Discrete slope delta modulation with recovery means

摘要

A method and apparatus for processing electrical signals by modifying delta modulation to discrete slope delta modulation includes converting its electrical signals into compressed digital information, and representing this digital information as a sequence of slops or deltas added to the past value of the representation. For each sample period, a slope is chosen from slope tables having multiple entries and each choice is represented by a Huffman code. Signal compression occurs in two steps: first the selection of a small number of possible slopes provides compression and also the most probable slopes are represented by the shortest Huffman codes providing additional compression. Depending on the history of the slope chosen, multiple tables can be accessed with different slop entries. Two check point values are provided which code absolute output levels instead of slopes in order to facilitate recovery of the signal in the event of transmission errors. Initial matching of a specific slope value sought in the same table wherein the next preceding value was found. In one embodiment, at least four slope tables each having at least four values is employed. The apparatus has components for performing the method.