code: def out_linear_to_mel(self, linear_spec):
      S = self.denormalize(linear_spec)
      S = self._db_to_amp(S)
      S = self._linear_to_mel(np.abs(S))
      S = self._amp_to_db(S)
      mel = self.normalize(S)
      return mel
  
imports: import librosa
  import soundfile
  import numpy
  import scipy.io.wavfile
  import scipy.signal
  from TTS.tts.utils.data import StandardScaler
label_desc: Use image node_id 18 for calling the AudioProcessor obj's underlying member method code with example usage: obj.out_linear_to_mel(linear_spec) and returns: mel