Compression and expansion technique for digital audio data

Abstract

A compression and expansion apparatus and method for compressing and expanding digital audio signals using adaptive differential pulse-coding-modulation for high fidelity music is described. The apparatus comprises a predictor, a first and second adder, a first and second adjuster, a quantizer, an inverse quantizer and a step-size adaptor. An input digital signal and predicted signal are added by the first adder, producing the difference between the two signals. The output of the first adder is coupled to the first adjuster which acts as a multiplier to alter the gain and normalize the signal. The signal is then quantized by the quantizer. The output of the quantizer is sent to both the inverse quantizer and the adaptor. The adaptor acts like an automatic-gain-control to control the gain provided by the first adjuster. After inverse quantization by the inverse quantizer, the signal is sent to the second adjuster to remove the effects of the first adjuster process, i.e. denormalize and remove gain. Then the signal is sent to the second adder to add back in the predicted signal removed by the first adder. Next the signal is outputted and sent to the predictor. The predictor uses the output signal to prepare another predicted signal for a subsequently inputted digital signal. Wherein, an inputted digital audio signal and a corresponding outputted digital audio signal are substantially similar.