16 kbps APC with hybrid quantization

This paper presents the results of a two year effort to develop an adaptive predictive coder for transmission of high quality speech over 16 Kbps channels with up to a 5% bit error rate. To maximize intelligibility and maintain bandwidth compatability with existing speech compression systems, an 8 KHz A-D sampling rate constraint was imposed. Our algorithm, called APC-HQ for "hybrid quantization," concentrates on improving the residual coding and uses both segmental quantization and center clipping quantization in a perceptually optimum manner. The result is an algorithm running in real time on an AP-120B [4] which yields high quality under the input bandwidth and noisy channel constraints, and whose speech quality exceeds that attainable with either technique alone.