Matrix product quantization for very-low-rate speech coding

Efficient block coding methods for LPC information play an essential role in very-low-rate speech coding systems. The subject of this contribution is a new suboptimal matrix quantization scheme for LPC parameters, called matrix product quantization (MPQ), which operates at bit rates between 300 and 700 b/s. MPQ encodes sequences of LPC parameter vectors using a product formulation of two matrices which describe the average parameter vector and the temporal contour. In fixed-rate coding systems for mobile communication, MPQ achieves a very high coding efficiency at a low coding delay. Compared to the multi-frame coding method (MFC) of Kemp et al. (1991), which causes a delay of 8 frames, the MPQ scheme operates more efficiently even at a coding delay of only 3 frames. Applying MPQ to a variable-rate segment vocoder, a bit rate reduction of 50% compared to memoryless VQ is obtained at a frame period of 20 ms