BELL SYSTEM TECHNICAL JOURNAL 



Fig. 1. Front view of experimental PCM terminal equipment, with covers removed 

 from a 12-channel group bay. 



Pulse Code Modulaiicn 



Sampling. A basic premise of pulse modulation systems is that the infor- 

 mation content of a v^ave can be conveyed by samples taken at sufficiently 

 frequent, equally spaced time intervals. The interval should be no greater 

 than half the period of the highest frequency speech component to be repro- 

 duced or, otherwise expressed, the sampling rate should be not less than twice 

 the frequency of the highest speech component present. This provision insures 



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