AudioToolbox.m

// Step 6: Allocate buffer
    for (int i = 0; i < maxBufferNum; i++) {
        // Step 6.1: allock the buffer
        status = AudioQueueAllocateBuffer(
                                          _queue,
                                          outBufferSize,
                                          &buffers[i]
                                          );
        if (status != noErr) NSLog(@"AudioQueueAllocateBuffer failed %d", status);

        // Step 6.2: Fill the audio data to buffer
        [self audioQueueOutputWithQueue:_queue
                            queueBuffer:buffers[i]];
    }