SoundTouch is an audio processing library

SoundTouch is a LGPL-licensed open-source audio processing library for
changing the Tempo, Pitch and Playback Rates of audio streams or files:

* Tempo (time-stretch): Changes the sound to play at faster or slower
  speed than original, without affecting the sound pitch.
* Pitch (key) : Changes the sound pitch or key, without affecting the
  sound tempo or speed.
* Playback Rate : Changes both the sound tempo and pitch, as if an LP
  disc was played at wrong RPM rate.

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.