Method and system for active noise cancellation
View Patent ↗A method and system for active noise cancellation is provided. The system employs subband processing, and preferably implements over-sampled filterbank. The system is applicable to adaptive noise cancellation, adaptive echo cancellation for portable listening devices, such as headsets and other similar listening devices.
1. A system for active noise cancellation, comprising:
an analog active noise cancellation (ANC) system for performing an active noise cancellation to a primary signal in a time-domain, the primary signal being associated with an acoustic signal and comprising noise;
a first analysis filter bank for transferring a reference signal in the time-domain into a plurality of subband reference signals in a frequency-domain, the reference signal being associated with the noise;
a second analysis filter bank for transferring the primary signal in the time-domain into a plurality of subband primary signals in the frequency-domain;
a subband processing module for processing the plurality of subband reference signals, the plurality of subband primary signals or a combination thereof, including detecting the analog ANC system at brink of instability, and adjusting one or more parameters of the analog ANC system based on the processing, the subband processing module comprising:
a subband estimator for estimating a subband acoustic transfer function, the subband acoustic transfer function modelling conversion of an electrical signal into an acoustic domain signal, the subband estimator being applied to the plurality of subband reference signals;
a subband adaptive filter for providing a plurality of subband output signals in response to the plurality of subband reference signals;
an adjustor for adjusting the subband adaptive filter in response to the plurality of subband primary signals and the plurality of estimated subband reference signals; and
a synthesis filter bank for transferring the plurality of subband output signals to a time-domain output signal.
2. A system as claimed in claim 1 , wherein:
the synthesis filter bank employs WOLA synthesis process to convert the plurality of subband output signals to the time-domain output signal.
3. A system for active noise cancellation, comprising:
an analog active noise cancellation (ANC) system for performing an active noise cancellation to a primary signal in a time-domain, the primary signal being associated with an acoustic signal and comprisinq noise;
an analysis filterbank for transferring the primary signal in the time-domain into a plurality of subband primary signals in a frequency-domain;
a subband processing module for processing the plurality of subband primary signals, including detecting the analog ANC system at brink of instability, and adjusting one or more parameters of the analog ANC system based on the processing, the subband processing module comprising:
a subband adaptive filter for providing a plurality of subband output signals in response to a plurality of subband reference signals;
a feed-back loop for adapting the subband adaptive filter, including:
a first subband estimator for estimating a subband acoustic transfer function, the subband acoustic transfer function modelling conversion of an electrical signal into an acoustic domain signal, the first subband estimator being applied to the plurality of subband output signals;
a signal path for generating the plurality of subband reference signals in response to the plurality of subband primary signals and the plurality of estimated subband output signals;
a second subband estimator for estimating the subband acoustic transfer function, the second subband estimator being applied to the plurality of subband reference signals; and
an adjustor for adjusting the subband adaptive filter in response to the plurality of subband primary signals and the plurality of estimated subband reference signals; and
a synthesis filterbank for transferring the plurality subband output signals into a time-domain output signal.
4. A system for active noise cancellation, comprising:
a first analysis filterbank for transferring a primary signal in a time-domain into a plurality of subband primary signals in a frequency-domain;
a second analysis filterbank for transferring a reference signal in the time-domain into a plurality of subband reference signals in the frequency-domain;
a time-domain adaptive filter for providing a time-domain output signal in response to the reference signal in the time-domain;
a feed-back loop for reconstructing the time-domain adaptive filter, including:
a time-domain estimator for an acoustic transfer function, the acoustic transfer function modelling conversion of an electrical signal into an acoustic domain signal, the time-domain estimator being applied to the time-domain output signal,
a signal path for providing the reference signal in the time-domain in response to the primary signal in the time-domain and the estimated time-domain output signal,
a subband estimator for the acoustic transfer function, the subband estimator being applied to the plurality of subband reference signals, and
an adjustor for adjusting a subband adaptive filter in response to the plurality of subband primary signals and the plurality of estimated reference signal, and
a synthesis filterbank for synthesizing the time-domain adaptive filter from the subband adaptive filter.
5. A system as claimed in claim 1 , wherein the system is implemented by an over-sampled filterbank.
6. A system as claimed in claim 1 , wherein the system is implemented by a WOLA filterbank.
7. A system for active noise cancellation, comprising:
an analog active noise cancellation (ANC) system for performing an active noise cancellation to a primary signal in a time-domain, the primary signal being associated with an acoustic signal and comprising noise;
a first over-sampled analysis filterbank for transferring a reference signal in the time-domain into a plurality of subband reference signals in a frequency-domain, the reference signal in the time-domain being associated with the noise;
a second over-sampled analysis filterbank for transferring the primary signal in the time-domain into a plurality of subband primary signals in the frequency-domain;
a time-domain adaptive filter for providing a time-domain output signal in response to the reference signal in the time-domain;
a subband processing module for processing the plurality of subband reference signals, the plurality of subband primary signals or a combination thereof, including detecting the analog ANC system at brink of instability, and adjusting one or more parameters of the analog ANC system based on the processing; the subband processing module comprising:
a subband estimator for estimating a subband acoustic transfer function, the subband acoustic transfer function modelling conversion of an electrical signal into an acoustic domain signal, the subband estimator being applied to the plurality of subband reference signals;
a subband adaptive filter for providing a plurality of subband output signals in response to the plurality of subband reference signals;
an adjustor for adjusting the subband adaptive filter in response to the plurality of subband primary signals and the plurality of estimated subband reference signals;
an over-sampled synthesis filterbank for synthesizing the time-domain adaptive filter from the subband adaptive filter.
8. A system as claimed in claim 7 , wherein the first over-sampled analysis filterbank is implemented by a first WOLA analysis filterbank, or the second over-sampled analysis filterbank is implemented by a second WOLA analysis filterbank, or a combination thereof.
9. A system as claimed in claim 8 , wherein the subband processing module implements one or more than one subband adaptive algorithm.
10. A system as claimed in claim 8 , wherein the subband processing module is provided for implementing one or more than one delayless subband adaptive algorithm.
11. A system as claimed in claim 7 , wherein:
the over-sampled synthesis filterbank comprises a WOLA synthesis filterbank for converting a plurality of subband adaptive filters into a time-domain filter.
12. A system as claimed in claim 11 , wherein a time-domain output signal is provided by the output of the time-domain filter or a combination of the output of the time-domain filter and the primary signal.
13. A system as claimed in claim 11 , wherein:
a time-domain output signal is provided by the output of the time-domain filter and the primary signal, and
the time-domain output signal is provided to the second over-sampled analysis filterbank.
14. A system as claimed in claim 7 , wherein the subband processing module is adaptive or re-programmable, and models one or more than one subband transfer function associated with an application of a listening device.
15. A system as claimed in claim 1 , wherein the adjustor implements NMSL adaptation algorithm.
16. A system as claimed in claim 7 , wherein the adjustable parameters of the analog ANC system include loop-filter frequency, loop-gain, similar parameters or combinations thereof.
17. A system as claimed in claim 7 , wherein the subband processing module is capable of modeling one or more than one acoustic transfer function, a transfer function for a microphone, a transfer function for a loudspeaker, or combinations thereof.
18. A system as claimed in claim 3 , wherein the system is implemented by an over-sampled filterbank.
19. A system as claimed in claim 3 , wherein the system is implemented by a WOLA filterbank.
20. A system as claimed in claim 4 , wherein the system is implemented by an over-sampled filterbank.
21. A system as claimed in claim 4 , wherein the system is implemented by a WOLA filterbank.
22. A system as claimed in claim 9 , wherein the subband adaptive algorithm includes Filtered-X LMS (FX-LMS) algorithm.
23. A system as claimed in claim 10 , wherein the delayless subband adaptive algorithm includes delayless Filtered-X LMS (FX-LMS) algorithm.
24. A system as claimed in claim 3 , wherein the adjustor implements NMSL adaptation algorithm.
25. A system as claimed in claim 4 , wherein the synthesis filterbank comprises a WOLA synthesis filterbank implementing a sequential synthesis or batch synthesis for reconstruction of the time-domain filter based on the plurality of subband adaptive filters.