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.

Recording
Audacity can record live audio through a microphone or mixer, or digitize recordings from cassette tapes, vinyl records, or minidiscs. With some sound cards, it can also capture streaming audio.

Record from microphone, line input, or other sources.

Dub over existing tracks to create multi-track recordings.

Record up to 16 channels at once (requires multi-channel hardware).

Level meters can monitor volume levels before, during, and after recording.

Import and Export
Import sound files, edit them, and combine them with other files or new recordings. Export your recordings in several common file formats.

Import and export WAV, AIFF, AU, and Ogg Vorbis files.

Import MPEG audio (including MP2 and MP3 files) with libmad.

Export MP3s with the optional LAME encoder library.

Create WAV or AIFF files suitable for burning to CD.

Import and export all file formats supported by libsndfile.

Open raw (headerless) audio files using the “Import Raw” command.

Note: Audacity does not currently support WMA, AAC, or most other proprietary or restricted file formats.

Editing

Easy editing with Cut, Copy, Paste, and Delete.

Use unlimited Undo (and Redo) to go back any number of steps.

Very fast editing of large files.

Edit and mix an unlimited number of tracks.

Use the Drawing tool to alter individual sample points.

Fade the volume up or down smoothly with the Envelope tool.

Effects

Change the pitch without altering the tempo, or vice-versa.

Remove static, hiss, hum, or other constant background noises.

Alter frequencies with Equalization, FFT Filter, and Bass Boost effects.

Adjust volumes with Compressor, Amplify, and Normalize effects.

Other built-in effects include:
- Echo
- Phaser
- Wahwah
- Reverse

Sound Quality

Record and edit 16-bit, 24-bit, and 32-bit (floating point) samples.

Record at up to 96 kHz.

Sample rates and formats are converted using high-quality resampling and dithering.

Mix tracks with different sample rates or formats, and Audacity will convert them automatically in realtime.

Plug-Ins

Add new effects with LADSPA plug-ins.

Audacity includes some sample plug-ins by Steve Harris.

Load VST plug-ins for Windows and Mac, with the optional VST Enabler.

Write new effects with the built-in Nyquist programming language.

Analysis

Spectrogram mode for visualizing frequencies.

“Plot Spectrum” command for detailed frequency analysis.

Free and Cross-Platform

Licensed under the GNU General Public License (GPL).

Runs on Mac OS X, Windows, and GNU/Linux.