[vorbis-dev] Using large-scale repetition in audio compression

Monty xiphmont at xiph.org
Thu Sep 19 16:03:34 PDT 2002

On Thu, Sep 19, 2002 at 12:44:42PM +0200, Lourens Veen wrote:
> This idea is so simple that I'm sure it must have been thought of 
> before, and discarded, since AFAIK it's not used anywhere. I did a 
> quick web search but that didn't turn up much, so I figured I'd put 
> it up for discussion here anyway.
> How about using large-scale repetition in audio compression? I'm 
> thinking of redundancy in repeated pieces of a song, ie a chorus. 
> Ofcourse, the different choruses aren't exactly the same (unless it 
> was mixed digitally and they cheated :-)), but wouldn't there be at 
> least some redundancy in the frequency domain? And could that be 
> used to lower the required bitrate for repeated parts of a song?

This is one of the earliest things I tried in 1993.  The answer was
'in fact, no'.  The problem is not compressing the predictable parts
of a song; that's only a few bytes a second.  The difficulty is
compressing the audible randomness.

The brute-force FFT/autocorelation compressor I wrote nearly ten years
ago know took several hours per song and when used in conjunction with
a standard LPC-style standard lossless compressor added as much
information to the stream as it eliminated.

In retrospect, this result should have been obvious.

> Obviously, it's not used (at least AFAIK) so there must be something 
> against it. Anyone care to enlighten me?

"It doesn't work the way you think it does".  Spend a few months on it
and you'll see why :-)

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