SoundTouch is an 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 source kit includes also an
example utility SoundStretch that allows processing .WAV audio files with
command-line interface.

WWW: http://www.surina.net/soundtouch/