Improving the performance of long history scalar and vector LSP quantizers

In order to obtain high quality decoded speech in low bit rate coding systems, it is essential to quantize codec parameters accurately with a minimum number of bits. A new and efficient quantization approach for codec parameters, called long history quantization (LHQ), has previously been proposed and applied to the scalar and vector quantization of line spectrum pair (LSP) coefficients, to achieve “transparency” at an average bit rate of about 22 and 19 bits per frame respectively. The paper presents certain improvements in these quantization schemes which further reduce the average LSP bit rates down to 20 and 17 bits per 20 ms frame