class_docstr: Tacotron 2 Model that is used to generate mel spectrograms from text
code: def validation_step(self, batch, batch_idx):
      audio, audio_len, tokens, token_len = batch
      (
          spec_pred_dec,
          spec_pred_postnet,
          gate_pred,
          spec_target,
          spec_target_len,
          alignments,
      ) = self.forward(
          audio=audio,
          audio_len=audio_len,
          tokens=tokens,
          token_len=token_len,
      )
  
      loss, gate_target = self.loss(
          spec_pred_dec=spec_pred_dec,
          spec_pred_postnet=spec_pred_postnet,
          gate_pred=gate_pred,
          spec_target=spec_target,
          spec_target_len=spec_target_len,
          pad_value=self.pad_value,
      )
      loss = {
          "val_loss": loss,
          "mel_target": spec_target,
          "mel_postnet": spec_pred_postnet,
          "gate": gate_pred,
          "gate_target": gate_target,
          "alignments": alignments,
      }
      self.validation_step_outputs.append(loss)
      return loss
  
imports: import contextlib
  from dataclasses import dataclass, field
  from typing import Any, Dict, List, Optional
  import torch
  from hydra.utils import instantiate
  from omegaconf import MISSING, DictConfig, OmegaConf, open_dict
  from omegaconf.errors import ConfigAttributeError
  from pytorch_lightning.loggers import TensorBoardLogger, WandbLogger
  from torch import nn
  from nemo.collections.common.parts.preprocessing import parsers
  from nemo.collections.tts.losses.tacotron2loss import Tacotron2Loss
  from nemo.collections.tts.models.base import SpectrogramGenerator
  from nemo.collections.tts.parts.utils.helpers import g2p_backward_compatible_support, get_mask_from_lengths, tacotron2_log_to_tb_func, tacotron2_log_to_wandb_func
  from nemo.core.classes.common import PretrainedModelInfo, typecheck
  from nemo.core.neural_types.elements import AudioSignal, EmbeddedTextType, LengthsType, LogitsType, MelSpectrogramType, SequenceToSequenceAlignmentType
  from nemo.core.neural_types.neural_type import NeuralType
  from nemo.utils import logging, model_utils
label_desc: Use image node_id 9 for calling the Tacotron2Model obj's underlying member method code with example usage: obj.validation_step(batch, batch_idx) and returns: loss