Evaluation of low rate speech coders for HF

In 1988, the NATO Tri-Service Group for Communications and Electronics Equipment (TSGCEE) Sub Group 11 (SG/11) established Working Group 2 (WG/2, Narrowband Speech) to develop a voice processor standard for a secure voice system for operation in the high frequency (HF) range. The voice processors evaluated had bit rates of 600, 800, 900, and 1200 bit/s. Forward error correction was added to bring the total bit rate up to 2400 bit/s. The authors compare the performance of the three candidate US low-rate speech coders to that of the standard 2400-bit/s linear predictive coder (LPC) under a number of different test conditions. Under the majority of the test conditions, the 800-bit/s speech coder is performing close to the present standard LPC-10 at 2400 bit/s. The one area where there is a loss of performance in the 800-bit/s speech coder relative to the LPC-10 is in the severe CVC (constant vowel consonant) intelligibility test conditions. All the tests were to be completed and a coder at 800 bit/s was to be selected at the WG/2 meeting in March 1993.<>