code: def mse(signal1, signal2):
      """Mean squared error"""
      return np.mean((signal1 - signal2) ** 2)
  
file_path: audiomentations/tests/test_mp3_compression.py
imports: import os
  import matplotlib.pyplot
  import numpy
  import pytest
  from audiomentations import Mp3Compression
  from audiomentations.core.audio_loading_utils import load_sound_file
  from demo.demo import DEMO_DIR
label_desc: Use image node_id 3 for calling a global function with example usage: mse(signal1, signal2) and returns: np