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A Method to Improve Conventional FM Stereo

The author is president of Omnia Audio in Cleveland.

The FM stereo transmission system employed in worldwide broadcasting has been in place since 1961. The rules governing stereophonic performance have not been altered since the mid-1980s (in the USA) when they were modified to allow an additional 0.5 percent total modulation (maximum of 110 percent total), for every 1 percent of SCA modulation, if an SCA was being utilized. The rules governing the requirements of the FM stereo baseband signal are quite explicit, and leave little — if any — room for improvement of the stereo transmission system.

This paper will offer, in detail, a method utilizing single-sideband suppressed carrier (SSBSC) modulation of the stereophonic subcarrier in the FM multiplex baseband that is compatible with existing radio receivers. Additionally, there are multiple overall benefits to the broadcast signal, which are perceivable to the listener. They reduce multipath-induced distortion, and offer additional protection to the spectrum used for RDS, SCA signals and HD Radio content — thereby improving data robustness in the receiver.

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