AUDIO CHANNEL STACKING WITH SPEECH COMPRESSION FOR NARROW BAND TRANSMISSION WITH PROVISION FOR DIALED CALLS

摘要

An analog signal stacking method and apparatus permits transmission of an analog signals of given spectrum width over a narrow band communication circuit (13) having bandwidth approximately equal to the spectrum width of one analog signal by compressing the spectrum of each signal by a factor of 1/n and frequency offsetting the compressed signals to occupy contiguous frequency bands within the bandwidth of the circuit. Received signals are processed to remove the frequency offset and expand the baseband signals to restore each analog signal to its normal spectrum. A dial through circuit (Figs. 6A and 6B) permits application of the stacking feature to place two conventional dialed calls on a single line (73, 74) of the telephone network using a circuit for processing both dial and voice signals.