code: def test_mel_scale():
      f = 16000.0
      x = MelScale.convert(f)
      f_back = MelScale.invert(x)
      assert torch.abs(f_back - f) < 0.1
      MelScale.bank(128, 16000.0)
  
imports: import torch
  from espnet2.layers.sinc_conv import BarkScale, LogCompression, MelScale, SincConv
label_desc: Use image node_id 6 for calling a global function with example usage: test_mel_scale() without return types