Archived from groups: rec.audio.pro (
More info?)
Anahata wrote:
> drichard wrote:
>
>> Sure there are. I'm hardly knowledgeable about them, but even I've
>> heard of FLAC, which stands for "Free Lossless Audio Compression".
> Quite right. I've used it too. The actual amount of compression cannot
> be guaranteed but it does average about 50% on 16/44.1 stereo WAV files.
As it turns out, one of the properties of any kind of lossless compression
(not just audio) is that the ratio can never be guaranteed for all
possible inputs.
If it could be guaranteed, then you could re-run the compression
algorithm on its output over and over again until you got any file
down as small as you wanted it. Getting a bigger hard disk would
never be necessary again, as you could always just compress the
files you have further and further if you were running low on space.
Also, there would be no limit to the amount of audio you could fit
on a CD-R, for instance.
On the other hand, if you have lossy compression, then you can always
design your algorithm to get a guaranteed ratio. If the ratio starts
getting too bad, just sacrifice quality. (At the very worst, all you
have to do is start chopping down the sample rate, although there are
probably better ways.)
Anyway, the key with lossless algorithms is to invent an algorithm
that is likely to get a good ratio with the type of inputs people
tend to throw at it. Then, in a way, you get around the mathematical
property that a lossless compression algorithm must actually sometimes
expand instead of compress.
- Logan
/www.monkeysaudio.com/comparison_compression.html
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