Noise control system

• US 6,418,228 B1
• Filed: 07/15/1999
• Issued: 07/09/2002
• Est. Priority Date: 07/16/1998
• Status: Expired due to Fees

• Current Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Hashimoto, Hiroyuki, Kakuhari, Isao, Terai, Kenichi
• Primary Examiner(s): Mei, Xu
• Assistant Examiner(s): PENDLETON, BRIAN T
• Application Number:
  US09/353,667
• Time in Patent Office: 1,090 Days
• Field of Search: 381/71.1, 381/71.8, 381/71.12, 381/71.14, 381/94.1, 381/94.9, 381/71.5
• US Class Current: 381/71.8
• CPC Class Codes: G10K 11/17825 Error signals
• CPC Class Codes: G10K 11/17833 by using a self-diagnostic function or a malfunction prevention function, e.g. detecting abnormal output levels
• CPC Class Codes: G10K 11/17854 the filter being an adaptive filter
• CPC Class Codes: G10K 11/17881 the reference signal being an acoustic signal, e.g. recorded with a microphone
• CPC Class Codes: G10K 2210/3012 Algorithms
• CPC Class Codes: G10K 2210/3027 Feedforward
• CPC Class Codes: G10K 2210/3039 Nonlinear, e.g. clipping, numerical truncation, thresholding or variable input and output gain

Abstract

A noise control system includes: a control sound generator for generating a control sound; an error detector for detecting an error signal between the control sound and noise; a noise detector for detecting a noise source signal; an adaptive filter for outputting a control signal; and a coefficient updator for updating a coefficient of the adaptive filter. The coefficient updator includes at least a first digital filter, a first coefficient update calculator, a second digital filter, a phase inverter, a third digital filter, and a second coefficient update calculator. Alternatively, the coefficient updator includes at least a first digital filter, a second digital filter, a third digital filter, a coefficient update calculator, a phase inverter, a first adder, and a second adder. In either case, the coefficient updator has a function of suppressing an increase in a coefficient gain of the adaptive filter in a predetermined frequency band.

Claims

1. A noise control system, comprising:

a control sound generator for generating a control sound;

an error detector for detecting an error signal between the control sound and noise;

a noise detector for detecting a noise source signal;

an adaptive filter for outputting a control signal;

a coefficient updator for updating a coefficient of the adaptive filter, the coefficient updator comprising at least a first digital filter, a first coefficient update calculator, a second digital filter, a phase inverter, a third digital filter, and a second coefficient update calculator;

the first digital filter approximates a propagation characteristic between the control sound generator and the error detector;

the second and third digital filters have a common passband frequency characteristic,

the second coefficient update calculator receives, as inputs thereto, processed outputs from the second and third digital filers;

wherein the coefficient updator has a function of suppressing an increase in a coefficient gain of the adaptive filter in a predetermined frequency band.

2. A noise control system according to claim 1, wherein the coefficient updator is such that:

the first digital filter receives, as an input thereto, an output of the noise detector;

the first coefficient update calculator receives, as inputs thereto, an output of the first digital filter and an output of the error detector;

the phase inverter inverts the output of the noise detector;

the second digital filter receives, as an input thereto, an output of the phase inverter;

the third digital filter receives, as an input thereto, the output of the error detector;

the first coefficient update calculator performs a calculation such that the output of the error detector is reduced, and updates the coefficient of the adaptive filter based on the calculation result; and

the second coefficient update calculator performs a calculation such that the output of the third digital filter is reduced, and updates the coefficient of the adaptive filter based on the output of the coefficient update calculator.

3. A noise control system according to claim 1, wherein the coefficient updator is such that:

the first digital filter receives, as an input thereto, an output of the noise detector;

the first coefficient update calculator receives, as inputs thereto, an output of the first digital filter and an output of the error detector;

the second digital filter receives, as an input thereto, an output of the noise detector;

the third digital filter receives, as an input thereto, the output of the error detector;

the phase inverter inverts an output of the second coefficient update calculator;

the first coefficient update calculator performs a calculation such that the output of the error detector is reduced, and updates the coefficient of the adaptive filter based on the calculation result; and

the second coefficient update calculator performs a calculation such that the output of the third digital filter is reduced, inverts and outputs the calculation result, and updates the coefficient of the adaptive filter based on the output of the second coefficient update calculator.

4. A noise control system according to claim 1 wherein:

the coefficient updator further comprises;

a first selection controller for thinning out the outputs of the first coefficient update calculator;

a second selection controller for thinning out the outputs of the second coefficient updator calculator; and

a selection control calculator for receiving an output signal of the third digital filter to control the first and second selection controllers;

the first digital filter receives, as an input thereto, an output of the noise detector;

the first coefficient update calculator receives, as inputs thereto, an output of the first digital filter and an output of the error detector;

the phase inverter inverts an output of the adaptive filter;

the third digital filter receives, as an input thereto, an output of the phase inverter;

the first coefficient update calculator performs a calculation such that the output of the error detector is reduced;

the second coefficient update calculator performs a calculation such that the output of the third digital filter is reduced; and

when a level of the output signal of the third digital filter exceeds a predetermined value, the selection control calculator updates the coefficient of the adaptive filter by controlling the first and second selection controllers so that the first selection controller performs the thinning-out operation at a thinning-out frequency lower than that of the second selection controller.

5. A noise control system according to claim 1, wherein:

the coefficient updator further comprises;

a first selection controller for switching between selecting an output of the first coefficient update calculator and selecting nothing;

a second selection controller for switching between selecting an output of the second coefficient update calculator and selecting nothing; and

a selection control calculator for receiving an output signal of the third digital filter to control the first and second selection controllers;

the first digital filter receives, as an input thereto, an output of the noise detector;

the first coefficient update calculator receives, as inputs thereto, an output of the first digital filter and an output of the error detector;

the phase inverter inverts an output of the adaptive filter;

the third digital filter receives, as an input thereto, an output of the phase inverter;

the first coefficient update calculator performs a calculation such that the output of the error detector is reduced;

the second coefficient update calculator performs a calculation such that the output of the third digital filter is reduced; and

when a level of the output signal of the third digital filter exceeds a predetermined value, the selection control calculator updates the coefficient of the adaptive filter by controlling the first and second selection controllers so that the first selection controller is switched to select nothing at a switching operation frequency lower than that at which the second selection controller is switched to select nothing.

6. A noise control system according to claim 1, wherein:

the coefficient updator further comprises;

a signal level converter for receiving an output signal of the third digital filter to convert a level of the signal; and

a multiplier for multiplying an output of the signal level converter by an output of the second coefficient update calculator so as to update the coefficient of the adaptive filter;

the first digital filter receives, as an input thereto, an output of the noise detector;

the first coefficient update calculator receives, as inputs thereto, an output of the first digital filter and an output of the error detector;

the second digital filter receives, as an input thereto, the output of the noise detector;

the phase inverter inverts an output of the adaptive filter;

the third digital filter receives, as an input thereto, an output of the phase inverter;

the first coefficient update calculator performs a calculation such that the output of the error detector is reduced;

the second coefficient update calculator performs a calculation such that the output of the third digital filter is reduced; and

the signal level converter has an input-output characteristic which is approximated to a characteristic obtained by normalizing an input-distortion characteristic of the control sound generator.

7. A noise control system according to claim 1, wherein the predetermined frequency band exists in a low frequency region.

8. A noise control system according to claim 7, wherein the predetermined frequency band is a frequency region where the frequency is less than or equal to a lower limit reproducible frequency of the control sound generator.

9. A noise control system, comprising:

a control sound generator for generating a control sound;

an error detector for detecting an error signal between the control sound and noise;

a noise detector for detecting a noise source signal;

an adaptive filter for outputting a control signal;

a coefficient updator for updating a coefficient of the adaptive filter, the coefficient updator comprising at least a first digital filter, a second digital filter, a third digital filter, a coefficient update calculator, a phase inverter, a first adder, and a second adder;

the first digital filter approximates a propagation characteristic between the control sound generator and the error detector; and

the second and third digital filers have a common passband frequency characteristic,

wherein the coefficient updator has a function of suppressing an increase in a coefficient gain of the adaptive filter in a predetermined frequency band.

10. A noise control system according to claim 9, wherein the coefficient updator is such that:

the first digital filter receives, as an input thereto, an output of the noise detector;

the second digital filter receives, as an input thereto, the output of the noise detector;

the first adder receives, as inputs thereto, an output of the first digital filter and an output of the second digital filter;

the second adder receives, as inputs thereto, an output of the error detector and an output of the third digital filter;

the coefficient update calculator receives, as inputs thereto, an output of the first adder and an output of the second adder;

the phase inverter inverts an output of the adaptive filter;

the third digital filter receives, as an input thereto, the output of the phase inverter; and

the coefficient update calculator performs a calculation such that the output of the second adder is reduced, and updates the coefficient of the adaptive filter based on the calculation result.

11. A noise control system according to claim 9, wherein the coefficient updator is such that:

the first digital filter receives, as an input thereto, an output of the noise detector;

the phase inverter inverts the output of the noise detector;

the second digital filter receives, as an input thereto, the output of the phase inverter;

the first adder receives, as inputs thereto, an output of the first digital filter and an output of the second digital filter;

the second adder receives, as inputs thereto, an output of the error detector and an output of the third digital filter;

the coefficient update calculator receives, as inputs thereto, an output of the first adder and an output of the second adder;

the third digital filter receives, as an input thereto, an output of the adaptive filter; and

the coefficient update calculator performs a calculation such that the output of the second adder is reduced, and updates the coefficient of the adaptive filter based on the calculation result.

12. A noise control system according to claim 9, wherein:

the coefficient updator further comprises;

a first coefficient controller for multiplying an output of the second digital filter by a first coefficient factor; and

a second coefficient controller multiplying an output of the third digital filter by a second coefficient factor;

the first digital filter receives, as an input thereto, an output of the noise detector;

the second digital filter receives, as an input thereto, the output of the noise detector;

the first adder receives, as inputs thereto, an output of the first digital filter and an output of the first coefficient controller;

the second adder receives, as inputs thereto, an output of the error detector and an output of the second coefficient controller;

the coefficient update calculator receives, as inputs thereto, an output of the first adder and an output of the second adder;

the phase inverter inverts an output of the adaptive filter;

the third digital filter receives, as an input thereto, the output of the phase inverter;

each of the first coefficient factor and the second coefficient factor is set to be equal to or more than 1; and

the coefficient update calculator performs a calculation such that the output of the second adder is reduced, and updates the coefficient of the adaptive filter based on the calculation results.

13. A noise control system according to claim 12, wherein the first coefficient controller is set so that in a passband of the second digital filter, the output of the first coefficient controller is larger than an output signal of the first digital filter.

14. A noise control system according to claim 12, wherein the second coefficient controller is set so that in a passband of the third digital filter, the output of the second coefficient controller is larger than an output signal of the error detector.

15. A noise control system according to claim 9, wherein:

the coefficient updator further comprises;

a first coefficient controller for multiplying an output of the first digital filter by a first coefficient factor; and

a second coefficient controller for multiplying an output of the error detector by a second coefficient factor;

the first digital filter receives, as an input thereto, an output of the noise detector;

the second digital filter receives, as an input thereto, the output of the noise detector;

the first adder receives, as inputs thereto, an output of the first coefficient controller and an output of the second digital filter;

the second adder receives, as inputs thereto, an output of the second coefficient controller and an output of the third digital filter;

the coefficient update calculator receives, as inputs thereto, an output of the first adder and an output of the second adder;

the phase inverter inverts an output of the adaptive filter;

the third digital filter receives, as an input thereto, the output of the phase inverter;

each of the first coefficient factor and the second coefficient factor is set to be less than an equal to 1; and

the coefficient update calculator performs a calculation such that the output of the second adder is reduced, and updates the coefficient of the adaptive filter based on the calculation result.

16. A noise control system according to claim 15, wherein the first coefficient controller is set so that in a passband of the second digital filter, the output of the first coefficient controller is smaller than an output signal of the first digital filter.

17. A noise control system according to claim 15, wherein the second coefficient controller is set so that in a passband of the third digital filter, the output of the second coefficient controller is smaller than an output signal of the error detector.

18. A noise control system according to claim 9, wherein the predetermined frequency band exists in a low frequency region.

19. A noise control system according to claim 18, wherein the predetermined frequency band is a frequency region where the frequency is less than or equal to a lower limit reproducible frequency of the control sound generator.

20. A noise control system according to claim 9, wherein the predetermined frequency band exists in a frequency region where there is a correlation between an output signal of the noise detector and an output signal of the error detector.