>
> Hiya,
>
> The polyphase filterbank has a delay of 511 (encoding + decoding together;
> there's no such thing as a delay in _only_ en- or decoding).
>
> Ciao,
>
> Segher
>
Hi Segher,
How did you get 511? observations, or analysis of the algorithm?
I've spent quite a lot of time on this, because these numbers had to
be known *exactly* to sync up the psymodel output with the quantization
of the MDCT coefficients. We need to know the actual delay of the
MDCT coefficients, which is the encode-only delay of the fitler bank +
MDCT. Thus we have to allow the conept of a delay for just the
encoding part - although maybe I am abusing the use of 'delay'?
+/- 1 is not going to matter much, but it is important to determine if
the (encode only) delay is 256 or 240.
I looked up in my notes and found that when I was first looking into
this, I measured the layer II (ISO code, encode, decode) delay: it was
about 480 (plus or minus a few samples). Layer II uses *only* the
polyphase filterbank (same one used in layer III) so this further
sugested the filterbank delay is 480 (+/- 1).
So I think a value of 481 agrees with both observations and
my analysis. But if you have evidence that it really 511, it
would be important to resolve this.
Mark
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