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Multichannel television sound, better known as MTS (often still as BTSC, for the Broadcast Television Systems Committee that created it), is the method of encoding three additional channels of audio into an NTSC-format audio carrier. It was adopted by the FCC as the U.S. standard for stereo television transmission in 1984. It has also been adopted by Canada, Mexico, Brazil, Argentina, Taiwan, and others, some of which use PAL instead of NTSC.
The first channel is the stereo difference (left minus right), used to add stereophonic sound to the existing monophonic (the left plus right stereo sum) audio track. The stereo information is dbx-encoded to increase the signal-to-noise ratio, to aid in noise reduction. Because of the use of dbx companding, every TV device that uses analog circuitry to decode MTS costs somewhat more because a royalty must be paid to THAT Corporation, until its patent runs out. These patents do not apply to some digital circuits, however.
The second audio program (SAP) also is part of the standard, providing another language, a video description service like DVS, or a completely separate service like a campus radio station or weatheradio.
A third PRO (professional) channel is provided for internal use by the station, and may handle audio or data. It is normally used with electronic news gathering during news broadcasts to talk to the remote location (such as a reporter on-location), which can then talk back through the remote link to the TV station. Receivers for this channel may not be sold to the public.
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