AMPLITUDE CHAR.ICTERISTICS OF TELEPHONIC SIGNALS 553 



compressor alone. The first, which uses a fairly high ratio of com- 

 pression, has been mentioned as one type of peak Hmiting device. The 

 second, using a moderate ratio of compression, is in connection with 

 announcing systems for use in very noisy locations. Its effect is to 

 amplify weak sounds more than strong sounds, which considerably 

 improves the intelligibility through high noise. For quiet locations it 

 is of less value, since the speech sounds lose some of their naturalness in 

 this process. 



Conclusion 



In the course of developing various types of the volume controlled 

 devices which have been described means have been worked out for 

 providing almost any combination of time constants, range of control, 

 and other characteristics which may be required. Some devices for 

 which there were specific commercial applications or useful functional 

 characteristics for experimental work have been constructed, with 

 resulting advantages which have been briefly mentioned. There 

 remain many possible ways to alter the characteristics of signal energy 

 such as speech to which these methods are applicable and which await 

 the special needs of new transmission problems. 



Bibliography 



1. C. C. I. F. White Book, 1 bis, pp. 77, 343. 



2. C. C. I. F. White Book, 1 bis, pp. 251-3. 



3. "A Vogad for Radio Telephone Control Terminals," S. Doba, Jr., Bell Labora- 



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Dickieson, Presented at /. R. E. Convention in New York, June 18, 1938; to 

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1934, Vol. 1, No. 1, pp. 7-9; Bell Lab. Record, Dec. 1934, Vol. 13, No. 4, 

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7. "Volume Limiter Circuits," G. W. Cowley, Bell Lab. Record, June 1937, Vol. 15, 



No. 10, pp. 311-15. 



8. "A Noise Reducer for Radio Telephone Circuits," N. C. Norman, Bell Lab. 



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9. "Radio Telephone Noise Reduction by Voice Control at Receiver," C. C. 



Taylor, Elec. Engg., Aug. 1937, Vol. 56, No. 8, pp. 971-4, 1011; Bell Sys. 

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10. "Higher Volumes Without Overloading," S. Doba, Jr., Bell Lab. Record, Jan. 



1938, Vol. 16, No. 5, pp. 174-8. 



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For the sake of completeness the following references are included, although no 

 allusion has been made to them under the specific device-names used in this paper. 



12. "Uber automatische Amplitudenbegrenzer," H. F. Mayer, E. N. T., 1928, 



Vol. 5, No. 11, pp. 468-72. 



