code: def display_window(self):
          
          if self.idx_chan.count() == 0:
              self.update()
  
          chan_name = self.idx_chan.currentText()
          lg.debug('Power spectrum for channel ' + chan_name)
  
          if chan_name:
              trial = 0
              data = self.parent.traces.data(trial=trial, chan=chan_name)
              self.display(data)
          else:
              self.scene.clear()
docs: Read the channel name from QComboBox and plot its spectrum.
  
          This function is necessary it reads the data and it sends it to
          self.display. When the user selects a smaller chunk of data from the
          visible traces, then we don't need to call this function.