Claims
- 1. A method for performing non-linear processing of an audio signal for selectively affecting background noise, comprising:
selectively estimating the background noise to produce an estimated background noise level; determining if the estimated background noise level exceeds a predetermined criteria; and selectively injecting predetermined background noise into the audio signal.
- 2. The method as claim 1, wherein the step of selectively estimating comprises:
if one of a near-end talker signal and a far-end talker signal is detected, halting estimation of the background noise; and if no near-end talker signal and no far-end talker signal is detected, estimating the background noise.
- 3. The method as claim 2, wherein the step of halting estimation of the background noise comprises:
detecting the near-end talker signal if the near-end talker signal occurred during a predetermined time window; and detecting the far-end talker signal if the far-end talker occurred during the predetermined time window.
- 4. The method as claim 1, wherein the step of selectively injecting predetermined background noise comprises:
selecting one of a plurality of noise types as the predetermined background noise.
- 5. The method as claim 1, wherein the predetermined background noise is approximately pink noise.
- 6. The method as claim 5, wherein the step of selectively injecting predetermined background noise into the audio signal comprises:
generating a plurality of pseudo-random numbers to generate the approximately pink noise.
- 7. The method as claim 1, wherein a level of the predetermined background noise is less than the estimated background noise level and is within four decibels of the estimated background noise level.
- 8. The method as claim 1, wherein the step of selectively injecting comprises:
gradually injecting the predetermined background noise into the audio signal over a predetermined window of time.
- 9. The method as claim 1, wherein the step of selectively injecting comprises:
detecting if an error signal level is below a first predetermined threshold.
- 10. The method as claim 9, wherein the step of selectively injecting further comprises:
detecting if the error signal level is below a second predetermined threshold.
- 11. The method as claim 10, wherein the step of selectively injecting further comprises:
if the error signal level is below the first and second predetermined thresholds, injecting the predetermined background noise into the audio signal.
- 12. The method as claim 11, wherein the first predetermined threshold is determined from a near-end talker signal and the second predetermined threshold is determined from a far-end talker signal.
- 13. The method as claim 10, wherein the step of selectively injecting comprises:
detecting if the error signal level is above a third predetermined threshold.
- 14. The method as claim 13, wherein the step of selectively injecting further comprises:
detecting if the error signal level is above a fourth predetermined threshold.
- 15. The method as claim 14, wherein the step of selectively injecting further comprises:
if the error signal level is above at least one of the third and fourth predetermined thresholds, halting injection of the predetermined background noise into the audio signal.
- 16. The method as claim 14, wherein the third predetermined threshold is determined from a near-end talker signal and the fourth predetermined threshold is determined from a far-end talker signal.
- 17. The method as claim 14, wherein the step of selectively injecting further comprises:
if the error signal level is above at least one of the first and second predetermined thresholds and below the third and fourth thresholds, maintaining a present state of injection.
- 18. The method as claim 1, wherein the step of selectively estimating the background noise comprises:
using a first algorithm to estimate the background noise during a first time period; and using a second algorithm to estimate the background noise during a second time period, wherein the first algorithm estimates the background noise more quickly than the second algorithm.
- 19. The method as claim 1, wherein the step of selectively estimating the background noise comprises:
estimating power of the background noise.
- 20. The method as claim 1, wherein the step of selectively estimating the background noise comprises:
estimating magnitude of the background noise.
- 21. The method as claim 1, wherein the step of selectively estimating the background noise comprises:
adapting the estimated background noise level at a first adaptation rate when the background noise is increasing; and adapting the estimated background noise level at a second adaptation rate when the background noise is decreasing, wherein the first adaptation rate is slower than the second adaptation rate.
- 22. The method as claim 1,.wherein the step of selectively estimating the background noise comprises:
selectively estimating the background noise during a plurality of time periods to produce a plurality of estimated background noise levels; selecting a minimum estimated background noise level from the plurality of estimated background noise levels; and using the minimum estimated background noise level as the estimated background noise level.
- 23. The method as claim 1, wherein the non-linear processing of the audio signal is used in an echo canceller.
- 24. An echo canceller, comprising:
an adaptive filter; control circuitry, coupled to the adaptive filter; and a non-linear processor, coupled to the control circuitry, for selectively estimating background noise, and for halting estimation of background noise if at least one of a near-end signal and a far-end signal is detected.
- 25 The echo canceller as in claim 24, wherein the non-linear processor uses a first algorithm to estimate the background noise during a first time period and uses a second algorithm to estimate the background noise during a second time period, wherein the first algorithm estimates the background noise more quickly than the second algorithm.
- 26. The echo canceller as claim 24, wherein the non-linear processor adapts the estimated background noise level at a first adaptation rate when the background noise is increasing and adapts the estimated background noise level at a second adaptation rate when the background noise is decreasing, and wherein the first adaptation rate is slower than the second adaptation rate.
- 1. A method for indicating whether a tone is present in a communication signal, comprising:
delaying the communication signal by a predetermined first delay to produce a first delayed signal; delaying the communication signal by a predetermined second delay to produce a second delayed signal; combining the first delayed signal, the second delayed signal, and the communication signal to produce an estimate signal; and using the estimate signal to indicate whether the tone is present.
- 2. A method as in claim 1, wherein the estimate signal is a power estimate signal.
- 3. A method as in claim 1, further comprising:
taking a magnitude of an intermediate signal to produce a magnitude signal;
- 4. A method as in claim 1, wherein the step of combining comprises:
performing a polynomial function using the first delayed signal, the second delayed signal, and the communication signal.
- 5. A method as in claim 4, wherein the step of performing the polynomial function comprises:
multiplying the first delayed signal by the first delayed signal to produce a first product; multiplying the second delayed signal by the communication signal to produce a second product; subtracting the second product from the first product to produce an intermediate signal; taking a magnitude of the intermediate signal to produce a magnitude signal; and low-pass filtering the magnitude signal to produce the estimate signal.
- 6. A method as in claim 1, wherein the step of using the estimate signal to indicate whether the tone is present comprises:
delaying the estimate signal by a predetermined third delay to produce a delayed estimate signal; determining a minimum estimate between the estimate signal and the delayed estimate signal; and determining a maximum estimate between the estimate signal and the delayed estimate signal.
- 7. A method as in claim 6, wherein the step of using the estimate signal to indicate whether the tone is present further comprises:
computing a ratio of the minimum estimate and the maximum estimate; comparing the ratio to a predetermined ratio threshold; repeating the step of computing the ratio; determining if the ratio has continuously exceeded the predetermined ratio threshold for a sufficient number of steps of repeating; and if the ratio has continuously exceeded the predetermined ratio threshold for the sufficient number of steps of repeating, providing a tone indicator signal which indicates that the tone has been detected.
- 8. A method as in claim 7, wherein the step of using the estimate signal to indicate whether the tone is present further comprises:
determining if the estimate signal has exceeded a predetermined ratio threshold for a sufficient number of steps of repeating;
- 9. A method as in claim 7, wherein the estimate signal is a power estimate signal and wherein the step of using the estimate signal to indicate whether the tone is present further comprises:
determining if the power estimate signal has exceeded a predetermined low power threshold; and if the power estimate signal has not exceeded a predetermined low power threshold, waiting until the power estimate signal has exceeded the predetermined low power threshold before performing the steps of computing, comparing, repeating, and determining if the ratio has continuously exceeded the predetermined ratio threshold.
- 10. A method as in claim 1, further comprising:
detecting whether the tone is a predetermined single frequency tone; and detecting phase reversal of the predetermined single frequency tone.
- 11. A method as in claim 10, wherein the step of detecting whether the tone is the predetermined single frequency tone comprises:
delaying the communication signal by a predetermined third delay to produce a third delayed signal; generating a generated sinusoidal signal with the predetermined single frequency; multiplying the generated sinusoidal signal by the communication signal to produce a correlation signal; multiplying the generated sinusoidal signal by the third delayed signal to produce a delayed correlation signal; low-pass filtering the correlation signal to produce a smooth correlation estimate; low-pass filtering the delayed correlation signal to produce a delayed smooth correlation signal; and using the smooth correlation signal and the delayed smooth correlation signal to detect whether the tone is the predetermined single frequency tone.
- 12. A method as in claim 1, further comprising:
using an impulsive change of the estimate signal to detect a phase change of the communication signal.
- 13. A method for indicating whether a tone is present in a communication signal, comprising:
delaying the communication signal by a predetermined delay to produce a delayed signal; generating a generated sinusoidal signal; combining the delayed signal, the generated sinusoidal signal, and the communication signal to produce a first correlation signal and a second correlation signal; and using the first correlation signal and the second correlation signal to indicate whether the tone has been detected.
- 14. A method as in claim 13, wherein the tone is a predetermined single frequency tone.
- 15. A method as in claim 13, wherein the step of combining comprises:
performing a polynomial function using the delayed signal, the generated sinusoidal signal, and the communication signal.
- 16. A method as in claim 15, wherein the step of performing the polynomial function comprises:
multiplying the generated sinusoidal signal by the communication signal to produce the first correlation signal; and multiplying the generated sinusoidal signal by the delayed signal to produce the second correlation signal.
- 17. A method as in claim 13, further comprising:
low-pass filtering the first correlation signal to produce a smooth correlation estimate; low-pass filtering the second correlation signal to produce a delayed smooth correlation signal.
- 18. A method as in claim 17, wherein the step of using the first correlation signal and the second correlation signal to indicate whether the tone is present comprises:
determining a magnitude of the smooth correlation estimate; determining a magnitude of the delayed smooth correlation estimate; and determining an effective smooth correlation signal by selecting a maximum between the magnitude of the smooth correlation estimate and the delayed smooth correlation estimate.
- 19. A method as in claim 18 wherein the step of using the first correlation signal and the second correlation signal to indicate whether the tone is present further comprises:
delaying the effective smooth correlation signal by a second predetermined delay to produce a delayed effective smooth correlation signal; determining a minimum estimate between the effective smooth correlation signal and the delayed effective smooth correlation signal; and determining a maximum estimate between the effective smooth correlation signal and the delayed effective smooth correlation signal.
- 20. A method as in claim 19, wherein the step of using the first correlation signal and the second correlation signal to indicate whether the tone is present further comprises:
computing a ratio of the minimum estimate and the maximum estimate; comparing the ratio to a predetermined ratio threshold; repeating the step of computing the ratio; determining if the ratio has continuously exceeded the predetermined ratio threshold for a sufficient number of steps of repeating; if the ratio has continuously exceeded the predetermined ratio threshold for the sufficient number of steps of repeating, providing a tone detector signal which indicates that the tone has been detected.
- 21. A method as in claim 13, further comprising:
if the tone has been detected, detecting a phase sign of the tone; and wherein the step of detecting the phase sign of the tone comprises determining a sign of one of the first and second correlation signals whose magnitude is equal to the effective smooth correlation signal.
- 22. A method as in claim 21, further comprising:
if the tone is detected, determining if a phase reversal of the tone occurs by monitoring the sign of the one of the first and second correlation signals whose magnitude is equal to the effective smooth correlation signal.
- 23. A method as in claim 22, further comprising:
if the phase reversal of the tone occurs, counting a number of times the phase reversal of the tone occurs.
- 24. A tone detector for detecting a tone in a communication signal, comprising:
a first circuit for providing a first delayed signal; a second circuit for providing a second delayed signal; estimator circuitry for combining the first delayed signal, the second delayed signal, and the communication signal to produce an estimate signal; and tone indication circuitry for using the estimate signal to indicate whether the tone is present.
RELATED APPLICATIONS
[0001] This is related to U.S. patent application having attorney docket number SC12026TS, filed on even date, and entitled “Monitoring and control of an Adaptive Filter in a Communication System,” U.S. patent application having attorney docket number SC12120TS, filed on even date, and entitled “Method and Apparatus for Pure Delay Estimation in a Communication System,” U.S. patent application having attorney docket number SC11993TS, filed on even date, and entitled “Method and Apparatus for Tone Indication,” and U.S. patent application having attorney docket number SC12107TS, filed on even date, and entitled “Method and Apparatus for Performing Adaptive Filtering,” all of which are assigned to the current assignee hereof.