Telephony by Pulse Code Modulation

T H I S paper describes an experiment in transmitting speech by P C M , or pulse code modulation. T h e writer is indebted to his colleagues in the Research D e p a r t m e n t , C. E. Shannon, J. R. Pierce and B. M. Oliver, for several interesting suggestions in connection with the basic principles of P C M given in this paper. Work on a different P C M system was carried on simultaneously in the Systems Development D e p a r t m e n t of the Bell Laboratories by H S. Black. This in turn led to the development of an 8-channel portable system for a particular application. This system is being described in a forthcoming paper by H. S. Black and J. O. Edson. 1 A method for pulse code modulation is proposed in a U. S. P a t e n t issued to A. H. Reeves. 2 T h e material now presented is composed of three parts. The first deals with basic principles, the second describes the experimental P C M system, while the last discusses the results obtained. BASIC PRINCIPLES P C M involves the application of two basic concepts. These concepts are namely, the time-division principle and the amplitude quantization * Paper presented in part at joint meeting of International Scientific Radio Union and Inst. Radio Engineers on May 5, 1947 at Washington, D. C. 1 Paper presented on June 11, 1947 at A. I. E. E. Summer General Meeting, Montreal, Canada. Accepted for publication in forthcoming issue of A. I. E. E. Transactions. 2 A. H. Reeves, U. S. Patent # 2,272,070, Feb. 3, 1942, assigned to International Standard Electric Corp.; also, French patent #852,183, October 23, 1939.