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

    Tempo (time stretch): Changes the sound to play at faster or
    slower tempo than originally without affecting the sound pitch.

    Pitch (key): Changes the sound pitch or key while keeping the
    original tempo (speed).

    Playback Rate: Changes both tempo and pitch together as if a
    vinyl disc was played at different RPM rate.

The SoundTouch library is intended  for application developers
writing sound processing tools that require tempo/pitch control
functionality, or just for playing around with the sound effects.