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.