[vorbis] Cascading?

[Segher Boessenkool]

Aleksandar Dovnikovic wrote:
> 
> During the interesting interview that binaryfreedom has made with Monty
> and Jack, Monty mentions cascading, a feature that will be added, quote:
> "Cascading is the ability to make multiple passes through the frequency
> spectrum, iteratively filling in more detail, like a progressive jpeg".
> What are the advantages of something like this - does this generally
> improves quality or is it used primarily to put more important audio data
> at the beggining of the block so that bitrate peeling might be effectively
> applied?

Using bigger (higher dimension) VQ codebooks improves compression ratios,
but we need to send all of the codebooks in the header, and the size
of the codebooks just explodes. Using cascading, the codebook sizes stay
controllable, while having almost as good a coding gain, and using bigger
dimensions.

Cheers,

Segher

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