Audacity

Audacity is open source tool, for Windows/Mac/Linux platform. Using this tool you can easily edit audio tracks in multiple formats (Mp3, Flac, Wav, ...). I use it to edit audio tracks (cutting, pasting, etc. ) and for spectrum preview, but it can apply many effects to audio file like compressor, echo, low/high pass filtering. I has also implemented some MIR algorithms like onset detection or beat tracking.

You can download Audacity from this place.