def count_occurence(manifest_file_id):
    """Count number of wav files in Dict manifest_file_id. Use for _TarredAudioToLabelDataset.
    Args: 
        manifest_file_id (Dict): Dict of files and their corresponding id. {'A-sub0' : 1, ..., 'S-sub10':100}
    Returns:
        count (Dict): Dict of wav files {'A' : 2, ..., 'S':10}
    """
    count = dict()
    for i in manifest_file_id:
        audio_filename = i.split("-sub")[0]
        count[audio_filename] = count.get(audio_filename, 0) + 1
    return count