The Crosby system was an FM stereophonic broadcasting standard, developed by Murray G. Crosby , that used an FM subcarrier for higher fidelity. It competed with the Zenith/GE system that used an AM subcarrier. Many audiophiles were disappointed when the Zenith/GE was chosen as the nationwide standard, since the Crosby system had many advantages.

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. The Crosby system's main advantage over the Zenith/GE system was its use of an FM subcarrier. FM is less susceptible to interference than AM. In addition, most AM radio stations do not reproduce faithfully sounds below 100 Hz or above 5 kHz; FM stations generally have a frequency range or 50 Hz to 15 kHz and the upper limit may be even higher.

However, the Crosby system 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 FM 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 monaural 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.