Re: [Phys-l] iPod music compression

["John Clement" <clement@hal-pc.org>]

I would agree that the subject of compression is not simple, and it really
depends on what you can hear, what your system can reproduce, how closely
you listen, and what you value in a recording.

According to some tests AAC sounds better at higher compression, but MP3 may
sound the same or better at lower compression.  Lossless compression works
well, but only achieves a ration of 2 to 3 depending on the source.

One problem you encounter is that the iPod may dissociate the tracks on a CD
so if you put symphonies on it, you will get mixed up results.  This can be
solved by using a consistent naming convention, but breaks in the middle of
works can result in small time delays.

There is also a type of encoding which varies the bit rate according to the
complexity of the music, but the iPod may not support this format.  iTunes
the standard program for loading an iPod supports a variety of formats, but
not the variable one.  The iPod is a closed device and once a track is
loaded Apple has discouraged users from copying the tracks to another
device.  There is third party software you can buy which can perform this
feat.  Apple also has frequent updates of iTunes, but in the process the
iTunes library becomes incompatible to older versions.  We have experienced
lock up of an iPod, and I have heard it skip sections of songs.

Other devices are available which look just like a hard drive and can be
readily loaded just by copying songs to them.  The Zen by Creative Labs is
an example of one of these.  These devices can also just be used a small
portable hard drive.  I have no information about which device is easier, or
more reliable.

The best advice has already been given to listen to various encoding
schemes.  iTunes is free and can be used on your computer without an iPod.
Music Match also has a free jukebox you can try.  After trying compressed
music you can make a much more informed decision.  Then consider buying a
device with 30 day return privileges.

We have successfully used an iPod for a folk dance group, but we much prefer
using a cheap laptop with iTunes.

John M. Clement
Houston, TX


> > 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."