Here is a question and answer from a recent Kim Komando newsletter that might be of interest to some.
Paul C.

Q. If WAV music files are 10 times the size of MP3s, who decides which
90 percent is removed? I prefer to buy my CDs at the store, as opposed
to downloading them off of the Web, because I prefer the best quality.
I have downloaded MP3 files from the Web to check out songs, and have
noticed that the quality of some is much better than others. Why, and
why are CDs better than MP3s?

A. Music files are huge. Uncompressed WAV files are about 10 times as
big as MP3s, so they would be difficult to download and store. The
individuals who compress their music files make the decision to use
MP3, because it works so well.

MP3s are lossy, which means that some data is lost in the compression
process. That's also true of JPGs, which are images. On the other hand,
ZIPs are not lossy. There is no data lost in the ZIP process.

Compression might be easier to understand with ZIPs, rather than
MP3s. Software to make ZIP files looks for patterns in a program.
For instance, if a Word file is being compressed, the software might
look for the word "the." In its index, it might show that the word
"the" is represented by a 1. The article "a" might be represented by
2, and the letters "ou" by 3, and so on. When the file is decoded
(or unzipped), the decoding program would change those numbers back
to the proper letters.

MP3s do something similar. They look for common patterns in the music
and create codes to represent them. They include information to tell
the decoding program how to read the codes.

But the MP3s also lose some information, intentionally. They use
psychoacoustics to remove sounds that human ears cannot hear. Very high
sounds are dropped, for instance. So are sounds that are masked by
other sounds. There is a great deal of such data in any piece of music.
For instance, a violin might be drowned out in places by horns.

Removing these sounds greatly contributes to the reduction in the
files' size. Once the sounds are removed by the MP3, they are gone.
They cannot be restored by the decoder software. That is different from
the compressed parts, which are recovered.

Can you hear the difference between the original CD and an MP3? Some
experts claim not. But if your hearing is especially acute, you might
rove them wrong.

The MP3 protocol stems from the work done by the Motion Picture Experts
Group (MPEG) in the early 1990s. They were actually looking for a way
to compress video, but needed audio compression to go along with it.
They developed three layers, with MP3 being the third. Because the MP3
is much smaller than an uncompressed WAV file, it made music
downloading possible.

It's true that some MP3s sound better than others. It all depends on
how much data is saved as the file is being made. They range from 64 to
320 kilobits per second. The more data saved, the better the sound. But
more data means a bigger file, so there's a tradeoff. CD quality sound
is generally placed at 128 Kbps.