Audacity

The free, open source, cross-platform audio editor

Recording

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

• Record from microphone, line input, USB/Firewire devices and others.
• Device Toolbar manages multiple input and output devices.
• Timer Record and Sound Activated Recording features.
• Dub over existing tracks to create multi-track recordings.
• Record at high sample rates in excess of 192,000 Hz (subject to appropriate hardware).
• Record multiple channels at once (subject to appropriate hardware).
• Level meters can monitor volume levels before, during and after recording. Clipping can be displayed in the waveform or in a label track.

Import and Export

Import sound files, edit them, and combine them with other files or new recordings. Export your recordings in many different file formats, including multiple files at once.

• Import and export WAV, AIFF, AU, FLAC and Ogg Vorbis files.
• Fast "On-Demand" import of WAV or AIFF files (letting you start work with the files almost immediately) if read directly from source. "On-Demand" import of other file formats is available with the optional FFmpeg library.
• Import and export all formats supported by libsndfile such as GSM 6.10, 32-bit and 64-bit float WAV and U/A-Law.
• Import MPEG audio (including MP2 and MP3 files) using libmad.
• Import raw (headerless) audio files using the "Import Raw" command.
• Create WAV or AIFF files suitable for burning to audio CD.
• Export MP3 files with the optional LAME encoder library.
• Import and export AC3, M4A/M4R (AAC) and WMA with the optional FFmpeg library (this also supports import of audio from video files).

Sound Quality

• Supports 16-bit, 24-bit and 32-bit (floating point) samples (the latter preserves samples in excess of full scale).
• Sample rates and formats are converted using high-quality resampling and dithering.
• Tracks with different sample rates or formats are converted automatically in real time.

Editing

• Easy editing with Cut, Copy, Paste and Delete.
• Unlimited sequential Undo (and Redo) to go back any number of steps.
• Edit and mix large numbers of tracks.
• Multiple clips are allowed per track.
• Label tracks with selectable Sync-Lock Tracks feature for keeping tracks and labels synchronized.
• Draw Tool to alter individual sample points.
• Envelope Tool to fade the volume up or down smoothly.
• Automatic Crash Recovery in the event of abnormal program termination.

Accessibility

• Tracks and selections can be fully manipulated using the keyboard.
• Large range of keyboard shortcuts.
• Excellent support for JAWS, NVDA and other screen readers on Windows, and for VoiceOver on Mac.

Effects

• Change the pitch without altering the tempo (or vice-versa).
• Remove static, hiss, hum or other constant background noises.
• Alter frequencies with Equalization, Bass Boost, High/Low Pass and Notch Filter effects.
• Adjust volume with Compressor, Amplify, Normalize and Fade In/Out effects.
• Remove Vocals from suitable stereo tracks.
• Create voice-overs for podcasts or DJ sets using Auto Duck effect.
• Other built-in effects include:
  • Echo
  • Phaser
  • Wahwah
  • Paulstretch (extreme stretch)
  • Reverse
  • Truncate Silence
• Run "Chains" of effects on a project or multiple files in Batch Processing mode.

Plug-ins

• Add new effects with LADSPA, Nyquist, VST and Audio Unit effect plug-ins.
• Effects written in the Nyquist programming language can be easily modified in a text editor - or you can even write your own plug-in.

Analysis

• Spectrogram view modes for visualizing frequencies.
• "Plot Spectrum" command for detailed frequency analysis.
• "Sample Data Export" for exporting a file containing amplitude values for each sample in the selection.
• Contrast Analysis for analyzing average rms volume differences between foreground speech and background music.
• Support for adding VAMP analysis plug-ins.

Free and Cross-Platform

• Licensed under the GNU General Public License (GPL).
• Runs on Windows, Mac OS X and GNU/Linux.

You can download it from here