code: def _linear_to_mel(self, spectrogram):
      return np.dot(self.mel_basis, spectrogram)
  
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 12 for calling the AudioProcessor obj's underlying member method code with example usage: obj._linear_to_mel(spectrogram) and returns: np