Double-Talk detector for echo canceller

• US 5,631,900 A
• Filed: 09/29/1995
• Issued: 05/20/1997
• Est. Priority Date: 09/29/1995
• Status: Expired due to Term

• Current Assignee: Cirrus Logic Incorporated
• Original Assignee: Crystal Semiconductor Corporation (Cirrus Logic Incorporated)
• Inventors: Hemkumar, Nariankadu D., McCaslin, Shawn R., Redheendran, Bheeshmar
• Primary Examiner(s): Safourek, Benedict V.
• Application Number:
  US08/536,986
• Time in Patent Office: 599 Days
• Field of Search: 370/32.1, 370/286, 370/287, 370/289, 370/290, 370/291, 379/406, 379/407, 379/410, 379/411
• US Class Current: 370/287
• CPC Class Codes: H04B 3/234 using double talk detection

Abstract

A double-talk detector for an echo canceller includes power estimators (60) and (62) which are utilized to measure the ERLE value in a calculator (64). This ERLE value is stored in a register (70) when it is the largest value generated. This register (70) is updated whenever a new and better ERLE occurs. A fraction of the value in register (70) is utilized as an input to a comparator (88), and then compared to the current ERLE value. If the current ERLE differs from the SERLE in register (70) an inhibit signal is generated for blocking the updates of an adaptive filter (40). The value stored in the register (70) is periodically decremented to reduce the value thereof. This decrement operation is performed in response to detection of an utterance from the far-end.

Claims

1. A double-talk detector for an echo canceller for selectively inhibiting the operation of an adaptive filter with coefficients that are updated and the echo canteller having an Echo Return Loss Enhancement (ERLE) value associated therewith, comprising:

an ERLE processor for calculating the current ERLE of the echo canceller;

a SERLE register for storing an ERLE value as a SERLE value and having a saved ERLE input connected to the output of said ERLE processor and an output;

a comparator for comparing the output of said ERLE processor with a value and, if less, then storing the output of said ERLE processor in said SERLE register; and

a modification device for modifying the SERLE value stored in said register upon the occurrence of a predetermined event.

2. The double-talk detector of claim 1, wherein said predetermined event is a periodic event based upon a time base, such that said modification device is operable to decrement the SERLE value stored in said SERLE register periodically.

3. The double-talk detector of claim 1, wherein said predetermined event comprises an utterance detected by an utterance detector for determining if a transient in the signal power at the far-end has occurred.

4. The double-talk detector of claim 3, wherein said utterance detector comprises:

a background noise estimator for estimating the background far-end noise power at the far-end input;

a background noise register for storing a background noise level;

an offset device for offsetting the values stored in said background noise register by a predetermined offset;

an utterance comparator for comparing the far-end input signal level to said offset background noise level; and

a decrementing device for decrementing the SERLE value stored in said SERLE register when said comparator output is true.

5. The double-talk detector of claim 4, and further comprising a counter for determining how many times said utterance comparator output is true and incrementing said counter each time said output of said utterance counter is true until said count equals or exceeds a predetermined count threshold value and declaring an utterance in response to said count value exceeding said predetermined count threshold value, said declared utterance causing said decrementing device to decrement said SERLE value in said SERLE register.

6. The double-talk detector of claim 4, and further comprising:

a background noise comparator for comparing the value stored in said background noise register with the estimated far-end power from said far-end power estimator; and

a control device for controlling said background noise register for updating the value stored in said background noise register whenever the estimated far-end power is less than the value stored in said background noise register.

7. The double-talk detector of claim 6, and further comprising:

a timing circuit for determining the length of time that said estimated far-end power is greater than the background noise value stored in said background noise register; and

a background noise incrementing device for incrementing the value stored in said background noise register when said estimated far-end power exceeds said background noise value stored in said background noise register for a predetermined amount of time.

8. The double-talk detector of claim 1, and further comprising:

a differential circuit for determining when the calculated value of said current ERLE as calculated by said ERLE processor is less than a predetermined percentage of SERLE value in said SERLE register; and

a blocking device for inhibiting updates of the coefficients by the adaptive filter when said differential circuit generates an output signal.

9. The double-talk detector of claim 1, wherein said comparator is operable to compare the current ERLE value determined by said ERLE processor with the SERLE value stored in said SERLE register scaled down by a predetermined scaling factor and generating a true output signal whenever said current ERLE value is less than or equal to said scaled down SERLE value;

and an decrementing device for decrementing the SERLE value stored in said SERLE register in response to generation of said true output.

10. The double-talk detector of claim 9, and further comprising an utterance detector for determining if a transient has occurred in the far-end signal power, and if so, generating an utterance output, said decrementing device only decrementing the contents of said SERLE register whenever both said ERLE is determined to be less than or equal to said scaled down SERLE value and said utterance has been detected.

11. The double-talk detector of claim 9, wherein updates of the coefficients by said adaptive filter are blocked whenever said current ERLE is determined to be less than or equal to said scaled down SERLE value stored in said SERLE register.

12. The double-talk detector of claim 1, and further comprising:

a power estimator for measuring the near-end power for a predetermined amount of time to provide an average thereof;

a register for storing the current near-end estimated power as current near-end noise power;

an offset device for offsetting said current near-end noise power by a predetermined percentage increase;

a near-end comparator for comparing the output of said offset device with said current near-end noise power stored in said register and providing a true output; and

an inhibiting device for inhibiting the adaptive filter from updating the coefficients whenever the output of said near-end comparator is true.

13. The double-talk detector of claim 1, wherein said predetermined event comprises a radical path change, wherein the adaptive filter is operable under a radical path change to modify the coefficients therein to converge the operation of the adaptive filter, comprising:

a coefficient monitor for determining whether the coefficients are modified in a positive or a negative manner;

an accumulator for accumulating a change value;

a modification device for determining if said change in the coefficients is positive and adding a value of "1" to the value stored in said accumulator, and determining if the change of coefficients is negative and subtracting a value of "1" from the value stored in said accumulator;

a radical path change comparator for comparing the absolute value of the contents of said accumulator with a predetermined threshold and, if it exceeds the threshold, outputting a true value; and

an decrementing device for decrementing the value stored in said SERLE register whenever said true output is measured, the contents of said accumulator only read after a predetermined amount of time and, if the contents of the accumulator have not exceeded said predetermined threshold, clearing and resetting the value in said accumulator.

14. A method for operating a double-talk detector for an echo canceller to selectively inhibit the operation of an adaptive filter with coefficients that are updated, the echo canceller having an Echo Return Loss Enhancement (ERLE) value associated therewith, comprising the steps of:

calculating the current ERLE of the echo canceller with an ERLE processor;

storing an ERLE value as a SERLE value in a SERLE register, the ERLE value stored being the best ERLE value calculated by the ERLE processor;

comparing the calculated ERLE value calculated by the ERLE processor with a value and, if less, providing a true comparison output and then storing the calculated ERLE value that was the subject of the step of comparing in the SERLE register; and

modifying the SERLE value stored in the SERLE register upon the occurrence of a predetermined event.

15. The method of claim 14, wherein the predetermined event is a periodic event based upon a time base, such that the step of modifying is operable to decrement the SERLE value stored in the SERLE register periodically.

16. The method of claim 14, wherein the predetermined event comprises an utterance which is detected by an utterance detector that determines if a transient in the signal power at the far-end has occurred.

17. The method of claim 16, wherein the step of determining if a transient in the signal power at the far-end has occurred comprises the steps of:

estimating the background far-end noise power at the far-end input;

storing a background noise level in a background noise register as determined by the step of estimating;

offsetting the value stored in the background noise register by a predetermined offset to provide an offset background noise level;

comparing the far-end input signal level to the offset background noise level and providing a true comparison if the far-end input signal level exceeds the offset background noise level; and

decrementing the SERLE value stored in the SERLE register when the step of comparing is true.

18. The method of claim 17, and further comprising the step of determining how many times the step of comparing has been determined to be true and maintaining a record of the number of times and the step of comparing has been determined to be true and, when the number of times that the step of comparing has compared true equals or exceeds a predetermined count threshold value, declaring an utterance, the step of declaring causing the step of decrementing to decrement the SERLE value in the SERLE register.

19. The method of claim 17, and further comprising the steps of:

comparing the value stored in the background noise register with the estimated far-end power from the far-end power estimator; and

controlling the background noise register to update the value stored in the background noise register whenever the estimated far-end power is less than the value stored in the background noise register.

20. The method of claim 19, and further comprising the steps of:

determining the length of time that the estimated far-end power is greater than the background noise value stored in the background noise register; and

incrementing the value stored in the background noise register where the estimated far-end power exceeds the background noise value stored in the background noise register for a pre-determined amount of time.

21. The method of claim 14, and further comprising the steps of:

determining when the calculated value of the current ERLE calculated by the ERLE processor is less than a predetermined percentage of the SERLE value stored in the SERLE register; and

inhibiting updates of the coefficients by the adaptive filter when the calculated value of the ERLE is determined to be less than a predetermined percentage of the SERLE value.

22. The method of claim 14, wherein:

the step of comparing is operable to compare the current ERLE value calculated by the ERLE processor with the SERLE value stored in the SERLE register scaled down by a predetermined scaling factor and then generating a true output signal from the step of comparing whatever the current ERLE value is less than or equal to the scaled down SERLE value; and

decrementing the SERLE value stored in the SERLE register in response to generation of the true output by the step of comparing.

23. The method of claim 22, and further comprising the step of detecting an utterance to determine if a transient has occurred in the far-end signal power, and if so, generating an utterance output, the step of only decrementing the contents of the SERLE register whenever both the ERLE is determined to be less than or equal to the scaled down SERLE value and an utterance has been detected.

24. The method of claim 22, wherein updates of the coefficients by the adaptive filter are blocked whenever the current ERLE is determined to be less than or equal to the scaled down SERLE value stored in the SERLE register.

25. The method of claim 14, and further comprising the steps of:

measuring the near-end power for a predetermined amount of time to provide an average thereof as current near-end estimated power;

storing the current near-end estimated power as current near-end noise power in a register;

offsetting the current near-end noise power by a predetermined percentage increase to provide an offset near-end noise power value;

comparing the offset near-end noise power value with the current near-end noise power stored in the register and providing a true output when the comparison is true; and

inhibiting the adaptive filter from updating the coefficients whenever the comparison step is true.

26. The method of claim 14, wherein the predetermined event comprises a radical path change, wherein the adaptive filter is operable under a radical path change to modify the coefficients therein to converge the operation of the adaptive filter, comprising the steps of:

determining whether the coefficients are modified in a positive or negative manner;

accumulating a change value in an accumulator;

determining in a modification step if the change of the coefficients is positive and adding a value of "1" to the value stored in the accumulator, and determining if the change of coefficients is negative and subtracting a value of "1" from the value stored in the accumulator;

comparing in a radical path change comparator the absolute value of the contents of the accumulator with a predetermined threshold, and if it exceeds the threshold, outputting a true value; and

decrementing the value stored in the SERLE register whenever the true output from the radical path change comparator is measured, the contents of the accumulator only read after a predetermined amount of time and, if the contents of the accumulator have not exceeded the predetermined threshold, clearing and resetting the value in the accumulator.