Electrical audio signal processing systems and devices – Acoustical noise or sound cancellation – Counterwave generation control path
Reexamination Certificate
1999-07-15
2002-07-09
Mei, Xu (Department: 2747)
Electrical audio signal processing systems and devices
Acoustical noise or sound cancellation
Counterwave generation control path
C381S071110
Reexamination Certificate
active
06418228
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a noise control system based on active noise control, for use in a noisy environment.
2. Description of the Related art
In recent years, an active noise control system has been proposed which eliminates environmental noise, using a control sound from a loud speaker, etc. This type of a noise control system in the conventional art employs an adaptive filter for calculating a noise control signal, and may further employ an auxiliary adaptive filter for preventing an increase in the gain of the adaptive filter, as disclosed in, for example, Japanese Laid-Open Publication No. 5-67948.
FIG. 22
is a block diagram illustrating a structure of such a conventional noise control system. Referring to
FIG. 22
, the noise control system includes a control speaker
1
, an error detection microphone
2
which functions as an error detector, a noise detection microphone
3
which functions as a noise detector, adaptive filters
4
and
15
, a digital filter
5
which approximates the propagation characteristic between the control speaker
1
and the error detection microphone
2
, coefficient update calculators
6
and
9
, and a digital filter
7
having a frequency band limiting characteristic.
With the structure illustrated in
FIG. 22
, noise generated from a noise source is detected by the noise detector
3
, and a noise source signal is generated based on the detection result. The generated noise source signal is processed by the adaptive filter
4
, so as tp output a control signal. A control sound is generated from the control speaker
1
based on the control signal so that the control sound interferes with the noise from the noise source, thereby reducing the noise.
Moreover, the state of interference between the control sound output from the control speaker
1
and the noise is measured by the error detector (microphone)
2
. The output of the error detector (microphone)
2
should ideally be zero as a result of the noise control. Therefore, the coefficient update calculator
6
performs a calculation such that the output signal of the error detector (microphone)
2
is reduced, and controls the coefficient of the adaptive filter
4
based on the calculation result.
On the other hand, the coefficient update calculator
9
performs a calculation such that the output of the adaptive filter
15
is reduced, and controls the coefficient of the adaptive filter
15
based on the calculation result. A band limiting signal produced by the digital filter
7
is input to the adaptive filter
15
, and the coefficient of the adaptive filter
15
converges into a value which suppresses signals in the band. The coefficients of the adaptive filters
4
and
15
can be shared by each other so as to combine the effects of the two coefficient update calculators
6
and
9
together, and the update operation of the coefficient of the adaptive filter
4
is suppressed in a band which is set in the digital filter
7
.
FIG. 23
is a block diagram illustrating a structure of another conventional noise control system as disclosed in Japanese Laid-Open Publication No. 7-271383. Referring to
FIG. 23
, the noise control system includes a control speaker
1
, an error detection microphone
2
which functions as an error detector, a noise detection microphone
3
which functions as a noise detector, an adaptive filter
4
, a digital filter
5
which approximates the propagation characteristic between the control speaker
1
and the error detection microphone
2
, coefficient update calculators
6
and
9
, digital filters
7
and
8
each having a frequency band limiting characteristic, and a switch section
32
.
With the structure illustrate din
FIG. 23
, noise generated from a noise source is detected by the noise detector
3
, and a noise source signal is generated based on the detection result. The generated noise source signal is processed by the adaptive filter
4
, so as to output a control signal. A control sound is generated from the control speaker
1
base don the control signal so that the control source interferes with the noise from the noise source, thereby reducing the noise.
Moreover, the state of interference between the control sound output from the control speaker
1
and the noise is measured by the error detector (microphone)
2
. The output of the error detector (microphone)
2
should ideally be zero as a result of the noise control. Therefore, the coefficient update calculator
6
performs a calculation such that the output signal of the error detector (microphone)
2
is reduced. A band limiting signal produced by the digital filter
7
and another band limiting signal produced by the digital filter
8
are input to the coefficient update calculator
9
, and the coefficient update calculator
9
performs a coefficient update calculation such that the adaptive filter
4
suppresses the output of the signal in the band. The switch section
32
switches between the outputs of the coefficient update calculators
6
and
9
, so as to control the update operation of the band limitation by the digital filters
7
and
8
.
However, the conventional noise control system as illustrated in
FIG. 22
requires the auxiliary adaptive filter
15
for controlling the update operation of the coefficient of the adaptive filter
4
, thereby increasing the amount of calculation to be performed.
The other conventional noise control system as illustrated in
FIG. 23
requires tow coefficient update calculators
6
and
9
, thereby increasing the amount of calculation to be performed. Moreover, since the witching between the outputs of the coefficient update calculators
6
and
9
is done by the switch section
32
, coefficient update operations of the adaptive filter by the coefficient update calculators
6
and
9
cannot be arbitrarily weighed.
SUMMARY OF THE INVENTION
A noise control system of the present invention 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 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 coefficient updator has a function of suppressing an increase in a coefficient gain of the adaptive filter in a predetermined frequency band.
In one embodiment, 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 second coefficient update calculator receives, as inputs thereto, outputs of the second and third digital filters; 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 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.
In another embodiment, the coefficient updator is such that: the first digital filter receives, as an input thereto, an output of the noi
Hashimoto Hiroyuki
Kakuhari Isao
Terai Kenichi
Matsushita Electric - Industrial Co., Ltd.
Mei Xu
Pendleton Brian Tyrone
Ratner & Prestia
LandOfFree
Noise control system does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Noise control system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Noise control system will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2886021