The video and audio of every source in the system must feed a multiplexer.
The multiplexer, sometimes called a modulator, mixes the video and audio
channels together. This forms an analog composite baseband signal employing
frequency domain multiplexing. Following the specifications set forth
by the National Television Standards Committee (NTSC), the video signal
consists of luminance information describing the amount of light in
each point of the picture and a chrominance signal modulated on a 3.58
MHz. subcarrier which provides information about the hue (which color)
and saturation (how much color). Left and right audio channels are modulated
on subcarriers of 10.7 and 11.5 MHz. respectively, completing the composite.
This signal is then fed to the switcher.