"mcp6453" wrote ...
When I edit an MP3 file in Cool Edit 2000, is it edited
AS an MP3 file or is it internally converted to a wave
and then compressed BACK into an MP3?

The answer is as close as the help menu...
"As an .mp3 file is opend, it's decompressed into Cool
Edit Pro's uncompressed internal format..."

This internal format is most likely identical to ".wav",
perhaps at 24-bit resolution (speculation).

If it is compressed a second time, that's not good.

Which is why CoolEdit posts a warning about saving in MP3.

Many of us consider MP3 to be a play-only format. No further
editing (at least not high quality editing) is possible.