Description of the French NATO candidate

This paper describes the narrow-band speech coder that was proposed by France as a candidate to the new NATO standard STANAG-4591. This dual-rate coder at 1.2 and 2.4 kbps is based on the HSX (Harmonic & Stochastic eXcitation) algorithm.. The 2.4 kbps version was first developed by the University of Sherbrooke (Laflamme et al. 1996), then refined by Thales Communications (formerly Thomson-CSF Communications). An extension at 1.2 kbps was later developed by Thales Communications. This half-rate version uses the same algorithmic core than the 2.4 kbps version, but achieves a lower bit rate by grouping 3 consecutive frames grouped into a single 67.5 ms super-frame (Gournay and Chartier 1998). A noise reduction procedure is considered as a part of the next NATO low bit rate speech coding standard.. This noise reduction system is based on the combination of two different noise reduction techniques. The first one is the Wiener filter under signal presence uncertainty. The second one is Lim´s filter, that takes into account the auto-regressive model of human voice (Guilmin et al. 2000). These new coders provide a low complexity solution with increased intelligibility and quality compatible with a growing number of military, professional and commercial applications.