A self-framing PCM system

A single channel pulse code modulation (PCM) speech communication system is described using a binary code with seven digits per code group and a sampling rate of 8000 per second. A unique feature of the system is the pulse group synchronization or framing scheme that is employed to co-ordinate the operations of the coder and the decoder. A method is outlined wherein the system is able to establish correct framing without the use of auxiliary framing digits. The framing information is inherent in the coded signals. The coder operates on the circulating pulse principle and is a modified version of a coder previously described by Hafer. The decoder is basically one of the pulse count type. The received code pulses produce binary amounts of charge which are stored as voltages on a capacitor. The voltage on the capacitor after one cycle of decoder operation is proportional to the amplitude of the original sample taken at the coder. Test results indicate that the performance is adequate for good quality reproduction of speech. The group synchronization scheme performed perfectly and correct framing was achieved in times so short that misframing noise was inaudible. The proposed framing scheme is adaptable to small PCM speech systems where simplicity in the instrumentation and economy in the use of the digits are important.Applied Science, Faculty ofElectrical and Computer Engineering, Department ofGraduat