code: def mix_wave(src, dst):
      
      if len(src) > len(dst):
          # output should be longer
          dst, src = src, dst
  
      for i, sv in enumerate(src):
          dv = dst[i]
          if sv < 128 and dv < 128:
              dst[i] = int(sv * dv / 128)
          else:
              dst[i] = int(2 * (sv + dv) - sv * dv / 128 - 256)
      return dst
docs: Mix two wave body into one.