[FFmpeg-devel] [PATCH] Simplify IMDCT in dca.c

Benjamin Larsson banan
Sat Aug 30 11:41:06 CEST 2008

Alexander E. Patrakov wrote:
> Michael Niedermayer wrote:
>> Hi
>> patch below replaces the duplicated IMDCT in dca.c by the standard one.
>> code is faster, simpler nicer, ....
>> yes the QMF of dca is a windowed IMDCT

Dca uses a cosine modulated pseudo QMF.

> Yes, here it brings the time to decode a ripped CD down from 1m11s to 51s.
> Unfortunately, I could not test the SSE patch by David Conrad and compare.
> Your change is not bit-exact WRT the previous version, but sounds right. The
> difference is of the form of 1-LSB-clicks (several random clicks per
> second - when amplified, sounds like a Geiger counter).

When I changed from from double to floats in I also got lsb differences.
Non audible ones.

Benjamin Larsson

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