Some article ago I've had to adapt the mp3 to playing on the web. The flash player unfortunately only support sampling 44.100Hz, but I have always recorded my songs to a higher quality: 48.000Hz.
I tried some small programs with graphical interface, but I had to resign to the use of command line (in some cases it is almost essential). To convert my mp3s I used “ffmpeg“, doubtless “the” program for multimedia on GNU / Linux.
The program “ffmpeg” is distributed by the main mirror, and is included in most of the open source distributions. It is often installed as a software not optional and is already present in various distributions.
To convert the file to launch this command:
ffmpeg-i ar input_file.wav 44100 output_file.mp3
|-i||indicates the input file|
|-would||indicates the change in Hz|