def __init__(self, audio_path, label_path):
        if not os.path.isfile(audio_path):
            raise IOError("Audio file at %s does not exist" % audio_path)
        if label_path and not os.path.isfile(label_path):
            raise IOError("MIDI file at %s does not exist" % label_path)

        self.audio_path = audio_path
        self.label_path = label_path