[vorbis-dev] patents and separate entropy coding

Frank Klemm pfk at fuchs.offl.uni-jena.de
Wed Dec 20 00:26:29 PST 2000

On Mon, Dec 18, 2000 at 01:54:40AM +0100, Segher Boessenkool wrote:
> > Vorbis also doesn't encode the spectral results of the MDCT.  The
> > spectral values are passed through a whitening filter first (the
> > 'floor' is effectively an IIR filter), and this distiction is
> > important.
> It is FIR, not IIR, I think? Only a finite number of samples
> are affected?
Characterizing a filter by the terms FIR and IIR is in this case really
stupid. You calculate the frequency response of a filter, which is basicly
a AR, a MA or a ARMA filter and use this frequency response for spectral
whitening. This is always a FIR filter, so the basic filter should be
characterized by the terms AR, MA or ARMA.

Filter	    		I-Responce	invers filter
AR (auto regressive)	mostly IIR	MA
MA (moving average)	always FIR	AR
ARMA (combination)	often IIR	ARMA

Frank Klemm

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