Active noise reduction device, movable body device, and active noise reduction method

Abstract

To provide an active noise reduction device that can shorten a delay concerning output of a correlation sound.SOLUTION: An active noise reduction device 10 includes: a first signal processor 11 that applies an adaptive filter to a reference signal having a correlation with noise in a space in a vehicle 50 to generate a cancellation signal for outputting a cancellation sound for reducing noise; a second signal processor 12 that updates a coefficient of the adaptive filter; and a sample rate converter 17. The first signal processor 11 operates in a cycle T1. The second signal processor 12 operates in a cycle T2 longer than the cycle T1. The sample rate converter 17 upsamples the coefficient of the adaptive filter updated by the second signal processor 12 for output to the first signal processor 11. The cycle T1 is longer than a difference between the maximum value and the minimum value of a processing time required until the second signal processor updates the coefficient of the adaptive filter after acquiring the reference signal.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to an active noise reduction device that actively reduces noise by interfering with a cancellation sound. [Background technology]

[0002] Conventionally, active noise reduction devices have been known that actively reduce noise by outputting a cancellation sound from a cancellation sound source to cancel out the noise using a reference signal that has a correlation with the noise and an error signal that is based on residual sound resulting from interference between the noise and the cancellation sound in a specified space (see, for example, Patent Documents 1 to 3). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2014 / 006846 [Patent Document 2] Japanese Patent Publication No. 2022-108195 [Patent Document 3] Japanese Patent Publication No. 2020-64101 Summary of the Invention [Problem to be solved by the invention]

[0004] The present disclosure provides an active noise reduction device that can reduce the delay associated with outputting a cancellation sound. [Means for solving the problem]

[0005] An active noise reduction device according to one aspect of the present disclosure includes a first signal processing unit that generates a cancellation signal for outputting a cancellation sound to reduce noise by applying an adaptive filter to a reference signal that has a correlation with noise in a space within a mobile device; a second signal processing unit that updates coefficients of the adaptive filter based on a filtered reference signal obtained by correcting the reference signal with a simulated transfer characteristic that simulates the acoustic transfer characteristic from a position of a cancellation sound source that outputs the cancellation sound to a position of an error signal source, and an error signal that is obtained from the error signal source and indicates the state of the noise when the cancellation sound is being output; and a sample rate conversion unit, wherein the first signal processing unit operates in a period T1 and the second signal processing unit operates in a period T2 that is longer than the period T1, and the sample rate conversion unit upsamples the coefficients of the adaptive filter updated by the second signal processing unit and outputs the upsampled coefficients to the first signal processing unit, and the period T1 is longer than the difference between the maximum and minimum values ​​of the processing time required for the second signal processing unit to update the coefficients of the adaptive filter after acquiring the reference signal. [Effects of the Invention]

[0006] An active noise reduction device according to one aspect of the present disclosure can reduce the delay associated with outputting a cancellation sound. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a diagram showing the functional configuration of an active noise reduction device according to an embodiment. [Figure 2] FIG. 2 is a flowchart of the operation of the active noise reduction device according to the embodiment. [Figure 3] FIG. 3 is a first diagram for explaining a delay that occurs in an active noise reduction device according to a comparative example. [Figure 4] FIG. 4 is a second diagram for explaining the delay that occurs in the active noise reduction device according to the comparative example. [Figure 5A] FIG. 5A is a first diagram for explaining a delay that occurs in the active noise reduction device according to the embodiment. [Figure 5B] FIG. 5B is a second diagram for explaining the delay that occurs in the active noise reduction device according to the embodiment. [Figure 6] FIG. 6 is a diagram showing an example of setting the characteristics of the LPF. [Figure 7] FIG. 7 is a diagram showing the functional configuration of an active noise reduction device when the coefficients of the adaptive filter are corrected. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, the embodiments will be described in detail with reference to the drawings. Note that the embodiments described below are all comprehensive or specific examples. The numerical values, shapes, materials, components, component placement and connection forms, steps, and step order shown in the following embodiments are merely examples and are not intended to limit the present disclosure. Furthermore, among the components in the following embodiments, components not recited in independent claims will be described as optional components.

[0009] Furthermore, each drawing is a schematic diagram and is not necessarily an exact illustration. In each drawing, substantially the same components are denoted by the same reference numerals, and duplicated explanations may be omitted or simplified.

[0010] (Embodiment) [composition] The configuration of an active noise reduction device according to an embodiment will be described below. Fig. 1 is a diagram showing the functional configuration of an active noise reduction device according to an embodiment. As shown in Fig. 1, a vehicle 50 includes a reference signal source 51, a cancellation sound source 52, a plurality of error signal sources 53, and an active noise reduction device 10.

[0011] The reference signal source 51 is a transducer that outputs a reference signal that has a correlation with noise in the space within the vehicle 50. The reference signal source 51 is, for example, an acceleration sensor, and is arranged outside the space within the vehicle 50. Specifically, the reference signal source 51 is attached to a subframe, a wheel well, or the like. The location where the reference signal source 51 is attached is not particularly limited. When the reference signal source 51 is an acceleration sensor, the active noise reduction device 40 can reduce the road noise component contained in the noise in the space within the vehicle 50. Because road noise has a complex propagation path, a configuration in which acceleration sensors are arranged at multiple locations is useful. The reference signal source 51 may also be a microphone.

[0012] The cancellation sound source 52 uses the cancellation signal to output a cancellation sound into the space within the vehicle 50. In the embodiment, the cancellation sound source 52 is a speaker, but the cancellation sound may also be output by vibrating a part of the structure of the vehicle 50 (for example, a sunroof) using a drive mechanism such as an actuator. Furthermore, a plurality of cancellation sound sources 52 may be installed within the vehicle 50. The installation position of the cancellation sound source 52 is not particularly limited.

[0013] The error signal source 53 detects residual sound obtained by interference between the noise and the cancellation sound in the space within the vehicle 50, and outputs an error signal based on the residual sound. The error signal source 53 is a transducer such as a microphone, and is preferably installed in a space within the vehicle 50, such as in the headliner. In the example of FIG. 1, two error signal sources 53 are installed within the vehicle 50, but it is sufficient that at least one error signal source 53 is installed within the vehicle 50.

[0014] Error signal source 53 is installed, for example, in a seat inside vehicle 50. If one of the two error signal sources 53 is installed in the driver's seat and the other is installed in the rear seat, the amount of noise reduction for the user sitting in the driver's seat and the amount of noise reduction for the users sitting in the rear seat can be adjusted separately.

[0015] The active noise reduction device 10 performs signal processing on a reference signal obtained from a reference signal source 51 to generate a cancellation signal for outputting a cancellation sound from a cancellation sound source 52. The cancellation sound is a sound for reducing noise in the space inside the vehicle 50. The active noise reduction device 10 is realized, for example, by a processor such as a DSP (Digital Signal Processor) or a microcomputer executing a computer program (software) stored in a storage unit (not shown).

[0016] Specifically, the active noise reduction device 10 includes a first signal processing unit 11, a second signal processing unit 12, LPFs (Low Pass Filters) 13-15, 16a, and 16b, and a sample rate conversion unit 17. The first signal processing unit 11 performs a process of applying an adaptive filter (corresponding to "ADF" in the upper part of FIG. 1), and the second signal processing unit 12 performs a process of generating a filtered reference signal (corresponding to C^ in FIG. 1) and a process of updating the filter coefficients of the adaptive filter (corresponding to "LMS" and "ADF" in the lower part of FIG. 1). The sample rate conversion unit 17 converts the sample rate (corresponding to "SRC" in FIG. 1).

[0017] Although not shown, the active noise reduction device 10 is equipped with an AD (Analog to Digital) converter that converts the reference signal output by the reference signal source 51 from an analog signal to a digital signal, a DA (Digital to Analog) converter that converts the cancellation signal output by the first signal processing unit 11 from a digital signal to an analog signal, and an AD converter that converts the error signal output by the error signal source 53 from an analog signal to a digital signal. In a configuration in which the reference signal and error signal are input to the active noise reduction device 10 via digital communication, and in a configuration in which the cancellation signal is output to an external device, it is not necessarily necessary to provide these converters.

[0018] [Operation] The operation of the active noise reduction device 10 will be described below with reference to Fig. 2 in addition to Fig. 1. Fig. 2 is a flowchart of the operation of the active noise reduction device 10. Note that the following explanation will mainly focus on the case where there is one error signal source 53, with a supplementary explanation of the case where there are multiple error signal sources 53.

[0019] First, a reference signal having a correlation with noise is input from reference signal source 51 to active noise reduction device 10 (S11).

[0020] The reference signal input to the active noise reduction device 10 is passed through an LPF 13 and then output to a first signal processing unit 11. The reference signal input to the active noise reduction device 10 is passed through an LPF 14 and then output to a second signal processing unit 12.

[0021] The first signal processing unit 11 applies (convolves) an adaptive filter to the reference signal to which the LPF 11 has been applied, thereby generating a cancellation signal (S12). The first signal processing unit 11 is realized by a so-called FIR filter or IIR filter. The cancellation signal generated by the first signal processing unit 11 is applied to the LPF 15, and then output to the cancellation sound source 52 (S13). The cancellation sound source 52 outputs a cancellation sound based on the cancellation signal.

[0022] Error signal source 53 detects residual sound resulting from interference between the cancellation sound output from cancellation sound source 52 and noise, and outputs an error signal corresponding to the residual sound. In other words, the error signal is a signal that indicates the state of noise in the space within vehicle 50 when the cancellation sound is being output. As a result, the error signal is input to active noise reduction device 10 (S14).

[0023] The error signal input to the active noise reduction device 10 is passed through the LPF 16a (or LPF 16b) and then output to the second signal processing unit 12.

[0024] The second signal processing unit 12 generates a filtered reference signal by correcting the reference signal with a simulated transfer characteristic that simulates the acoustic transfer characteristic from the position of the cancellation sound source 52 to the position of the error signal source 53 (i.e., the acoustic transfer characteristic in the space inside the vehicle 50) (S15). The simulated transfer characteristic is, for example, actually measured in advance in the space inside the vehicle 50 and stored in a storage unit (not shown) provided in the active noise reduction device 10. Note that the simulated transfer characteristic may be determined by an algorithm that does not use a predetermined value.

[0025] The second signal processing unit 12 sequentially updates the coefficient W of the adaptive filter based on the error signal to which the LPF 16a (or LPF 16b) has been applied and the generated filtered reference signal (S16).

[0026] Specifically, the second signal processing unit 12 uses the LMS (Least Mean Square) method to calculate the coefficients of the adaptive filter so as to minimize the sum of squares of the error signal, and outputs the calculated coefficients of the adaptive filter to the first signal processing unit 11. The second signal processing unit 12 also sequentially updates the coefficients of the adaptive filter. If the error signal is e and the vector of the filtered reference signal is R, the coefficient W of the adaptive filter is expressed by the following (Equation 1). Note that n is a natural number and represents the nth sample in the sampling period Ts. μ is a scalar quantity and a step size parameter that determines the amount of update of the coefficient W of the adaptive filter per sampling.

[0027]

number

[0028] In addition, when two error signal sources 53 are provided in the vehicle 50, two filtered reference signals corresponding to the two error signal sources 53 are used as R 000 , R 001 , the two error signal vectors are e´0 and e´1, and the step size parameter is μ 000 , μ 001 As a result, the coefficients of the adaptive filter W 00is expressed by the following (Equation 2). Note that the coefficient W of the adaptive filter when considering the leak coefficient α is 00 is expressed by the following (Equation 3).

[0029]

number

[0030] As described above, the active noise reduction device 10 can generate a cancellation signal by applying an adaptive filter, the coefficients of which are updated based on the error signal, to the reference signal.

[0031] [Delay Occurring in the Active Noise Reduction Device According to the Comparative Example] In the active noise reduction device 10, the first signal processing unit 11 operates at a sampling period T1, the second signal processing unit 12 operates at a sampling period T2 that is longer than the sampling period T1, and the sample rate conversion unit 17 upsamples the coefficients of the adaptive filter updated by the second signal processing unit 12 and outputs the upsampled coefficients to the first signal processing unit 11. This makes it possible to reduce the delay (latency) that occurs in the active noise reduction device 10.

[0032] First, we will explain the delay that occurs in an active noise reduction device according to a comparative example, which does not perform processing by dividing the sampling period like the active noise reduction device 10. FIG. 3 is a first diagram for explaining the delay that occurs in the active noise reduction device according to the comparative example. In the following explanation of FIG. 3, as an example, the active noise reduction device 10 operates in a periodic process based on an interrupt due to AD conversion, but the type of interrupt, such as an interrupt due to TDM transfer, is not important. Here, the interrupt frequency is assumed to be FS_B=48 kHz. In the explanation, it is assumed that the reference signal input to the active noise reduction device 10 is converted into a digital signal with a sampling period TAD=20.83 μs (sampling frequency FsAD=48 kHz), and the cancellation signal is converted into an analog signal with a sampling period TDA=20.83 μs (sampling frequency FsDA=48 kHz). The hatching in FIG. 3 indicates the correspondence between the reference signal used in a certain noise reduction operation and the cancellation signal output by that noise reduction operation.

[0033] In the example of Fig. 3, the active noise reduction device of the comparative example acquires an AD-converted reference signal at timing t0, generates a filtered reference signal, and updates the filter coefficients. The active noise reduction device also convolves an adaptive filter (filter coefficients) with the AD-converted reference signal at timing t0 to update the cancellation signal. As soon as the cancellation signal has been updated, at the following DA conversion timing t1, the cancellation signal is converted into an analog signal and output. Note that in the example of Fig. 3, the sampling frequency Fs1, which corresponds to the cycle for acquiring the reference signal, is fixed at 3 kHz.

[0034] The processing time from when the reference signal is acquired until the cancellation signal is output is not constant and varies. If the processing time lag is longer than the timing of the DA conversion, the output timing of the cancellation signal will be off from the input reference signal. The output timing of the cancellation signal can sometimes be off by several DA conversions. If the delay time changes with each processing, the acoustic transfer characteristics will change from the simulated transfer characteristics measured in advance, resulting in a decrease in the amount of noise reduction and a decrease in the stability of the noise reduction operation.

[0035] Fig. 4 is a second diagram for explaining the delay that occurs in an active noise reduction device according to a comparative example. In the example of Fig. 4, the cancellation signal is updated immediately after an interrupt. This suppresses deviations in the output timing of the cancellation signal. In other words, compared to the example of Fig. 3, it is possible to suppress a decrease in the amount of noise reduction and a decrease in the stability of the noise reduction operation, but because the cancellation sound is output in the next cycle after the reference signal is acquired, a delay of T1 = 333.3 μs (= 1 / Fs1) inevitably occurs.

[0036] [Delay Occurring in the Active Noise Reduction Device According to the Embodiment] Figure 5A is a diagram illustrating delays that occur in active noise reduction device 10. In the following explanation of Figure 5A, it is assumed that the reference signal input to active noise reduction device 10 is converted into a digital signal with a sampling period TAD = 20.83 μs (sampling frequency FsAD = 48 kHz), and the cancellation signal is converted into an analog signal with a sampling period TDA = 20.83 μs (sampling frequency FsDA = 48 kHz). The hatching in Figure 5A indicates the correspondence between the reference signal used in a certain noise reduction operation and the cancellation signal output by that noise reduction operation.

[0037] In FIG. 5A, the first signal processing unit 11 operates at a sampling period T1=83.3 μs (sampling frequency Fs1=12 kHz), and the second signal processing unit 12 operates at a sampling period T2=333.3 μs (sampling frequency Fs2=3 kHz) that is longer than the sampling period T1.

[0038] The second signal processing unit 12 acquires the AD converted reference signal at timing t(n), generates a filtered reference signal from the acquired reference signal, and updates the filter coefficients. The sample rate conversion unit 17 upsamples the updated filter coefficients to update the filter coefficients of the first signal processing unit 11. The update of the filter coefficients of the first signal processing unit 11 ends, for example, at timing t_update(m), which is later than timing t(n+1) and earlier than timing t(n+2).

[0039] Meanwhile, the first signal processing unit 11 acquires a reference signal at the timing of AD conversion immediately after the completion of the update process of the cancellation signal that started at timing t(n). The first signal processing unit 11 convolves the acquired reference signal with an adaptive filter (filter coefficients) updated at t_update(m-1) (not shown) before timing t(n), and starts the update process of the cancellation signal at timing t(n+1). The first signal processing unit 11 outputs the updated cancellation signal at the timing of DA conversion immediately after the update process has finished.

[0040] Furthermore, the first signal processing unit 11 acquires the AD converted reference signal at timing t(n+1), convolves the acquired reference signal with the adaptive filter (filter coefficient) updated at t_update(m), and starts updating the cancellation signal at timing t(n+2) (not shown). The first signal processing unit 11 outputs the updated cancellation signal at the timing of DA conversion immediately after the update process is completed.

[0041] Furthermore, the first signal processing unit 11 acquires the AD converted reference signal at timing t(n+2), convolves the adaptive filter (filter coefficient) updated at t_update(m) with the acquired reference signal, and starts updating the cancellation signal at timing t(n+3) (not shown). The first signal processing unit 11 outputs the updated cancellation signal at the timing of DA conversion immediately after the update process is completed.

[0042] The first signal processing unit 11 also acquires the AD converted reference signal at timing t(n+3), convolves the adaptive filter (filter coefficients) updated at t_update(m) with the acquired reference signal, and starts updating the cancellation signal at timing t(n+4). The first signal processing unit 11 outputs the updated cancellation signal at the timing of DA conversion immediately after the update process is completed.

[0043] The first signal processing unit 11 also acquires the AD converted reference signal at timing t(n+4), convolves the adaptive filter (filter coefficients) updated at t_update(m) with the acquired reference signal, and starts updating the cancellation signal at timing t(n+5). The first signal processing unit 11 outputs the updated cancellation signal at the timing of DA conversion immediately after the update process is completed.

[0044] On the other hand, the second signal processing unit 12 acquires the AD converted reference signal at timing t(n+4) after t_update(m), generates a filtered reference signal from the acquired reference signal, and updates the filter coefficients. Furthermore, the sample rate conversion unit 17 upsamples the updated filter coefficients to update the filter coefficients of the first signal processing unit 11.

[0045] Thus, in active noise reduction device 10, first signal processing unit 11 updates the cancellation signal four times while second signal processing unit 12 updates the filter coefficient once. The delay from when the reference signal is acquired until the cancellation sound is output is T1 = 83.3 μs (= 1 / 12 kHz), which is shorter than the 333.3 μs that occurs in the example of Fig. 4. In other words, active noise reduction device 10 can reduce the delay from when the reference signal is acquired until the cancellation sound is output (the delay related to the output of the cancellation sound).

[0046] As described above, the sampling periods T1 and T2 are merely examples. In the active noise reduction device 10, the first signal processing unit 11 may update the cancellation signal k times (k is an integer equal to or greater than 2) while the second signal processing unit 12 updates the filter coefficient once.

[0047] 5A shows an example of the processing timing of the first signal processing unit and the second signal processing unit when a multi-core processor is applied to the active noise reduction device 10, but a single-core processor may also be applied to the active noise reduction device 10. FIG. 5B is a diagram showing an example of the processing timing when a single-core processor is applied to the active noise reduction device 10.

[0048] 5A, the signal processing of the first signal processing unit 11 and the signal processing of the second signal processing unit 12 and sample rate conversion unit 17 are executed in parallel. In contrast to this, in Fig. 5B, when the signal processing of the first signal processing unit 11 is called during the signal processing of the second signal processing unit 12, the signal processing of the second signal processing unit 12 is interrupted and the signal processing of the first signal processing unit 11 is executed, and after the signal processing of the first signal processing unit 11 is completed, the continuation of the signal processing of the second signal processing unit 12 begins.

[0049] In the example of Fig. 5B, while the second signal processing unit 12 updates the filter coefficient once, the first signal processing unit 11 updates the cancellation signal four times. The delay from when the reference signal is acquired to when the cancellation sound is output is T1 = 83.3 μs (= 1 / 12 kHz), which is shorter than the 333.3 μs that occurs in the example of Fig. 4. In other words, the active noise reduction device 10 to which a single-core processor is applied can also reduce the delay from when the reference signal is acquired to when the cancellation sound is output (the delay related to the output of the cancellation sound).

[0050] [Example of setting the sampling period T1] When the active noise reduction device 10 has multiple operation modes, such as an operation mode that focuses on the seat position to perform noise reduction operation and a fail-safe operation mode, the time from acquiring the reference signal to updating the adaptive filter (hereinafter also referred to as processing time) performed by the second signal processing unit 12 can vary significantly. For example, if the number of adaptive filters varies for each operation mode, the processing time can vary significantly.

[0051] Furthermore, in an operating mode in which a relatively large amount of processing is added, such as performing additional calculations when a predetermined condition is met, the processing time significantly increases or decreases depending on whether or not the predetermined condition is met. For example, in the active noise reduction device described in JP 2020-64101 A, a compressor performs compression processing when a reference signal having an amplitude equal to or greater than a threshold is input, but the processing time significantly increases or decreases depending on whether or not the compressor performs compression processing.

[0052] Therefore, the sampling period T1 of the first signal processing unit 11 is set to, for example, a time longer than the difference between the maximum and minimum values ​​of the processing time required for updating the coefficients of the adaptive filter after the second signal processing unit 12 acquires the reference signal. The maximum and minimum values ​​here refer to the maximum and minimum values ​​when the update process is performed steadily, excluding extreme cases where the update process is essentially stopped. Note that the maximum and minimum values ​​may be the maximum and minimum values ​​specified.

[0053] As a result, even if the processing time increases or decreases, the increase or decrease (variation) in the processing time can be absorbed by the length of the sampling period T1, so the delay occurring in the active noise reduction device 10 can be kept constant.

[0054] Furthermore, the sampling period T1 of the first signal processing unit 11 may be set to a time longer than a predetermined time determined by the variation in the processing time required for the second signal processing unit 12 to update the coefficients of the adaptive filter after acquiring the reference signal. The variation here refers to the variation when the update process is performed steadily, excluding extreme cases where the update process essentially stops. The predetermined time determined by the variation is expressed, for example, as the standard deviation of the processing time multiplied by N, where N is a natural number such as 1, 2, or 3, but may be any positive number.

[0055] As a result, even if the processing time increases or decreases, the increase or decrease (variation) in the processing time can be absorbed by the length of the sampling period T1, so the delay occurring in the active noise reduction device 10 can be kept constant.

[0056] [LPF characteristic setting example] An example of setting the characteristics of LPFs 13 to 15 will be described. Fig. 6 is a diagram showing an example of setting the characteristics of LPFs 13 to 15. As described above, LPF 13 is an LPF applied to the reference signal input to first signal processing unit 11, and LPF 14 is an LPF applied to the reference signal input to second signal processing unit 12. LPF 15 is an LPF applied to the cancellation signal output from first signal processing unit 11.

[0057] In the setting example 1 shown in FIG. 6, the second LPF is used for the LPF 13 and the LPF 14, and the first LPF is used for the LPF 15.

[0058] Here, the first LPF is an LPF that can obtain a sufficiently large amount of attenuation at the Nyquist frequency (sampling frequency × 2) of the first signal processing unit 11. In other words, the first LPF is an LPF that can obtain an amount of attenuation equal to or less than a predetermined value at a frequency of 1 / (2 × T1), where T1 is the sampling period of the first signal processing unit 11. An amount of attenuation equal to or less than a predetermined value is, for example, an amount of attenuation equal to or less than −60 dB (such as −80 dB) based on the gain of the passband. There are no particular limitations on the filter order of the first LPF.

[0059] The second LPF is an LPF that can obtain a sufficiently large amount of attenuation at the Nyquist frequency (sampling frequency × 2) of the second signal processing unit 12. In other words, the second LPF is an LPF that can obtain an amount of attenuation equal to or less than a predetermined value at a frequency of 1 / (2 × T2), where T2 is the sampling period of the second signal processing unit 12. An amount of attenuation equal to or less than a predetermined value is, for example, an amount of attenuation equal to or less than −60 dB (such as −80 dB) based on the gain of the passband. There are no particular limitations on the filter order of the second LPF.

[0060] As in setting example 1, if the second LPF is used for LPF13 and LPF14 and the first LPF is used for LPF15, the group delay can be shortened by relaxing the characteristics of LPF15 (the LPF applied to the cancellation signal).

[0061] 6, a first LPF is used for LPF 13 and LPF 15, and a second LPF is used for LPF 14. In setting example 2, the group delay can be reduced by relaxing the characteristics of LPF 13 and LPF 15, which are located on the path that generates the cancellation signal.

[0062] [Adaptive filter coefficient correction] In setting example 2, since the characteristics of LPF 13 (first LPF) applied to the reference signal input to the first signal processing unit 11 and LPF 14 (second LPF) applied to the reference signal input to the second signal processing unit 12 are different, the coefficients of the adaptive filter may not be optimized, and noise reduction performance may be reduced.

[0063] Therefore, the second signal processing unit 12 may optimize the coefficients of the adaptive filter by correcting the updated coefficients of the adaptive filter based on the attenuation characteristics of the first LPF and the attenuation characteristics of the second LPF. Fig. 7 is a diagram showing the functional configuration of the active noise reduction device 10 when the coefficients of the adaptive filter are corrected.

[0064] The "correction" block shown in FIG. 7 corresponds to the correction of the adaptive filter coefficients performed by the second signal processing unit 12. Specifically, the second signal processing unit 12 corrects the adaptive filter coefficients by convolving the inverse characteristics of the second LPF and the characteristics of the first LPF into the adaptive filter coefficients. In other words, the second signal processing unit 12 corrects the difference between the characteristics of LPF 13 (first LPF) and the characteristics of LPF 14 (second LPF). The sample rate conversion unit 17 upsamples the adaptive filter coefficients corrected by the second signal processing unit 12 and outputs the upsampled results to the first signal processing unit 11.

[0065] This allows the active noise reduction device 10 to reduce the group delay while maintaining noise reduction performance.

[0066] [Effects, etc.] Below, examples of techniques that can be obtained from the disclosure of this specification will be given, and the effects and the like that can be obtained from these techniques will be described.

[0067] The first technology is an active noise reduction device (10) including a first signal processing unit (11) that generates a cancellation signal for outputting a cancellation sound to reduce noise by applying an adaptive filter to a reference signal that is correlated with noise in a space within a vehicle (50); a second signal processing unit (12) that updates the coefficients of the adaptive filter based on a filtered reference signal obtained by correcting the reference signal with a simulated transfer characteristic that simulates the acoustic transfer characteristic from the position of a cancellation sound source (52) that outputs the cancellation sound to the position of an error signal source (53) and an error signal that indicates the state of noise when the cancellation sound is being output; and a sample rate conversion unit (17). The first signal processing unit (11) operates with a period T1, and the second signal processing unit (12) operates with a period T2 that is longer than the period T1. The sample rate conversion unit (17) upsamples the coefficients of the adaptive filter updated by the second signal processing unit (12) and outputs them to the first signal processing unit (11). The period T1 is longer than the difference between the maximum and minimum values ​​of the processing time required for the second signal processing unit to update the coefficients of the adaptive filter after acquiring the reference signal. The vehicle (50) is an example of a mobile device.

[0068] Such an active noise reduction device 10 can reduce the delay related to the output of the cancellation sound, while keeping the delay constant even if the processing time increases or decreases.

[0069] Technique 2 relates to an active noise reduction device 10 including a first signal processing unit 11 that generates a cancellation signal for outputting a cancellation sound to reduce noise by applying an adaptive filter to a reference signal that has a correlation with noise in the space within a vehicle 50; a second signal processing unit 12 that updates the coefficients of the adaptive filter based on a filtered reference signal obtained by correcting the reference signal with a simulated transfer characteristic that simulates the acoustic transfer characteristic from the position of a cancellation sound source 52 that outputs the cancellation sound to the position of an error signal source 53, and an error signal that is obtained from the error signal source 53 and indicates the state of the noise when the cancellation sound is being output; and a sample rate conversion unit 17, wherein the first signal processing unit 11 operates in a period T1 and the second signal processing unit 12 operates in a period T2 that is longer than the period T1, and the sample rate conversion unit 17 upsamples the coefficients of the adaptive filter updated by the second signal processing unit 12 and outputs the upsampled coefficients to the first signal processing unit 11, and the period T1 is longer than a predetermined time that is determined by variability in the processing time required from when the second signal processing unit acquires the reference signal to when it updates the coefficients of the adaptive filter.

[0070] Such an active noise reduction device 10 can reduce the delay related to the output of the cancellation sound, while keeping the delay constant even if the processing time increases or decreases.

[0071] Technique 3 is the active noise reduction device 10 of Technique 1 or 2, in which a first LPF that provides an attenuation amount equal to or less than a predetermined value at a frequency of 1 / (2×T1) is applied to the cancellation signal generated by the first signal processing unit 11, and a second LPF that provides an attenuation amount equal to or less than a predetermined value at a frequency of 1 / (2×T2) is applied to the reference signal input to the first signal processing unit 11 and the second signal processing unit 12.

[0072] Such an active noise reduction device 10 can reduce the group delay (delay related to the output of the cancellation sound) by relaxing the characteristics of the LPF applied to the cancellation signal.

[0073] The fourth technique includes a first signal processing unit (11) that generates a cancellation signal for outputting a cancellation sound for reducing noise by applying an adaptive filter to a reference signal that has a correlation with noise in a space within a vehicle (50), a second signal processing unit (12) that updates the coefficients of the adaptive filter based on a filtered reference signal obtained by correcting the reference signal with a simulated transfer characteristic that simulates the acoustic transfer characteristic from the position of a cancellation sound source (52) that outputs the cancellation sound to the position of an error signal source (53), and an error signal that is obtained from the error signal source (53) and indicates the state of the noise when the cancellation sound is being output, and a sample rate conversion unit (17). In this active noise reduction device 10, the first signal processing unit 11 operates in a period T1, the second signal processing unit 12 operates in a period T2 longer than the period T1, the sample rate conversion unit 17 upsamples the coefficients of the adaptive filter updated by the second signal processing unit 12 and outputs the result to the first signal processing unit 11, a first LPF that provides an attenuation amount equal to or less than a predetermined value at a frequency of 1 / (2×T1) is applied to the reference signal input to the first signal processing unit 11, and a second LPF that provides an attenuation amount equal to or less than a predetermined value at a frequency of 1 / (2×T2) is applied to the reference signal input to the second signal processing unit.

[0074] Such an active noise reduction device 10 can reduce the group delay (delay related to the output of the cancellation sound) by relaxing the characteristics of the LPF 13 located in the path for generating the cancellation signal.

[0075] Technique 5 is the active noise reduction device 10 of Technique 4, in which the second signal processing unit 12 corrects the coefficients of the updated adaptive filter based on the attenuation characteristics of the first LPF and the attenuation characteristics of the second LPF, and the sample rate conversion unit 17 upsamples the coefficients of the adaptive filter corrected by the second signal processing unit 12 and outputs them to the first signal processing unit 11.

[0076] Such an active noise reduction device 10 can reduce the group delay (delay related to the output of the cancellation sound) while maintaining noise reduction performance.

[0077] Technique 6 is a mobile device (vehicle 50) that includes an active noise reduction device 10 according to any one of techniques 1 to 5, a reference signal source 51 that outputs a reference signal, a cancellation sound source 52, and an error signal source 53.

[0078] Such a mobile device can reduce the delay associated with outputting the cancellation sound.

[0079] Technique 7 is an active noise reduction method including: a first signal processing step of generating a cancellation signal for outputting a cancellation sound to reduce noise by applying an adaptive filter to a reference signal that has a correlation with noise in a space within a vehicle (50); a second signal processing step of updating coefficients of the adaptive filter based on a filtered reference signal obtained by correcting the reference signal with a simulated transfer characteristic that simulates the acoustic transfer characteristic from the position of a cancellation sound source that outputs the cancellation sound to the position of an error signal source (53) and an error signal that indicates the state of noise when the cancellation sound is being output, and a sample rate conversion step; wherein the first signal processing step is performed in a period T1, and the second signal processing step is performed in a period T2 that is longer than the period T1; and wherein the sample rate conversion step upsamples the coefficients of the adaptive filter updated in the second signal processing step so that they can be used in the first signal processing step, and the period T1 is longer than the difference between the maximum and minimum values ​​of the processing time required from acquiring the reference signal in the second signal processing step to updating the coefficients of the adaptive filter.

[0080] Such an active noise reduction method can reduce the delay related to the output of the cancellation sound, while keeping the delay constant even if the processing time increases or decreases.

[0081] Technique 8 is an active noise reduction method including: a first signal processing step of generating a cancellation signal for outputting a cancellation sound to reduce noise by applying an adaptive filter to a reference signal that has a correlation with noise in the space within the vehicle 50; a second signal processing step of updating coefficients of the adaptive filter based on a filtered reference signal obtained by correcting the reference signal with a simulated transfer characteristic that simulates the acoustic transfer characteristic from the position of a cancellation sound source that outputs the cancellation sound to the position of an error signal source 53, and an error signal that is obtained from the error signal source 53 and indicates the state of noise when the cancellation sound is being output; and a sample rate conversion step, wherein the first signal processing step is performed in a period T1, and the second signal processing step is performed in a period T2 that is longer than the period T1, and the sample rate conversion step upsamples the coefficients of the adaptive filter updated in the second signal processing step so that they can be used in the first signal processing step, and the period T1 is longer than a predetermined time that is determined by variability in the processing time required from acquiring the reference signal in the second signal processing step to updating the coefficients of the adaptive filter.

[0082] Such an active noise reduction method can reduce the delay related to the output of the cancellation sound, while keeping the delay constant even if the processing time increases or decreases.

[0083] The 9th technique includes a first signal processing step of generating a cancellation signal for outputting a cancellation sound for reducing noise by applying an adaptive filter to a reference signal that has a correlation with noise in a space within the vehicle 50; a second signal processing step of updating the coefficients of the adaptive filter based on a filtered reference signal obtained by correcting the reference signal with a simulated transfer characteristic that simulates the acoustic transfer characteristic from the position of a cancellation sound source that outputs the cancellation sound to the position of an error signal source 53, and an error signal that is obtained from the error signal source 53 and indicates the state of the noise when the cancellation sound is being output; and a sample rate conversion step, wherein the first signal processing step , a period T1, a second signal processing step is performed in a period T2 longer than the period T1, in a sample rate conversion step, the coefficients of the adaptive filter updated by the second signal processing step are upsampled so that they can be used in the first signal processing step, a first LPF that provides an attenuation amount equal to or less than a predetermined value at a frequency of 1 / (2×T1) is applied to the reference signal used in the first signal processing step, and a second LPF that provides an attenuation amount equal to or less than a predetermined value at a frequency of 1 / (2×T2) is applied to the reference signal used in the second signal processing step.

[0084] Such an active noise reduction method can reduce the group delay (delay related to the output of the cancellation sound) by relaxing the characteristics of the LPF 13 located in the path for generating the cancellation signal.

[0085] (Other embodiments) Although the embodiments have been described above, the present disclosure is not limited to the above-described embodiments.

[0086] For example, in the above embodiment, the active noise reduction device is a device that performs noise control based on the Filtered-X LMS algorithm, but it may also be realized as a device that performs noise control using a SAN (Single-frequency Adaptive Notch filter) algorithm or a SAN Filtered-x LMS algorithm.

[0087] The active noise reduction devices according to the above embodiments may be mounted on a mobile device other than a vehicle. The mobile device may be, for example, an aircraft or a ship. The present disclosure may also be implemented as such a mobile device other than a vehicle.

[0088] The configuration of the active noise reduction device according to the above embodiment is an example. For example, the active noise reduction device may include components such as a DA converter, a filter, a power amplifier, or an AD converter.

[0089] Furthermore, the processing performed by the active noise reduction device according to the above embodiment is merely an example. For example, part of the digital signal processing described in the above embodiment may be realized by analog signal processing.

[0090] Furthermore, for example, in the above-described embodiment, the processing performed by a specific processing unit may be performed by another processing unit, the order of multiple processing operations may be changed, or multiple processing operations may be performed in parallel.

[0091] In the above-described embodiments, each component may be realized by executing a software program suitable for that component, or by a program execution unit such as a CPU or processor reading and executing a software program recorded on a recording medium such as a hard disk or semiconductor memory.

[0092] Furthermore, in the above-described embodiments, each component may be realized by hardware. For example, each component may be a circuit (or an integrated circuit). These circuits may form a single circuit as a whole, or each may be a separate circuit. Furthermore, each of these circuits may be a general-purpose circuit or a dedicated circuit.

[0093] Each component may be a circuit (or integrated circuit). These circuits may form a single circuit as a whole, or each may be a separate circuit. Each of these circuits may be a general-purpose circuit or a dedicated circuit.

[0094] Furthermore, the general or specific aspects of the present disclosure may be realized as a system, an apparatus, a method, an integrated circuit, a computer program, or a non-transitory recording medium such as a computer-readable CD-ROM, or as any combination of a system, an apparatus, a method, an integrated circuit, a computer program, and a computer-readable non-transitory recording medium.

[0095] For example, the present disclosure may be realized as an active noise reduction method executed by an active noise reduction device (computer or DSP), or as a program for causing a computer or DSP to execute the active noise reduction method. The present disclosure may also be realized as an application program installed in a user interface device. The present disclosure may also be realized as a computer-readable non-transitory recording medium on which such a program is recorded.

[0096] In addition, this disclosure also includes forms obtained by applying various modifications to each embodiment that a person skilled in the art would think of, or forms realized by arbitrarily combining the components and functions of each embodiment within the scope of this disclosure. [Industrial Applicability]

[0097] The active noise reduction device of the present disclosure is useful, for example, as a device that can reduce noise inside a vehicle cabin. [Explanation of symbols]

[0098] 10 Active noise reduction device 11 First signal processing section 12 Second signal processing section 13, 14, 15, 16a, 16b LPFs 17 Sample rate conversion section 50 Vehicles (mobile equipment) 51 Reference signal source 52 Cancellation sound source 53 Error signal source

Claims

1. a first signal processing unit that applies an adaptive filter to a reference signal that has a correlation with noise in a space within the mobile device, thereby generating a cancellation signal for outputting a cancellation sound that reduces the noise; a second signal processing unit that updates the coefficients of the adaptive filter based on a filtered reference signal obtained by correcting the reference signal with a simulated transfer characteristic that simulates the acoustic transfer characteristic from the position of a cancellation sound source that outputs the cancellation sound to the position of an error signal source, and an error signal that is obtained from the error signal source and indicates the state of the noise when the cancellation sound is being output; a sample rate conversion unit; the first signal processing unit operates in a cycle T1; the second signal processing unit operates in a period T2 that is longer than the period T1, the sample rate conversion unit upsamples the coefficients of the adaptive filter updated by the second signal processing unit and outputs the upsampled coefficients to the first signal processing unit; The period T1 is longer than the difference between the maximum and minimum values ​​of the processing time required from when the second signal processing unit acquires the reference signal until when the second signal processing unit updates the coefficient of the adaptive filter. Active noise reduction devices.

2. a first signal processing unit that applies an adaptive filter to a reference signal that has a correlation with noise in a space within the mobile device, thereby generating a cancellation signal for outputting a cancellation sound that reduces the noise; a second signal processing unit that updates the coefficients of the adaptive filter based on a filtered reference signal obtained by correcting the reference signal with a simulated transfer characteristic that simulates the acoustic transfer characteristic from the position of a cancellation sound source that outputs the cancellation sound to the position of an error signal source, and an error signal that is obtained from the error signal source and indicates the state of the noise when the cancellation sound is being output; a sample rate conversion unit; the first signal processing unit operates in a cycle T1; the second signal processing unit operates in a period T2 that is longer than the period T1, the sample rate conversion unit upsamples the coefficients of the adaptive filter updated by the second signal processing unit and outputs the upsampled coefficients to the first signal processing unit; The period T1 is longer than a predetermined time determined by variations in the processing time required from when the second signal processing unit acquires the reference signal to when the coefficient of the adaptive filter is updated. Active noise reduction devices.

3. a first LPF that can obtain an attenuation amount equal to or less than a predetermined value at a frequency of 1 / (2×T1) is applied to the cancellation signal generated by the first signal processing unit; A second LPF that obtains an attenuation amount equal to or less than the predetermined value at a frequency of 1 / (2×T2) is applied to the reference signal input to the first signal processing unit and the second signal processing unit.

2. The active noise reduction device of claim 1.

4. a first signal processing unit that applies an adaptive filter to a reference signal that has a correlation with noise in a space within the mobile device, thereby generating a cancellation signal for outputting a cancellation sound that reduces the noise; a second signal processing unit that updates the coefficients of the adaptive filter based on a filtered reference signal obtained by correcting the reference signal with a simulated transfer characteristic that simulates the acoustic transfer characteristic from the position of a cancellation sound source that outputs the cancellation sound to the position of an error signal source, and an error signal that is obtained from the error signal source and indicates the state of the noise when the cancellation sound is being output; a sample rate conversion unit; the first signal processing unit operates in a cycle T1; the second signal processing unit operates in a period T2 that is longer than the period T1, the sample rate conversion unit upsamples the coefficients of the adaptive filter updated by the second signal processing unit and outputs the upsampled coefficients to the first signal processing unit; a first LPF that can obtain an attenuation amount equal to or less than a predetermined value at a frequency of 1 / (2×T1) is applied to the reference signal input to the first signal processing unit; A second LPF that obtains an attenuation amount equal to or less than the predetermined value at a frequency of 1 / (2×T2) is applied to the reference signal input to the second signal processing unit. Active noise reduction devices.

5. the second signal processing unit corrects coefficients of the adaptive filter after updating based on the attenuation characteristics of the first LPF and the attenuation characteristics of the second LPF; The sample rate conversion unit upsamples the coefficients of the adaptive filter corrected by the second signal processing unit and outputs the upsampled coefficients to the first signal processing unit.

5. An active noise reduction device according to claim 4.

6. An active noise reduction device according to any one of claims 1 to 5; a reference signal source that outputs the reference signal; The cancellation sound source; the error signal source. Mobile device.

7. a first signal processing step of generating a cancellation signal for outputting a cancellation sound for reducing noise by applying an adaptive filter to a reference signal having a correlation with noise in a space within the mobile device; a second signal processing step of updating the coefficients of the adaptive filter based on a filtered reference signal obtained by correcting the reference signal with a simulated transfer characteristic that simulates the acoustic transfer characteristic from the position of a cancellation sound source that outputs the cancellation sound to the position of an error signal source, and an error signal that is obtained from the error signal source and indicates the state of the noise when the cancellation sound is being output; a sample rate conversion step; The first signal processing step is performed at a period T1; the second signal processing step is performed in a period T2 that is longer than the period T1; In the sample rate conversion step, the coefficients of the adaptive filter updated in the second signal processing step are upsampled so that they can be used in the first signal processing step; The period T1 is longer than the difference between the maximum and minimum values ​​of the processing time required from acquiring the reference signal to updating the coefficients of the adaptive filter in the second signal processing step. Active noise reduction methods.

8. a first signal processing step of generating a cancellation signal for outputting a cancellation sound for reducing noise by applying an adaptive filter to a reference signal having a correlation with noise in a space within the mobile device; a second signal processing step of updating the coefficients of the adaptive filter based on a filtered reference signal obtained by correcting the reference signal with a simulated transfer characteristic that simulates the acoustic transfer characteristic from the position of a cancellation sound source that outputs the cancellation sound to the position of an error signal source, and an error signal that is obtained from the error signal source and indicates the state of the noise when the cancellation sound is being output; a sample rate conversion step; The first signal processing step is performed at a period T1; the second signal processing step is performed in a period T2 that is longer than the period T1; In the sample rate conversion step, the coefficients of the adaptive filter updated in the second signal processing step are upsampled so that they can be used in the first signal processing step; The period T1 is longer than a predetermined time determined by variations in the processing time required from acquiring the reference signal to updating the coefficient of the adaptive filter in the second signal processing step. Active noise reduction methods.

9. a first signal processing step of generating a cancellation signal for outputting a cancellation sound for reducing noise by applying an adaptive filter to a reference signal having a correlation with noise in a space within the mobile device; a second signal processing step of updating the coefficients of the adaptive filter based on a filtered reference signal obtained by correcting the reference signal with a simulated transfer characteristic that simulates the acoustic transfer characteristic from the position of a cancellation sound source that outputs the cancellation sound to the position of an error signal source, and an error signal that is obtained from the error signal source and indicates the state of the noise when the cancellation sound is being output; a sample rate conversion step; The first signal processing step is performed at a period T1; the second signal processing step is performed in a period T2 that is longer than the period T1; In the sample rate conversion step, the coefficients of the adaptive filter updated in the second signal processing step are upsampled so that they can be used in the first signal processing step; a first LPF that can obtain an attenuation amount equal to or less than a predetermined value at a frequency of 1 / (2×T1) is applied to the reference signal used in the first signal processing step; The reference signal used in the second signal processing step is subjected to a second LPF that provides an attenuation amount equal to or less than the predetermined value at a frequency of 1 / (2×T2). Active noise reduction methods.

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