Methods of efficiently recording an audio signal in semiconductor memory

摘要

An audio signal is recorded in a semiconductor memory in a plurality of hierarchical levels, with the lowest level being adequate for reproduction with a certain reduced degree of fidelity. Successively higher hierarchical lends provide successively greater fidelity when produced. When the memory has been determined to have reached maximum capacity, recording continues by overwriting the highest hierarchical level of data currently stored in the memory with lower hierarchical levels of new data. A code is recorded in the memory, indicating the number of hierarchical levels recorded therein, for subsequent reproduction. The audio signal can furthermore be recorded in variable-length frames and reproduced at high speed by reading every N-th frame, N being a positive integer, or by reading only frames having at least a certain minimum length.