[vorbis-dev] patents and separate entropy coding

[Monty]

> > Thing is, I understand that they have a patent on compressing audio by
> > transforming to the frequency domain, quantising, and then entropy
> > encoding, which is what Ogg Vorbis does, so there's trouble. Now, I've
> 
> Vorbis uses a vector quantizer. A vector quantizer is _not_ the same
> as first quantizing, and then entropy encoding. Part of the entropy
> encoding is already included in the quantizer, and they are not
> separable. So this patent won't work.

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.

Monty

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