Audacity is free audio editor. You can record, play sounds, import and export WAV, AIFF and mp3 files, and more.
Use it to edit your sounds using cut, copy and paste (with unlimited Undo`s), mix tracks or add effects to your recordings.
It also has its own amplifier, an adjustable spectogram mode and a frequency analysis window for audio analysis applications. Effects include Bass Boost, Wahwah and noise reduction, and it also supports VST plug-in effects.