Circuit for nulling the talker's speech in a conference call and method thereof

• US 5,054,021 A
• Filed: 03/06/1990
• Issued: 10/01/1991
• Est. Priority Date: 03/06/1990
• Status: Expired due to Term

• Current Assignee: Polycom Incorporated (Plantronics, Inc.)
• Original Assignee: ConferTech International, Inc. (Frontier Communications Parent, Inc.)
• Inventors: Epps, David C.
• Primary Examiner(s): Olms, Douglas W.
• Assistant Examiner(s): Hsu, Alpus H.
• Application Number:
  US07/490,092
• Time in Patent Office: 574 Days
• Field of Search: 370/62, 370/68, 370/61, 370/68.1, 370/66, 370/77, 370/79, 370/110.1, 370/58.1, 370/58.2, 370/58.3, 379/202, 379/206, 379/207
• US Class Current: 370/268
• 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 method and circuit for nulling each talker'"'"'s speech in a conference call having a plurality of parties who are selectively talkers and listeners. The parties are interconnected on PCM telephone carrier lines (T1 or CEPT) which are connected to a digitized conference bridge. The circuit of the present invention has a summation circuit for adding together all of the speech data on the carrier lines occurring in the conference call during a particular time slot. A circuit is used for delaying the speech of each individual talker. Finally, the circuit of the present invention utilizes a subtraction circuit for subtracting the delayed speech of each individual talker from the summation of all speech for delivery back to the ears of the individual talker. The delaying circuit precisely delays the speech of each individual talker so as to corespond in timing with the output of the summation circuit. The present invention fully deletes the individual talker speech so as to totally eliminate echo and the timing is such so as to eliminate distortion.

Claims

1. A circuit (10) for nulling each talker'"'"'s speech in a conference call, said conference call having a plurality of parties (n) who are talkers and listeners on PCM telephone carrier lines (k) connected to a digitized conference bridge, said circuit comprising:

means (40) connected to said PCM telephone carrier lines for digitally outputting the sum of all speech (20) on said PCM telephone carrier lines, all of said listeners who are not talking in said conference call receiving said sum of all speech,

means (50) connected to said PCM telephone carrier lines for delaying the speech of each individual talker,

means (60) connected to said outputting means and to said delaying means for subtracting the digital value of said delayed speech of each individual talker from said sum of all speech, said subtracting means delivering (30) said sum of all speech less said individual talker'"'"'s speech as said individual talker listens, said delaying means delaying said speech of each said individual talker to match the timing of each said talker'"'"'s speech in said sum of all speech.

2. The nulling circuit of claim 1 wherein said digitally outputting means (40) comprises:

means (400) receptive of PCM speech data on said PCM telephone carrier lines for converting said PCM speech data from PCM format to linear format,

means (410) connected to said converting means for adding said speech data in linear format found in each PCM time slot together,

means (420) connected to said adding means for converting said added linear speech data in each said PCM time slot from linear format to said sum of all speech in PCM format.

3. The nulling circuit of claim 2 wherein said PCM format is in μ

-law companded format for T1 transmission.

4. The nulling circuit of claim 2 wherein said PCM format is in A-law companded format for CEPT transmission.

5. The nulling circuit of claim 2 wherein said PCM to linear converting means is a look-up table.

6. The nulling circuit of claim 2 wherein said adding means is a sixteen bit adder.

7. The nulling circuit of claim 2 wherein said linear to PCM converting means is a look-up table.

8. The nulling circuit of claim 1 wherein said subtracting means (60) comprises:

means (900) receptive of said delayed speech of each said individual talker from said delaying means and of said sum of all speech from said digitally outputting means for converting both said delayed speech and said sum of all speech from PCM format to linear format,

means (910) connected to the aforesaid converting means for subtracting said delayed speech in linear format from said sum of all speech signal in linear format to output a resultant linear subtracted speech data so that said individual talker'"'"'s speech is nulled out,

means (920) receptive of said subtracted speech data from said subtracting means for converting said subtracted speech data from linear format to PCM format.

9. The nulling circuit of claim 8 wherein said PCM format is in μ

-law companded format for T1 transmission.

10. The nulling circuit of claim 8 wherein said PCM format is in A-law companded format for CEPT transmission.

11. The nulling circuit of claim 8 wherein said PCM to linear converting means is a look-up table.

12. A circuit (10) for nulling each talker'"'"'s speech in a conference call, said conference call having a plurality parties (n) who are talkers and listeners on PCM telephone carrier lines (k) connected to a digitized conference bridge, said circuit comprising:

means (400) receptive of PCM speech data from said talkers on said PCM telephone carrier lines for converting said PCM signals from PCM format to linear format,

means (410) connected to said converting means for adding the linear speech data from said talkers found in each PCM time slot together,

means (420) connected to said adding means for converting said added linear speech data from said talkers in each said PCM time slot from linear format to in PCM format,

means (50) connected to said PCM telephone carrier lines for delaying said speech data from each individual talker,

means (900) receptive of said delayed speech data from each said individual talker from said delaying means and of said added PCM speech data for converting said delayed speech data and said added PCM speech data from PCM format to linear format,

means (910) receptive of the aforesaid converted linear speech data for subtracting said delayed speech data in linear format from said added speech data in linear format to output a resultant linear speech data with said individual talker'"'"'s speech nulled out,

means (920) receptive of said resultant linear speech data from said subtracting means for converting said resultant linear speech data from linear format to PCM format.

13. The nulling circuit of claim 12 wherein said PCM format is in μ

-law companded format for T1 transmission.

14. The nulling circuit of claim 12 wherein said PCM format is in A-law companded format for CEPT transmission.

15. A method for nulling each talker'"'"'s speech in a conference call, said conference call having a plurality of parties(n) who are talkers and listeners in a companded PCM speech format on PCM telephone carrier lines (k) connected to a digitized conference bridge, said method comprising the steps of:

linearly summing all PCM companded speech data from said parties on said PCM telephone carrier lines,

delaying the PCM companded speech data of each individual talker by the amount of time necessary to complete the aforesaid step,

linearly subtracting the delayed PCM companded speech data from each individual talker form the sum of all PCM companded speech,

delivering the sum of all PCM companded speech on said PCM telephone carrier lines to all listeners who are not talking, and

delivering the sum of all PCM companded speech having the delayed PCM companded speech from each individual talker subtracted therefrom to each individual listener who is talking.

16. A method for nulling each talker'"'"'s speech in a conference call, said conference call having a plurality of parties (n) who are talkers and listeners in a companded PCM format on PCM telephone carrier lines (k) connected to a digitized conference bridge, said method comprising the steps of:

summing all PCM companded speech data from said parties on said PCM telephone carrier lines, said step of summing further comprising the steps of;

(a) converting said PCM companded speech data on said PCM telephone carrier lines from PCM format to linear format,

(b) adding the speech data in linear format for each party together,

(c) converting said linearly added speech data from linear format to PCM format,

delaying the PCM companded speech data of each individual talker by the amount of time necessary to complete the aforesaid steps,

subtracting the delayed PCM companded speech data from each individual talker from the sum of all PCM companded speech, said step of subtracting further comprising;

(a) converting said delayed PCM companded speech data and said sum of all PCM companded speech from PCM format to linear format,

(b) subtracting the delayed speech data in linear format from the sum of all PCM companded speech in linear format,

(c) converting the speech data representing difference from said subtraction from linear format to PCM format,

delivering the sum of all PCM companded speech on said PCM telephone carrier lines to all listeners who are not talking,

delivering the sum of all PCM companded speech having the delayed PCM companded speech from each individual talker subtracted therefrom to each individual listener who is talking.