"Dave" wrote in message
oups.com...
I have been disappointed with the audio quality of some CDs I have
bought recently. Is there a free program I can use to get an accepted
measurement of fidelity? (like a signal to noise ratio)

I have my suspicious that some may have been stored an MP3s and then
"unripped" in the factory. So how can I tell for certain if my CD has
been an MP3, or other lossy format? I'd hope mp3 storage would leave
different markers than the original tape, for example.

To get a good measure I'd expect some Fourier transforms and signal
analysis to be done, so this should be relevant to sci.physics.


Dave,

You can, to some extent, find out what the mp3 process does to the audio for yourself. You
could get an audio editor, like Cool Edit (now in Adobe's Audition), and do some recording
yourself. Save the piece as mp3, with different bitrates, reopen it, and you'll get an idea
of what artifacts the lossy compression introduces. Years ago, when mp3 codecs were newer,
the lower bit rates, like 64K, produced a watery sound. I know that's not terribly
descriptive, but it's the best way I can describe it. They seem to be better now. The
low-data-rate streaming internet radio stations have that watery sound. You'll also notice
high-frequency loss at the lower rates. As the bit rate goes up, all that diminishes. Just
for grins, I once took a very clean-sounding piece, and compared an mp3 of it (128K, I think
it was) to the original wav, subtracting one from the other. The result was a very watery
glub-glub sound, though relatively low in amplitude compared to the original.

Regards from Virginia Beach,

Earl Kiosterud