Pulse code modulation
H. S. Black, J. O. Edson · Transactions of the American Institute of Electrical Engineers · 1947
A radically new modulation technique for multichannel telephony has been developed which involves the conversion of speech waves into coded pulses. An 8-channel system employing pulse code modulation (PCM) and embodying these principles was produced. The method appears to have exceptional possibilities from the standpoint of freedom from interference, but its full significance in connection with future radio and wire transmission may take some time to reveal.