class_docstr: A data helper for raw waveforms.
  
  For compatibility with the spectral network architectues, we add a second
  (redundant) channel and zero-pad along the time axis.
code: def waves_to_data(self, waves):
      waves = waves[:, :, None, :]
      pad = tf.zeros([tf.shape(waves)[0], 768, 1, 1])
      waves = tf.concat([pad, waves, pad], axis=1)
      return tf.concat([waves, waves], axis=3)
  
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 3 for calling the DataWaveHelper obj's underlying member method code with example usage: obj.waves_to_data(waves) and returns: tf