Crosby system

The Crosby system was an FM stereo standard, developed by Murray G. Crosby, that used an FM sub-carrier for higher fidelity. It competed with the Zenith/GE system that used an AM sub-carrier. The Crosby system's signal was less noisy, offering the best frequency response in stereo with less degradation under weak signal conditions. It utilized the matrix principle, transmitting the sum signal L+R as the main channel modulation and the difference signal L-R as a 50 kHz subcarrier. However, it was incompatible with existing subsidiary communications authorizations (SCAs) which used various subcarrier frequencies including 41 and 67 kHz. Many revenue-starved FM stations used SCAs for "storecasting" and other non-broadcast purposes. 1960 FCC tests confirmed that the GE/Zenith stereo multiplexing technique was compatible with 67 kHz SCA operation. Several FM stations relying on SCA revenue urged the FCC to adopt the GE/Zenith standard.

On April 19, 1961, the FCC released its Final Order selecting the Zenith/GE system as the stereophonic broadcasting standard. That system continues to be used today for stereo FM broadcasting, which accounts for the poor quality of stereo signals in comparison with monaural signals. When reception is poor, the stereo AM GE/Zenith signal will typically fade in and out, while the FM signal remains relatively strong. On most car radios, this manifests itself as a "STEREO" light flickering on and off.

References

• Nichols, Roger: I Can't Keep Up With All The Formats, 2003.
• Schoenherr, Steven E.: Stereophonic Sound, 2001.