Active noise control device

1. An active noise control device that performs active noise control for controlling a speaker based on an error signal that changes in accordance with combined sound of a noise transmitted from a vibration source and an anti-noise sound for cancelling the noise, output from the speaker, the active noise control device comprising one or more processors that execute computer-executable instructions stored in a memory,

wherein the one or more processors execute the computer-executable instructions to cause the active noise control device to:

generate a standard signal in accordance with a control target frequency;

generate a control signal for controlling the speaker by signal-processing the standard signal through a control filter that is an adaptive notch filter;

generate an estimated noise signal by signal-processing the standard signal through a primary path filter that is an adaptive notch filter;

generate a first estimated anti-noise signal by signal-processing the control signal through a secondary path filter that is an adaptive notch filter;

generate a reference signal by signal-processing the standard signal through the secondary path filter;

generate a second estimated anti-noise signal by signal-processing the reference signal through the control filter;

generate a first virtual error signal from the error signal, the first estimated anti-noise signal, and the estimated noise signal;

generate a second virtual error signal from the second estimated anti-noise signal and the estimated noise signal;

successively and adaptively update a coefficient of the secondary path filter so as to minimize magnitude of the first virtual error signal, based on the control signal and the first virtual error signal;

successively and adaptively update a coefficient of the control filter so as to minimize magnitude of the second virtual error signal, based on the reference signal and the second virtual error signal;

store initial values of the coefficient of the secondary path filter into an initial value table in association with a frequency, in a table format;

store updated values of the coefficient of the secondary path filter into an updated value table in association with the frequency, in a table format;

write the initial values of the initial value table into the updated value table as the updated values at start of the active noise control and write the coefficient of the secondary path filter updated during the active noise control, into the updated value table as the updated values; and

read the updated value corresponding to the frequency from the updated value table before updating the coefficient of the secondary path filter, and update the coefficient of the secondary path filter, using the read updated value as a previous value.

2. The active noise control device according to claim 1 , wherein the one or more processors cause the active noise control device to successively and adaptively update a coefficient of the primary path filter so as to minimize the magnitude of the first virtual error signal, based on the standard signal and the first virtual error signal.

3. The active noise control device according to claim 1 , wherein the one or more processors cause the active noise control device to rewrite the initial values in the initial value table with the updated values of the updated value table at end of the active noise control.

4. The active noise control device according to claim 3 , wherein the one or more processors cause the active noise control device to:

determine whether an abnormality or divergence has occurred in the active noise control, at the end of the active noise control, and

not rewrite the initial values in the initial value table with the updated values of the updated value table when it is determined, in the determining, that an abnormality or divergence has occurred in the active noise control.

5. The active noise control device according to claim 1 , wherein the one or more processors cause the active noise control device to perform weighted averaging of the coefficient of the secondary path filter updated according to an updating formula and the updated values in the updated value table.

6. The active noise control device according to claim 1 , wherein the one or more processors cause the active noise control device to update the coefficient of the secondary path filter, by using, as the previous value, a value obtained by adding the coefficient of the secondary path filter after the previous updating of the coefficient of the secondary path filter and the read updated value at a predetermined ratio.

7. The active noise control device according to claim 1 , wherein the one or more processors cause the active noise control device to:

determine whether an abnormality or divergence has occurred in the active noise control, at end of the active noise control;

store result values of the coefficient of the secondary path filter into a result value table in association with the frequency, in a table format; and

rewrite the result values in the result value table with the updated values of the updated value tale when it is determined that an abnormality or divergence has occurred in the active noise control.

8. The active noise control device according to claim 1 , wherein the one or more processors cause the active noise control device to:

make an adjustment so as to increase magnitude of the second estimated anti-noise signal used for generation of the second virtual error signal;

make an adjustment so as to reduce magnitude of the estimated noise signal used for generation of the second virtual error signal;

make an adjustment so as to reduce magnitude of the first estimated anti-noise signal used for generation of the first virtual error signal; or

make an adjustment so as to increase the magnitude of the estimated noise signal used for generation of the first virtual error signal.