docstr: Evaluate one batch
docstr_tok: ["Evaluate","one","batch"]
code: def evaluate_batch(self, batch, stage):
      """Evaluate one batch"""
      out = self.compute_forward(batch, stage=stage)
      loss = self.compute_objectives(out, batch, stage=stage)
      loss_g = loss["G_loss"]
      return loss_g.detach().cpu()
  
imports: import sys
  import torch
  import copy
  from hyperpyyaml import load_hyperpyyaml
  import speechbrain
  from speechbrain.utils.data_utils import scalarize
  import torchaudio
  import os
label_desc: Use image node_id 4 for calling the HifiGanBrain obj's underlying member method code with example usage: obj.evaluate_batch(batch, stage) and returns: loss_g