With this program from musetips.com we can with easy to edit any mp3 files. With this program you can out unwanted part of the audio, change volume by specifying a percentage value, create a fade in or fade out, and convert the audio between stereo and mono.

full features:

Delete Selected - Deletes selected part from the mp3 document.
Delete Unselected - Deletes unselected part from the mp3 document.
Change Volume - Changes audio volume by specifying a percentage value.
Maximize Volume - Increases volume as high as possible without distortion.
Fade In - Gradually increases the volume throughout the selection.
Fade Out - Gradually decreases the volume throughout the selection.
Convert to Stereo - Duplicates mono track to make a stereo track.
Convert to Mono- Mixes all channels to make a mono track.