Example of using Audio Queue Services

Question

I am seeking an example of using Audio Queue Services.

I would like to create a sound using a mathematical equation and then hear it.

Answer 1

This is a version using C# of the same sample from @lucius

    void SetupAudio ()
    {
        AudioSession.Initialize ();
        AudioSession.Category = AudioSessionCategory.MediaPlayback;

        sampleRate = AudioSession.CurrentHardwareSampleRate;
        var format = new AudioStreamBasicDescription () {
            SampleRate = sampleRate,
            Format = AudioFormatType.LinearPCM,
            FormatFlags = AudioFormatFlags.LinearPCMIsSignedInteger | AudioFormatFlags.LinearPCMIsPacked,
            BitsPerChannel = 16,
            ChannelsPerFrame = 1,
            BytesPerFrame = 2,
            BytesPerPacket = 2, 
            FramesPerPacket = 1,
        };

        var queue = new OutputAudioQueue (format);
        var bufferByteSize = (sampleRate > 16000)? 2176 : 512; // 40.5 Hz : 31.25 Hz 
        var buffers = new AudioQueueBuffer* [numBuffers];
        for (int i = 0; i < numBuffers; i++){
            queue.AllocateBuffer (bufferByteSize, out buffers [i]);
            GenerateTone (buffers [i]);
            queue.EnqueueBuffer (buffers [i], null);
        }
        queue.OutputCompleted += (object sender, OutputCompletedEventArgs e) => {
            queue.EnqueueBuffer (e.UnsafeBuffer, null);
        };

        queue.Start ();
        return true;
    }

This is the tone generator:

    void GenerateTone (AudioQueueBuffer *buffer)
    {
        // Make the buffer length a multiple of the wavelength for the output frequency.
        uint sampleCount = buffer->AudioDataBytesCapacity / 2;
        double bufferLength = sampleCount;
        double wavelength = sampleRate / outputFrequency;
        double repetitions = Math.Floor (bufferLength / wavelength);
        if (repetitions > 0) 
            sampleCount = (uint)Math.Round (wavelength * repetitions);

        double      x, y;
        double      sd = 1.0 / sampleRate;
        double      amp = 0.9;
        double      max16bit = Int16.MaxValue;
        int i;
        short *p = (short *) buffer->AudioData;

        for (i = 0; i < sampleCount; i++) {
            x = i * sd * outputFrequency;
            switch (outputWaveForm) {
                case WaveForm.Sine: 
                    y = Math.Sin (x * 2.0 * Math.PI);
                    break;
                case WaveForm.Triangle:
                    x = x % 1.0;
                    if (x < 0.25)
                        y = x * 4.0; // up 0.0 to 1.0
                    else if (x < 0.75)
                        y = (1.0 - x) * 4.0 - 2.0; // down 1.0 to -1.0
                    else 
                        y = (x - 1.0) * 4.0; // up -1.0 to 0.0
                    break;
                case WaveForm.Sawtooth:
                    y  = 0.8 - (x % 1.0) * 1.8;
                    break;
                case WaveForm.Square:
                    y = ((x % 1.0) < 0.5)? 0.7: -0.7;
                    break;
                default: y = 0; break;
            }
            p[i] = (short)(y * max16bit * amp);
        }
        buffer->AudioDataByteSize = sampleCount * 2;
    }
}

You also want these definitions:

    enum WaveForm {
        Sine, Triangle, Sawtooth, Square
    }
    WaveForm outputWaveForm;
    const float outputFrequency = 220;