code: def high_frequency_content(spectrogram):
      """
      High Frequency Content.
  
      Parameters
      ----------
      spectrogram : :class:`Spectrogram` instance
          Spectrogram instance.
  
      Returns
      -------
      high_frequency_content : numpy array
          High frequency content onset detection function.
  
      References
      ----------
      .. [1] Paul Masri,
             "Computer Modeling of Sound for Transformation and Synthesis of
             Musical Signals",
             PhD thesis, University of Bristol, 1996.
  
      """
      # HFC emphasizes high frequencies by weighting the magnitude spectrogram
      # bins by their respective "number" (starting at low frequencies)
      hfc = spectrogram * np.arange(spectrogram.num_bins)
      return np.asarray(np.mean(hfc, axis=1))
  
imports: from __future__ import absolute_import, division, print_function
  import numpy
  from scipy.ndimage import maximum_filter, minimum_filter, uniform_filter
  from ..audio.signal import smooth
  from ..processors import BufferProcessor, OnlineProcessor, ParallelProcessor, SequentialProcessor
  from ..utils import combine_events
label_desc: Use image node_id 3 for calling a global function with example usage: high_frequency_content(spectrogram) and returns: np