Rubber Band

Rubber Band is a high quality software library for audio time-stretching and pitch-shifting. It permits you to change the tempo and pitch of an audio stream or recording dynamically and independently of one another. Rubber Band is a library intended for use by developers creating their own application programs rather than directly by end users, although it does also include a simple command-line utility program that you can use for fixed adjustments to the speed and pitch of existing audio files.