Description of the French NATO candidate

Abstract

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 [1], 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 [2]. 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 [3]. These new coders provide a low complexity solution with increased intelligibility and quality compatible with a growing number of military, professional and commercial applications.

Joint quantisation strategies for low bit-rate sinusoidal coding

“…Once the grouping is performed, the voicing strengths within the metaframe are quantized using joint vector quantization similar to [2], [14], [15].…”

“…After determination of the metaframe type, other parameters can be quantized accordingly. Joint quantization techniques can be used to increase efficiency [2], [3], [14], [15]. All the pitch values within a metaframe are combined in a vector.…”

Research and implementation of an improved 800BPS speech coding algorithm

“…France's HSX (Harmonic Stochastic eXcitation) [2] and Turkey's SB-LPC (Split-Band Linear Predictive Coding) [3].…”