300 BELL SYSTEM TECHNICAL JOURNAL 



no doubt will be more serious than experienced in the Philadelphia- 

 Washington demonstration. Such a volume compression-expansion 

 system requires additional apparatus at the sending and receiving 

 terminals of the line circuit. At the sending end this apparatus is 

 used to raise in volume the weak passages of the music or other program 

 for transmission over the line circuits in order that the proper ratio 

 between the desired program and unwanted noises may be retained. 

 At the receiving terminal coordinating apparatus reexpands the com- 

 pressed volume range to the volume range originally applied to the 

 transmitting terminal. 



In the demonstration, to provide supplementary control features 

 required by Dr. Stokowski at Washington for communicating with 

 the orchestra at Philadelphia, additional wire circuits were established 

 between these points. Order wire circuits also were provided for 

 communication between the terminals and repeater points to make 

 possible the location troubles if any should arise. Rather elaborate 

 switching means were included at the terminals to permit switching 

 the carrier channels to different microphones and to different amplifier 

 equipment at the loud speaker end. To take care of the contingency 

 of a cable pair failure, spare pairs of wires were made available to be 

 switched in at short notice. Fortunately, none of the reserve facilities 

 actually were required for the demonstration. 



References 



1. "Long Distance Cable Circuits for Program Transmission," A. B. Clark and 



C. W. Green. A. I. E. E. Trans., v. 49, 1930, p. 1514-23. 



2. "Thermal Agitation of Electricity in Conductors," J. B. Johnson. Phys. Rev., 



V. 32, 1928, p. 97. 



3. "Thermal Agitation of Electric Charge in Conductors," H. Nyquist. Phvs. Rev., 



V. 32, 1928, p. 110. 



4. "Carrier in Cable," A. B. Clark and B. W. Kendall. Elec. Engg., Julv 1933, p. 



477-81. ^s - J - 



