View Full Version : compression

Brent Aliverti
2004-12-03, 08:42
I just finished reading the ExtremeTech Audio Codec Shootout
(http://www.extremetech.com/article2/0,1558,1560783,00.asp). It was
interesting, and their hearts were in the right place in devising their
single-blind methodology, but I think it was flawed to an extent. They put
together 4 CDs, each containing several versions of the same song. The first
track was the source uncompressed file and the listeners knew this. The rest
of the tracks had been compressed with various codecs and then decompressed
back to .WAV before burning the CD. The listeners didn't know which were
which and were asked to rate the tracks from 1 (lowest) to 5 (highest) in
comparison to the first track (the reference track).

The most telling thing for me is that they included a lossless track in
there as well. Since it is bit-for-bit identical to track 1 that had never
been compressed, it should have warranted a score of 5 each time. It didn't.
That underscores how much psychology (and individual pre-conception) plays
into people's perception of audio quality. It also makes me wish they had
not told the users that track 1 was the uncompressed file. Instead, they
could have just given listeners CDs without any idea of which versions of
the song were compressed and which weren't. Sure, psychology would still
have been a factor, but I think it would have forced listeners to abandon
their pre-conceived notions that compressed music is inferior to
uncompressed music. Instead they would be forced to rate the quality of each
track on its own merit.

The other thing is, they mention that their VBR scores were done by
specifying a "98% Audio Quality". I'm not sure what setting that corresponds
to in LAME. Did they use -alt preset standard, -alt preset extreme, or
something else?

Lastly, I'm puzzled that a factor in their rating of MP3 (represented by
LAME 3.95) a 6 out of 10 is that LAME did a poor job at 64kbps. Well, duh.
LAME isn't optimized for 64kbps and most anyone that has done comparisons
will tell you that at 64kbps, Franhofer is the MP3 codec to use, so scoring
it down for that, seems unfair. And even so, MP3 just doesn't hold up well
at 64kbps.