600 bps voice digitizer

This paper presents an analysis/synthesis method whereby speech may be transmitted at 600 bps, a data rate which is less than 1 percent of the PCM transmission rate for original speech sounds. This R&D effort was motivated by the pressing need for very-low-data rate (VLDR) voice digitizers to meet some of the current military voice communication requirements. The use of a VLDR voice digitizer makes it possible to transmit speech signals over adverse channels which support data rates of only a few hundred bps, or to transmit speech signals over more favorable channels with redundancies for error protection and other useful applications. The 600 bps synthesized speech loses some of its original speech quality, but the intelligibility is sufficiently high to permit the use of the system in certain specialized military applications. One of the most attractive features of the 600 bps voice digitizer is that it is a simple extension of the 2400 bps linear predictive encoder (LPE) which has been under intensive investigation by various government agencies, including the Navy, and is presently entering advanced development. In essence, the 600 bps voice digitizer is a combination of an LPE and a format vocoder, which is realized by adding a processor to the existing 2400 bps LPE. This add-on processor converts the 2400 bps speech data to 600 bps speech data at the transmitter, and reconverts the data to 2400 bps at the receiver.