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SAP is part of MTS, the Multichannel Television Sound standard set by the National Television Systems Committee ( NTSC )in 1984 in the U.S. The NTSC Video Format and MTS are also used in Canada and Mexico , and in Japan . MTS features, including Stereo and SAP, travel on Subcarrier s of the Audio Carrier , much like stereo information for an FM Radio broadcast. The SAP subcarrier is located at 78.670 KHz , which is five times the 15.734 kHz MTS Pilot Signal . In turn, the MTS pilot is locked to the horizontal Sync Frequency of the video carrier for stability. The SAP channel contains Mono Audio which has been Dbx - Encode d for Noise Reduction , to improve the Signal-to-noise Ratio . The SAP audio goes from 60 Hz to 12 kHz, which is less than the "regular" audio channel accepting from 50 Hz to 15 kHz. Though not technically a SAP channel, television stations can also broadcast a "PRO" ( Professional ) audio subcarrier which is used to communicate with station personnel. This one-way audio channel allows individuals at the television station to send messages to people located away from the station and is frequently employed during newscasts. This channel is located at 6.5 times the pilot, and is also part of the MTS standard. Because of its 251 kHz bandwidth, the audio carrier used in the NTSC television system can easily handle multiple audio channels. |
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