void GenerateBall()
    {
        int note = GetNote();

        ChordBall ball = Instantiate(_chordBallPrefab);

        ball.SetGenerator(this);
        ball.SetNote(note, _noteDur);
        ball.transform.position = GetSpawnPos();
        _balls.Add(ball);
    }
    public void RefreshNoteFromCurChord(ChordBall ball)
    {
        int note = GetNote();

        ball.SetNote(note, _noteDur);
    }
 public void OnBallDone(ChordBall ball)
 {
     _balls.Remove(ball);
     Destroy(ball.gameObject);
 }