Talk:Multichannel Television Sound

No info on modulation?
I'm missing nformation on the carriers used. The article mentions the L+R/L-R format, optional extra channelsand a pilot tone, but gives no information how the extra channels are actually carried: for example similar to FM radio or using SSB. —Preceding unsigned comment added by 217.19.29.156 (talk) 14:51, 17 January 2010 (UTC)


 * AM suppressed carrier, like FM stereo, but with a 15734Hz pilot, instead of 19kHz. and using the TV horizontal rate as the source for the pilot. Gah4 (talk) 23:45, 19 February 2017 (UTC)

Askierkiewicz (talk) 13:16, 24 November 2017 (UTC)The sub carriers of the BTSC encoding used multiples of the color horizontal sync frequency, 15,734 Hz. L-R was modulated on 2x horizontal, SAP at 5x horizontal and PRO at 6.5x horizontal. The entire audio baseband signal was limited to 50-105 kHz. Since the horizontal sync was used as a pilot, any variations in that signal produced phase distortion in the decoded signals. This made UHF transmitters of the day, difficult to adapt for BTSC. Transmitters using klystron final amplifiers added excessive ICPM (Incidental Carrier Phase Modulation). It was determined during testing that ICPM needed to be kept below 4.5%.Askierkiewicz (talk) 13:16, 24 November 2017 (UTC)

PBS Stereo Tags
PBS dosen't have it's own stereo tag. PBS stations often use stereo disclaimers during or after the opening sequence. For example:

On Reading Rainbow (began stereo episodes in 1984 part-time, full time in 1988) - the stereo tag appears after the "hosted by LEVAR BURTON" text fades out.

Sesame Street (began 1992) has theirs during a cold open segment. If there is no cold open segment, the stereo tag appears after the opening sequence. ACMEWikiNet (talk) 14:53, 21 February 2012 (UTC)

dbx
I always knew that dbx was used for SAP, but I didn't know that it was also used for the stereo subcarrier. Is there a reference for that? Gah4 (talk) 23:47, 19 February 2017 (UTC)

Those of us (WTTW Engineering) involved in the project called for noise reduction in the sub channel (L-R) from the very beginning (ca. 1975). This would produce less noise in the decoder than standard FM broadcasts. Initially Dolby A was used but would require a higher license fee than other systems. dBx was chosen in the licensing negotiations that followed. dBx became part of the standard adopted by the FCC following the testing phase. The license fee was added to each receiver final sales price. As I remember it was $0.49/receiver at the beginning. To prevent any confusion, SAP was a mono signal. — Preceding unsigned comment added by Askierkiewicz (talk • contribs) 13:08, 24 November 2017 (UTC)


 * FM stereo, with the 38kHz AM-SC with the same amplitude as L+R, results in the same signal as switching between L and R at 38kHz. I don't know if modulators and demodulators are actually built that way. If the L-R is dbx encoded, that math doesn't work. The accuracy of (L-R) then depends on how close the dbx demodulation is, and so the resulting stereo separation. Gah4 (talk) 21:28, 24 November 2017 (UTC)

External links modified (February 2018)
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close enough?
The article mentions 15734Hz, but it is slightly more than that, as actually the color subcarrier frequency divided by 227.5, so closer to 15734.26Hz. Is 15734Hz close enough for this article? Gah4 (talk) 19:31, 7 January 2020 (UTC)