class_docstr: A data helper for Linear Spectrograms.
code: def _map_fn(
      self, wave, one_hot_label
  ):  # pytype: disable=signature-mismatch  # overriding-parameter-count-checks
      waves = wave[tf.newaxis, :, :]
      data = self.waves_to_data(waves)
      return data[0], one_hot_label
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  from magenta.models.gansynth.lib import datasets
  from magenta.models.gansynth.lib import train_util
  from magenta.models.gansynth.lib.specgrams_helper import SpecgramsHelper
  import tensorflow.compat.v1
label_desc: Use image node_id 2 for calling the DataSTFTNoIFreqHelper obj's underlying member method code with example usage: obj._map_fn(wave, one_hot_label) and returns: data,  one_hot_label