2 channel voice communications sytem - has reduced bit rate whilst maintaining intelligibility by using delta, PCM or DPCM converters

摘要

The voice communications systems has a good intelligibility and sound quality using a reduced bit rate from the A/D and D/A converters at the end stations. (The system described in the main patent has D/A and A/D converters for both the lower and upper channels). The lower channel (K1) is provided with an A/D and a D/A converter (AD1, DA1) for delta modulation, multi-bit PCM modulation or for DPCM modulation. The upper channel is provided with an A/D and a D/A converter (ad2, DA2) for 1 bit PCM modulation. The voice band is divided by BP filters (bf1, BF2) into 300-600 Hz and 0.8-3.4 Hz. Two more BP filters are located at the output side.