> >
> > 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?
Well, it says so in the literature. But analysis of the formula's (not
much algorithm, I'm afraid) suggests so as well. It is not a perfect
reconstruction filterbank, that's why I say suggests.
>
> 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'?
There is no such thing as an encode-only delay. After encode, we are in
a different domain (not time domain anymore, but some kind of
mixed time/frequency domain).
If you have to, you could say the "encode delay" is 255.5, just half of
the delay, 'cause the decode part is pretty symmetrical to the encode part.
>
> +/- 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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