One comment. Once an audio file is converted (compressed) to an MP3 for example, the full fidelity of the original wav file (or CD audio file) is lost (what extent is lost depends on the compressed file type or bitrate). Converting it back to a wav file, for instance, will not restore the fidelity. You will still have the fidelity of the MP3 file.
I'm a musician and have a recording studio. I've had people bring me a CD with MP3 files and ask if I can convert it and make it better. The answer is always no.
Jack