code: def _build_mel_basis(
      self,
  ):
      if self.mel_fmax is not None:
          assert self.mel_fmax <= self.sample_rate // 2
      return librosa.filters.mel(
          self.sample_rate,
          self.fft_size,
          n_mels=self.num_mels,
          fmin=self.mel_fmin,
          fmax=self.mel_fmax,
      )
  
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 2 for calling the AudioProcessor obj's underlying member method code with example usage: obj._build_mel_basis() and returns: librosa