code: def fast_autocorr(original, delayed, t=1):
      if t == 0:
          return np.corrcoef([original[::4], delayed[::4]])[1, 0]
      elif t < 0:
          return np.corrcoef([original[-t::4], delayed[:t:4]])[1, 0]
      else:
          return np.corrcoef([original[:-t:4], delayed[t::4]])[1, 0]
  
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 1 for calling a global function with example usage: fast_autocorr(original, delayed, t) and returns: np, np, np