Rogue Amoeba’s Fission for Mac OS X is an editor for sound files that is easy to use and has all of the really essential features required for day-to-day editing.
It is with MP3s that Fission really comes into its own, however, since it is able to work with MP3 files without decompressing them first. Most sound file editors have to decompress MP3 files and then compress them again if you specify MP3 as the output file format. That means degradation of the audio, since MP3 is a “lossy” format that produces small files at the cost of throwing some audio information away. With Fission, it isn’t an issue: you just load your MP3 file, edit it, and save it, confident that the audio quality has been maintained.
Here’s another use for Fission. On rare occasions, iTunes will be unable to permanently change the tags in an MP3 file, perhaps because there is some sort of corruption to the tag data. Load the MP3 into Fisison and save a copy. iTunes will work fine with the copy.
For more information about Fission, see Rogue Amoeba’s site. Their other products are also worth considering, especially Audio Hijack Pro.