[music-dsp] A good guitar distortion algorithm?

[music-dsp] A good guitar distortion algorithm?
Nick music-dsp@ceait.calarts.edu
Mon Dec 1 07:30:01 2003

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Hey Christoph,
I have recently done some research into the subject and have a great
article for you. Let me know if it helps (quite frankly it is a little
over my head so if you get it maybe you can share the knowledge). I
guess for that matter if anybody on the list can explain it, I would be
very appreciative.


http://www.tele.ntnu.no/akustikk/meetings/DAFx99/schattschneider.pdf

Good Luck,
Nick

On Monday, December 1, 2003, at 07:29 AM, Christoph Jung wrote:

> Hello everybody,
>
> I'm working on a distortion algorithm for guitar with the aim of a
> future
> DSP-implementation. My question is: What would be the right approach to
> achieve aliasing-free and flexible guitar overdrive with efficient use
> of the
> processing power?
>
> So far, I've experimented with several non-linear functions like tanh,
> arctan, 1/x, etc.
> but immediately encounter the problem of audible aliasing for higher
> gain
> settings - no matter which function is in use. Pre- and post
> equalization and
> separation into frequency bands (distortion decreases with increasing
> frequency) can be of help but don't give me full control of the
> harmonic
> content of the output signal.
>
> A second approach of mine was the implementation of chebyshev
> polynomial
> waveshaping which has been occasionally mentioned in this mailing
> list. On my opinion,
> this method is fine for full control of harmonic additives but only
> works with not too
> complex input signals. Given a single note or a sine as input, my
> version of polynomial
> WS produces smooth overdrive with absolutely no aliasing. But as soon
> as polyphonic
> input signals occur, this method produces new tones ("intermodulation
> partials") which
> sound totally unmusical. This gets worse with increasing complexity of
> the input signal.
> If a full guitar chord is given as input signal, the harmonic output
> consists of roughly nothing
> else than noise - due to the huge amount of unwanted intermodulation
> partials. Knowing that
> polynomial WS works fine with sine-like signals, I could improve my
> algorithm by dividing
> the input signal into different frequency bands and applying
> waveshaping individually. But
> what if the input signal consists of two tones that lie very close to
> each other? Do i need to
> separate these tones with two different filters? Doesn't the
> complexity of such an algorithm
> exceed the computational capacity of a standard low-cost DSP?
>
> In general, my question is: What would be the right way to achieve a
> good sounding guitar
> distortion algorithm? Should I continue with the polynomial WS? Or
> should I concentrate on
> the usage of non-linear functions (and maybe apply some oversampling
> for filtering of
> unwanted partials)? Or are there other ways? How does digital
> "modelling" of guitar amplifiers
> or stomp boxes work? Is there any expert in guitar effects processing
> around here to give me a hint?
>
> Thanks
> Christoph
>
> dupswapdrop -- the music-dsp mailing list and website: subscription
> info, FAQ, source code archive, list archive, book reviews, dsp links
> http://shoko.calarts.edu/musicdsp
> http://ceait.calarts.edu/mailman/listinfo/music-dsp

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Hey Christoph,

I have recently done some research into the subject and have a great
article for you. Let me know if it helps (quite frankly it is a
little over my head so if you get it maybe you can share the
knowledge). I guess for that matter if anybody on the list can
explain it, I would be very appreciative.

Times


http://www.tele.ntnu.no/akustikk/meetings/DAFx99/schattschneider.pdf


Good Luck,

Nick


On Monday, December 1, 2003, at 07:29 AM, Christoph Jung wrote:


Hello everybody,


I'm working on a distortion algorithm for guitar with the aim of a
future

DSP-implementation. My question is: What would be the right approach to

achieve aliasing-free and flexible guitar overdrive with efficient use
of the

processing power?


So far, I've experimented with several non-linear functions like tanh,
arctan, 1/x, etc.

but immediately encounter the problem of audible aliasing for higher
gain

settings - no matter which function is in use. Pre- and post
equalization and

separation into frequency bands (distortion decreases with increasing

frequency) can be of help but don't give me full control of the
harmonic

content of the output signal.


A second approach of mine was the implementation of chebyshev
polynomial

waveshaping which has been occasionally mentioned in this mailing
list. On my opinion,

this method is fine for full control of harmonic additives but only
works with not too

complex input signals. Given a single note or a sine as input, my
version of polynomial

WS produces smooth overdrive with absolutely no aliasing. But as soon
as polyphonic

input signals occur, this method produces new tones ("intermodulation
partials") which

sound totally unmusical. This gets worse with increasing complexity of
the input signal.

If a full guitar chord is given as input signal, the harmonic output
consists of roughly nothing

else than noise - due to the huge amount of unwanted intermodulation
partials. Knowing that

polynomial WS works fine with sine-like signals, I could improve my
algorithm by dividing

the input signal into different frequency bands and applying
waveshaping individually. But

what if the input signal consists of two tones that lie very close to
each other? Do i need to

separate these tones with two different filters? Doesn't the
complexity of such an algorithm

exceed the computational capacity of a standard low-cost DSP?


In general, my question is: What would be the right way to achieve a
good sounding guitar

distortion algorithm? Should I continue with the polynomial WS? Or
should I concentrate on

the usage of non-linear functions (and maybe apply some oversampling
for filtering of

unwanted partials)? Or are there other ways? How does digital
"modelling" of guitar amplifiers

or stomp boxes work? Is there any expert in guitar effects processing
around here to give me a hint?


Thanks

Christoph


dupswapdrop -- the music-dsp mailing list and website: subscription
info, FAQ, source code archive, list archive, book reviews, dsp links
http://shoko.calarts.edu/musicdsp
http://ceait.calarts.edu/mailman/listinfo/music-dsp


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