Hear Birds Again is a real-time audio pitch shifting application for iOS. It is intended primarily for field use by bird enthusiasts who can no longer hear high-pitched bird sounds. It shifts high-pitched sounds down into a lower pitch range so they can be heard.
The initial version of the app uses a simple time domain overlap-add (OLA) pitch shifting algorithm. A subsequent version will use a more sophisticated frequency domain algorithm.
The app is distributed via Apple's App Store.
Hear Birds Again is a project of the nonprofit Miracle of Nature, and was developed by Lang Elliott and Harold Mills. For more about the app, please see hearbirdsagain.org.