Abstract: A codec uses a number of different signal processing techniques to improve audio compression. These techniques include (1) dynamically varying the size of the processing block to match the duration of the signal over which the audio signal can be considered to be substantially constant, (2) reducing the power gain of the LPC coefficients to reduce leakage of coding noise from one block into the following block, (3) allocating bits to the residual signal in accordance with both objective and subjective criteria, and (4) computing a modified residual signal to take into account the zero input response of the synthesis filters to the reconstruction noise of past blocks.

Abstract: A residual signal quantization technique used in the adaptive predictive coding of speech signals is based in the frequency domain. In predictive coders, a residual signal that results after redundancies are removed from the input signal using linear prediction techniques is quantized. The technique invented involves a transformation of the residual signal to the frequency domain and a quantization of the frequency domain coefficients. Further, the number of bits used to quantize each frequency coefficient is determined by an estimate of the power of the input signal at that frequency. Once the number of bits to be used for quantization is determined, the quantization noise power spectrum is shaped, and can be selectively shaped so as to form a desired reconstruction noise power distribution.