Audacity
(Version 1.3.5b)

Audacity is a sound editing program which can record, playback, and mix sounds or apply effects using a variety of filters. Edit your sounds using Cut, Copy and Paste (with unlimited Undo) and mix multiple tracks together. Save your files in a number of formats, including WAV, Ogg Vorbis and AIFF, or use Audacity's native project format for high performance editing. MP3 support is available using the external LAME MP3 encoder, which is included with CDex, or can be installed from here after installing Audacity. It also has a built-in amplitude envelope editor, a customisable spectrogram mode and a frequency analysis window for audio analysis applications. Built-in effects include Bass Boost, Wahwah, and Noise Removal. This full-featured program is fast and stable, and is also available for Linux and MacOS X.