Music Sync problem. Keep 2 Metronomes in Sync, one by code, one by audio file

Unity Engine
,
1

Hello, this problem drives me crazy, so i have to post my first ever question.

Im am prototyping a rythm game, and i am trying to keep my code in sync with the music.
In my simple test case, the music is a looping audio clip consisting of 4 clicks, at 125 BPM. So with a beat every 0.48 seconds, the Clip is 1.920 seconds long.

Now i want anotcher click to be played in the same pace, at exactly the same time, but by code. So i ceate a AudioSource, and .play() it everytime my code determines a beat is completed. This seems to work fine for the first few loops, but after a while it loses sync. I made a short video to demonstrate the difference (20 seconds in it cuts to out of sync)

I’ve read through several tutorials for unity rythm games, and made use of dspTime and playSheduled. Can you guys see other problems with my approach? Here is my code:

    // Start is called before the first frame update
    void Start()
    {
        //Calculate the number of seconds in each beat
        secPerBeat = 60f / songBpm; //125 bpm

        songStartDelay = secPerBeat * 4;

        //Record the time when the music starts
        dspSongTime = AudioSettings.dspTime + songStartDelay;

        //Start the music
        audioSource.PlayScheduled(AudioSettings.dspTime + songStartDelay);
    }

    void Update()      
    {
        //determine song position, with delta if we dont get a new position
        if(AudioSettings.dspTime != lastDSPTime)
        {
            lastDSPTime = AudioSettings.dspTime;
            songPosition = AudioSettings.dspTime - dspSongTime;
        }
        else
        {
            songPosition += Time.unscaledDeltaTime;
        }

        //determine how many beats since the song started
        songPositionInBeats = songPosition / secPerBeat;

        //calculate the loop position
        if (songPositionInBeats >= (completedLoops + 1) * beatsPerLoop)
            completedLoops++;

        loopPositionInBeats = songPositionInBeats - completedLoops * beatsPerLoop;
        loopPositionInAnalog = loopPositionInBeats / beatsPerLoop;
        //detect new beat
        beatPositionInAnalog = songPositionInBeats - completedBeats;

        if (beatPositionInAnalog >= 1)
        {
            MusicDelayText.text = beatPositionInAnalog.ToString();
            debugClap.PlayScheduled(AudioSettings.dspTime);
            completedBeats++;
    }
}

Maybe the Problem is that i try to detect a new beat by checking if “beatPositionInAnalog” is >= 1? as you can see in the video, it never equals 1, so maybe the delay adds up over time? But i dont know how to prevent this, IF this causes the problem.

Any feedback would be highly appriciated.

2

Update lastDSPTime = AudioSettings.dspTime;