code: def delta_delta(fbank, sr=8000, feature_size=40):
      """
      params:
        fbank: [nframe, nfbank]
      return : [nframe, nfbank, 3]
      """
      del sr, feature_size
      assert fbank.ndim == 2
      delta = psf.delta(fbank, N=2)
      _delta_delta = psf.delta(delta, N=2)
      return np.stack([fbank, delta, _delta_delta], axis=-1)
  
file_path: delta/delta/data/feat/speech_feature.py
imports: import os
  import numpy
  import delta.compat
  from absl import logging
  from delta.data.feat import speech_ops
  from core.ops import py_x_ops
  from delta.data.feat import python_speech_features
label_desc: Use image node_id 8 for calling a global function with example usage: delta_delta(fbank, sr, feature_size) and returns: np