Returns splits.

def _split_generators(self, dl_manager):
    """Returns splits."""
    dl_urls = {
        split: _BASE_DOWNLOAD_PATH + "%s.tfrecord" % split for split in _SPLITS
    }
    dl_urls["instrument_labels"] = (_BASE_DOWNLOAD_PATH +
                                    "instrument_labels.txt")
    dl_paths = dl_manager.download_and_extract(dl_urls)

    instrument_labels = tf.io.gfile.GFile(dl_paths["instrument_labels"],
                                          "r").read().strip().split("\n")
    self.info.features["instrument"]["label"].names = instrument_labels

    return [
        tfds.core.SplitGenerator(  # pylint: disable=g-complex-comprehension
            name=split,
            num_shards=_SPLIT_SHARDS[split],
            gen_kwargs={"path": dl_paths[split]}) for split in _SPLITS
    ]