Active noise control system and on-vehicle audio system

1. An on-vehicle audio system mounted in a vehicle, comprising:

an active noise control device for reducing noise, comprising:

a speaker configured to output a cancellation sound which cancels noise at a predetermined noise cancel position;

a microphone configured to pick-up a synthetic sound of the noise with the cancellation sound and to output the picked up synthetic sound as an error signal; and

a cancellation sound generation unit configured to generate the cancellation sound output from the speaker,

wherein the cancellation sound generation unit includes:

an adaptive filter configured to use, as an input, a noise signal which is a signal indicating noise which a noise source of the noise generates;

a first filter configured to use an output of the adaptive filter as an input and to output the cancellation sound; and

a second filter configured to use the output of the adaptive filter as an input,

wherein the adaptive filter is configured to update a transfer function for the adaptive filter by a predetermined adaptive algorithm using a difference between an output of the microphone and an output of the second filter as an error,

wherein a transfer function for the first filter is set in the first filter, and the transfer function for the first filter is set so that the noise at the noise cancellation position is canceled when the cancellation sound generation unit generates, as the cancellation sound, a sound which is obtained by applying the transfer function for the first filter to the noise signal in a predetermined standard state, and

wherein a transfer function for the second filter is set in the second filter, and the transfer function for the second filter is set so that the error is an output of a virtual microphone disposed at the noise cancellation position when the transfer function for the adaptive filter is a transfer function which sets, as an output, an input as it is in the predetermined standard state; and

an audio device for a user who sits in a first seat of the vehicle, the audio device configured to emit audio into the vehicle,

wherein:

the noise is the audio which is emitted from the audio device,

the noise signal is an audio signal output from a sound source of the audio device,

the noise cancellation position is a position of an ear of a user who sits in a second seat of the vehicle, and

the microphone is disposed near the position of the ear of the user who sits in the second seat.

2. An active noise control device reducing noise, comprising:

a speaker configured to output a cancellation sound which cancels noise at a predetermined noise cancel position;

a microphone configured to pick-up a synthetic sound of the noise with the cancellation sound and to output the picked-up synthetic sound as an error signal; and

a cancellation sound generation unit configured to generate the cancellation sound output from the speaker,

wherein the cancellation sound generation unit includes:

an adaptive filter configured to use, as an input, a noise signal which is a signal indicating noise which a noise source of the noise generates;

a first filter configured to use an output of the adaptive filter as an input and output the cancellation sound; and

a second filter configured to use the output of the adaptive filter as an input,

wherein the adaptive filter is configured to update a transfer function of the adaptive filter by a predetermined adaptive algorithm using a difference between an output of the microphone and an output of the second filter as an error,

wherein a transfer function for the first filter learned by a predetermined learning processing is set in the first filter and a transfer function for the second filter learned by the learning processing is set in the second filter,

wherein the transfer function for the first filter is:

− V ( z )/ Sv ( z )

 where V(z) is set as a transfer function from the noise source to the noise cancellation position and Sv(z) is set as a transfer function from the cancellation sound generation unit to the noise cancellation position at a time when the learning processing is executed, and

wherein the transfer function for the second filter is:

P ( z ){ V ( z )/ Sv ( z )} S ( z )

 where P(z) is set as a transfer function from the noise source to the microphone and S(z) is set as a transfer function from the cancellation sound generation unit to the microphone at a time when the learning processing is executed.

3. The active noise control device according to claim 2 , further comprising:

a learning processing execution unit configured to perform the learning processing to set the transfer function for the first filter in the first filter and the transfer function for the second filter in the second filter.

4. An on-vehicle audio system mounted in a vehicle and including the active noise control device according to claim 3 , the on-vehicle audio system comprising:

an audio device for a user who sits in a first seat of the vehicle, where the audio device is configured to emit audio into the vehicle,

wherein:

the noise is audio which is emitted from the audio device,

the noise signal is an audio signal output from a sound source of the audio device,

the noise cancellation position is a position of an ear of a user who sits in a second seat of the vehicle, and

the microphone is disposed near the position of the ear of the user who sits in the second seat.

5. An active noise control device reducing noise, comprising:

a speaker configured to output a cancellation sound which cancels noise at a predetermined noise cancel position;

a microphone configured to pick-up a synthetic sound of the noise with the cancellation sound and to output the picked-up synthetic sound as an error signal; and

a cancellation sound generation unit configured to generate the cancellation sound output from the speaker,

wherein the cancellation sound generation unit includes:

an adaptive filter configured to use, as an input, a noise signal which is a signal indicating noise which a noise source of the noise generates;

a first filter configured to use an output of the adaptive filter as an input and to output the cancellation sound; and

a second filter configured to use the output of the adaptive filter as an input,

wherein the adaptive filter is configured to update the transfer function of the adaptive filter by a predetermined adaptive algorithm using a difference between an output of the microphone and an output of the second filter as an error,

wherein a transfer function for the first filter learned by a predetermined learning processing is set in the first filter and a transfer function for the second filter learned by the learning processing is set in the second filter, and

wherein the learning processing comprises:

learning, as the transfer function for the first filter, a first transfer function of which the noise at the noise cancellation position is canceled in the configuration in which the cancellation sound generation unit is replaced with a first learning unit configured to generate, as the cancellation sound, a sound obtained by applying the first transfer function to the noise signal, and

learning, as the transfer function for the second filter, a second transfer function without the difference between the output of the microphone and the sound obtained by applying the second transfer function to the noise signal in the configuration in which the cancellation sound generation unit is replaced with the second learning unit configured to generate, as the cancellation sound, the sound obtained by applying the transfer function for the first filter to the noise signal.

6. The active noise control device according to claim 5 , further comprising:

a learning processing execution unit configured to perform the learning processing to set the transfer function for the first filter in the first filter and to set the transfer function for the second filter in the second filter.

7. An on-vehicle audio system mounted in a vehicle and including the active noise control device according to claim 6 , the on-vehicle audio system comprising:

an audio device for a user who sits in a first seat of the vehicle, where the audio device is configured to emit audio into the vehicle,

wherein the noise is audio which is emitted from the audio device,

wherein the noise signal is an audio signal output from a sound source of the audio device,

wherein the noise cancellation position is a position of an ear of a user who sits in a second seat of the vehicle, and

wherein the microphone is disposed near the position of the ear of the user who sits in the second seat.