Re: [Phys-l] iPod music compression

[John Mallinckrodt <ajm@csupomona.edu>]

> I have 3000+ CD's, and am thinking of buying an iPod. Does anyone know how
> the iPod compresses songs? Specifically, what frequencies get chopped off?

It's not that simple.  The popular encoding schemes including MP3 and 
AAC use sophisticated perceptual encoding routines based on results 
from psychoacoustics that point to those aspects of acoustic 
waveforms that have strong perceptual correlates and those that do 
not.

If you are interested in the details you can find plenty of 
information on the web by googling on things like "mp3 compression."

> And can a music enthusiast like myself really hear a difference between
> the compressed music file and the original song on CD?

I consider myself a music enthusiast, one who even has a little 
experience as a professional recording engineer.  My tastes run to 
VERY cleanly recorded and produced acoustic music and jazz, e.g. 
Alison Krauss and Donald Fagen.  I can routinely tell the difference 
at an encoding rate of 128 kbs if the two are A-B'd.  Nevertheless, I 
don't find 128 kbs encoding particularly objectionable to listen to. 
At 160 kbs or beyond it gets more difficult to tell the difference 
and I can truly say that I find NO objectionable artifacts.

--
John "Slo" Mallinckrodt

Professor of Physics, Cal Poly Pomona
<http://www.csupomona.edu/~ajm>

and

Lead Guitarist, Out-Laws of Physics
<http://www.csupomona.edu/~hsleff/OoPs.html>