docstr: Gets called when a stage (either training, validation, test) starts.
docstr_tok: ["Gets","called","when","a","stage","(","either","training",",","validation",",","test",")","starts","."]
code: def on_stage_start(self, stage, epoch=None):
      "Gets called when a stage (either training, validation, test) starts."
      self.train_metrics = self.hparams.train_stats()
  
      self.noise_datasets = [
          self.hparams.add_noise,
          self.hparams.add_noise_musan,
          self.hparams.add_music_musan,
      ]
      self.speech_datasets = [
          self.hparams.add_speech_musan,
          self.hparams.add_speech_musan,
          self.hparams.add_speech_musan,
      ]
  
      if stage != sb.Stage.TRAIN:
          self.valid_metrics = self.hparams.test_stats()
  
file_path: speechbrain/recipes/LibriParty/VAD/train.py
imports: import sys
  import torch
  import logging
  import numpy
  import speechbrain
  from hyperpyyaml import load_hyperpyyaml
  from speechbrain.utils.distributed import run_on_main
  from data_augment import augment_data
label_desc: Use image node_id 3 for calling the VADBrain obj's underlying member method code with example usage: obj.on_stage_start(stage, epoch) without return types