MetaButtonVolumeController.cs

//Part of the script
/// <summary>
/// Loop for lowering the volume
/// </summary>
private IEnumerator UpdateRoutine()
{
    while (true)
    {
        UpdateVolume();
        yield return new WaitForSeconds(_targetTime);
    }
}

/// <summary>
/// Lower the volume
/// </summary>
private void UpdateVolume()
{
    AudioListener.volume = Mathf.Clamp01(AudioListener.volume + _currentDelta);
}