[FFmpeg-devel] [TeX] DCA subband transform
Alexander E. Patrakov
patrakov
Sun Sep 7 15:31:52 CEST 2008
Michael Niedermayer wrote:
> It would be more interresting to know if every "pseudo"QMF is a windowed
> *DCT and if every windowed *DCT is a "pseudo"QMF
Good idea. However, I don't know the definition of a windowed *DCT, except
for the case when there are only two overlapped windows. I.e., Wikipedia
says:
> MDCT ... has half as many outputs as inputs (instead of the same
> number). In particular, it is a linear function F : R^{2N} -> R^{N} (where
> R denotes the set of real numbers).
(i.e., they use N as the number of MDCT outputs, and, thus, IMDCT inputs)
Further, they say:
> In typical signal-compression applications, the transform properties are
> further improved by using a window function wn (n = 0, ..., 2N-1)
...and then discuss that the window must be shifted by the half of its
length each time, and write the Princen-Bradley condition that applies only
to this case.
I.e., their window has twice as many points as the number of MDCT outputs,
which is not the case for DCA, while DCA and MP2 have 32 IMDCT inputs and
512 points in the window, and I don't know the equivalent of the
Princen-Bradley condition for this situation.
--
Alexander E. Patrakov
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