Multi-speaker conferencing over narrowband channels

• US 5,317,567 A
• Filed: 09/12/1991
• Issued: 05/31/1994
• Est. Priority Date: 09/12/1991
• Status: Expired due to Fees

• Current Assignee: United States Of America As Represented By The Secretary Of The Air Force
• Original Assignee: United States Of America As Represented By The Secretary Of The Air Force
• Inventors: Champion, Terrence G.
• Primary Examiner(s): Olms, Douglas W.
• Assistant Examiner(s): BLUM, RUSSELL
• Application Number:
  US07/760,021
• Time in Patent Office: 992 Days
• Field of Search: 370/62, 370/80, 370/118, 370/79, 379/158, 379/202, 379/206, 381/29, 381/30, 381/31
• US Class Current: 370/267
• CPC Class Codes: H04M 3/561 by multiplexing
• CPC Class Codes: H04M 3/568 audio processing specific to telephonic conferencing, e.g. spatial distribution, mixing of participants echo suppression in two-way loud-speaking telephone systems H04M9/02; sound field processing per se H04S7/30

Abstract

A system for digital conferencing over narrowband channels which allows use by multiple simultaneous speakers and which allow for interfacing between vocoders which operate at different bit rates. The system takes advantage of the properties of multi-rate parametric vocoders (which includes the Sinusoidal Transform Coder and the Multi-Band Excitation Vocoder, as well as embedded coders), defined as parametric vocoders for whom the basic model and parameter set remain unchanged over a wide range of bit-rates. The system performs signal summation. To maintain quality for a single speaker while allowing multiple speakers, the system adaptively allocates channel bandwidth based on the number of speakers to be represented. This system also provides digital-to-digital conversion between narrow-band digitizers (vocoders) operating at different bit-rates. The system takes advantage of the characteristics of a particular class of coders, sine-wave based coders, which perform parameter estimation by sine-wave summation. Digital-to-digital conversion is performed by estimating the parameter set associated with the lower bit-rate digitizer from the parameter set associated with the higher bit-rate.

Claims

1. A process of facilitating multispeaker conferencing for users of a digitally encoded voice system, wherein each of said users is capable of outputting encoded digital voice signals in a bit stream at a system data rate, wherein said process comprises the steps of:

counting a number of active conferees to produce thereby a count number N, said active conferences being users of said digitally encoded voice system which are speaking when said counting step is performed;

compressing each of the encoded digital voice signals produced by said active conferees down to a plurality of compressed digital signals which each have a compressed data rate, wherein said counting and compressing steps are performed using a microprocessor which is electrically connected to each of said users of said digitally encoded voice system using telephone lines and a plurality of modem units, wherein said microprocessor is programmed to perform as a conferencing bridge and to perform said counting and compressing steps, wherein said compressing step comprises digitally compressing each of said encoded digital voice signals into said compressed digital signals such that their compressed data rate has a bit rate given by SDR/N, where SDR is the system data rate, and N is the number of active conferees;

a digital signal summation step, in which the compressed digital signals are combined to output thereby a combined compressed digital signal which is transmitted to said users at the system data rate; and

decoding said combined compressed digital signal to output thereby an artificial voice signal to said users of the digitally encoded voice system, wherein said artificial voice signal represents voices of all the active conferees which are speaking.

2. A process, as defined in claim 1, wherein said counting and compressing steps are performed using a microprocessor which is electrically connected to each of said users of said digitally encoded voice system using telephone lines and a plurality of modem units, wherein said microprocessor is programmed to perform as a conferencing bridge and to perform said counting and compressing steps.

3. A process, as defined in claim 2, wherein said counting step is performed by counting users of a vocoder system which has the system data rate of about 4.8 kilobits per second, and wherein said compressing step comprises:

compressing each of the encoded digital voice signals into approximately 2.4 kilobit per second data stream when there are two active conferees;

compressing each of the encoded digital voice signals into approximately 1.6 kilobit per second data stream when there are three active conferees;

compressing each of the encoded digital voice signals into approximately 1.2 kilobit per second data stream when there are four active conferees;

compressing each of the encoded digital voice signals into approximately 0.96 kilobit per second data stream when there are five active conferees; and

compressing each of the encoded digital voice signals into approximately 0.8 kilobit per second data stream when there are six active conferees.

4. A process, as defined in claim 1, wherein said counting step is performed by counting users of a vocoder system which has the system data rate of about 4.8 kilobits per second, and wherein said compressing step comprises:

compressing each of the encoded digital voice signals into approximately 1.2 kilobit per second data stream when there are four active conferees;

compressing each of the encoded digital voice signals into approximately 0.96 kilobits per second data stream when there are five active conferees; and

compressing each of the encoded digital voice signals into approximately 0.8 kilobit per second data stream when there are six active conferees.

5. A process of facilitating multispeaker conferencing for users of a digitally encoded voice system, wherein each of said users is capable of outputting encoded digital voice signals in a bit stream at a system data rate, wherein said process comprises the steps of:

counting a number of active conferees to produce thereby a count number N, said active conferees being users of said digitally encoded voice system which are speaking when said counting step is performed;

compressing each of the encoded digital voice signals produced by said active conferees down to a plurality of compressed digital signals which each have a compressed data rate, wherein said digitally encoded voice system used in said process comprises a set of vocoders which operate over a narrowband with said system data rate ranging substantially between 2.4 and 32.0 kb/s, and wherein said counting and compressing steps are performed using a microprocessor which is electrically connected to each of said users of said digitally encoded voice system using telephone lines and a plurality of modem units, wherein said microprocessor is programmed to perform as a conferencing bridge and to perform said counting compressing steps, wherein

said compressing step comprises digitally compressing each of said encoded digital voice signals into said compressed digital signals such that their compressed data rate has a bit rate given by SDR/N, where SDR is the system data rate, and N is the number of active conferees;

a digital signal summation step, in which the compressed digital signals rae combined to output thereby a combined compressed digital signal which is transmitted to said users at the system data rate; and

decoding said combined compressed digital signal to output thereby an artificial voice signal to said users of the digitally encoded voice system, wherein said artificial voice signal represents voices of all the active conferees which are speaking.

6. A process, as defined in claim 5, wherein said counting step is performed by counting users of a vocoder system which has the system data rate of about 4.8 kilobits per second, and wherein said compressing step comprises:

compressing each of the encoded digital voice signals into approximately 2.4 kilobit per second data stream when there are two active conferees;

compressing each of the encoded digital voice signals into approximately 1.2 kilobit per second data stream when there are three active conferees;

compressing each of the encoded digital voice signals into approximately 1.2 kilobit per second data stream when there are four active conferees;

compressing each of the encoded digital voice signals into approximately 0.96 kilobit per second data stream when there are five active conferees; and

compressing each of the encoded digital voice signals into approximately 0.8 kilobit per second data stream when there are six active conferees.

7. A system for facilitating multispeaker conferencing for users of a digitally encoded voice system, wherein each of said users is capable of outputting encoded digital voice signal in a bit stream at a system data rate, wherein said system comprises:

a means for counting a number of active conferees to produce thereby a count number N, said active conferees being users of said digitally encoded voice system which are actually speaking;

a means for compressing each of the encoded digital voice signals produced by said active conferees down to a plurality of compressed digital signals which each have a compressed data rate;

wherein said counting and compressing means comprises a microprocessor which is electrically connected to each of said users of said digitally encoded voice system using telephone lines and a plurality of modem units, wherein said microprocessor is programmed to perform as a conferencing bridge and to perform said counting and compressing, wherein said compressing means digitally compresses each of said encoded digital voice signals into said compressed digital signals such that their compressed data rate has a bit rate given by SDR/N, where SDR is the system data rate, and N is the number of active conferees;

a means for a digital signal summation in which the compressed digital signals are combined to output thereby a combined compressed digital signal which is sent back to said users at the system data rate; and

a means for decoding the combined compressed digital signal to output thereby an artificial voice signal to said users of the digitally encoded voice system, wherein said artificial voice signal represents voices of all the active conferees which are speaking.

8. A system for facilitating multispeaker conferencing for users of a digitally encoded voice system, wherein each of said users is capable of outputting encoded digital voice signals in a bit stream at a system data rate, wherein said system comprises:

a means for monitoring the users as they output said digital voice signals serially when one of said users is speaking, and monitoring said users as they output said digital voice signals simultaneously, when multiple users and speaking; and

a means for producing a conferencing signal usable by all of said users, and conferencing signal representing one digital voice signal when one of said users is speaking, said conferencing signal representing multiple digital voice signals when multiple users are speaking simultaneously, wherein said producing means comprises a microprocessor which is electrically connected to each of said users of said digitally encoded voice system, using telephone lines and a plurality of modem units, wherein said microprocessor is programmed to perform as a conferencing bridge and to perform said producing of said conference signal.

9. A process for facilitating multispeaker conferencing for users of a digitally encoded voice system, wherein each of said users is capable of outputting encoded digital voice signals in a bit stream at a system data rate, wherein said process comprises the steps of:

counting a number of active conferees to produce thereby a count number N, said active conferees being users of said digitally encoded voice system which are speaking when said counting step is performed;

compressing each of the encoded digital voice signals produced by said active conferees down to a plurality of compressed digital signals which each have a compressed data rate, wherein said counting and compressing steps are performed using a microprocessor which is electrically connected to each of said users of said digitally encoded voice system, wherein said microprocessor is programmed to perform as a conferencing bridge and to perform said counting and compressing steps, wherein said compressing step comprises digitally compressing each of said encoded digital voice signals into said compressed digital signals such that their compressed data rate has a bit rate give by SDR/N, where SDR is the system data rate, and N is the number of active conferees;

a digital signal summation step, in which the compressed digital signals are combined to output thereby a combined compressed digital signal which is transmitted to said users at the system data rate; and

decoding said combined compressed digital signal to output thereby an artificial voice signal to said users of the digitally encoded voice system, wherein said artificial voice signal represents voices of all the active conferees which are speaking.