New Nato Stanag Narrow Band Voice Coder at 600 Bits/s

Abstract

This paper describes a new very low bit rate speech coder at 600 bits/s based on the MELPe algorithm (A.V. McCree and T.P. Barnwell III, 1995). This coder associated with the other bit rates at 2400 bits/s and 1200 bits/s constitute the new NATO standard STANAG 4591. The STANAG 4591 noise pre-processor is also part of the 600 bits/s coder. At 600 bits/s, four consecutive frames are grouped into a super-frame and jointly quantized to obtain high coding efficiency. The inter-frame redundancy is exploited with distinct quantization schemes for different unvoiced/voiced frame combinations in the super-frame. The paper gives a brief description of the algorithm, presents the quantization process operating at 600 bits/s, and gives some evaluation results together with CPU and memory requirements for its implementation on DSP. We also propose a FEC (forward error corrector) scheme adapted to the new HF NATO communications standard STANAG 4444 (1999)