An audio signal is recorded in a semiconductor memory in a plurality of hierarchical levels, with the lowest level sufficing for reproduction with a certain reduced degree of fidelity. Successively higher hierarchical levels provide successively greater fidelity when reproduced. When the memory...http://www.google.com.tw/patents/US5752221?utm_source=gb-gplus-share專利 US5752221 - Method of efficiently recording an audio signal in semiconductor memory
