Does anyone know how I could record some audio on the iphone then change the pitch of the audio?
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Unless you wonder how to create an app to do that, the question probably belongs on superuser.com. – Tor Haugen Nov 02 '09 at 15:10
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Download and use the I-AM-T-Pain application ;-)
Chris Ballance
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Good answer for superuser.com, but not terribly helpful if he's looking to write his own pitch changer... – Matt Poush Nov 02 '09 at 15:19
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@Matt the "semicolon-dash-parens" sequence often signifies a joke. For example, ;-) – Rex M Nov 02 '09 at 19:42
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@Rexm actually ;-) is the endline character in the HappyEnding++ programming language – Chris Ballance Nov 02 '09 at 19:51
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1I have not found the T-Pain app to be nearly autotuney enough. I wanted my money back instantly. – Nathan Bowers Nov 02 '09 at 21:44
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It looks like you'll want to start with the Core Audio Framework: http://developer.apple.com/IPhone/library/documentation/MusicAudio/Conceptual/CoreAudioOverview/
There doesn't seem to be a whole wealth of information on the AutoTune algorithm, but a good start would be to use a Fast Fourier Transform to analyze the pitch to determine what pitch your audio is actually at. It's a relatively simple to change the pitch from what it is to what it needs to be. For example, A is 440 Hz. Assuming the input is actually 466.164 (A#), and you want it to be A, you adjust the waveform by 0.94387383 (440 / 466.16400). An A# becomes an A.
If you want to achieve an auto tune effect, you'll want to subdivide the recording into tiny audio clips that you can re-pitch individually.
More info on pitch detection: http://en.wikipedia.org/wiki/Pitch_detection_algorithm
Matt Poush
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