DissonanceFmodDSP.cs

public class FMODStreamCallback
    : MonoBehaviour
{
    [SerializeField] public AudioGenerator Generator;

    private Channel _channel;
    private GCHandle _handle;
    private DSP _dsp;

    private void OnEnable()
    {
        var ddesc = new DSP_DESCRIPTION
        {
            numinputbuffers = 0,
            numoutputbuffers = 1,
            read = ReadDsp,
        };
        RuntimeManager.CoreSystem.createDSP(ref ddesc, out _dsp);

        _handle = GCHandle.Alloc(Generator);
        _dsp.setUserData((IntPtr)_handle);

        RuntimeManager.CoreSystem.playDSP(_dsp, default, false, out _channel);
        _channel.set3DMinMaxDistance(3, 100);
        _channel.setMode(MODE._3D);
    }
    
    private static RESULT ReadDsp(ref DSP_STATE dsp_state, IntPtr _, IntPtr outbuffer, uint length, int _, ref int outchannels)
    {
        // Demo of how to query the DSP state for relevant info
        var functions = (DSP_STATE_FUNCTIONS)Marshal.PtrToStructure(dsp_state.functions, typeof(DSP_STATE_FUNCTIONS));
        var rate = 0;
        functions.getsamplerate(ref dsp_state, ref rate);

        // Get the GC heap object stashed in UserData, pump it for audio
        functions.getuserdata(ref dsp_state, out var userdata);
        var tgt = (AudioGenerator)GCHandle.FromIntPtr(userdata).Target;
        tgt.GetAudio(outbuffer, length, (uint)outchannels);

        return RESULT.OK;
    }
}