Patent Description:
<CIT> discloses systems and methods for detecting a divergence in an adaptive system including determining a power of a component of an error signal at a first frequency, the component being correlated to a noise-cancellation signal, the noise-cancellation signal being produced by an adaptive filter and being configured to cancel noise within a predetermined volume when transduced into acoustic signal, wherein the error signal represents a magnitude of a residual noise within the predetermined volume; determining a time gradient of the power of the component of the error signal; and comparing a metric to a threshold, wherein the metric is based, at least in part, on a value of the time gradient of the power of the component of the error signal over a period of time.

<CIT> discloses an active noise control (ANC) system configured to generate at least one anti-noise signal configured to drive a speaker to generate sound waves to destructively interfere with an undesired sound present in a target space. The at least one anti-noise signal is adjusted based an output signal of an audio system. The at least one anti-noise signal may be adjusted based on at least one of a volume level of the audio system, a power level of at least one predetermined frequency or frequency range of the output signal of the audio system, frequency content of an output signal of the audio system. The ANC system receives an error signal to adjust generation of the at least one anti-noise signal. The error signal is adjusted to compensate for adjustment of the at least one anti-noise signal based on the output signal of the audio system.

<CIT> discloses a noise cancellation system including a microphone, a transmission line that propagates the electrical signal from the microphone, a speaker that reproduces a sound wave from the electrical signal from the transmission line, a phase inversion circuit that is provided between the microphone and the speaker, and inverses the phase of the electrical signal, a gain adjustment circuit that is provided between the microphone and the speaker, and adjusts a gain for amplifying the electrical signal, and a delay adjustment circuit that is provided between the microphone and the speaker, and adjusts the amount of delay of the electrical signal.

<CIT> discloses an acoustic device with a conversation support function for clear conversation between persons.

<CIT> discloses methods and systems for active noise control in a vehicle. The system includes a position sensor for sensing an occupant position. A first controller is configured to receive an error signal corresponding to audible noise from a microphone and generate a modified error signal by modifying the error signal based on the occupant position with respect to the microphone. A second controller is configured to generate an anti-noise signal based at least in part on the modified error signal. The system also includes a loudspeaker for receiving the anti-noise signal from the second controller and producing sound corresponding to the anti-noise signal to negate at least some of the audible noise.

As an active noise control technique, as illustrated in <FIG>, an active noise control system in which sound, such as music, output from a sound source apparatus <NUM> for a user in a first area to a speaker <NUM> for the user in the first area is determined as noise for a user in a second area and a noise canceling sound that is generated by an adaptive filter <NUM> is emitted from a speaker <NUM> in the second area is disclosed in <CIT>.

In such an active noise control system, the adaptive filter <NUM> determines an output of an error microphone <NUM> located in the second area as an error and determines an output of an estimation filter <NUM> having a transfer function C^(z) set therein estimated as a transfer function C(z) from a speaker <NUM> to the error microphone <NUM> in the second area as a filtered reference signal, a coefficient update section <NUM> updates a tap coefficient of a variable filter <NUM> that generates a noise canceling sound using the output of the sound source apparatus <NUM> based on a Filtered-X LMS algorithm for performing LMS algorithm so that an error is minimized.

Consider a case where the active noise control system shown in <FIG> is applied to a system in which users in individual seats in a car listen to music using left and right speakers provided respectively for the seats and the music being listened to by the other users is cancelled as noise for the individual users.

In this case, it is preferable, for left and right ears of one of the users, that left and right error microphones located in positions of the left and right ears of the user and adaptive filters corresponding to a combination of left and right speakers of a seat of the user are provided so that music listened to by the other user can be canceled and noise canceling sounds generated by the adaptive filters corresponding to the left and right speakers are output from the left and right speakers so that noise canceling is performed for the positions of the left and right ears of the user.

However, this may increase the number of adaptive filters, resulting in an excessive scale and an excessive processing load.

Therefore, the number of adaptive filters may be reduced by combining sounds output from the left and right error microphones into a monaural sound, and sharing a noise canceling sound generated by one adaptive filter using this monaural sound as an output of a single error microphone as the noise canceling sound to be output from the left and right speakers. However, since the same noise canceling sound is output from the left and right speakers in this way, when there is a relatively large difference in a transfer function, such as a gain or a delay time from the other user's speaker, which is a noise source, to the left and right error microphones (left and right ears of the user), the noise output from the other user's speaker may not be appropriately canceled.

Therefore, an object of the present invention is to provide an active noise control system having a plurality of error microphones with a relatively simple configuration that sufficiently cancels noise even when there is a relatively large difference between transfer functions from a noise source to the individual error microphones.

The invention relates to active noise control system according to the appended claims. Embodiments are disclosed in the dependent claims.

According to an aspect of the present invention, there is provided an active noise control system that reduces noise, including a first microphone that is disposed in a position displaced in a first direction relative to a user, a second microphone that is disposed in a position displaced in a second direction relative to the user, a first speaker configured to emit sound toward an area around the position where the first microphone is disposed, a second speaker configured to emit sound toward an area around the position where the second microphone is disposed, an error signal generator configured to generate an addition signal by adding an output of the first microphone and an output of the second microphone, an adaptive filter configured to perform an adaptive operation of minimizing an error using a signal correlated with the noise as a reference signal and the addition signal as the error so as to generate a noise canceling sound to be output to the first and second speakers, and a gain adjustment section configured to adjust a ratio between a loudness level of a first noise canceling sound which is the noise canceling sound to be output to the first speaker and a loudness level of a second noise canceling sound which is the noise canceling sound to be output to the second speaker. Here, the gain adjustment section performs the adjustment so that the ratio of the loudness level of the second noise canceling sound to the loudness level of the first noise canceling sound matches a ratio of a loudness level of noise transmitted from a noise source of the noise to the second microphone to a loudness level of noise transmitted from a noise source of the noise to the first microphone.

The active noise control system may include, instead of the gain adjustment section or in addition to the gain adjustment section, a delay adjustment section configured to adjust a delay time between a first noise canceling sound which is the noise canceling sound output to the first speaker and a second noise canceling sound which is the noise canceling sound output to the second speaker. The delay adjustment section may perform the adjustment so that a delay time of the second noise canceling sound relative to the first noise canceling sound matches a delay time of noise transmitted from a noise source of noise to the second microphone relative to the noise transmitted from the noise source of the noise to the first microphone.

In the active noise control system, when one of a position near a left ear of the user and a position near a right ear of the user is determined as a first position and the other is determined as a second position, the first microphone may be disposed in the first position and the second microphone may be disposed in the second position.

In this case, when one of the left and right seats of the car is the first seat and the other is the second seat, the user may be the user seated in the first seat, and the noise may be sound output from a loudspeaker near the second seat to an occupant of the second seat.

According to the active noise control system, since the relationship between a gain and a delay time that matches the relationship between a gain and a delay time of noise from the noise source to the first microphone and the second microphone may be assigned between noise canceling sounds output from the first speaker that emits sound toward the position where the first microphone is disposed and the second speaker that emits sound toward the position where the second microphone is disposed, even when a gain of the noise or a difference between delay times is comparatively large, the noise may be appropriately canceled using the adaptive filter with an addition signal, as an error, obtained by adding the output of the first microphone to the output of the second microphone.

The following is a description of embodiments of the present invention, taking as an example an application to a system in which users in a left front seat and a right front seat of a car listen to music using left and right loudspeakers provided at the seats, respectively.

<FIG> is a diagram illustrating a configuration of an in-vehicle system according to an embodiment.

As shown in the figure, the in-vehicle system includes a left-seat sound source apparatus <NUM> which is a sound source apparatus for a user in a left front seat in a cabin, a left-seat left speaker <NUM> which is a left channel speaker for the user in the left front seat, a left-seat right speaker <NUM> which is a right channel speaker for the user in the left front seat, a left-seat left channel adder <NUM>, a left-seat right channel adder <NUM>, a left-seat left microphone <NUM>, a left-seat right microphone <NUM>, and a left-seat canceling sound generator <NUM>.

The in-vehicle system further includes a right-seat sound source apparatus <NUM> for a user in a right front seat in the cabin, a right-seat left speaker <NUM> which is a left channel speaker for the user in the right front seat, a right-seat right speaker <NUM> which is a right channel speaker for the user in the right front seat, a right-seat left channel adder <NUM>, a right-seat right channel adder <NUM>, a right-seat left microphone <NUM>, a right-seat right microphone <NUM>, and a right-seat canceling sound generator <NUM>.

As shown in embodiments according to <FIG>, the left-seat left speaker <NUM> is located on a left side of a head of the user seated in the left front seat, and the left-seat right speaker <NUM> is located on a right side of the head of the user seated in the left front seat. The left-seat left microphone <NUM> is positioned on the left side of the head of the user seated in the left front seat, and the left-seat right microphone <NUM> is positioned on the right side of the head of the user seated in the left front seat.

The right-seat left speaker <NUM> is positioned on a left side of a head of the user seated in the right front seat, and the right-seat right speaker <NUM> is located on a right side of the head of the user seated in the right front seat. The right-seat left microphone <NUM> is positioned on the left side of the head of the user seated in the right front seat, and the right-seat right microphone <NUM> is positioned on the right side of the head of the user seated in the right front seat.

Returning to <FIG>, the left-seat sound source apparatus <NUM> outputs a left channel audio LA_L and a right channel audio LA_R, such as music. The left channel audio LA_L is added, by the left-seat left channel adder <NUM>, to a left-seat left channel canceling sound LC_L output from the left-seat canceling sound generator <NUM> and is output to the left-seat left speaker <NUM>. The right channel audio LA_R is added, by the left-seat right channel adder <NUM>, to a left-seat right channel canceling sound LC_R output from the left-seat canceling sound generator <NUM> and is output to the left-seat right speaker <NUM>.

The right-seat sound source apparatus <NUM> outputs a left channel audio RA_L and a right channel audio RA_R, such as music. The left channel audio RA_L is added, by the right-seat left channel adder <NUM>, to a right-seat left channel canceling sound RC_L output from the right-seat canceling sound generator <NUM> and is output to the right-seat left speaker <NUM>. The right channel audio RA_R is added, by the right-seat right channel adder <NUM>, to a right-seat right channel canceling sound RC_R output from the right-seat canceling sound generator <NUM> and is output to the right-seat right speaker <NUM>.

Then, the left-seat canceling sound generator <NUM> determines the left channel audio RA_L and the right channel audio RA_R of the right-seat sound source apparatus <NUM> output from the right-seat left speaker <NUM> and the right-seat right speaker <NUM> as noise and generates a left-seat left channel canceling sound LC_L and a left-seat right channel canceling sound LC_R that cancel the noise transmitted from right using an output LM_L of the left-seat left microphone <NUM> and an output LM_R of the left-seat right microphone <NUM> as errors.

Furthermore, the right-seat canceling sound generator <NUM> determines the left channel audio LA_L and the right channel audio LA_R of the left-seat sound source apparatus <NUM> output from the left-seat left speaker <NUM> and the left-seat right speaker <NUM> as noise and generates a right-seat left channel canceling sound RC_L and a right-seat right channel canceling sound RC_R that cancel the noise transmitted from left using an output RM_L of the right-seat left microphone <NUM> and an output RM_R of the right-seat right microphone <NUM> as errors.

The left-seat canceling sound generator <NUM> will be described below.

<FIG> is a diagram illustrating an embodiment of a configuration of a left-seat canceling sound generator <NUM>.

As shown in <FIG>, the left-seat canceling sound generator <NUM> includes a reference signal adder <NUM> that generates a reference signal R by adding the left channel audio RA_L and the right channel audio RA_R of the right-seat sound source apparatus <NUM>, an error adder <NUM> that generates an error signal E by adding the output LM_L of the left-seat left microphone <NUM> and the output LM_R of the left-seat right microphone <NUM>, an adaptive filter <NUM> that generates a noise canceling sound LC using the reference signal R by performing an adaptive operation using the reference signal R and the error signal E, a left channel gain adjustment section <NUM>, a left channel delay section <NUM>, a right channel gain adjustment section <NUM>, and a right channel delay section <NUM>.

The adaptive filter <NUM> includes an estimation filter <NUM> in which a transfer function C^(z) estimated as a transfer function C(z) from an output of the adaptive filter <NUM> to an output of the error adder <NUM>, a coefficient updating section <NUM>, and a variable filter <NUM>.

The reference signal R output from the reference signal adder <NUM> serves as an input of the estimation filter <NUM> and the variable filter <NUM>, and the coefficient updating section <NUM> updates a tap coefficient of the variable filter <NUM> such that power of the error signal E output from the error adder <NUM> is minimized by the Filtered-X LMS algorithm that performs the LMS algorithm using an output of the estimation filter <NUM> as a filtered reference signal to update a transfer function W(z) of the variable filter <NUM>.

An output of the variable filter <NUM> is then output from the adaptive filter <NUM> as noise canceling sound LC.

The noise canceling sound LC output from the variable filter <NUM> is adjusted in a loudness level by a preset gain G_L in the left channel gain adjustment section <NUM>, delayed by a preset delay time Z_L in the left channel delay section <NUM>, and thereafter, output as a left-seat left channel canceling sound LC_L to the left-seat left speaker <NUM> via the left-seat left channel adder <NUM>.

The noise canceling sound LC output from the variable filter <NUM> is adjusted in a loudness level by a preset gain G_R in the right channel gain adjustment section <NUM>, delayed by a preset delay time Z_R in the right channel delay section <NUM>, and thereafter, output as a left-seat right channel canceling sound LC_R to the left-seat right speaker <NUM> via the left-seat right channel adder <NUM>.

Here, the gain G_L of the left channel gain adjustment section <NUM> and the gain G_R of the right channel gain adjustment section <NUM> are set such that a ratio G_L/G_R between the gains matches a ratio M_L/M_R between a loudness level M_L of the noise transmitted from the noise source to the output LM_L of the left-seat left microphone <NUM> and a loudness level M_R of the noise transmitted from the noise source to the output LM_R of the left-seat right microphone <NUM>.

The delay time Z_L of the left channel delay section <NUM> and the delay time Z_R of the right channel delay section <NUM> are set such that a difference Z_L-Z_R in delay time matches a difference d_L-d_R between a delay time d_L of the noise from the noise source to the output LM_L of the left-seat left microphone <NUM> and a delay time d_R of the noise from the noise source to the output LM_R of the left-seat right microphone <NUM>.

Here, since the noise sources of noise to be canceled by the left-seat canceling sound generator <NUM> are the right-seat left speaker <NUM> and the right-seat right speaker <NUM>, the gain G_L of the left channel gain adjustment section <NUM>, the gain G_R of the right channel gain adjustment section <NUM>, the delay time Z_L of the left channel delay section <NUM>, and the delay time Z_R of the right channel delay section <NUM> may be set in advance, for example, as follows.

Specifically, a test sound is output from both the right-seat left speaker <NUM> and the right-seat right speaker <NUM> or from a measurement speaker installed in a center position between the right-seat left speaker <NUM> and the right-seat right speaker <NUM>.

A loudness level M_L of the output test sound transmitted to the output LM_L of the left-seat left microphone <NUM> and a loudness level M_R of the output test sound transmitted of the output LM_R of the left-seat right microphone <NUM> are then determined, and the gain G_L of the left channel gain adjustment section <NUM> and the gain G_R of the right channel gain adjustment section <NUM> are set such that the obtained ratio M_L/M_R matches the ratio G_L/G_R.

Furthermore, a difference d_L-d_R between a delay time to the output LM_L of the left-seat left microphone <NUM> and a delay time to the output LM_R of the left-seat right microphone <NUM> is obtained and the delay time Z_L of the left channel delay section <NUM> and the delay time Z_R of the right channel delay section <NUM> are set such that the difference Z_L-Z_R matches the obtained difference d_L-d_R.

More specifically, for example, when waveforms of the output LM_L of the left-seat left microphone <NUM> and the output LM_R of the left-seat right microphone <NUM> obtained for the output test sound are those shown in <FIG>, assuming that a loudness level of a peak that first appears in the output LM_L of the left-seat left microphone <NUM> is M_L and a loudness level of a peak that first appears in the output LM_R of the right-seat left microphone <NUM> is M_R, the gain G_L of the left channel gain adjustment section <NUM> and the gain G_R of the right channel gain adjustment section <NUM> are set such that the ratio G_L/G_R matches the ratio M_L/M_R.

Furthermore, a delay of the peak that first appears in the output LM_R of the right-seat left microphone <NUM> with respect to the peak that first appears in the output LM_L of the left-seat left microphone <NUM> is determined as d_L-d_R, and the delay time Z_L of the left channel delay section <NUM> and the delay time Z_R of the right channel delay section <NUM> are set such that the difference d_L-d_R matches the difference Z_L-Z_R.

Here, when d_L-d_R is positive, Z_L=d_L-d_R and Z_R=<NUM> may be satisfied. Furthermore, in this case, the right channel delay section <NUM> may be omitted. Moreover, when d_L-d_R is negative, Z_L=<NUM> and Z_R=-(d_L-d_R) may be satisfied. Furthermore, in this case, the left channel delay section <NUM> may be omitted.

According to the left-seat canceling sound generator <NUM> described herein, since the relationship between gains or delay times that matches the relationship between gains or delay times of noise from the noise source to the output LM_L of the left-seat left microphone <NUM> and the output LM_R of the left-seat right microphone <NUM> may be assigned between the left-seat left channel canceling sound LC_L output from the left-seat left speaker <NUM> and the left-seat right channel canceling sound LC_R output from the left-seat right speaker <NUM>, even when a gain of the noise or a difference between delay times is comparatively large, the noise may be appropriately canceled using the adaptive filter <NUM> with an addition signal, as an error, obtained by adding the output LM_L of the left-seat left microphone <NUM> to the output LM_R of the left-seat right microphone <NUM>.

Next, a right-seat canceling sound generator <NUM> has a configuration in which the left seat and the right seat are replaced with each other in the above description of the left-seat canceling sound generator <NUM>.

Claim 1:
An active noise control system that is configured to reduce noise, the active noise control system comprising:
a first microphone (<NUM>, <NUM>) that is disposed in a position displaced in a first direction relative to a user;
a second microphone (<NUM>, <NUM>) that is disposed in a position displaced in a second direction relative to the user;
a first speaker (<NUM>, <NUM>) configured to emit sound toward an area around the position where the first microphone is disposed;
a second speaker (<NUM>, <NUM>) configured to emit sound toward an area around the position where the second microphone is disposed;
an error signal generator (<NUM>, <NUM>) configured to generate an addition signal (E) by adding an output (LM_L) of the first microphone (<NUM>, <NUM>) and an output (LM_R) of the second microphone (<NUM>, <NUM>);
an adaptive filter (<NUM>) configured to perform an adaptive operation of minimizing an error using a signal correlated with a noise as a reference signal (R) and the addition signal (E) as the error so as to generate a noise canceling sound (LC) to be output to the first and second speakers; and characterized in that the system comprises
a gain adjustment section (<NUM>, <NUM>) configured to adjust a ratio between a loudness level of a first noise canceling sound (LC_L) which is the noise canceling sound to be output to the first speaker (<NUM>) and a loudness level of a second noise canceling sound (LC_R) which is the noise canceling sound to be output to the second speaker (<NUM>), wherein
the gain adjustment section (<NUM>, <NUM>) performs the adjustment such that the ratio of the loudness level of the second noise canceling sound (LC_R) to the loudness level of the first noise canceling sound (LC_L) matches a ratio of a loudness level (M_R) of noise transmitted from a noise source (<NUM>, <NUM>) of the noise to the second microphone (<NUM>) to a loudness level (M_L) of noise transmitted from the noise source (<NUM>, <NUM>) of the noise to
the first microphone (<NUM>).