Adaptive noise rejection system and method

• US 6,320,968 B1
• Filed: 06/28/2000
• Issued: 11/20/2001
• Est. Priority Date: 06/28/2000
• Status: Expired due to Fees

• Current Assignee: Esion-Tech LLC
• Original Assignee: Esion-Tech LLC
• Inventors: Linder, Frank X.
• Primary Examiner(s): Mei, Xu
• Application Number:
  US09/605,569
• Time in Patent Office: 510 Days
• Field of Search: 381/71.1, 381/71.2, 381/71.8, 381/71.9, 381/71.11, 381/71.13, 381/71.14, 381/FOR.123, 381/57, 381/92, 381/94.1, 381/94.2, 381/94.3, 381/94.7, 381/FOR.124, 381/95, 381/97
• US Class Current: 381/94.7
• CPC Class Codes: G10L 2021/02085 Periodic noise
• CPC Class Codes: G10L 21/02 Speech enhancement, e.g. noise reduction or echo cancellation reducing echo effects in line transmission systems H04B3/20; echo suppression in hands-free telephones H04M9/08
• CPC Class Codes: G10L 21/0208 Noise filtering
• CPC Class Codes: H03G 3/345 Muting during a short period of time when noise pulses are detected, i.e. blanking H03G3/348 takes precedence

Abstract

An adaptive noise rejection method and apparatus. An information signal having an information component and a repetitive noise component having a varying characteristic frequency is delayed the information signal by a reference delay time that is equal that is equal to a predetermined number of periods of the characteristic frequency to form a delayed information signal. The delayed information signal is subtracted from the information signal to form a processed information signal in which the information component is substantial and the noise component is negligible. The amplitude of the noise component of the processed information signal is constantly monitored. The delay of the information signal is varied as the characteristic frequency of the noise component changes so as to maintain the amplitude of the noise component of the processed information signal at a predetermined level.

Claims

1. A method of rejecting noise introduced into an information signal, comprising the steps of:

a) receiving an information signal having an information component and a repetitive noise component having a varying characteristic frequency;

b) delaying the information signal by a reference delay time that is equal to a predetermined number of periods of the characteristic frequency to form a delayed information signal;

c) processing the information signal and the delayed information signal to form a processed reference information signal in which the information component is substantial and the noise component is negligible;

d) determining the amplitude of the noise component of the processed reference information signal; and

e) varying the delay of the information signal as the characteristic frequency of the noise component changes in order to maintain the noise component of the processed reference information signal at a predetermined level.

2. The method according to claim 1 wherein the predetermined number of periods is one period of the characteristic frequency.

3. The method according to claim 1 wherein the delaying step (b) further comprises simultaneously providing (i) a second delayed information signal that is delayed, with respect to the information signal, by an amount of time that is less than the reference delay time, and (ii) a third delayed information signal that is delayed, with respect to the information signal, by an amount of time that is greater than the reference delay time.

4. The method according to claim 3 wherein processing step (c) further comprises the steps of:

processing the second delayed information signal with the received information signal to provide a second processed signal; and

processing the third delayed information signal with the received information signal to provide a third information signal.

5. The method according to claim 4 wherein varying step (e) comprising the steps of:

determining the amplitude of the noise component of the second processed signal;

determining the amplitude of the noise component of the third information signal;

comparing the amplitude of the noise component of the reference processed information signal with the noise components of the second and third processed information signals;

maintaining the current reference delay time if the amplitude of the noise component of the referenced processed information signal is relatively lower than the amplitudes of the noise components of both the second and third processed information signals;

decreasing the reference delay time if the amplitude of the noise component of the second processed information signal is relatively lower than the amplitude of the noise components of both the referenced processed information signal and the third processed information signal; and

increasing the reference time delay if the amplitude of the noise component of the third processed information signal is relatively lower than the amplitude of the noise components of both the referenced processed information signal and the second processed information signal.

6. The method according to claim 1 wherein determining step (d) comprises the step of detecting the amplitude of the noise component of the reference processed information signal.

7. A method as defined in claim 5 wherein the step of determining the amplitude of the noise component of the second processed information signal comprises the step of detecting the amplitude of the noise component of the second processed information signal.

8. The method according to claim 5 wherein the step of determining the amplitude of the noise component of the third processed information signal comprises the step of detecting the amplitude of the noise component of the third processed information signal.

9. The method according to claim 4 wherein prior to varying step (e), the method further comprises the step of filtering the reference, second and third processed information signals to remove the information component.

10. The method according to claim 1 wherein processing step (c) comprises the step of subtracting the delayed information signal from the received information signal.

11. The method according to claim 4 wherein the step of processing the second delayed information signal with the received information signal comprises the step of subtracting the second delayed information signal from the received information signal.

12. The method according to claim 4 wherein the step of processing the third delayed information signal with the received information signal comprises the step of subtracting the third delayed information signal from the received information signal.

13. The method according to claim 1 wherein the information signal received in step (a) is an analog signal and wherein receiving step (a) includes the step of converting the analog information signal into a digital information signal.

14. The method according to claim 1 further including the step of converting the reference processed information signal into a processed analog signal.

15. The method according to claim 4 further comprising the step filtering the reference, second and third processed information signals to remove the information component.

16. The method according to claim 15 wherein the filtering step comprises the step of inputting the reference, second and third processed information signals into respective band pass filters, each filter having a pass band and a center frequency, the varying step (e) further comprising varying the center frequency of the pass bands of the filters to match the characteristic frequency of the noise component.

17. An apparatus for rejecting noise introduced into an information signal, comprising:

an input interface for receiving an information signal having an information component and a repetitive noise component having a varying characteristic frequency;

means for delaying the information signal by a reference delay time that is equal to a predetermined number of periods of the characteristic frequency to form a delayed information signal;

means for processing the information signal and the delayed information signal to form a processed reference information signal in which the information component is substantial and the noise component is negligible;

means for determining the amplitude of the noise component of the processed reference information signal; and

means for varying the delay of the information signal as the characteristic frequency of the noise component changes in order to maintain the noise component of the processed reference information signal at a predetermined level.

18. The apparatus according to claim 17 wherein the delaying means further comprises means for simultaneously providing (i) a second delayed information signal that is delayed, with respect to the information signal, by an amount of time that is less than the reference delay time, (ii) a third delayed information signal that is delayed, with respect to the information signal, by an amount of time that is greater than the reference delay time.

19. The apparatus according to claim 18 further comprising:

a first means for processing the second delayed information signal with the received information signal to provide a second processed signal; and

a second means for processing the third delayed information signal with the received information signal to provide a third information signal.

20. The apparatus according to claim 19 further comprising:

a first means for determining the amplitude of the noise component of the second processed signal;

a second means for determining the amplitude of the noise component of the third information signal;

comparing the amplitude of the noise component of the reference processed information signal with the noise components of the second and third processed information signals;

means for maintaining the current reference delay time if the amplitude of the noise component of the referenced processed information signal is relatively lower than the amplitudes of the noise components of both the second and third processed information signals;

means for decreasing the reference delay time if the amplitude of the noise component of the second processed information signal is relatively lower than the amplitude of the noise components of both the referenced processed information signal and the third processed information signal; and

means for increasing the reference time delay if the amplitude of the noise component of the third processed information signal is relatively lower than the amplitude of the noise components of both the referenced processed information signal and the second processed information signal.

21. The apparatus according to claim 17 further comprising means for detecting the amplitude of the noise component of the reference processed information signal.

22. The apparatus according to claim 20 wherein the first determining means comprises means for detecting the amplitude of the noise component of the second delayed information signal.

23. The apparatus according to claim 20 wherein the second determining means comprises means for detecting the amplitude of the noise component of the third delayed information signal.

24. The apparatus according to claim 19 further comprising a filter for removing the information signal from the reference processed information signal.

25. The apparatus according to claim 24 wherein the filter is a band pass filter having a pass band and a center frequency.

26. The apparatus according to claim 25 wherein the varying means comprises means for varying the center frequency of the pass band of the filter to match the characteristic frequency of the noise component.

27. The apparatus according to claim 19 further comprising:

a first filter for filtering the second processed information signal to remove the information component; and

a second filter for filtering the third processed information signal to remove the information component.

28. The apparatus according to claim 27 further comprising:

a first detector for detecting the amplitude of the noise component of the filtered second processed information signal; and

a second detector for detecting the amplitude of the noise component of the filtered third processed information signal.

29. The apparatus according to claim 17 wherein the processing means comprises a circuit for subtracting the delayed information signal from the received information signal to provide the processed reference processed information signal.

30. The apparatus according to claim 19 wherein the:

first processing means comprises a circuit for subtracting the second delayed information signal from the received information signal to provide the second processed information signal; and

second processing means comprises a circuit for subtracting the third delayed information signal from the received information signal to provide the third processed information signal.

31. The apparatus according to claim 17 wherein the received information signal is an analog information signal, the apparatus further comprising an analog-to-digital converter for converting the analog information signal to a digital information signal.

32. The apparatus according to claim 17 wherein the processed reference information signal is a digital signal, the apparatus further comprising a digital-to-analog converter for converting the processed reference information signal into an analog information signal.