Tree encoding of the LPC residual

In speech coding quantization has traditionally been done on a sample by sample basis. According to rate distortion theory there is much to be gained by applying multidimensional schemes to the quantization at low bit rates. This paper presents the use of a tree-encoder for quantization of the LPC-residual. The perceptual speech quality for the straightforward encoding is however not satisfactory and a frequency weighted error criterion which greatly improves the perceptual speech quality is suggested.