Diemazz

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.

History

It was adopted by the FCC as the U.S. standard for stereo television transmission in 1984. Sporadic network transmission of stereo audio began on NBC on July 26, 1984, with the The Tonight Show Starring Johnny Carson, although at the time, only the NBC station in New York City had stereo broadcast capability;^[1] regular stereo transmission of NBC programs began in 1985. ABC and CBS followed suit in 1986 and 1987, respectively.

Adopted in

It has also been adopted by

• Canada for NTSC
• Mexico for NTSC
• Chile for NTSC
• Brazil for PAL-M (television)
• Argentina for PAL-N
• Taiwan for NTSC

How MTS works

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.

In other words the normal mono television audio consists of L+R information. A second signal (MTS) rides on top of this mono carrier wave. This MTS signal consists of L minus R.

• When the two audio channels are added together, or summed (L+R plus L-R), the left channel is derived.
• When the second audio channel is subtracted from the first by a phase reversal (L+R minus L-R), the right channel is derived.

MTS real world performance

• In ideal circumstances MTS Stereo is about 1.5 db better in performance than standard VHF FM stereo.
• Usually with MTS, as with VHF FM stereo, a certain amount of crosstalk is encountered, limiting stereo separation.

The stereo information is dbx-encoded to increase the signal-to-noise ratio (at low levels), to aid in noise reduction.

MTS licensing

Because of the use of dbx companding, every TV device that decoded MTS originally required the payment of royalties, first to dbx, Inc., then to THAT Corporation which was spun off from dbx in 1989 and acquired its MTS patents in 1994; however, those patents expired worldwide in 2004.^[2] Though THAT now owns some patents related to digital implementations of MTS, a letter from THAT to the National Telecommunications and Information Administration in 2007 confirms that no license is required from THAT for all analog and some digital implementations of MTS.^[3]

How MTS audio channels are used

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. The PRO channel 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.

• Specialized receivers for the PRO channel are generally only sold to broadcast professionals.
• NICAM has a similar pro-channel feature that has only been implemented in the UK (http://tallyho.bc.nu/~steve/nicam.html#SPARE).

MTS signals are indicated to the television receiver by adding a 15.734 kHz pilot tone to the signal.

MTS and the DTV transition in the United States

As a component of the NTSC standard, MTS will no longer be used in U.S. full-power television broadcasting after February 17, 2009, when the DTV transition in the United States concludes and ATSC becomes the sole U.S. broadcast TV standard. It will remain in use in LPTV and in analogue cable television. All coupon-eligible converter boxes (CECBs) are required to output stereo sound via RCA connectors, but MTS is merely an optional requirement for the RF modulator that every CECB contains. NTIA has stated that MTS was made optional for cost reasons;^[4] this may have been due to a belief that MTS still required royalty payments to THAT Corporation, which is no longer true except for some digital implementations.^[3]

THAT has created consumer pages on the DTV transition and how it affects MTS.^[5] However, the site attempts to spin the situation by claiming that most consumers with CECBs will lose stereo TV sound, since RF-only connections are common and MTS is optional for CECBs. Though the site is correct in that an RF-only connection will be in mono unless the CECB's RF modulator has MTS built-in, this problem can also be remedied by connecting the CECB's RCA connectors to the TV's line level stereo and composite video inputs, which bypasses the RF modulator (and also tends to provide a better video signal). The few stereo TVs without RCA connectors may instead try computer sound card speakers with a Y-adapter attached to their mini phone jack, or a separate RF modulator with RCA inputs and MTS. The stereo outputs of a CECB may also be connected directly to the auxiliary line-input jacks of a home stereo system.

See also

• NICAM
• Zweikanalton

References

1. ^ Peter W. Kaplan, "TV Notes," New York Times, July 28, 1984, sec. 1, p. 46.
2. ^ dbx-TV Timeline (THAT Corporation)
3. ^ ^{a b} Letter to NTIA, August 21, 2007 (THAT Corporation)
4. ^ NTIA Letter to THAT Corporation, August 2, 2007
5. ^ dbx-TV and the Digital TV Transition (THAT Corporation)

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