[sdiy] Digital filtering (Oversampling and downsampling)

[Antti Huovilainen]

On Mon, 17 Aug 2009, Scott Gravenhorst wrote:

> Thank you Aaron, that was great.  I finally had a chance to listen (the 
> first time). Very interesting stuff on the Chebychev polynomials and 
> digital waveshaping. Definately an alternative to using naive constructs 
> with over/down sampling and a brick wall filter. The thing about those 
> naive constructs, however, is their simplicity.

And the fact they work over more than a very limited range. Polynomial 
distortion only works in the range where the prototype shaper wouldn't 
produce additional harmonics. In practise that means only quite mild 
nonlinearity and never downright clipping. Plus you still need to 
oversample.

I have discovered one method to waveshape with arbitrary shaper using only 
modest oversampling (2x-4x) and resulting in very little aliasing (no 
audible aliasing for reasonable signals).

Antti

"No boom today. Boom tomorrow. There's always a boom tomorrow"
   -- Lt. Cmdr. Ivanova