3895322 is referenced by 5 patents and cites 3 patents.

A fixed power level frequency pilot tone, typically 4000 Hz, is inserted into the transmission baseband closely associated with each voice channel of a multichannel telephone cable system. The fixed-frequency pilot tone is a control signal that is transmitted through a voice transmitter compressor of a compandor system, together with the voice signal, and the pilot control signal is utilized at the voice receiver end to correctly expand the voice signal back to the required signal power level. The doubling of a transmission error of a conventional 2:1 compandor system is substantially reduced, being typically held to a few tenths of a dB.

Title
Tone controlled compandored system
Application Number
05/450,956
Publication Number
3895322
Application Date
March 14, 1974
Publication Date
July 15, 1975
Inventor
Zellmer Neale A
Stewart James A
Agent
Cannon Russell A
Cool Leonard R
Assignee
GTE Automatic Electric Laboratories Incorporated
IPC
H04b 01/64
H04B 01/62
H03G 07/00
H04B 01/64
H03G 07/06
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