Since the No. 40 uses a card cage design, all of the No. 40 boards plug into a backplane. Since the No. 40s Video Processors backplane was designed before HDMI existed it cannot accommodate HDMI video, so the HDMI video signal is passed straight through from one of the three HDMI inputs on the HDMI card to the system’s display device via the HDMI output. Plugging the No. 40 HDMI card into the Audio Processor allows us to capture the HDMI audio signal and process it.