, 2002 at 12:45:07 +0200, Cournapeau David wrote:
> Hi,
>      I am trying to write a little plug in to emulate a 'tube amp'. The
> problem is... I don't know anything about electronics and tubes.
>     In fact, I assumed that a tube amp is like a waveshapper, and I am
> trying different 'regular' functions for my waveshapper : hyperbolic
> tangent, 'sigmoïdes'  ( sorry, I don't know the english name for this
> function : I discover it in a Neural Network book, and the function is :
> f(x) = (exp(s*x)-1)/(exp(s*x)+1); s is a fixed parameter ).
>     My problem is that the result sucks : the distorted sound is good for a
> few band of frequencies ( the bass around 500-600 Hz ), but with other, it
> is really bad ( the high bands are transformed into noise). So I wonder if a

I would guess this is due to aliasing from the high frequency components.

There is an ok tube waveshaper on one of the DAFX pages:

You can help the aliasing by oversampling the input to the function and
decimating on the output.

- Steve

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