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

def add_spectrogram(self, view=None):
        """
        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

        """
        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