144 BELL SYSTEM TECHNICAL JOURNAL 



adequate, however, for program transmission because of the different 

 character of the transmitted material. The bulk of present-day 

 broadcast programs consists of musical selections, including a fair 

 amount of high-grade material. To reproduce music, and particu- 

 larly high-grade music, in a pleasing manner calls for a materially 

 widened band. This wider band also gives a high degree of natural- 

 ness to speech which is particularly desirable when loudspeakers are 

 used for reception. 



At the present time in the United States the frequency band which 

 is transmitted over the long distance program chains extends from 

 about 100 cycles to about 5,000 cycles. It is, of course, possible to 

 transmit an even wider band than this, although the cost of the 

 circuits will, of course, increase as the band is widened. In consider- 

 ing how wide the band should be, the complete system, including 

 pickup apparatus, wire transmission line, radio transmitters, radio 

 transmission paths through the ether, radio receiving apparatus and 

 loud speakers must be considered. It seems probable that as the art 

 progresses a band wider than the above will be found desirable. On 

 the wire line systems, development work is going forward looking 

 toward the possibility that such wider bands may be found desirable 

 in the future. At the lower frequencies, where most people consider 

 that improvement is particularly desirable, consideration is being 

 given to the possible extension of the band down to 50 cycles and 

 possibly lower. Consideration is also being given to the possible 

 addition of two or three thousand cycles to the top of the band. 



In addition to this broad band transmission requirement, program 

 transmission circuits must be designed to handle wide ranges of vol- 

 ume, particularly for the transmission of musical programs. Much 

 of the enjoyment in listening to good music appears to come from 

 the ranges of volume, so that in order to deliver such musical programs 

 properly these ranges of volume must be preserved in large part at 

 least. At the present time the volume ranges are "compressed" 

 somewhat by adjustment of amplification under control of an operator 

 at the pickup point. This tends to make easier the radio trans- 

 mission problem as well as the wire transmission problem. The 

 range of volume which is now delivered, as read by a "volume indi- 

 cator" (a meter which roughly indicates the peaks), is of the order 

 of 30 decibels (3.4 nepers), which means that during the fortissimo 

 parts of programs the power which is transmitted is about 1,000 times 

 as great as it is during the pianissimo portions. 



The designer of the wire circuits must be concerned lest during 

 those periods when the program power is strong, the program circuits 



