US 4,301,333 AGranted

Speech compression

AssigneeMcDonnell Douglas Corporation

InventorRichard J. Gillette

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Abstract

A device for providing real time speech compression and expansion and method therefor which enables speech data, sampled at a predetermined rate, and consisting of a preselected number of bits per sample, to be compressed in real time by a factor of approximately 2:1, and upon decompression, to be essentially indistinguishable from the original digitized speech. In particular, the apparatus employs a method which involves the digitizing of the input data, determining the maximum amplitude of the data over a short given period, compressing the data by dividing the largest amplitude constant from the data over the given period to obtain a data sample, and storing the reduced data sample and corresponding amplitude constant or gain factor in a suitable storage medium. In the preferred embodiment, the storage medium is a rotating memory or a recirculating shift register. Amplitude or gain factor data is stored in a memory that need be only one sixty-fourth the size of the main memory, since, in the embodiment illustrated, a single gain factor data representation is used with sixty-four sets of sample data. On recall, sets of the sample data are multiplied by their corresponding gain factor to reproduce the data for use.

Claims4

Dependent claims

A system for real time audio data compression and expansion, comprising:

means for digitizing input audio data;
means for sampling the digitized audio data;
means for determining the maximum amplitude of the audio data over some predetermined time period;
a first programmable read-only memory means having an input side operatively connected to said maximum amplitude determining means for encoding the maximum amplitude to obtain a gain factor at an output side;
a second programmable read-only memory means having a first input operatively connected to the output side of said first programmable read-only memory means and a second input for receiving the digitized audio data corresponding to the predetermined time period for which the gain factor is determined, said second programmable read-only memory means utilizing the gain factor at its first input in conjunction with the digitized audio data at its second input to obtain a scaled value of the audio data so as to provide a reconstituted compressed sample data at its output side thereby obtaining an approximate two-to-one reduction in the bit size of the compressed sample data as compared to the bit size of the digitized audio data;
means for transmitting the reconstituted compressed sample data from the output side of the second programmable read-only memory means and the gain factor from the output side of the first programmable read-only memory means to a storage medium;
means for storing all of the reconstituted compressed data from the output side of said second programmable read-only memory means but only one occurrence of the corresponding gain factor applied at the first input of said second programmable read-only memory means for the compressed data for said predetermined time period on the storage medium.

4 more elements

Dependencies are inferred from the claim text.