Crosby system
Encyclopedia
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 audiophile
s 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. Another (albeit relatively minor) factor was that radios used vacuum tube
s in those days; the additional tubes for an all-FM system would have increased the size, weight, cost of and heat generated by each tuner or receiver.
According to Jack Hannold:
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.
At 9:59 A.M. on the day that the FCC's rule came out, Crosby-Teletronics stock was worth $15 a share; by 2:00 P.M. it was down to less than $2.50.
Frequency modulation
In telecommunications and signal processing, frequency modulation conveys information over a carrier wave by varying its instantaneous frequency. This contrasts with amplitude modulation, in which the amplitude of the carrier is varied while its frequency remains constant...
subcarrier
Subcarrier
A subcarrier is a separate analog or digital signal carried on a main radio transmission, which carries extra information such as voice or data. More technically, it is an already-modulated signal, which is then modulated into another signal of higher frequency and bandwidth...
for higher fidelity
High fidelity
High fidelity—or hi-fi—reproduction is a term used by home stereo listeners and home audio enthusiasts to refer to high-quality reproduction of sound or images, to distinguish it from the poorer quality sound produced by inexpensive audio equipment...
. It competed with the Zenith/GE system that used an AM
Amplitude modulation
Amplitude modulation is a technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. AM works by varying the strength of the transmitted signal in relation to the information being sent...
subcarrier. Many audiophile
Audiophile
An audiophile is a person who enjoys listening to recorded music, usually in a home. Some audiophiles are more interested in collecting and listening to music, while others are more interested in collecting and listening to audio components, whose "sound quality" they consider as important as the...
s 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
Federal Communications Commission
The Federal Communications Commission is an independent agency of the United States government, created, Congressional statute , and with the majority of its commissioners appointed by the current President. The FCC works towards six goals in the areas of broadband, competition, the spectrum, the...
tests confirmed that the GE/Zenith stereo multiplexing
Multiplexing
The multiplexed signal is transmitted over a communication channel, which may be a physical transmission medium. The multiplexing divides the capacity of the low-level communication channel into several higher-level logical channels, one for each message signal or data stream to be transferred...
technique was compatible with 67 kHz SCA operation. Several FM stations relying on SCA revenue urged the FCC to adopt the GE/Zenith standard. Another (albeit relatively minor) factor was that radios used vacuum tube
Vacuum tube
In electronics, a vacuum tube, electron tube , or thermionic valve , reduced to simply "tube" or "valve" in everyday parlance, is a device that relies on the flow of electric current through a vacuum...
s in those days; the additional tubes for an all-FM system would have increased the size, weight, cost of and heat generated by each tuner or receiver.
According to Jack Hannold:
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
FM broadcasting
FM broadcasting is a broadcasting technology pioneered by Edwin Howard Armstrong which uses frequency modulation to provide high-fidelity sound over broadcast radio. The term "FM band" describes the "frequency band in which FM is used for 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.
At 9:59 A.M. on the day that the FCC's rule came out, Crosby-Teletronics stock was worth $15 a share; by 2:00 P.M. it was down to less than $2.50.