public class FMODStreamPlayer
{
    public PCMAudioProducer audioProducer;

    public uint bufferSize = 8192;
    public float gain = 0.5f;
    public static int toneFrequency = 120;

    FMOD.System fmodSystem;
    Sound sound;

    public FMODStreamPlayer(PCMAudioProducer producer)
    {
        audioProducer = producer;
        fmodSystem = FMODUnity.RuntimeManager.LowlevelSystem;

        audioProducer.Created += CreateStream;
        audioProducer.Play += PlayStream;
        audioProducer.Pause += PauseStream;
        audioProducer.Close += CloseStream;
    }

    ~FMODStreamPlayer()
    {
        if (audioProducer != null)
        {
            audioProducer.Created -= CreateStream;
            audioProducer.Play -= PlayStream;
            audioProducer.Pause -= PauseStream;
            audioProducer.Close -= CloseStream;
        }
    }

    void CreateStream(int channels, int bitDepth, int frequency)
    {
        UnityEngine.Debug.Log("create fmod stream");

        CREATESOUNDEXINFO exinfo = new CREATESOUNDEXINFO();
        exinfo.decodebuffersize = bufferSize;
        exinfo.length = 8192;
        exinfo.numchannels = channels;
        exinfo.defaultfrequency = frequency;
        exinfo.format = SOUND_FORMAT.PCM16;
        exinfo.pcmreadcallback = pcmreadcallback;
        exinfo.pcmsetposcallback = DoSetPos;
        exinfo.suggestedsoundtype = SOUND_TYPE.RAW;

        RESULT r = fmodSystem.createStream(String.Empty, MODE.OPENUSER | MODE.LOOP_NORMAL, ref exinfo, out sound);
        if (r != 0)
        {
            UnityEngine.Debug.LogError("Error: " + r);
            return;
        }
    }

    RESULT pcmreadcallback(IntPtr soundraw, IntPtr data, uint datalen)
    {
        //UnityEngine.Debug.Log("PCMReadCallback from FMOD");
        //UnityEngine.Debug.Log("Thread id = " + Thread.CurrentThread.ManagedThreadId);

        byte[] bytes;
        int receivedBytes;
        bool success = audioProducer.GetAudioBytes((int)datalen, out bytes, out receivedBytes);

        short[] shorts = new short[bytes.Length / 2];
        PCMConverter.BytesToShorts(bytes, ref shorts);

        Sound sound = new Sound(soundraw);

        Marshal.Copy(shorts, 0, data, shorts.Length);

        return RESULT.OK;
    }

    void PlayStream()
    {
        UnityEngine.Debug.Log("Play fmod stream");
        Channel channel;
        fmodSystem.playSound(sound, null, false, out channel);
    }

    void PauseStream()
    {
        UnityEngine.Debug.Log("Pause fmod stream");
        Channel channel;
        fmodSystem.playSound(sound, null, true, out channel);
    }

    void CloseStream()
    {
        UnityEngine.Debug.Log("Close fmod stream");
        sound.release();
    }

    RESULT DoSetPos(IntPtr soundraw, int subsound, uint position, FMOD.TIMEUNIT postype)
    {
        return FMOD.RESULT.OK;
    }
}


public class PCMAudioGenerator : PCMAudioProducer
{
    public int sampleRate = 48000;
    public int toneFrequency = 480;

    public override bool GetAudioBytes(int bufferSize, out byte[] bytes, out int receivedBytes)
    {
        //Debug.Log("Getting test audio bytes. Amount = " + numBytes);

        receivedBytes = bufferSize;
        bytes = new byte[bufferSize];

        double multiplier = ((double)sampleRate / (double)toneFrequency) / (2 * Math.PI);
        for (int i = 0; i < bytes.Length; i += 2)
        {
            short sample = (short)(Math.Sin((i) / multiplier) * short.MaxValue) ;
            byte[] sampleBytes = BitConverter.GetBytes(sample);
            bytes[i] = sampleBytes[1]; // little endian
            bytes[i + 1] = sampleBytes[0];
        }

        return true;
    }

    …

}