def load_tonic(path):
    """
    load tonic value frojm text file at <path>
    Text file should contain only a pitch number.

    :param path: path to load tonic from
    :type path: str

    :return: tonic in Hz
    :rtype: float
    """
    with open(path) as f:
        rd = f.read()
    return float(rd)