Initial work on design and testing of a stereophonic audio system began in 1975 when Telesonics approached Chicago public television station WTTW.
WTTW was producing a music show titled Soundstage at that time, and was simulcasting the stereo audio mix on local FM stations.
Telesonics offered a way to send the same stereo audio over the existing television signals, thereby removing the need for the FM simulcast.
Telesonics and WTTW formed a working relationship and began developing the system which was similar to FM stereo modulation.
Twelve WTTW studio and transmitter engineers added the needed broadcast experience to the relationship.
In 1979, WTTW had installed a stereo Grass Valley master control switcher and had added a second audio channel to the microwave STL (Studio Transmitter Link).
PBS member stations who wished to deliver Soundstage in stereo were provided with a four-track (left, right, vertical drive, and time code) audiotape that could be synced with the video machines in those cities.
The Matsushita Quasar TV manufacturing plant and laboratory, just west of Chicago, was used as the source for all testing of the competing systems.
Following EIA and FCC recommendations, the BE modulator was modified to meet BTSC specifications, and by August 1984 was in full-time use on WTTW.
Networks in Canada and Mexico, which also used the NTSC video standard, utilized MTS sound when made available.
As a component of the NTSC standard, MTS is no longer being used in U.S. full-power television broadcasting after the June 12, 2009 DTV transition in the United States.
[4] THAT created consumer pages on the DTV transition and how it affected MTS by the choice of CECB, as some only receive stereo-incompatible RF signals and only output mono sound.
AM is known to be susceptible to interference and noise reduction to the sub-channel aids in the improvement of SNR over standard FM broadcast.
Viewers who owned mono TV sets would hear normal audio, only limited to 15 kHz bandwidth.
The original specifications called for a brick wall elliptical filter in each of the audio channels prior to encoding.
The elliptical filter was chosen for having the greatest bandwidth with the lowest phase distortion at the cutoff frequency.
In comparison, standard FM modulators filter the audio at slightly higher frequencies but still must protect the 19 kHz pilot signal.
Maintaining the phase stability of the horizontal sync is essential to good audio in the decode process.
Later UHF transmitter designs improved ICPM performance and allowed MTS stereo transmission.
[4] Several nations outside North America using the NTSC standard adopted the MTS format for their analog systems, including Chile, Colombia, Taiwan and the Philippines.