Coefficient updating method for an adaptive filter

• US 5,668,747 A
• Filed: 01/25/1995
• Issued: 09/16/1997
• Est. Priority Date: 03/09/1994
• Status: Expired due to Term

• Current Assignee: Fujitsu Limited
• Original Assignee: Fujitsu Limited
• Inventors: Ohashi, Tadashi
• Primary Examiner(s): Mai, Tan V.
• Application Number:
  US08/377,726
• Time in Patent Office: 965 Days
• Field of Search: 364/724.19, 364/724.2, 375/229, 375/230, 375/231, 375/232, 375/233
• US Class Current: 708/322
• CPC Class Codes: G06F 17/10 Complex mathematical operations function generation by table look-up G06F1/03; evaluation of elementary functions by calculation G06F7/544
• CPC Class Codes: G10K 11/17825 Error signals
• CPC Class Codes: G10K 11/17854 the filter being an adaptive filter
• CPC Class Codes: G10K 11/17857 Geometric disposition, e.g. placement of microphones
• CPC Class Codes: G10K 11/17881 the reference signal being an acoustic signal, e.g. recorded with a microphone
• CPC Class Codes: G10K 2210/3016 Control strategies, e.g. energy minimization or intensity measurements
• CPC Class Codes: G10K 2210/3053 Speeding up computation or convergence, or decreasing the computational load
• CPC Class Codes: G10K 2210/503 Diagnostics; Stability; Alarms; Failsafe

Abstract

A coefficient updating method stops updating filter coefficients for a plurality of adaptive filters when a convergence condition is achieved. Active noise control within a system simulates an original noise signal with a simulated noise signal which is equal and opposite to the original noise signal. To detect feedback in such a system, a reference signal or "white noise" is generated by a speaker, transmitted through the system and received by a microphone. Coefficients of multiple filters such as an anti-feedback filter, a C filter, and a noise control filter are then updated to minimize adverse parameters such as original noise and feedback. Coefficient updating of the adaptive filters is stopped when a minimum average value is reached.

Claims

1. A coefficient updating method comprising the steps of:

inputting a reference signal to a signal transmission system, a first adaptive filter, and a second adaptive filter;

receiving the transmitted reference signal from the signal transmission system;

subtracting an output of the first adaptive filter from the transmitted reference signal to determine a first error signal;

updating filter coefficients of said first adaptive filter to minimize the first error signal;

subtracting an output of the second adaptive filter from the transmitted error signal to determine a second error signal;

updating filter coefficients of said second adaptive filter to minimize the second error signal;

determining a minimum value of said second error signal; and

stopping the coefficient updating of said first and second adaptive filters when the second error signal is the minimum value.

2. A coefficient updating method for an adaptive filter according to claim 1, further comprising the steps of:

changing the reference signal when the minimum value of said second error signal is obtained; and

testing whether the changing of the reference signal further reduces the minimum value of the second error signal.

3. A coefficient updating method for an adaptive filter according to claim 1, wherein white noise is used as said reference signal.

4. A coefficient updating method for an adaptive filter according to claim 1, wherein the minimum second error signal is a moving average of a plurality of second error signals.

5. An adaptive filter coefficient updating method comprising the steps of:

inputting a reference signal from a reference signal generator to an acoustic feedback transmission system, an anti-feedback filter, and an auxiliary filter;

receiving the transmitted reference signal from the signal transmission system;

subtracting an output of the anti-feedback filter from the transmitted reference signal to determine a first error signal;

updating coefficients of the anti-feedback filter to minimize the first error signal;

subtracting an output of the auxiliary filter from the transmitted reference signal to determine a second error signal;

updating coefficients of the auxiliary filter to minimize the second error signal; and

stopping the coefficient updating of said anti-feedback filter and the auxiliary filter when the second error signal reaches a minimum value.

6. An adaptive filter coefficient updating method according to claim 5, further comprising the steps of:

changing the reference signal when the minimum value of the second error signal is achieved; and

testing whether said step of changing the reference signal further reduces the minimum value of the second error signal.

7. An adaptive filter coefficient updating method according to claim 5, further comprising the step of:

transferring the updated coefficients of said auxiliary filter to the anti-feedback filter.

8. An adaptive filter coefficient updating method according to claim 7, further comprising the steps of:

changing the reference signal when the minimum of the second error signal is achieved; and

testing whether the minimum value of the second error signal is further reduced in response to the changing of the reference value.

9. An adaptive filter coefficient updating method according to claim 5, wherein white noise is used as said reference signal.

10. An adaptive filter coefficient updating method according to claim 5, wherein the minimum second error signal is a moving average of a plurality of second error signals.

11. An adaptive filter coefficient updating method comprising the steps of:

inputting a reference signal from a reference signal generator to a transmission system and a first filter;

subtracting an output of the first filter from the transmitted reference signal to determine an error signal;

updating coefficients of the first filter in response to the error signal;

inputting the error signal into an estimation scattering filter;

updating coefficients of the estimation scattering filter to simulate the transmission system; and

stopping coefficient updating of said estimation scattering filter when the error signal reaches a minimum value.

12. An adaptive filter coefficient updating method according to claim 11, further comprising the steps of:

changing the reference signal when the minimum value of the error signal is reached; and

testing whether said step of changing the reference signal further reduces the minimum value of the error signal.

13. An adaptive filter coefficient updating method according to claim 11, wherein the first filter is an anti-feedback filter;

and

the coefficients of said anti-feedback filter are updated to minimize acoustical feedback of said transmission system.

14. An adaptive filter coefficient updating method according to claim 13, further comprising the steps of:

changing the reference signal when the minimum value of said error signal with respect to a given reference signal is achieved; and

testing whether said minimum value is further reduced in response to the changing of the reference value.

15. An adaptive filter coefficient updating method according to claim 13, wherein white noise is used as said reference signal.

16. An adaptive filter coefficient updating method according to claim 13, wherein the minimum error signal is a moving average of a plurality of error signals.