Variable gain echo suppressor

• US 5,668,794 A
• Filed: 11/03/1995
• Issued: 09/16/1997
• 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: McCaslin, Shawn Robert, Hemkumar, Nariankadu Datatreya
• Primary Examiner(s): Safourek, Benedict V.
• Application Number:
  US08/552,558
• Time in Patent Office: 683 Days
• Field of Search: 370/286, 370/288, 370/289, 379/406, 379/409, 379/410, 379/411
• US Class Current: 370/288
• CPC Class Codes: H04B 3/234 using double talk detection

Abstract

A variable gain echo suppressor is provided that utilizes two variable attenuators (410) and (412) that are disposed in the receive and transmit paths, respectively, of a communication system. An echo suppressor (414) receives the input from the far end and transmits the output from the near end and controls the two attenuators to set a variable gain therein. The echo suppressor utilizes a normalized power level which is normalized with respect to the background noise at the respective end and then takes the ratio of this normalized power and the normalized power at the opposite end to define an associated power ratio. This power ratio value is utilized to determine the attenuation for the associated end. When the power ratio is high, this indicates that a stronger signal is being received from that end and a small amount of attenuation is associated in the transmit path from that end. When they aye equal, this will result in both systems having approximately the same attenuation, a mid-level attenuation. This is provided through a look up table (450) for the far end and a look up table (452) for the near end. Additionally, the signal power is derived from a peak detection IIR filter (420) and (428) which has the characteristics thereof changed as a function of the power ratio. This is achieved by changing the value of the pole in the IIR filter.

Claims

1. A variable gain echo suppressor for use with a full-duplex communication system for connecting between a far end and a near end, comprising:

a first variable attenuator disposed between the far end and the near end;

a near-end power detector for receiving the near end transmit signal and determining the power level thereof;

a near-end normalizer for normalizing the power level at the output of said near-end power detector to provide a near-end normalized power signal;

a far-end power detector for receiving the far-end transmit signal and determining the power associated therewith;

a far-end normalizer for normalizing the power level at the output of said far-end power detector to provide a far-end normalized power signal; and

a controller for setting the attenuation of said first variable attenuator as a function of said near-end and far-end normalized power levels, to allow for full-duplex communication.

2. The variable gain echo suppressor of claim 1, wherein each of said near-end and far-end power detectors comprises a peak power estimator for averaging energy estimates generated over predetermined sample times, the average thereof comprising the detected power level.

3. The variable gain echo suppressor of claim 2, wherein said near-end and far-end power detectors each comprise an Infinite Impulse Response (IIR) low pass filter.

4. The variable gain echo suppressor of claim 3, wherein said IIR filter comprises a single-pole filter, and further comprising an IIR control device for changing the value of said single pole as a function of said associated near-end or far-end normalized power level.

5. The variable gain echo suppressor of claim 4, and further comprising a second variable attenuator disposed between the near-end and the far-end, said controller for setting the attenuation of each of said first and second variable attenuators as a function of said near-end and far-end normalized power levels.

6. The variable gain echo suppressor of claim 4, wherein there are first and second pole values, said first pole value associated with a fast response and said second pole value associated with a slower response, said IIR control selecting said first pole value when said first variable attenuator is to be set at a low attenuation value, and selecting said second pole value when said attenuator value for said first variable attenuator is to be set at a mid-to-high attenuation value.

7. The variable gain echo suppressor of claim 1, wherein said near-end and far-end normalizers are each operable to normalize the output of said associated near-end and far-end power detector to the associated background noise.

8. The variable gain echo suppressor of claim 1, wherein said controller includes a far-end ratio device for detecting the ratio of said far-end normalized power signal to said near-end normalized power signal, and said far-end ratio device determining the attenuation value of said first variable attenuator.

9. The variable gain echo suppressor of claim 8, wherein said far-end ratio values have a range of values, with said range of values corresponding to predetermined scaling factors, said predetermined scaling factors for said far-end ratio values stored in a far-end table and said controller operable to access the associated far-end scaling factors for defining the attenuation operation of said first variable attenuator.

10. The variable gain echo suppressor of claim 1, and further comprising:

a white noise generator for generating white noise;

a first variable white noise attenuator for receiving on the input thereof the output of said white noise generator;

a first summation device associated with said first variable attenuator and with said first variable white noise attenuator for summing the output of said first variable attenuator with said first variable white noise attenuator; and

a control circuit for setting the attenuation of said first variable white noise attenuator to reduce the amount of attenuation thereof by an amount corresponding to the increase in attenuation in said first variable attenuator and to increase the attenuation thereof by an amount corresponding to a decrease in attenuation in said first variable attenuator.

11. A variable gain echo suppressor for use with a full-duplex communication system for connecting between a far-end and a near-end, comprising:

a first variable attenuator disposed between the far-end and the near-end;

a near-end power detector for receiving the near-end transmit signal and determining the power level thereof, and having a predetermined response in the time domain, which response is variable;

a far-end power detector for receiving the far-end transmit signal and determining the power associated therewith, and having a predetermined response in the time domain, which response is variable;

a controller for setting the attenuation of said first variable attenuator as a function of said near-end and far-end detected power levels, to allow for full-duplex communication; and

a response control device that is operable to vary the response of said near-end and far-end power detectors as a function of the attenuation value of said first variable attenuator, such that said far-end power detector has a fast response for high attenuation values and a slow response for low attenuation values.

12. The variable gain echo suppressor of claim 11, wherein each of said near-end and far-end power detectors comprises a peak power estimator for averaging energy estimates generated over predetermined sample times, the average thereof comprising the detected power level.

13. The variable gain echo suppressor of claim 12, wherein said near-end and far-end power detectors each comprise an Infinite Impulse Response (IIR) low pass filter.

14. The variable gain echo suppressor of claim 13, wherein said IIR filter comprises a single-pole filter, said response control device comprising an IIR control device for changing the value of said single pole as a function of said associated or far-end detected power level.

15. The variable gain echo suppressor of claim 14, and further comprising a second variable attenuator disposed between the near-end and the far-end, said controller for setting the attenuation of each of said first and second variable attenuators as a function of said near-end and far-end normalized power levels.

16. The variable gain echo suppressor of claim 14, wherein there are first and second pole values, said first pole value associated with a fast response and said second pole value associated with a slower response, said IIR control selecting said first pole value when said first variable attenuator is to be set at a mid-to-high attenuation value, and selecting said second pole value when said attenuator value for said first variable attenuator is to be set at a low attenuation value.

17. The variable gain echo suppressor of claim 12, wherein the output of said far-end and near-end power detectors are normalized to the associated background noise to provide near-end and far-end normalized power signals, said normalized power signals utilized by said controller.

18. The variable gain echo suppressor of claim 17, wherein said controller includes a far-end ratio device for detecting the ratio of said far-end normalized power signal to said near-end normalized power signal, and said far-end ratio device determining the attenuation value of said first variable attenuator.

19. The variable gain echo suppressor of claim 18, wherein said far-end ratio values have a range of values, with said range of values corresponding to predetermined scaling factors, said predetermined scaling factors for said far-end ratio values stored in a far-end table and said controller operable to access the associated far-end scaling factors for defining the attenuation operation of said first variable attenuator.

20. The variable gain echo suppressor of claim 11, and further comprising:

a white noise generator for generating white noise;

a first variable white noise attenuator for receiving on the input thereof the output of said white noise generator;

a first summation device associated with said first variable attenuator and with said first variable white noise attenuator for summing the output of said first variable attenuator with said first variable white noise attenuator; and

a control circuit for setting the attenuation of said first variable white noise attenuator to reduce the amount of attenuation thereof by an amount corresponding to the increase in attenuation in said first variable attenuator and to increase the attenuation thereof by an amount corresponding to a decrease in attenuation in said first variable attenuator.