code: def preemphasis(signal, shift=1, cof=0.98):
      
  
      rolled_signal = np.roll(signal, shift)
      return signal - cof * rolled_signal
docs: preemphasising on the signal.
  
      Args:
          signal (array): The input signal.
          shift (int): The shift step.
          cof (float): The preemphasising coefficient. 0 equals to no filtering.
  
      Returns:
             array: The pre-emphasized signal.