For trimming time off of the beginning and end of MP3 files without re-encoding them, I use MP3Trim as already mentioned.



That works, and it's more or less the method I use. But you must remember that it's only successful if:
- Tags have been stripped out of the files first. If you don't do that you might get a "pop" in the audio where there is a tag in place of audio data, or, you'll have the old multiple tag problem.
- The files, if they are VBR, have had the VBR time sequencing tag metadata removed from the file before concatenating them. If you don't do that, then the playback time counter will look wonky on the file, and/or you won't be able to fast forward and rewind the file properly.

Both of those things can be accomplished by TidyMP3. I recommend running that on any files you're expecting to join together with a copy /B command.

Regarding the prior suggestion of Audacity... It is a good audio editor, and it will do these things too. But I think that if you try to do them in Audacity it will mean that the audio data is getting opened in its raw form and thus must be re-compressed again when you re-save it back to a new MP3. For the particular files in question, that might not be a big deal, but as a general practice that's something I try to avoid because it causes additional quality loss.

The advantage to MP3Trim and TidyMP3 is that they simply slice and dice the MP3 file itself on frame boundaries and tag boundaries, without decompressing/recompressing the audio data. So although there might be a small "pop" at the join point, the majority of the data will be identical after all the trimming and editing.