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Multi channel television sound (MTS) is a format for standard broadcast allowing two channels of sound to be incorporated into TV programming. It is transmitted through standard television carrier wavelength as defined by the U.S. federal communications commission (FCC) and the U.S. national association of broadcasters. MTS incorporates a third channel that is termed as a separate audio program and used for alternate language tracks.
MTS encodes additional channels of audio into the National Television System Committee (NTSC) format for audio carriers. MTS was adopted by Canada for NTSC, Mexico for NTSC, Chile for NTSC, Brazil for PAL-M, Argentina for PAL-N, Taiwan for NTSC, and the Philippines for NTSC.
Multi channel television sound was initially adopted by the FCC as a U.S. standard for stereo television transmission. The first channel is termed as the stereo difference and used as stereophonic sound to existing monophonic audio tracks. Normal mono television audio generally has L+R information. A second MTS signal rides on top of the mono carrier wave and contains L-R information. The left channel is derived when the two audio channels are added or summed. The right channel is obtained when the second audio channel is subtracted from the first by phase reversal.
The real world MTS stereo is 1.5 db better in performance than the standard very high frequency (VHF) FM stereo. A small amount of crosstalk is encountered, limiting the stereo separation. This information is dbx-encoded to increase signal to noise ratio and aids in noise reduction. As dbx companding is used, all TV devices decoding MTS require payment of royalties.
The second audio program is also part of the standard providing another language, video description services or a complete service like a campus radio station or weather radio. The third channel, PRO, is also provided for internal use by stations and may handle audio or data. PRO channels are used with electronic news gathered during news broadcast to talk to remote locations. Specialized receivers for PRO channels are sold to broadcast professionals.
MTS channels are indicated to television receivers by adding a 15.734 kHz pilot tone to the signal. MTS pilots are locked or derived from the horizontal sync signal used to lock video displays. The variations in phase or frequency of horizontal sync are transferred to audio.