Feedback residue compression for digital speech systems

• US 3,973,081 A
• Filed: 09/12/1975
• Issued: 08/03/1976
• Est. Priority Date: 09/12/1975
• Status: Expired due to Term

• Current Assignee: TRW Inc. (Northrop Grumman Corporation)
• Original Assignee: TRW Inc. (Northrop Grumman Corporation)
• Inventors: Hutchins, Sandra E.
• Primary Examiner(s): Claffy, Kathleen H.
• Assistant Examiner(s): Kemeny, E. Matt
• Application Number:
  US05/612,992
• Time in Patent Office: 326 Days
• Field of Search: 179/1 SA, 179/1 SC, 179/1 VL, 179/15.55 R, 333/14, 325/62, 325/38 R, 325/38 A, 325/38 B
• US Class Current: 704/230
• CPC Class Codes: G10L 19/04 using predictive techniques

Abstract

A digital speech compression system uses a predictive feedback loop. The digital speech signals are compressed within the feedback loop for reducing the transmitter bandwidth. The system comprises a first adder into which the digital signal is fed followed by a quantizer and a compression logic. The predictive loop includes a second adder coupled to the compression logic and followed by a digital predictive filter. The output of the filter is impressed in a negative sense on the first adder and in a positive sense on the second adder. Specifically, the quantizer and compression logic may consist of a two-valued limiter followed by a compressor and a converter in the feedback loop or alternatively the limiter may be followed by a converter while the compressor is disposed outside the feedback loop to provide sample by sample compression.

Claims

1. A digital speech compression system comprising:

a. a digital source of speech;

b. a first digital adder;

c. a quantizer;

d. a compression logic, said source having its output connected to said first adder, and said quantizer and compression logic being connected in cascade to an output of said first adder, the output of said compression logic being the compressed digital speech; and

e. a predictor loop connected between said compression logic and a negative input of said first adder, said predictor loop including;

f. a second digital adder; and

g. a digital predictive filter, said compression logic being coupled to an input of said adder which in turn is connected to said filter and to the negative input of said first adder, the output of said filter being further connected to another input of said second adder, whereby the residue stream of digital data is estimated inside said predictor loop.

2. A digital speech system having a sample-by-sample compression and comprising:

a. a source of digital speech signals;

b. a first digital adder;

c. a two-valued limiter for generating quantized digital signals;

d. means for converting the quantized digital signals into a coded set of digital signals;

e. a second digital adder, said first adder, limiter, means for converting and second adder being connected in cascade;

f. a digital predictive filter having its input connected to the output of said second adder and having its output connected in a negative sense to said first adder and in a positive sense to said second adder; and

g. a compressor coupled to said means for converting for generating digital output signals having fewer levels than those of the quantized digital signals.

3. A digital speech system having sample-by-sample compression and comprising:

a. a source of digital speech signals;

b. a first digital adder;

c. a two-valued limiter for generating quantized digital signals;

d. a digital compressor having digital output signals having fewer levels than the quantized digital signals, said limiter and compressor being connected in cascade to the output of said adder; and

e. a predictor loop, said loop including;

f. a digital converter for converting the digital output signals of said compressor to a coded set of digital levels corresponding to the set of quantized digital signals;

g. a second digital adder; and

h. a predictive digital filter, said converter having its output connected to said adder, the output of said second adder being connected to said filter, said filter having its output connected to said second adder as an input and further having its output connected to said first adder in a negative sense.

4. A digital speech system having sample-by-sample compression and comprising:

a. a source of digital speech signals;

b. a first digital adder;

c. a digital two-valued limiter for generating quantized digital signals;

d. a digital converter for converting the quantized digital signals into a coded set of digital signals, said adder, said limiter and said converter being connected in cascade;

e. a second digital adder having its input connected to the output of said converter;

f. a predictive digital filter having its input connected to said second adder and having its output connected to the negative input of said first adder and to the input of said second adder; and

g. a compressor connected to the output of said converter for converting the coded set of digital signals into digital output signals having fewer levels.

5. A digital speech system having block-by-block compression and comprising:

a. a source of digital speech signals;

b. a blocking control;

c. a first digital adder connected to said blocking control, said digital speech signal being impressed on said blocking control, said blocking control passing consecutive input signals block by block;

d. a decision logic circuit following said first adder and for generating digital output signals having fewer levels than the digital input signals;

e. a sequence generator for generating cyclically a coded set of digital signals;

f. a second digital adder coupled to said sequence generator; and

g. a predictive digital filter having its input connected to said second adder and having its output connected in a negative sense to said first adder and in a positive sense to said second adder, said decision logic circuit being coupled to said filter;

said decision logic circuit including means for generating the mean squared of an earlier signal and for deciding upon the smallest error signal within each block to generate the digital output signal and to store successive digital signals corresponding to the least mean squared value previously found.

6. A digital speech system as defined in claim 5 wherein said decision logic circuit includes means for squaring and summing the error signal obtained from said first adder, a comparator following said summer, a decision circuit following said comparator, a first memory for said filter coupled to said decision circuit and to said filter, a second memory for the current output signal and coupled to said decision circuit and to said sequence generator, a third memory for the best output signal coupled to said filter, and a fourth memory for the sum of the square of the error signal having its output coupled to said comparator and to said first memory and having its input coupled to said decision circuit.