Voice recorder records insanely accelerated voice

I’m just starting to learn the theory of digital audio and fmod.
My task is to record voice from a microphone for some seconds and transfer the recorded data to create an unity audioclip. I was able to implement a system that allows me to hear my microphone and read the raw data, but apparently I am reading it incorrectly - when I create an audio clip with this data, my audio speeds up several times. My starting point is https://fmod.com/docs/2.02/unity/examples-dsp-capture.html example.

using FMOD;
using FMODUnity;
using System;
using System.Runtime.InteropServices;
using UnityEngine;

public class FMODVoiceProcessor : MonoBehaviour
    public event Action<float[]> FrameCaptured;
    private int _recordDeviceId = 0;

    private float[] _sampleBuffer;

    private CREATESOUNDEXINFO _exinfo;
    private ChannelGroup _masterCG;
    private Channel _channel;
    private Sound _sound;

    private DSP _captureDSP;
    private GCHandle _objHandle;

    public void EnableRecording()
        RESULT res = RuntimeManager.CoreSystem.getRecordNumDrivers(out int numofDrivers, out int numOfDriversConnected);

        RuntimeManager.CoreSystem.getRecordDriverInfo(_recordDeviceId, out _, 0,
            out Guid micGUID, out int _sampleRate, out SPEAKERMODE speakerMode, out int captureNumChannels, out DRIVER_STATE driverState);

        // create sound where capture is recorded
        _exinfo.cbsize = Marshal.SizeOf(typeof(CREATESOUNDEXINFO));
        _exinfo.numchannels = captureNumChannels;
        _exinfo.format = SOUND_FORMAT.PCM16;
        _exinfo.defaultfrequency = _sampleRate;
        _exinfo.length = (uint)_sampleRate * sizeof(short) * (uint)captureNumChannels;

            ref _exinfo, out _sound);
        RuntimeManager.CoreSystem.recordStart(_recordDeviceId, _sound, true);

        // play sound on dedicated channel in master channel group
        if (RuntimeManager.CoreSystem.getMasterChannelGroup(out _masterCG) != RESULT.OK)
            UnityEngine.Debug.LogWarningFormat("FMOD: Unable to create a master channel group: masterCG");

        RuntimeManager.CoreSystem.getMasterChannelGroup(out _masterCG);
        RuntimeManager.CoreSystem.playSound(_sound, _masterCG, true, out _channel);

        // Allocate a data buffer large enough for 8 channels, pin the memory to avoid garbage collection
        RuntimeManager.CoreSystem.getDSPBufferSize(out uint bufferLength, out int numBuffers);
        _sampleBuffer = new float[bufferLength * 8];

        // Get a handle to this object to pass into the callback
        _objHandle = GCHandle.Alloc(this);
        if (_objHandle != null)
            // Define a basic DSP that receives a callback each mix to capture audio
            DSP_DESCRIPTION desc = new DSP_DESCRIPTION();
            desc.numinputbuffers = 1;
            desc.numoutputbuffers = 1;
            desc.read = CaptureDSPReadCallback;
            desc.userdata = GCHandle.ToIntPtr(_objHandle);

            // Create an instance of the capture DSP and attach it to the master channel group to capture all audio            
            if (RuntimeManager.CoreSystem.createDSP(ref desc, out _captureDSP) == RESULT.OK)
                if (_masterCG.addDSP(0, _captureDSP) != RESULT.OK)
                    UnityEngine.Debug.LogWarningFormat("FMOD: Unable to add mCaptureDSP to the master channel group");
                UnityEngine.Debug.LogWarningFormat("FMOD: Unable to create a DSP: mCaptureDSP");
            UnityEngine.Debug.LogWarningFormat("FMOD: Unable to create a GCHandle: mObjHandle");

    static RESULT CaptureDSPReadCallback(ref DSP_STATE dsp_state, IntPtr inbuffer, IntPtr outbuffer, uint length, int inchannels, ref int outchannels)
        DSP_STATE_FUNCTIONS functions = (DSP_STATE_FUNCTIONS)Marshal.PtrToStructure(dsp_state.functions, typeof(DSP_STATE_FUNCTIONS));

        functions.getuserdata(ref dsp_state, out IntPtr userData);

        GCHandle objHandle = GCHandle.FromIntPtr(userData);
        FMODMicrophoneRecorder obj = objHandle.Target as FMODMicrophoneRecorder;

        // Copy the incoming buffer to process later
        int lengthElements = (int)length * inchannels;
        Marshal.Copy(inbuffer, obj._sampleBuffer, 0, lengthElements);

        // Copy the inbuffer to the outbuffer so we can still hear it
        Marshal.Copy(obj._sampleBuffer, 0, outbuffer, lengthElements);

        //for some reason i have 6 in/out channles and and 4 of them are empty,
        //more details here - https://qa.fmod.com/t/dsp-read-callback-show-6-in-out-channels-instead-of-1/21088,
        //so I had to extract only the non - empty data, but this event send all data from obj._sampleBuffer
        return RESULT.OK;

    private void Start()
MicrophoneRecorder receive data frame from FMODVoiceProcessor using an event FrameCapture
public class MicrophoneRecorder: MonoBehaviour
    public FMODVoiceProcessor VoiceProcessor;

    public AudioSource AudioSource;
    public AudioClip AudioClip;

    public float[] fbuffer;

    public int RecorderBufferSize = 100000;
    public int RecordedFloats = 0;

    private void OnFrameCaptured(float[] capturedFrame)
        if (RecordedFloats + capturedFrame.Length > fbuffer.Length)

        Buffer.BlockCopy(capturedFrame, 0, fbuffer, RecordedFloats, capturedFrame.Length * 4);
        RecordedFloats += capturedFrame.Length;

    private void CreateSound()
        AudioClip = AudioClip.Create("Test", fbuffer.Length, 1, 48000, false);
        AudioClip.SetData(fbuffer, 0);

    private void PlaySound()
        AudioSource.clip = AudioClip;

    private void InitializeFloatBuffer()
        fbuffer = new float[RecorderBufferSize];
        RecordedFloats = 0;

    public void StartCapture()
        VoiceProcessor.FrameCaptured+= OnFrameCaptured;

    public void StopCapture()
        VoiceProcessor.FrameCaptured-= OnFrameCaptured;

I would appreciate any help.

Could you verify and fix the code snippets such that they don’t require modification to function correctly? For example, FMODVoiceProcessor contains references to a class FMODMicrophoneRecorder, and the use of this type make me unsure as to whether this class is supposed to be FMODVoiceProcessor, MicrophoneRecorder, or some other class.

Speaking generally though:

  • If by “insanely accelerated” you mean the pitch (and resulting speed) of the audio has increased, it’s likely there’s a mismatch between the format of FMOD and Unity’s audio system that is causing the speedup. Increased sample rate relative to the source is the usual culprit here.

  • If by “insanely accelerated” you mean that the audio maintains the same pitch while seeming to jump forward rapidly, it’s likely there’s a mismatch in how the source and destination buffers are being processed - i.e. Unity audio is playing back less data than the amount of data FMOD is providing in the same timeframe.

I can’t say exactly what type of these problems I have because the sound is very much accelerated and difficult to recognize, but it seems to me that in addition to the acceleration, some parts of the sound are missing.

Actually I already solved my problem just by using sound.lock/unlock instead of DSP_READ_CALLBACK

Thanks for the answer

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