Foti to Detail Stereo Improvement Plan to NRSC

Frank Foti thinks FM stereo can be improved, and he'll share his idea of how to do it with the National Radio Systems Committee during the upcoming Radio Show convention.

According to NAB's Radio TechCheck newsletter, Foti, head of processing manufacturer Omnia Audio, will talk about a way to improve the performance of conventional FM stereo transmission by modifying the L–R stereo subcarrier signal. He believes the approach also would reduce multipath and better protect the baseband spectrum, and would be compatible with existing radio receivers.

Foti earlier submitted a white paper discussing the approach, which uses single-sideband suppressed-carrier (SSB-SC) modulation of the stereophonic subcarrier in the FM multiplex baseband. The idea was influenced by a 1997 paper by William H. Gillman.

The graphic shown here is from Gillman's paper; NAB engineers said it illustrates the concept: "The upper spectrum in this figure depicts a conventional baseband FM stereo spectrum, showing the double-sideband suppressed carrier (DSB-SC) L–R audio channel, centered at 38 kHz," NAB wrote in its summary. "In the lower spectrum, the upper sideband of the L–R subcarrier is eliminated and the amplitude of the lower sideband is increased by 6 dB, to support the correct L+R/L–R matrixing in the receiver."

Commission rules require DSB-SC modulation of the L–R channel, so the technique would require a rules change to be used widely.

In reply to followup questions, Foti told Radio World: “While working on our Omnia.11 project, it occurred to me that we finally had the MIPS to test the concept. So after testing and proving it works, I shared an informal white paper of my own with a friend, who passed it onto NAB. They’ve asked me to make this presentation at the NRSC meeting.” Foti said the feature is offered as a selectable parameter in the stereo generator of the Omnia.11 processor.

“I can tell you this, switching off the upper sideband of the FM stereo signal does not change the stereo sound field at all, when decoded back through a stereo radio. I had a demo of this running at IBC in Amsterdam, and everyone who heard it claimed they could not tell the difference when the decoded audio was DSB or SSB.”

He added as an aside: “Should the receiver industry get behind this, and rethink the stereo multiplexing method in their radios, there is a potential 4 dB improvement of signal-to-noise performance for stereo listening.”

NRSC also will hear presentations from the Internet Media Device Alliance and RadioDNS, both of which have been profiled in past recent issues of Radio World.

"Award-Winner: RadioDNS" (June 2010)

"IMDA Charts Course for Internet Radio" (Sept. 2010)

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Comment List:

C-QAM is not useable with any carrier phase ambiguity. Platform shifting is the result when there is phase ambiguity caused by interference by sky waves from other stations. The AM-FM system also known as Magnavox stereo "AM" system was far superior to the C-QAM stereo "AM" system and the FCC agreed after testing the five systems for several years. The only reason that the FCC changed their mind is because of the desire to brown nose with the new President, Ronald Reagan.
By Anonymous Texan on 9/2/2011
Another reason why I wonder if we should even bother with HD radio. There are improvements that can be made to analog radio (both FM AND AM) that can make it sound even better without causing interference to their radio neighbors. CQuam AM is a no-brainer to use - it works great over huges distances as WSM once proved; SSB-SC on FM is another no-brainer; FMEXTRA is another no-brainer; making mandatory minimum receiver requirements for AM tuners is a no-brainer; giving AM stations preference for FM translators over LPFM/FM translators; not stealing every ounce of spectrum for the inefficient "pay for play" broadband...there is so much the FCC should be doing differently - their priorities are wrong, and the NAB should be trying to point the FCC the correct direction (abandon the broadband pillage and improve existing services)! Soapbox mode off.
By Anonymous on 9/15/2010
I always wondered why this was not done before. It would be interesting to quantify the amount of multipath reduction and the perceived improvement of S/N ratio. It's a pity so many mobile receivers blend to mono so soon.
By Anonymous on 9/14/2010

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