code: def test_mel2(self):
      top_db = 80.0
      s2db = transforms.AmplitudeToDB("power", top_db)
  
      waveform = self.waveform.clone()  # (1, 16000)
      waveform_scaled = self.scale(waveform)  # (1, 16000)
      mel_transform = transforms.MelSpectrogram()
      # check defaults
      spectrogram_torch = s2db(
          mel_transform(waveform_scaled)
      )  # (1, 128, 321)
      self.assertTrue(spectrogram_torch.dim() == 3)
      self.assertTrue(
          spectrogram_torch.ge(spectrogram_torch.max() - top_db).all()
      )
      self.assertEqual(spectrogram_torch.size(1), mel_transform.n_mels)
      # check correctness of filterbank conversion matrix
      self.assertTrue(mel_transform.mel_scale.fb.sum(1).le(1.0).all())
      self.assertTrue(mel_transform.mel_scale.fb.sum(1).ge(0.0).all())
      # check options
      kwargs = {
          "window_fn": torch.hamming_window,
          "pad": 10,
          "win_length": 500,
          "hop_length": 125,
          "n_fft": 800,
          "n_mels": 50,
      }
      mel_transform2 = transforms.MelSpectrogram(**kwargs)
      spectrogram2_torch = s2db(
          mel_transform2(waveform_scaled)
      )  # (1, 50, 513)
      self.assertTrue(spectrogram2_torch.dim() == 3)
      self.assertTrue(
          spectrogram_torch.ge(spectrogram_torch.max() - top_db).all()
      )
      self.assertEqual(
          spectrogram2_torch.size(1), mel_transform2.n_mels
      )
      self.assertTrue(mel_transform2.mel_scale.fb.sum(1).le(1.0).all())
      self.assertTrue(mel_transform2.mel_scale.fb.sum(1).ge(0.0).all())
      # check on multi-channel audio
      filepath = common_utils.get_asset_path(
          "steam-train-whistle-daniel_simon.wav"
      )
      x_stereo = common_utils.load_wav(filepath)[
          0
      ]  # (2, 278756), 44100
      spectrogram_stereo = s2db(
          mel_transform(x_stereo)
      )  # (2, 128, 1394)
      self.assertTrue(spectrogram_stereo.dim() == 3)
      self.assertTrue(spectrogram_stereo.size(0) == 2)
      self.assertTrue(
          spectrogram_torch.ge(spectrogram_torch.max() - top_db).all()
      )
      self.assertEqual(spectrogram_stereo.size(1), mel_transform.n_mels)
      # check filterbank matrix creation
      fb_matrix_transform = transforms.MelScale(
          n_mels=100,
          sample_rate=16000,
          f_min=0.0,
          f_max=None,
          n_stft=400,
      )
      self.assertTrue(fb_matrix_transform.fb.sum(1).le(1.0).all())
      self.assertTrue(fb_matrix_transform.fb.sum(1).ge(0.0).all())
      self.assertEqual(fb_matrix_transform.fb.size(), (400, 100))
  
imports: import math
  import torch
  import torchaudio
  import torchaudio.functional
  import torchaudio.transforms
  from torchaudio_unittest import common_utils
label_desc: Use image node_id 6 for calling the Tester obj's underlying member method code with example usage: obj.test_mel2() without return types