Active noise control device

Abstract

The present invention provides an active noise control device. The active noise control device (10) controls a speaker (18) to output a canceling sound in order to cancel out noise transmitted from a vibration source. The active noise control device comprises a control signal generating unit (68), a secondary path filter updating unit (84), and a feedback filter setting unit (23). The control signal generating unit (68) processes a reference signal corresponding to a specified frequency through a feedback filter and an adaptive notch filter as a decimation filter to generate a control signal for controlling the speaker (18); the secondary path filter updating unit (84) adaptively updates the secondary path filter in sequence; and the feedback filter setting unit (23) sets the feedback filter according to the secondary path filter. Thus, noise can be reduced even if the transmission characteristics change.

Description

Technical Field

[0001] The present invention relates to an active noise control device. Background Art

[0002] Japanese Patent Application Publication No. 2007-025527 discloses an active noise reduction device. This device generates a signal to control a speaker. In response, the speaker outputs an interference sound. This interference sound reduces the sound pressure of noise such as road noise. Summary of the Invention

[0003] The active noise control device disclosed in Japanese Patent Application Laid-Open No. 2007-025527 generates a control signal for controlling a speaker based on the transmission characteristics between the speaker and the microphone. In this active noise control device, the transmission characteristics between the speaker and the microphone are fixed. Therefore, there is a technical problem that the active noise control device cannot reduce the sound pressure of noise when the transmission characteristics change.

[0004] The purpose of the present invention is to solve the above-mentioned technical problems.

[0005] The present invention provides an active noise control device that controls a loudspeaker based on a component in a frequency band centered around a predetermined frequency of an error signal output by a detector that detects a synthetic sound at a control point. The synthetic sound is a composite sound of noise transmitted from a vibration source and a canceling sound output from the loudspeaker to cancel the noise. The active noise control device includes a reference signal generator, a control signal generator, an estimated canceling sound signal generator, a decimation signal generator, a hypothetical error signal generator, a difference signal generator, a secondary path filter updater, a decimation filter updater, and a feedback filter setting unit. The reference signal generator generates a reference signal corresponding to the predetermined frequency. The control signal generator processes the reference signal using a feedback filter and a decimation filter that is an adaptive notch filter to generate a control signal for controlling the loudspeaker. The estimated canceling sound signal generator generates a reference signal corresponding to the predetermined frequency. The signal generation unit processes the control signal using an adaptive notch filter as a secondary path filter to generate an estimated cancellation sound signal. The decimation signal generation unit processes the reference signal using the decimation filter to generate a decimation signal. The virtual error signal generation unit generates a virtual error signal based on the error signal and the estimated cancellation sound signal. The difference signal generation unit generates a difference signal based on the error signal and the decimation signal. The secondary path filter update unit adaptively updates the secondary path filter in sequence based on the control signal and the virtual error signal to minimize the virtual error signal. The decimation filter update unit adaptively updates the decimation filter in sequence based on the reference signal and the difference signal to minimize the difference signal. The feedback filter setting unit sets the feedback filter based on the secondary path filter.

[0006] The active noise control device of the present invention can reduce noise even if the transmission characteristics vary.

[0007] The above-mentioned objects, features and advantages will be easily understood from the following description of the embodiments with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 A diagram illustrating an overview of active noise control performed in an active noise control device.

[0009] Figure 2 Schematic diagram showing the structure of an active noise control device.

[0010] Figure 3 This is the control block diagram of the signal processing unit.

[0011] Figure 4This is the control block diagram of the signal processing unit. DETAILED DESCRIPTION

[0012] [First embodiment]

[0013] Figure 1 1 is a diagram illustrating an overview of active noise control performed in active noise control device 10 .

[0014] The wheels 16 vibrate due to the forces they receive from the road surface while the vehicle is traveling. This vibration is transmitted to the vehicle body via the suspension, generating road noise within the cabin 14 of the vehicle 13. Road noise has a peak in the 40-50 Hz frequency band. This 40-50 Hz frequency band is excited by the acoustic resonance characteristics within a confined space such as the cabin 14. Narrowband components centered around the peak frequency and having a certain bandwidth generate a "booming..." sound also known as drumming noise. Drumming noise can easily cause discomfort to passengers.

[0015] Active noise control device 10 of this embodiment causes speaker 18 provided in vehicle interior 14 to output a canceling sound, thereby reducing the sound pressure of low-frequency noise at a control point in vehicle interior 14 .

[0016] Figure 2 2 is a schematic diagram showing the configuration of the active noise control device 10 . The active noise control device 10 includes a signal processing unit 22 and a feedback filter setting unit 23 .

[0017] The active noise control device 10 includes a calculation unit and a storage unit (not shown). The calculation unit realizes the signal processing unit 22 and the feedback filter setting unit 23 described above.

[0018] The computing unit is constituted by a processor such as a CPU (Central Processing Unit) or a GPU (Graphics Processing Unit).

[0019] The calculation unit includes a determination unit and a control unit (not shown). The determination unit and the control unit are realized by the calculation unit executing a program stored in the storage unit.

[0020] Furthermore, at least a portion of the determination unit and the control unit may be implemented by an integrated circuit such as an ASIC (Application Specific Integrated Circuit) or an FPGA (Field-Programmable Gate Array). Furthermore, at least a portion of the determination unit and the control unit may be formed by an electronic circuit including discrete components.

[0021] The storage unit is composed of volatile memory (not shown) and non-volatile memory (not shown). Examples of volatile memory include RAM (Random Access Memory). Examples of non-volatile memory include ROM (Read Only Memory) and flash memory. Data, etc., are stored in the volatile memory. Programs, tables, maps, etc., are stored in the non-volatile memory. At least a portion of the storage unit may be provided in the aforementioned processor, integrated circuit, etc.

[0022] [Structure of the signal processing unit]

[0023] Figure 3 This is a control block diagram of the signal processing unit 22. The signal processing unit 22 performs feedback signal processing. During this feedback signal processing, a control signal u0_a is generated. This control signal u0_a is used to cause the speaker 18 to output a canceling sound that cancels out low-frequency noise. This control signal u0_a is generated based on the error signal e output from the microphone 32 located at the control point. Hereinafter, the sound transmission path from the speaker 18 to the microphone 32 is referred to as the secondary path, and the transmission characteristic of the secondary path is denoted by C.

[0024] In this embodiment, the vicinity of the passenger's ear is set as the control point. Figure 1 As shown, a microphone 32 is provided on a headrest 36 of a seat 34 in a vehicle cabin 14. The error signal e is a signal output from the microphone 32 which detects a composite sound of the control point noise d and the control point cancellation sound y.

[0025] The signal processing unit 22 includes a reference signal generating unit 67, a control signal generating unit 68, an estimated cancellation sound signal generating unit 70, an estimated noise signal generating unit 76, an extraction signal generating unit 77, a hypothetical error signal generating unit 78, a differential signal generating unit 81, an adjustment filter updating unit 82, a secondary path filter updating unit 84, and an extraction filter updating unit 85.

[0026] The reference signal generating unit 67 generates a reference signal xc (= cos(2π × fx × t)) and a reference signal xs (= sin(2π × fx × t)). The reference signal xc is a cosine signal of the control target frequency fx. The reference signal xs is a sine signal of the control target frequency fx. Here, t represents time. The control target frequency fx is set to the peak frequency of the low-frequency noise or a frequency near the peak frequency.

[0027] Control signal generator 68 generates control signals u0_a and u1_a. Reference signals xc and xs are processed by feedback filter FB and decimation filter A. Control signal generator 68 includes a phase adjuster 86, a signal decimator 88, and a gain adjuster 90.

[0028] Using the gain FBG, the filter coefficient FBP0 and the filter coefficient FBP1, the feedback filter FB is expressed as FB=FBG(FBP0+iFBP1). In addition, i represents an imaginary number. In addition, FBP0 2 +FBP1 2 = 1. The feedback filter FB is set by the feedback filter setting unit 23. The setting of the feedback filter FB will be described in detail later. The details of the decimation filter A will be described together with the decimation signal generating unit 77 described later.

[0029] The phase adjustment unit 86 generates a phase adjustment signal p0_a and a phase adjustment signal p1_a by performing signal processing on the reference signal xc and the reference signal xs using the phase adjustment filter FBP.

[0030] The phase adjustment unit 86 includes a first phase adjustment filter 86a, a second phase adjustment filter 86b, a third phase adjustment filter 86c, a fourth phase adjustment filter 86d, an inverting amplifier 86e, an adder 86f, and an adder 86g.

[0031] The first phase adjustment filter 86a has a filter coefficient FBP0. The second phase adjustment filter 86b has a filter coefficient FBP1. The third phase adjustment filter 86c has a filter coefficient FBP0. The fourth phase adjustment filter 86d has a filter coefficient FBP1.

[0032] The second phase adjustment filter 86b receives the reference signal -xs, whose polarity has been inverted by the inverting amplifier 86e. The adder 86f adds the reference signal xc, whose amplitude has been adjusted by the first phase adjustment filter 86a, and the reference signal -xs, whose amplitude has been adjusted by the second phase adjustment filter 86b. This generates the phase adjustment signal p0_a.

[0033] The adder 86g adds the reference signal xs whose amplitude is adjusted by the third phase adjustment filter 86c and the reference signal xc whose amplitude is adjusted by the fourth phase adjustment filter 86d, thereby generating a phase adjustment signal p1_a.

[0034] The signal extraction unit 88 performs signal processing on the phase adjustment signal p0_a and the phase adjustment signal p1_a using the decimation filter A. In response, an extraction signal a0_a and an extraction signal a1_a are generated.

[0035] The signal extraction unit 88 includes a first decimation filter 88a, a second decimation filter 88b, a third decimation filter 88c, a fourth decimation filter 88d, an inverting amplifier 88e, an adder 88f, and an adder 88g.

[0036] The first decimation filter 88a has a filter coefficient A0. The second decimation filter 88b has a filter coefficient A1. The third decimation filter 88c has a filter coefficient A0. The fourth decimation filter 88d has a filter coefficient A1.

[0037] The adder 88f adds the phase adjustment signal p0_a whose amplitude is adjusted by the first decimation filter 88a and the phase adjustment signal p1_a whose amplitude is adjusted by the second decimation filter 88b, thereby generating a decimated signal a0_a.

[0038] Phase adjustment signal -p1_a, whose polarity has been inverted by inverting amplifier 88e, is input to third decimation filter 88c. Adder 88g adds phase adjustment signal -p1_a, whose amplitude has been adjusted by third decimation filter 88c, and phase adjustment signal p0_a, whose amplitude has been adjusted by fourth decimation filter 88d, to generate decimated signal a1_a.

[0039] The gain adjustment unit 90 performs signal processing on the extraction signal a0_a and the extraction signal a1_a using the gain filter FBG, thereby generating the control signal u0_a and the control signal u1_a.

[0040] The gain adjustment unit 90 includes a first gain adjustment filter 90a and a second gain adjustment filter 90b. The first gain adjustment filter 90a has a gain FBG, and the second gain adjustment filter 90b has a gain FBG.

[0041] The first gain adjustment filter 90a adjusts the amplitude of the extracted signal a0_a. This generates a control signal u0_a. The second gain adjustment filter 90b adjusts the amplitude of the extracted signal a1_a. This generates a control signal u1_a. The control signal u0_a is converted to an analog signal by the digital-to-analog converter 69 and output to the speaker 18.

[0042] In the estimated cancellation sound signal generation unit 70 described next, the control signal u0_a is used as a real number component, and the control signal u1_a is used as an imaginary number component.

[0043] The estimated canceling sound signal generating unit 70 performs signal processing on the control signal u0_a and the control signal u1_a through the secondary path filter C^, thereby generating an estimated canceling sound signal y_a^.

[0044] In the estimated cancellation sound signal generation unit 70, an adaptive notch filter (e.g., a SAN (Single-frequency Adaptive Notch) filter) is used as the secondary path filter C^. This filter is updated by the secondary path filter update unit 84, described later. This allows the filter C^ to converge to the transmission characteristics C of the sound in the secondary path. The filter coefficients C0^ and C1^ are used to represent the secondary path filter C^ as C^ = C0^ + iC1^. Here, i represents an imaginary number.

[0045] The estimated canceling sound signal generation unit 70 includes a first secondary path filter 70 a , a second secondary path filter 70 b , and an adder 70 c .

[0046] The first path filter 70a has a filter coefficient C0^. The second path filter 70b has a filter coefficient C1^. Adder 70c adds the control signal u0_a, whose amplitude has been adjusted by the first path filter 70a, and the control signal u1_a, whose amplitude has been adjusted by the second path filter 70b, to generate an estimated canceling sound signal y_a^.

[0047] Estimated noise signal generator 76 processes reference signal xc and reference signal xs using adjustment filter P. This generates estimated noise signal d_a^. Estimated noise signal generator 76 uses an adaptive notch filter (e.g., a SAN filter) as adjustment filter P to adjust the characteristics of reference signal xc and reference signal xs. Adjustment filter P is updated by adjustment filter updater 82, described later. Adjustment filter P is represented by P = P0 + iP1 using filter coefficients P0 and P1. "i" represents an imaginary number.

[0048] The estimated noise signal generating unit 76 includes a first adjustment filter 76a, a second adjustment filter 76b, an inverting amplifier 76c, and an adder 76d. The first adjustment filter 76a has a filter coefficient P0, and the second adjustment filter 76b has a filter coefficient P1.

[0049] The second adjustment filter 76b receives the reference signal -xs, whose polarity has been inverted by the inverting amplifier 76c. The adder 76d adds the reference signal xc, whose amplitude has been adjusted by the first adjustment filter 76a, and the reference signal -xs, whose amplitude has been adjusted by the second adjustment filter 76b. This generates the estimated noise signal d_a^.

[0050] The decimation signal generation unit 77 processes the reference signal xc and the reference signal xs using a decimation filter A. This generates the decimation signal efr. In the decimation signal generation unit 77, an adaptive notch filter (e.g., a SAN filter) is used as the decimation filter A. The decimation filter A is updated and optimized by the decimation filter update unit 85, described later. The decimation filter A has filter coefficients A0 and A1 that match the amplitude and phase of the reference signal xc and the reference signal xs with the low-frequency noise.

[0051] The decimation signal generator 77 includes a first decimation filter 77a, a second decimation filter 77b, and an adder 77c. The first decimation filter 77a has a filter coefficient A0, and the second decimation filter 77b has a filter coefficient A1.

[0052] The adder 77 c adds the reference signal xc whose amplitude is adjusted by the first decimation filter 77 a and the reference signal xs whose amplitude is adjusted by the second decimation filter 77 b , thereby generating an decimated signal efr.

[0053] The virtual error signal generating unit 78 generates a virtual error signal e1 based on the error signal e, the estimated noise signal d_a^, and the estimated cancellation sound signal y_a^. The virtual error signal generating unit 78 includes an inverting amplifier 78a, an inverting amplifier 78b, and an adder 78c.

[0054] The error signal e converted to a digital signal by the analog / digital converter 79, the estimated noise signal -d_a^ obtained by inverting the polarity by the inverting amplifier 78a, and the estimated cancellation sound signal -y_a^ obtained by inverting the polarity by the inverting amplifier 78b are added together by the adder 78c. This generates a virtual error signal e1.

[0055] The differential signal generating unit 81 generates a differential signal e0 based on the error signal e and the extracted signal efr. The differential signal generating unit 81 includes an adder 81a. The adder 81a adds the error signal e and the extracted signal efr, thereby generating a differential signal e0.

[0056] The adjustment filter updating unit 82 adaptively updates the adjustment filter P in sequence using an adaptive algorithm (eg, LMS (Least Mean Square) algorithm) to minimize the virtual error signal e1.

[0057] The adjustment filter updating unit 82 includes a first adjustment filter coefficient updating unit 82a and a second adjustment filter coefficient updating unit 82b. The first adjustment filter coefficient updating unit 82a and the second adjustment filter coefficient updating unit 82b update the filter coefficient P0 and the filter coefficient P1 according to the following equation. Here, n represents the number of time steps (n = 0, 1, 2, ...). The signal processing unit 22 performs signal processing at a predetermined cycle. The time step represents the length of the cycle. The time step number indicates the number of cycles of signal processing. μ0 P 、μ1 P Represents the step size parameter.

[0058] P0 n+1 =P0 n -μ0 P ×e1 n ×xc n

[0059] P1 n+1 =P1 n -μ1 P ×e1 n ×XS n

[0060] The secondary path filter updating unit 84 adaptively updates the secondary path filter C^ in sequence using an adaptive algorithm (eg, LMS algorithm) to minimize the virtual error signal e1.

[0061] The secondary path filter updating unit 84 includes a first secondary path filter coefficient updating unit 84a and a second secondary path filter coefficient updating unit 84b. The first secondary path filter coefficient updating unit 84a and the second secondary path filter coefficient updating unit 84b update the filter coefficient C0^ and the filter coefficient C1^ according to the following equation. Where n represents the number of time steps (n = 0, 1, 2, ...), μ0 C 、μ1 C Represents the step size parameter.

[0062] C0^ n+1 =C0^ n -μ0 C ×e1 n ×u0_a n

[0063] C1^ n+1 =C1^ n -μ1 C ×e1 n ×u1_a n

[0064] The decimation filter updating section 85 adaptively updates the decimation filter A in sequence using an adaptive algorithm (eg, LMS algorithm) to minimize the differential signal e0.

[0065] The decimation filter updating unit 85 includes a first decimation filter coefficient updating unit 85a and a second decimation filter coefficient updating unit 85b. The first decimation filter coefficient updating unit 85a and the second decimation filter coefficient updating unit 85b update the filter coefficient A0 and the filter coefficient A1 according to the following equation. Where n represents the number of time steps (n = 0, 1, 2, ...), μ0 A 、μ1 A Represents the step size parameter.

[0066] A0 n+1 =A0 n -μ0 A ×e0 n ×xc n

[0067] A1 n+1 =A1 n -μ1 A ×e0 n ×xs n

[0068] [Feedback filter FB setting]

[0069] The feedback filter setting unit 23 sets the feedback filter FB according to the secondary path filter C^. Next, the setting of the feedback filter FB will be described.

[0070] The sensitivity function S, which is a transfer function between the error signal e and the noise d, is expressed by the following equation. The sensitivity function S represents the amount of reduction in the noise d.

[0071]

[0072] Here, E is the frequency characteristic of the error signal e, and D is the frequency characteristic of the noise d. When the secondary path transmission characteristic C is replaced by the secondary path filter C^, the feedback filter FB is expressed by the following equation.

[0073]

[0074] The value of the sensitivity function S is predetermined. For example, to reduce the sound pressure of low-frequency noise by approximately 6 dB, the sensitivity function S is approximately 0.5. When the sensitivity function S is 0.5, the feedback filter setting unit 23 sets the value obtained by normalizing the real part of 1 / C^ by |1 / C^| as the filter coefficient FBP0, and sets the value obtained by normalizing the imaginary part of 1 / C^ by |1 / C^| as the filter coefficient FBP1.

[0075] The feedback filter setting unit 23 sets the gain FBG to gradually increase from an initial value to 1 / |C^|. If the secondary path filter C^ is updated infrequently and learning is not progressing, the value of 1 / |C^| may increase dramatically. Therefore, by gradually increasing the gain FBG, it is possible to suppress the output of loud sound pressure from speakers 18 that would be offensive to the occupants. The initial value of the gain FBG is not set to 0, but rather to a value small enough to prevent the output of sound from speakers 18 that would be offensive to the occupants. This is because if the initial value of the gain FBG is set to 0, learning of the secondary path filter C^ will not progress.

[0076] Furthermore, the feedback filter setting unit 23 may set the gain FBG to an initial value when the gain |C^| of the secondary path filter C^ is below a predetermined value. By keeping the gain FBG at the initial value until learning of the secondary path filter C^ progresses, it is possible to prevent the speaker 18 from outputting sounds that may be offensive to the occupants.

[0077] Furthermore, if the gain change or phase change resulting from updating the secondary path filter C^ exceeds a specified value, the feedback filter setting unit 23 may restore the gain FBG to its initial value. If the position of microphone 32 changes, the secondary path transmission characteristic C may significantly change. In this case, relearning of the secondary path filter C^ is performed. Therefore, by temporarily setting the gain FBG to its initial value and then gradually increasing the gain FBG from the initial value to 1 / |C^|, it is possible to suppress the high sound pressure output from the speaker 18 that could cause discomfort to the occupants.

[0078] [Effects]

[0079] In the active noise control device 10 of this embodiment, the control signal generator 68 processes the reference signal xc and the reference signal xs through the feedback filter FB and the decimation filter A. This generates the control signal u0_a for controlling the speaker 18. Furthermore, the feedback filter setting unit 23 sets the feedback filter FB based on the secondary path filter C^. Furthermore, the secondary path filter updater 84 sequentially and adaptively updates the secondary path filter C^. This allows the secondary path filter C^ to follow the transfer characteristic C even when the secondary path transfer characteristic C changes. By generating the control signal u0_a in accordance with the change in the transfer characteristic C, the sound pressure of low-frequency noise can be reduced.

[0080] Furthermore, in active noise control device 10 of this embodiment, feedback filter setting unit 23 sets feedback filter FB based on secondary path filter C^ and a predetermined noise reduction value (sensitivity function S). This reduces the amount of calculation required to set feedback filter FB, thereby suppressing the load on the computing unit.

[0081] In the active noise control device 10 of this embodiment, the feedback filter setting unit 23 gradually increases the gain FBG of the feedback filter FB from a predetermined initial value to a gain of 1 / |C^|. This can suppress the output of loud sound pressure from the speaker 18 that may cause discomfort to the occupant.

[0082] Furthermore, in active noise control device 10 of this embodiment, feedback filter setting unit 23 sets gain FBG of feedback filter FB to a predetermined initial value when gain |C^| of secondary path filter C^ is below a predetermined value. Thus, gain FBG remains set to the initial value until learning of secondary path filter C^ progresses, thereby preventing speaker 18 from outputting sounds that may be offensive to the occupant.

[0083] Furthermore, in active noise control device 10 of this embodiment, when the gain or phase of secondary path filter C^ changes by a predetermined amount or more, feedback filter setting unit 23 sets the gain FBG of feedback filter FB to a predetermined initial value. This prevents loud sound pressure from being output from speaker 18, which could cause discomfort to the occupants.

[0084] [Second embodiment]

[0085] The active noise control device 10 of this embodiment has a signal processing unit 22 that partially differs from the signal processing unit 22 of the first embodiment in configuration. Furthermore, the feedback filter setting unit 23 differs from the feedback filter setting unit 23 of the first embodiment in the method of setting the feedback filter FB.

[0086] [Structure of the signal processing unit]

[0087] The signal processing unit 22 performs feedback signal processing. During this feedback signal processing, a control signal u0_b is generated. This control signal u0_b is used to cause the speaker 18 to output a canceling sound that cancels out low-frequency noise. This control signal u0_b is generated based on the error signal e output from the microphone 32 located at the control point. Hereinafter, the sound transmission path from the wheel 16 to the microphone 32 is referred to as the primary path, and the transmission characteristic of the primary path is denoted by H. Furthermore, the sound transmission path from the speaker 18 to the microphone 32 is referred to as the secondary path, and the transmission characteristic of the secondary path is denoted by C.

[0088] Figure 4 1 is a control block diagram of the signal processing unit 22. The signal processing unit 22 includes a reference signal generating unit 67, a control signal generating unit 68, an estimated cancellation sound signal generating unit 70, an estimated noise signal generating unit 75, a decimation signal generating unit 77, a hypothetical error signal generating unit 78, a difference signal generating unit 81, a primary path filter updating unit 83, a secondary path filter updating unit 84, and a decimation filter updating unit 85.

[0089] The reference signal generating unit 67 generates a reference signal xc (= cos(2π × fx × t)) and a reference signal xs (= sin(2π × fx × t)). Reference signal xc is a cosine signal of the control target frequency fx. Reference signal xs is a sine signal of the control target frequency fx. Here, t represents time. The control target frequency fx is pre-set to a value near the peak frequency of low-frequency noise.

[0090] In the control signal generator 68 , the reference signals xc and xs are processed by the feedback filter FB and the decimation filter A. This generates the control signals u0_b and u1_b. The control signal generator 68 includes a signal extraction unit 92 , a phase adjustment unit 94 , and a gain adjustment unit 96 .

[0091] The feedback filter FB is expressed as FB=FBG(FBP0+iFBP1) using the gain FBG, the filter coefficient FBP0, and the filter coefficient FBP1. In addition, i represents an imaginary number. In addition, FBP0 2 +FBP1 2 = 1. The feedback filter FB is set by the feedback filter setting unit 23. The setting of the feedback filter FB will be described in detail later.

[0092] The signal extraction unit 92 performs signal processing on the reference signal xc and the reference signal xc using the decimation filter A. In response, an decimation signal a0_b and an decimation signal a1_b are generated.

[0093] The signal extraction unit 92 includes a first decimation filter 92a, a second decimation filter 92b, a third decimation filter 92c, a fourth decimation filter 92d, an inverting amplifier 92e, an adder 92f, and an adder 92g.

[0094] The first decimation filter 92a has a filter coefficient A0. The second decimation filter 92b has a filter coefficient A1. The third decimation filter 92c has a filter coefficient A0. The fourth decimation filter 92d has a filter coefficient A1.

[0095] The second decimation filter 92b receives the reference signal -xs, whose polarity is inverted by the inverting amplifier 92e. The adder 92f adds the reference signal xc, whose amplitude has been adjusted by the first decimation filter 92a, and the reference signal -xs, whose amplitude has been adjusted by the second decimation filter 92b. This generates the decimated signal a0_b.

[0096] The adder 92g adds the reference signal xs whose amplitude is adjusted by the third decimation filter 92c and the reference signal xc whose amplitude is adjusted by the fourth decimation filter 92d, thereby generating the decimated signal a1_b.

[0097] The phase adjustment unit 94 performs signal processing on the extracted signal a0_b and the extracted signal a1_b using the phase adjustment filter FBP, thereby generating a phase adjustment signal p0_b and a phase adjustment signal p1_b.

[0098] The phase adjustment unit 94 includes a first phase adjustment filter 94 a , a second phase adjustment filter 94 b , a third phase adjustment filter 94 c , a fourth phase adjustment filter 94 d , an inverting amplifier 94 e , an adder 94 f , and an adder 94 g .

[0099] The first phase adjustment filter 94a has a filter coefficient FBP0. The second phase adjustment filter 94b has a filter coefficient FBP1. The third phase adjustment filter 94c has a filter coefficient FBP0. The fourth phase adjustment filter 94d has a filter coefficient FBP1.

[0100] The adder 94f adds the extracted signal a0_b whose amplitude is adjusted by the first phase adjustment filter 94a and the extracted signal a1_b whose amplitude is adjusted by the second phase adjustment filter 94b, thereby generating a phase adjustment signal p0_b.

[0101] The extracted signal -a1_b, whose polarity has been inverted by the inverting amplifier 94e, is input to the third phase adjustment filter 94c. The extracting signal -a1_b, whose amplitude has been adjusted by the third phase adjustment filter 94c, and the extracting signal a0_b, whose amplitude has been adjusted by the fourth phase adjustment filter 94d, are added together by the adder 94g. This generates the phase adjustment signal p1_b.

[0102] The gain adjustment unit 96 performs signal processing on the phase adjustment signal p0_b and the phase adjustment signal p1_b using the gain filter FBG, thereby generating the control signal u0_b and the control signal u1_b.

[0103] The gain adjustment unit 96 includes a first gain adjustment filter 96a and a second gain adjustment filter 96b. The first gain adjustment filter 96a has a gain FBG, and the second gain adjustment filter 96b has a gain FBG.

[0104] The first gain adjustment filter 96a adjusts the amplitude of the phase adjustment signal p0_b. This generates a control signal u0_b. The second gain adjustment filter 96b adjusts the amplitude of the phase adjustment signal p1_b. This generates a control signal u1_b. The control signal u0_b is converted to an analog signal by the digital-to-analog converter 69 and output to the speaker 18.

[0105] In the estimated cancellation sound signal generation unit 70 described next, the control signal u0_b is used as a real number component, and the control signal u1_b is used as an imaginary number component.

[0106] The estimated canceling sound signal generating unit 70 performs signal processing on the control signal u0_b and the control signal u1_b through the secondary path filter C^, thereby generating an estimated canceling sound signal y_b^.

[0107] In the estimated cancellation sound signal generation unit 70, an adaptive notch filter (e.g., a SAN filter) is used for the secondary path filter C^. This filter is updated by the secondary path filter update unit 84 (described later) to converge to the sound transmission characteristic C in the secondary path. The secondary path filter C^ is represented by C^=C^+iC^ using the filter coefficients C^ and C^. Here, i represents an imaginary number.

[0108] The estimated canceling sound signal generation unit 70 includes a first secondary path filter 70 a , a second secondary path filter 70 b , and an adder 70 c .

[0109] The first path filter 70a has a filter coefficient C0^. The second path filter 70b has a filter coefficient C1^. Adder 70c adds the control signal u0_b, whose amplitude has been adjusted by the first path filter 70a, and the control signal u1_b, whose amplitude has been adjusted by the second path filter 70b. This generates an estimated canceling sound signal y_b^.

[0110] The estimated noise signal generating unit 75 performs signal processing on the extracted signal a0_b and the extracted signal a1_b through the first-stage path filter H^, thereby generating an estimated noise signal d_b^.

[0111] In the estimated noise signal generation unit 75, an adaptive notch filter (e.g., a SAN filter) is used for the primary path filter H^. The primary path filter H^ is updated by the primary path filter update unit 83 (described later) to converge to the sound transmission characteristic H in the primary path. The primary path filter H^ is represented by H^ = H0^ + iH1^ using the filter coefficients H0^ and H1^. Here, i represents an imaginary number.

[0112] The estimated noise signal generator 75 includes a first primary path filter 75a, a second primary path filter 75b, an inverting amplifier 75c, and an adder 75d. The first primary path filter 75a has a filter coefficient H0^, and the second primary path filter 75b has a filter coefficient H1^.

[0113] The extracted signal -a1_b, whose polarity has been inverted by the inverting amplifier 75c, is input to the second primary path filter 75b. The extracted signal a0_b, whose amplitude has been adjusted by the first primary path filter 75a, and the extracted signal -a1_b, whose amplitude has been adjusted by the second primary path filter 75b, are added together by the adder 75d. This generates the estimated noise signal d_b^.

[0114] The decimation signal generator 77 processes the reference signal xc and the reference signal xs using a decimation filter A. This generates the decimation signal efr. In the decimation signal generator 77, an adaptive notch filter (e.g., a SAN filter) is used as the decimation filter A. The decimation filter A is updated and optimized by the decimation filter updater 85, described later. The decimation filter A has filter coefficients A0 and A1 that match the amplitude and phase of the reference signal xc and the reference signal xs with the low-frequency noise.

[0115] The decimation signal generator 77 includes a first decimation filter 77a, a second decimation filter 77b, and an adder 77c. The first decimation filter 77a has a filter coefficient A0, and the second decimation filter 77b has a filter coefficient A1.

[0116] The adder 77c adds the reference signal xc whose amplitude is adjusted by the first decimation filter 77a and the reference signal xs whose amplitude is adjusted by the second decimation filter 77b, thereby generating an decimated signal efr.

[0117] The virtual error signal generator 78 generates a virtual error signal e2 based on the error signal e, the estimated noise signal d_b^, and the estimated cancellation sound signal y_b^. The virtual error signal generator 78 includes an inverting amplifier 78a, an inverting amplifier 78b, and an adder 78c.

[0118] The error signal e converted to a digital signal by the analog / digital converter 79, the estimated noise signal -d_b^ obtained by inverting the polarity by the inverting amplifier 78a, and the estimated cancellation sound signal -y_b^ obtained by inverting the polarity by the inverting amplifier 78b are added together by the adder 78c. This generates a virtual error signal e2.

[0119] The differential signal generating section 81 generates a differential signal e0 based on the error signal e and the extracted signal efr. The differential signal generating section 81 includes an adder 81a. The adder 81a adds the error signal e and the extracted signal efr to generate the differential signal e0.

[0120] The primary path filter updating unit 83 adaptively updates the primary path filter H^ in sequence by using an adaptive algorithm (eg, LMS algorithm) to minimize the virtual error signal e2.

[0121] The primary path filter updating unit 83 includes a first primary path filter coefficient updating unit 83a and a second primary path filter coefficient updating unit 83b. The first primary path filter coefficient updating unit 83a and the second primary path filter coefficient updating unit 83b update the filter coefficient H0^ and the filter coefficient H1^ according to the following equation. Where n represents the number of time steps (n = 0, 1, 2, ...), μ0 H 、μ1 H Represents the step size parameter.

[0122] H0^ n+1 =H0^ n -μ0 H ×e2 n ×a0_b n

[0123] H1^ n+1 =H1^ n -μ1 P ×e2 n ×a1_b n

[0124] The secondary path filter updating unit 84 adaptively updates the secondary path filter C^ in sequence using an adaptive algorithm (eg, LMS algorithm) to minimize the virtual error signal e2.

[0125] The secondary path filter updating unit 84 includes a first secondary path filter coefficient updating unit 84a and a second secondary path filter coefficient updating unit 84b. The first secondary path filter coefficient updating unit 84a and the second secondary path filter coefficient updating unit 84b update the filter coefficient C0^ and the filter coefficient C1^ according to the following equation. Where n represents the number of time steps (n = 0, 1, 2, ...), μ0 C、μ1 C Represents the step size parameter.

[0126] C0^ n+1 =C0^ n -μ0 C ×e2 n ×u0_b n

[0127] C1^ n+1 =C1^ n -μ1 C ×e2 n ×u1_b n

[0128] The decimation filter updating section 85 adaptively updates the decimation filter A in sequence using an adaptive algorithm (eg, LMS algorithm) to minimize the differential signal e0.

[0129] The decimation filter updating unit 85 includes a first decimation filter coefficient updating unit 85a and a second decimation filter coefficient updating unit 85b. The first decimation filter coefficient updating unit 85a and the second decimation filter coefficient updating unit 85b update the filter coefficient A0 and the filter coefficient A1 according to the following equation. Where n represents the number of time steps (n = 0, 1, 2, ...), μ0 A 、μ1 A Represents the step size parameter.

[0130] A0 n+1 =A0 n -μ0 A ×e0 n ×xc n

[0131] A1 n+1 =A1 n -μ1 A =e0 n ×xs n

[0132] [Feedback filter FB setting]

[0133] The feedback filter setting unit 23 sets the feedback filter FB based on the primary path filter H ^ and the secondary path filter C ^. Next, the setting of the feedback filter FB will be described.

[0134] When the primary path filter H^ converges to the transmission characteristic H of the primary path and the secondary path filter C^ converges to the transmission characteristic C of the secondary path, the primary path filter H^ is expressed by the following equation.

[0135] H^=C^·FB

[0136] This equation is solved for the feedback filter FB, and the feedback filter FB is expressed as follows.

[0137] FB=H^ / C^

[0138] The feedback filter setting unit 23 sets the value obtained by normalizing the real part of H^ / C^ by |H^ / C^| as the filter coefficient FBP0. The feedback filter setting unit 23 sets the value obtained by normalizing the imaginary part of H^ / C^ by |H^ / C^| as the filter coefficient FBP1.

[0139] The feedback filter setting unit 23 gradually increases the gain FBG from its initial value to |1 / C^|. When the primary path filter H^ and the secondary path filter C^ are updated infrequently and learning is not progressing, the value of |1 / C^| may increase dramatically. Therefore, by gradually increasing the gain FBG, it is possible to suppress the output of loud sound pressure from the speaker 18 that would be offensive to the occupants. The initial value of the gain FBG is not set to 0, but rather to a value small enough to prevent the output of sound from the speaker 18 that would be offensive to the occupants. This is because if the initial value of the gain FBG were set to 0, the learning of the secondary path filter C^ would not progress.

[0140] Furthermore, the feedback filter setting unit 23 may set the gain FBG to an initial value when the gain |H^| of the primary path filter H^ or the gain |C^| of the secondary path filter C^ is below a predetermined value. By keeping the gain FBG at the initial value until learning of the primary path filter H^ and the secondary path filter C^ progresses, it is possible to prevent the speaker 18 from outputting sounds that may be offensive to the occupants.

[0141] Furthermore, the feedback filter setting unit 23 may restore the gain FBG to its initial value when at least one of the following four conditions is satisfied. The four conditions are the following conditions (1) to (4).

[0142] (1) The gain change caused by updating the primary path filter H is greater than the specified amount.

[0143] (2) The phase change caused by updating the primary path filter H is greater than a specified amount.

[0144] (3) The gain change caused by updating the secondary path filter C^ is greater than a specified amount.

[0145] (4) The phase change caused by updating the secondary path filter C^ is greater than a specified amount.

[0146] When the position of microphone 32 changes, the secondary path transmission characteristic C may change significantly. In this case, relearning of the secondary path filter C^ is performed. In this case, by temporarily setting the gain FBG to an initial value and then gradually increasing the gain FBG from the initial value to |H^ / C^|, it is possible to suppress the output of loud sound pressure from speaker 18 that could cause discomfort to the occupants.

[0147] [Effects]

[0148] In the active noise control device 10 of this embodiment, the control signal generator 68 processes the reference signal xc and the reference signal xs using the feedback filter FB and the decimation filter A. This generates the control signal u0_b for controlling the speaker 18. Furthermore, the feedback filter setting unit 23 sets the feedback filter FB based on the secondary path filter C^. Furthermore, the secondary path filter updater 84 sequentially and adaptively updates the secondary path filter C^. This allows the secondary path filter C^ to follow the transfer characteristic C even when the secondary path transfer characteristic C changes. As a result, the control signal u0_b can be generated in accordance with changes in the transfer characteristic C, thereby reducing the sound pressure of low-frequency noise.

[0149] Furthermore, in the active noise control device 10 of this embodiment, the feedback filter setting unit 23 sets the feedback filter FB based on the primary path filter H ^ and the secondary path filter C ^. This reduces the amount of calculation required to set the feedback filter FB, thereby suppressing the load on the calculation unit.

[0150] [Technical Concepts Achievable by Implementation Methods]

[0151] The following describes the technical ideas that can be grasped from the above-mentioned embodiments.

[0152] An active noise control device (10) controls a speaker (18) based on a component of a frequency band centered on a predetermined frequency of an error signal output by a detector (32) that detects a synthetic sound at a control point, wherein the synthetic sound is a synthetic sound of noise transmitted from a vibration source and a canceling sound output from the speaker (18) to cancel the noise. The active noise control device (10) comprises a reference signal generating unit (67), a control signal generating unit (68), an estimated canceling sound signal generating unit (70), a decimation signal generating unit (77), a hypothetical error signal generating unit (78), a difference signal generating unit (81), a secondary path filter updating unit (84), a decimation filter updating unit (85), and a feedback filter setting unit (23). The reference signal generating unit (67) generates a reference signal corresponding to the predetermined frequency; the control signal generating unit (68) processes the reference signal through a feedback filter and a decimation filter as an adaptive notch filter to generate a signal for controlling the speaker. the estimated cancellation sound signal generating unit (70) processes the control signal through a secondary path filter as an adaptive notch filter to generate an estimated cancellation sound signal; the decimation signal generating unit (77) processes the reference signal through the decimation filter to generate a decimation signal; the hypothetical error signal generating unit (78) generates a hypothetical error signal based on the error signal and the estimated cancellation sound signal; the differential signal generating unit (81) generates a differential signal based on the error signal and the decimation signal; the secondary path filter updating unit (84) adaptively updates the secondary path filter in sequence based on the control signal and the hypothetical error signal to minimize the size of the hypothetical error signal; the decimation filter updating unit (85) adaptively updates the decimation filter in sequence based on the reference signal and the differential signal to minimize the size of the differential signal; and the feedback filter setting unit (23) sets the feedback filter based on the secondary path filter.

[0153] In the above-described active noise control device, the feedback filter setting unit may gradually increase the gain of the feedback filter from a predetermined initial value.

[0154] In the above-described active noise control device, the feedback filter setting unit may set the gain of the feedback filter to a predetermined initial value when the gain of the secondary path filter is equal to or less than a predetermined value.

[0155] In the active noise control device described above, the feedback filter setting unit may set the gain of the feedback filter to a predetermined initial value when a change in gain or phase of the secondary path filter is greater than a predetermined amount.

[0156] In the above-described active noise control device, the feedback filter setting unit may set the feedback filter based on the secondary path filter and a predetermined noise reduction amount.

[0157] The active noise control device may further include an estimated noise signal generating unit (75) and a primary path filter updating unit (83), wherein the estimated noise signal generating unit (75) processes the extracted signal using a primary path filter as an adaptive notch filter to generate an estimated noise signal; the primary path filter updating unit (83) updates the primary path filter based on the reference signal and the hypothetical error signal so as to minimize the magnitude of the hypothetical error signal; the hypothetical error signal generating unit generates the hypothetical error signal based on the error signal, the estimated noise signal, and the estimated cancellation sound signal; and the feedback filter setting unit calculates the feedback filter based on the primary path filter and the secondary path filter.

Claims

1. An active noise control device (10) for controlling a speaker (18) based on a component of a frequency band centered on a predetermined frequency of an error signal output by a detector (32) that detects a synthesized sound at a control point, wherein: The synthesized sound is a synthesized sound of the noise transmitted from the vibration source and the canceling sound output from the speaker (18) to cancel the noise. The active noise control device is characterized in that: The invention comprises a reference signal generating unit (67), a control signal generating unit (68), an estimated cancellation sound signal generating unit (70), a decimation signal generating unit (77), an estimated noise signal generating unit (75, 76), a hypothetical error signal generating unit (78), a difference signal generating unit (81), a secondary path filter updating unit (84), a decimation filter updating unit (85), and a feedback filter setting unit (23), wherein: The reference signal generating unit (67) generates a reference signal corresponding to the prescribed frequency; The control signal generating unit (68) performs signal processing on the reference signal through a feedback filter and a decimation filter as an adaptive notch filter to generate a control signal for controlling the speaker; The estimated cancellation sound signal generating unit (70) processes the control signal through a secondary path filter as an adaptive notch filter to generate an estimated cancellation sound signal; The decimation signal generating unit (77) performs signal processing on the reference signal through the decimation filter to generate a decimation signal; The estimated noise signal generating unit (75, 76) generates an estimated noise signal by processing the reference signal using an adjustment filter as an adaptive notch filter, or generates an estimated noise signal by processing the extracted signal using a primary path filter as an adaptive notch filter. The hypothetical error signal generating unit (78) generates a hypothetical error signal based on the error signal, the estimated cancellation sound signal, and the estimated noise signal; The differential signal generating unit (81) generates a differential signal based on the error signal and the extracted signal; The secondary path filter updating unit (84) adaptively updates the secondary path filter in sequence according to the control signal and the hypothetical error signal, so as to minimize the size of the hypothetical error signal; The decimation filter updating unit (85) adaptively updates the decimation filter in sequence according to the reference signal and the differential signal, so as to minimize the size of the differential signal; The feedback filter setting unit (23) sets the feedback filter according to the secondary path filter.

2. The active noise control device according to claim 1, characterized in that: The feedback filter setting unit gradually increases the gain of the feedback filter from a predetermined initial value.

3. The active noise control device according to claim 1 or 2, characterized in that: The feedback filter setting unit sets the gain of the feedback filter to a predetermined initial value when the gain of the secondary path filter is equal to or less than a predetermined value.

4. The active noise control device according to claim 1 or 2, characterized in that: The feedback filter setting unit sets the gain of the feedback filter to a predetermined initial value when a change in the gain or phase of the secondary path filter is equal to or greater than a predetermined amount.

5. The active noise control device according to claim 1 or 2, characterized in that: The feedback filter setting unit sets the feedback filter based on the secondary path filter and a predetermined noise reduction amount.

6. The active noise control device according to claim 1 or 2, characterized in that: It has a primary path filter updating unit (83), The primary path filter updating unit (83) updates the primary path filter based on the reference signal and the hypothetical error signal so as to minimize the magnitude of the hypothetical error signal. The feedback filter setting section calculates the feedback filter based on the primary path filter and the secondary path filter.

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