Compression - Shadows of phycoacoustical compression: or a feature that most MP2-3, AAC codecs lack

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Shadows of phycoacoustical compression: or a feature that most MP2-3, AAC codecs lack

Max Power

2005-03-11, 8:55 am

Shadows of phycoacoustical compression: or a feature that most MP2-3, AAC
codecs lack.

When you encode a CD, the coding process goes like this:
CD Media --> "WAV" temporary storeage (in memory) --> MP3 codec --> MP3 file

However, this does not tell you what signals have been masked!

To hear the signals that have been masked you need to:

1. CD --> WAV

2A. WAV --> MP3 codec --> MP3 file (no change here!)
2B. WAV --> WAV file

3. WAV file [frame] - MP3 file [frame] = WAV "difference frame" --> WAV file

Steps 2 & 3 could be implimented at the codec itself, so that the codec
could output a difference file in WAV format.

During MP2 R&D this was necessary to tune the codec.

I suspect that most (generic) MP3 codecs are not that well "tuned" for the
material they are encoding.

The masking shadow files would make for interesting lisening!
At higher bit rates there is less and less to hear.

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