class_docstr: Normalize per raw audio by removing the
  mean and divided by the standard deviation
code: def __call__(self, signal):
      signal_std = 0.0 if np.std(signal) == 0.0 else np.std(signal)
      signal_mean = np.mean(signal)
      return (signal - signal_mean) / signal_std
  
imports: import random
  import cv2
  import numpy
  import torch
  from scipy import signal
label_desc: Use image node_id 1 for calling the NormalizeUtterance obj's underlying member method code with example usage: obj.__call__(signal) and returns: unknown