code: def add_spectrogram(self, view=None):
          
          spectrolayer = self.__add_spectrogram(0)
          spectroruler = self.__add_time_ruler()
          if view is None:
              view = self.__add_view()
          self.__add_layer_reference(view, spectroruler)
          self.__add_layer_reference(view, spectrolayer)
          return view
docs: add a spectrogram layer to the environment
          
          Kwargs:
            view(<DOM Element: view>): environment view used to display the spectrogram, if set to None, a new view is created
            
          Returns:
            <DOM Element: view>: the view used to store the spectrogram