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Asked: 2026-05-19T12:04:25+00:00

I am looking at Audio Unit Development Fundamentals . Assuming UInt32 sessionCategory = kAudioSessionCategory_PlayAndRecord;

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I am looking at Audio Unit Development Fundamentals. Assuming 

   UInt32 sessionCategory = kAudioSessionCategory_PlayAndRecord;
   status = AudioSessionSetProperty(
            kAudioSessionProperty_AudioCategory,
            sizeof(sessionCategory),
            &sessionCategory);

with sample rate 44,1000 and allocate the buffer large enough to hold 1 second recording

  1. How often the recording callback method will be called?
  2. Once per second?
  3. What’s the algorithm to decide to call the callback method?

Thanks in advance for your help

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1 Answer

  1. Editorial Team

    Assuming that you haven’t set the kAudioUnitProperty_MaximumFramesPerSlice property on the Audio Unit in question, a render cycle will execute (thus calling your callback) once every FRAMES_PER_SLICE / SAMPLE_RATE seconds. At 44.1kHz, and with the default maximum frames per slice of 1024, this works out to 1024 / 44100, or ~0.023 seconds / ~23 milliseconds. That’s just over 43 times per second.

    I’m not sure about your third question. Are you asking how the Audio Unit determines internally whether or not to call (one of) its callback(s)?

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