void SetDifficulty()
    {
        switch (PlayerPrefs.GetInt("Difficulty"))
        {
        case (int)Difficulty.EASY: rate = 0.4f;

            sound.ChangeMusic(2);

            break;

        case (int)Difficulty.NORMAL: rate = 0.25f;

            sound.ChangeMusic(3);

            break;

        case (int)Difficulty.HARD: rate = 0.1f;

            sound.ChangeMusic(4);

            break;
        }
    }