[FFmpeg-devel] [TeX] DCA subband transform

Alexander E. Patrakov patrakov
Sun Sep 7 14:26:53 CEST 2008


recently there was a discussion whether the DCA subband transform is a
windowed MDCT or something else. The attached TeX file contains the proof
that the original obfuscated transform is in fact, up to a constant factor,
a pseudo-QMF cosine modulation ?lter bank combined with the sign ?ip of
subband inputs whose number is congruent to 1 or 2 modulo 4.

I will use this math in order to write a higher-level simplification of the
transform code, in particular, I will remove the "noidea" history buffer.

Alexander E. Patrakov
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