audioqueue kAudioQueueParam_Pitch

Question

The documentation for Audio Queue Services under OS 10.6 now includes a pitch parameter:

kAudioQueueParam_Pitch The number of cents to pitch-shift the audio queue’s playback, in the range -2400through 2400 cents (where 1200 cents corresponds to one musical octave.) This parameter is usable only if the time/pitch processor is enabled.

Other sections of the same document still say that volume is the only available parameter, and I can't find any reference to the time/pitch processor mentioned above.

Does anyone know what this refers to? Directly writing a value to the parameter has no effect on playback (although no error is thrown). Similarly writing the volume setting does work.

Frustrating as usual with no support from Apple.

Answer 1

This is only available on OSX until iOS 7. If you look at AudioQueue.h you'll find it is conditionally available only on iOS 7. [note: on re-reading I see you were referring to OS X, not iOS, but hopefully the following is cross-platform]

Also, you need to enable the queue for time_pitch before setting the time_pitch algorithm, and only the Spectral algorithm supports pitch (all of them support rate)

result = AudioQueueNewOutput(&(pAqData->mDataFormat), aqHandleOutputBuffer, pAqData,
                             0, kCFRunLoopCommonModes   , 0, &(pAqData->mQueue));
// enable time_pitch
UInt32 trueValue = 1;
AudioQueueSetProperty(pAqData->mQueue, kAudioQueueProperty_EnableTimePitch, &trueValue, sizeof(trueValue)); 
UInt32 timePitchAlgorithm = kAudioQueueTimePitchAlgorithm_Spectral; // supports rate and pitch
 AudioQueueSetProperty(pAqData->mQueue, kAudioQueueProperty_TimePitchAlgorithm, &timePitchAlgorithm, sizeof(timePitchAlgorithm));