class_docstr: TIMIT to characters.
class_docstr_tok: ["TIMIT","to","characters","."]
code: def hparams(self, defaults, model_hparams):
      hp = defaults
      hp.modality = {
          "inputs": modalities.ModalityType.SPEECH_RECOGNITION,
          "targets": modalities.ModalityType.SYMBOL,
      }
      hp.vocab_size = {"inputs": None, "targets": 256}
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import os
  from tensor2tensor.data_generators import problem
  from tensor2tensor.data_generators import text_encoder
  from tensor2tensor.layers import modalities
  from tensor2tensor.utils import registry
  import tensorflow.compat.v1
label_desc: Use image node_id 2 for calling the AudioTimitCharactersTune obj's underlying member method code with example usage: obj.hparams(defaults, model_hparams) without return types