def vowelduration(amparray, maxamp):
    """ Vowel Duration audio feature:
    High Predictability rate (82%)

    :param amparray: array of maximum amplitudes (float)
    :param maxamp: maximum pitch amplitude
    :return voweldur: vowel duration in msec (float)
    """

    voweldur = 0
    threshold = 0.7 * maxamp

    for amp in amparray:
        v = 0
        if amp >= threshold:
            v = 1

        voweldur += (v/2)

    voweldur *= 0.23
    return voweldur