SoundTouch is a LGPL-licensed open-source audio processing library for changing the Tempo, Pitch and Playback Rates of audio streams or files. The SoundTouch library is suited for application developers writing sound processing tools that require tempo/pitch control functionality, or just for playing around with the sound effects. The SoundTouch library source kit includes an example utility SoundStretch which allows processing .wav audio files from a command-line interface.