relen;139515 Wrote: 
> On the subject of lossless formats: they're the realtime audio
> equivalent of Zip and Stuffit - what you get out is exactly,
> bit-for-bit, what you put in (otherwise it wouldn't be "lossless").

Yes, that's it exactly.  No one argues that a Word document obtained
directly and the same one that's been extracted from a .zip archive
aren't bit-for-bit identical.  Yet somehow the same thing done to audio
doesn't apply.

Perhaps audio files are more magical?  :-)

> The penalty is somewhat larger files than perceptual coding produces.

"Somewhat" is an understatement - most of my FLACs are in the 25-35 MB
range (and I'm using maximum compression) while the equivalent MP3s are
3-5 MB.

But disc space is cheap.

> I am not aware of FLAC (for example) coding putting a bigger load on a
> playback device than any other codec: in fact you might expect the
> opposite to be true as FLAC files are not as highly compressed.

Actually MP3 files aren't radically more compressed than FLAC files -
the space reduction comes from -discarding- audio information entirely.
I'm not sure what additional compression is done but it's possible that
FLAC is actually more compressed - mathematically compressed that is,
not audio compressed.  Perhaps lossy formats are a little more
mathematically compressed, but not radically so - you can't achieve the
80% reduction over lossless compressed through mathematical compression
alone.  A FLAC encoder at compression setting 8 is working quite hard
to pack the bits in, it's hard to achieve 80% more.  :-)

So you have lossless uncompressed like WAV and AIFF, lossless
compressed like FLAC and ALAC, and lossy compressed like MP3 and AAC. 
Lossless compressed and lossless uncompressed are bit-for-bit identical
or else they wouldn't be lossless and the format would be quickly
abandoned.  Lossy compressed can never be bit-for-bit identical to the
original because audio data has been lost in the encoding process.


-- 
Mark Lanctot
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