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Change pitch during audio queue playback
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Change pitch during audio queue playback


  • Subject: Change pitch during audio queue playback
  • From: Sebastian Morsch <email@hidden>
  • Date: Wed, 20 May 2009 14:49:40 +0200

Dear list,

I'm new to audio programming, but thanks to Apple's tutorial on audio queues I was able to implement playback of audio files quite easily, which is really great!

But now i have to leave the secure area of the tutorial as I try to create a "pitch slider", that changes the pitch (just the sample rate, no pitch-shifting!) during playback of my audio files. Pretty much like on a DJ's turntable, only with a wider range.

I managed to change the pitch of an audio file's playback *before* the audio queue is created by simply changing the sample rate in AudioStreamBasicDescription. But that doesn't seem to work during playback.

Can anyone give me a hint on how to do that while an audio queue is playing? Do I have to pre-process the raw PCM data by "really converting" it's sample rate in the callback? That would be hard for me because I would probably have to do the decoding of compressed audio myself. The fact that audio queues eat compressed packets is what makes it so attractive for newbies like me.

Any help on this is very much appreciated. Thank you!
Sebastian
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