Audacity : Open source software for recording and editing sounds
Audacity is free, open source software for recording and editing sounds. It is available for Mac OS X, Microsoft Windows, GNU/Linux, and other operating systems. You can record sounds, 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), mix tracks together, or apply effects to your recordings.
It also has a built-in amplitude envelope editor, a customizable spectrogram mode and a frequency analysis window for audio analysis applications. Built-in effects include Bass Boost, Wahwah, and Noise Removal, and it also supports VST plug-in effects
The latest release of Audacity is 1.3.9 (Beta). Because it is a work in progress and does not yet come with complete documentation or translations into foreign languages, it is recommended for more advanced users. See New Features in 1.3 for more information about the 1.3.x Beta series.
