signal processing circuits inside the television set use the brightness, colour, and sound information contained in the received signal to control the television set's output devices. the display output device may be a cathode ray tube (crt) or a plasma or liquid crystal display screen. the audio output device might be a magnetically driven audio speaker. the display output devices convert the signal processing circuits' brightness and colour information into the visible image displayed on a screen. the audio output device converts the processed sound information into sounds that can be heard by listeners.