NARROW BAND DIGITAL SPEECH COMMUNICATION SYSTEM

• US 3,750,024 A
• Filed: 06/16/1971
• Issued: 07/31/1973
• Est. Priority Date: 06/16/1971
• Status: Expired due to Term

• Current Assignee: ITT Corporation (ITT, Inc.)
• Original Assignee: James G. Dunn, John R. Cowan
• Inventors: Dunn, James G., Cowan, John R.
• Primary Examiner(s): Safourek, Benedict V.
• Application Number:
  US05/153,591
• Time in Patent Office: 776 Days
• Field of Search: 179/15BW,1SA,15.55R,15.55T 178/DIG.3 325/38B
• US Class Current: 704/212
• CPC Class Codes: H04B 1/66 for reducing bandwidth of signals; for improving efficiency of transmission H04B1/68 takes precedence
• CPC Class Codes: H04B 14/064 with adaptive feedback

Abstract

Speech to be transmitted is sampled at a given rate with each of the samples being converted to a binary representation of its amplitude. A digital arithmetic unit under control of predetermined program determines from the binary representations of the two immediately preceeding samples the redundant information of the speech, a weighting parameter of the redundant information and removes this redundant information from the speech to produce a residual non-redundant signal. The weighting parameter is transmitted according to a predetermined binary code having a given number of binary bits and the residual signal is transmitted by delta modulation. The binary code representation of the weighting parameter and the delta modulation representing the residual signal are time multiplexed for transmission to a receiver. At least one distinctive combination of bits of a code group of the weighting parameter is employed to indicate an outof-synchronization condition. The clock recovery, framing and timing signal at the receiver are derived from the code groups representing the weighting parameter. A digital arithmetic units in the receiver responds to the weighting parameter code groups and the delta modulation to reconstruct the binary representations of the speech samples. The binary representations of the speech samples are converted to a analog signal and passed through a low pass filter to reconstruct the speech for utilization. The size of the delta modulation step is adjusted in the receiver in accordance with the number of delta modulation bits having a given polarity in sequence.

Claims

1. A speech communication system comprising:

a source of speech;

first means coupled to said source responsive to said speech to determine the redundant information of said speech, to determine at least one weighting parameter of said redundant information and to remove said redundant information from said speech to produce a residual signal;

second means coupled to said first means to transmit said residual signal and said parameter of said redundant information; and

third means coupled to said second means responsive to said residual signal and said parameter of said redundant information to reconstruct said speech for utilization.

2. A system according to claim 1, wherein said second means transmits said residual signal in the form of delta modulation and said parameter of said redundant information in the form of binary code groups.

3. A system according to claim 1, wherein said first means provides periodically said parameter of said redundant information in the form of n bit binary code groups, where n is an integer greater than two, and said second means includes means to translate said n bit binary code groups into (n-1) bit binary code groups for transmission.

4. A system according to claim 3, wherein at least one distinctive combination of bits of said (n-1) bit binary code groups is employed for synchronization.

5. A system according to claim 4, wherein the presence of said distinctive combination of bits indicates an out-of-synchronization condition.

6. A system according to claim 1, wherein said first means includes fourth means coupled to said source to sample said speech at a given rate and convert said samples to binary representation thereof, fifth means coupled to said fourth means to store said binary representation of a predetermined number of immediately preceeding ones of said samples, and sixth means coupled to said fifth means and said fourth means responsive to said binary representation of the present one of said samples and said immediately preceeding ones of said samples to determine said redundant information, to determine said parameter of said redundant information and to produce said residual signal.

7. A system according to claim 6, wherein said predetermined number equals two.

8. A system according to claim 6, wherein said sixth means is a binary arithmetic arrangement which provides said parameter of said redundant information in the form of n bit binary code groups, where n is an integer greater than two, and said residual signal in the form of binary code groups.

9. A system according to claim 8, wherein said second means includes seventh means coupled to said sixth means to convert said binary residual signal into a delta modulation signal for transmission, and eighth means coupled to said sixth means to convert said n bit binary code groups into a (n-1) bit binary code groups for transmission, at least one distinctive combination of bits of said (n-1) bit binary code group providing an indication of lack of synchronization.

10. A system according to claim 9, wherein said third means includes ninth means coupled to said seventh and eighth means to receive said delta modulation signal and to receive said (n-1) bit binary code groups, 10th means coupled to said ninth means to translate said (n-1) bit binary code groups into said n bit binary code groups, 11th means coupled to said ninth means to recover quantized steps of proper polarity represented by said delta modulation signal, 12th means coupled to said tenth and eleventh means to reconstruct said binary representations of said samples, and 13th means coupled to said twelfth means to convert said binary representation into said speech for utilization.

11. A system according to claim 10, wherein said 11th means responds to the sequence of similar bits in said delta modulation signal to control the amplitude of said quantized steps.

12. A system according to claim 11, further including 14th means coupled to said seventh and eighth means to multiplex on a time basis said delta modulation signal and said (n-1) bit binary code groups prior to transmission, and 15th means coupled between said 14th means and said ninth means to demultiplex on a time basis said delta modulation signal and said (n-1) bit binary code groups, said 15th means including means responding to to said (n-1) bit binary code groups to maintain said system synchronized where response to said one distinctive combination of bits of said (n-1) bit binary code groups indicates an out-of-synchronization condition.

13. A speech transmitter comprising:

a source of speech;

first means coupled to said source responsive to said speech to determine the redundant information of said speeCh, to determine at least one weighting parameter of said redundant information and to remove said redundant information from said speech to produce a residual signal; and

second means coupled to said first means to transmit said residual signal and said parameter of said redundant information.

14. A transmitter according to claim 13, wherein said second means transmits said residual signal in the form of delta modulation and said parameter of said redundant information in the form of binary code groups.

15. A transmitter according to claim 13, wherein said first means provides periodically said parameter of said redundant information in the form of n bit binary code groups, where n is an interger greater than two, and said second means includes means to translate said n bit binary code groups into (n-1) bit binary code groups for transmission.

16. A transmitter according to claim 15, wherein at least one distinctive combination of bits of said (n-1) bit binary code groups is employed for synchronization.

17. A transmitter according to claim 16, wherein the presence of said distinctive combination of bits indicates an out-of-synchronization condition.

18. A receiver to provide speecj output comprising:

a source of delta modulation signals representing a non-redundant portion of said speech and binary code groups representing at least one weighting parameter for a redundant portion of said speech;

an arithmetic unit coupled to said source responsive to said delta modulation signals and the present one and a given number of immediately preceeding ones of said binary code groups to reconstruct a binary code representation of samples of said speech; and

a digital to analog converter arrangement coupled to said arithmetic unit to provide said speech output.

19. A receiver accoreing to claim 18, wherein said given number equals two.