Abstract:
An active noise control apparatus that controls by a control sound a noise which is output from a noise source, includes: a control sound generating section which inputs a control signal, and produce the control sound; a residual noise detecting section which detects, as a residual noise signal, a noise remaining after the noise control by the control sound; a control signal generating section which inputs, as a reference signal, a signal concerning the noise or the generation state of the noise, and generates the control signal; and a controlling section which inputs the control signal and the residual noise signal, detects the components that cannot be identified in the control signal generating section, and controls the generation of the control signal in the control signal generating section.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2008-108690, filed on Apr. 18, 2008, the entire contents of which are incorporated herein by reference. 
     FIELD 
     The embodiments discussed herein are related to an active noise control apparatus which makes a sonic wave having the same amplitude and opposite phase as those of a noise interfere with the noise, thereby actively controlling the noise. 
     BACKGROUND 
     There is known a technique called an active noise control (ANC) for making a sonic wave (control sound) having the same amplitude and opposite phase as those of a noise interfere with the noise, thereby controlling the noise by the interference effect. In recent years, there is proposed an active noise control apparatus for an air conditioning noise and an indoor noise in a factory or an automobile and the like. 
       FIG. 1  is a block diagram of a conventional active noise control apparatus having high noise control performance with a small calculation amount (see Japanese Patent No. 2872545, for example). Here, the conventional technique illustrated in  FIG. 1  is called a conventional technique  1 . 
     As illustrated in  FIG. 1 , a reference signal detecting section  10  disposed in a coming direction of a noise detects a signal (reference signal) concerning a noise generating state, an adaptive filter  20  produces a control signal from the reference signal, and a control sound generating section  30  outputs a control sound based on the produced control signal. A residual noise detecting section  40  disposed in a region where it is desired to control a sound detects a residual noise after the interference, the adaptive filter  20  adaptively obtains a coefficient of a filter which produces the control signal from the reference signal such that the residual noise becomes minimum, so that it is possible to obtain a stable noise control performance which can excellently follow aged deterioration of the control sound generating section  30  and the residual noise detecting section  40  and temperature and humidity changes of a space propagation system from the control sound generating section  30  to the residual noise detecting section  40 . The active noise control apparatus having the structure described above is called a feedforward ANC. 
     Many algorithms such as LMS and RLS have been proposed as adaptive algorithm used here heretofore, but since a control sound is required to be produced in real time, Filtered-X LMS (Least Mean Square) algorithm is frequently used in view of a small calculation amount (see B. Widrow and S. Stearns, “Adaptive Signal Processing” (Prentice-Hall, Englewood, Cliffs, N.J., 1985) and “Active Noise Control”, Corona written by Seiji NISHIMURA, Takeshi USAGAWA, and Shirou ISE). The basic principle is for renewing a filter coefficient based on a steepest-descent method so that the residual noise is reduced in consideration of a transfer function from the control sound generating section to the residual noise detecting section. As illustrated in  FIG. 1 , if a reference signal at time
 
 t  
 
     is defined as
 
 x ( t ),
 
     the reference signal is vectorized to obtain
 
 x ( t )=[ x ( t ), x ( t− 1), . . . , x ( t−N   w +1)],
 
     to which a transfer function of an error path from the control sound generating section to the residual noise detecting section
 
 ĉ=[ĉ (1), ĉ (2), . . . , ĉ ( N   w )]
 
(wherein,
 
 N   w  
 
     is the number of taps of filters of the error path is convoluted to obtain a signal (filter reference signal), the signal is given as illustrated in the equation (1).
 
 r ( t )= ĉ*x ( t )  (1)
 
     (* represents a convolution calculation of vector) 
     For a renewal equation of filter coefficient, this signal is vectorized to obtain
 
 r ( t )=[ r ( t ), r ( t− 1), . . . , r ( t−N   h +1)]
 
     Using this, the renewal equation can be formulated as follows.
 
 h ( t+ 1)= h ( t )+μ· e ( t )· r ( t )  (2)
 
Wherein,
 
 e ( t )
 
     represents, at time
 
 t  
 
     a residual noise signal,
 
μ
 
     represents a step size parameter,
 
 h ( t )=[ h (1, t ), h (2, t ), . . . , h ( N   h   ,t )]
 
(wherein,
 
 N   h  
 
     represents the number of taps of the adaptive filter), at time
 
 t  
 
     represents filter coefficient of the adaptive filter. 
     In the conventional technique  1  explained with reference to  FIG. 1 , when an excessive large control signal is input to the control sound generating section, harmonic distortion or cross modulation distortion is generated due to nonlinearity of a vibration system or a driving system of the control sound generating section (see Japanese Laid-open Patent Publication No. H8-317490, for example). 
       FIG. 2  is a schematic diagram illustrating that harmonic distortion is generated in a control sound when the excessive large control signal is input to the control sound generating section. 
     Even if a control signal which is input to the control sound generating section is an undistorted signal as illustrated with a solid line in  FIG. 2 , when its amplitude is excessively large, a control sound which is output from the control sound generating section becomes a distorted signal having such a shape that a peak portion is slightly crushed as illustrated with a broken line in  FIG. 2 , and third harmonic illustrated with a chain line in  FIG. 2  is included in this distorted signal in addition to the original frequency signal. When original noise exists in the same band as that of the third harmonic, the generation of harmonic deteriorates the sound control effect in the same band as that of this harmonic. 
       FIG. 3  is a block diagram illustrating another example of the conventional active noise control apparatus (see Japanese Patent No. 3503155, for example). Here, the conventional technique illustrated in  FIG. 3  is called a conventional technique  2 . 
     The conventional technique  2  illustrated in  FIG. 3  is different from the conventional technique  1  illustrated in  FIG. 1  in that a control signal correcting section  50  is disposed between the adaptive filter  20  and the control sound generating section  30 . In the control signal correcting section  50 , a harmonic is calculated from a control signal which is output from the adaptive filter  20 , a correction coefficient is renewed based on a signal in which an error function from the control sound generating section to the residual noise detecting section for the harmonic is convoluted, and a residual noise signal, the harmonic is corrected using the renewed correction coefficient, and the corrected harmonic is added to the control signal which is output from the adaptive filter  20 . 
     Here, the conventional technique  1  explained with reference to  FIG. 1  has an adverse effect that if an excessive large control signal is input to the control sound generating section, a harmonic distortion is generated in the control sound due to nonlinearity of the vibration system or the driving system of the control sound generating section, and the sound controlling effect in a band where harmonic is generated is deteriorated. Hence, there is conceived a method in which a signal which cancels an influence of the harmonic distortion is adaptively sought as illustrated in  FIG. 3 , so that the control signal is corrected, thereby preventing the noise control performance from being deteriorated due to generation of distortion. 
     The conventional technique  2  illustrated in  FIG. 3  has no problem if a harmonic component is correctly estimated and cancelled, but if a frequency component of integral multiple is included in the original noise or a harmonic component is erroneously estimated due to characteristic change of a space transmission system of an error path, there is a problem that not only the adverse effects of the harmonic remains, but also the noise control performance is deteriorated due to the generation of the erroneous counteracting signal. 
       FIG. 4  is an explanatory diagram of the problem of the conventional technique  2  illustrated in  FIG. 3 . 
     Here, it is indicated that noise is generated in two frequency bands before the ANC operation, and the noise in one of the frequency bands is cancelled after the ANC operation, but the noise in the other band corresponding to a harmonic can not controlled sufficiently. When the band where noise is not sufficiently controlled is more important subjectively, the problem is serious. 
     SUMMARY 
     An active noise control apparatus that controls by a control sound a noise which is output from a noise source, includes: 
     a control sound generating section which inputs a control signal, and produce the control sound; 
     a residual noise detecting section which detects, as a residual noise signal, a noise remaining after the noise control by the control sound; 
     a control signal generating section which inputs, as a reference signal, a signal concerning the noise or the generation state of the noise, and generates the control signal; and 
     a controlling section which inputs the control signal and the residual noise signal, detects the components that cannot be identified in the control signal generating section, and controls the generation of the control signal in the control signal generating section. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram of a conventional active noise control apparatus; 
         FIG. 2  is a schematic view illustrating that a harmonic distortion is generated in a control sound when an excessive large control signal is input to a control sound generating section; 
         FIG. 3  is a block diagram illustrating another example of a conventional active noise control apparatus; 
         FIG. 4  is an explanatory diagram of a problem of the conventional active noise control apparatus illustrated in  FIG. 3 ; 
         FIG. 5  is a block diagram of a first embodiment of an active noise control apparatus of the present invention; 
         FIG. 6  is an explanatory diagram of operation of the active noise control apparatus of the first embodiment; 
         FIG. 7  is a detailed block diagram of a reference signal detecting section, a control signal generating section and a residual noise detecting section of the active noise control apparatus of the first embodiment; 
         FIG. 8  is a detailed block diagram of a controlling section of the active noise control apparatus of the first embodiment; 
         FIG. 9  is a flowchart illustrating operations of the active noise control apparatus of the first embodiment; 
         FIG. 10  is a block diagram of a second embodiment of the active noise control apparatus of the present invention; and 
         FIG. 11  is a detailed block diagram of a threshold value changing section of the active noise control apparatus of the second embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Preferred embodiments of the present invention will be explained with reference to accompanying drawings. 
       FIG. 5  is a block diagram of a first embodiment of an active noise control apparatus of the present invention. 
     The active noise control apparatus of the first embodiment illustrated in  FIG. 5  includes a control sound generating section  30  and a residual noise detecting section  40  which are similar to those of the conventional techniques illustrated in  FIGS. 1 and 3 . The active noise control apparatus also includes a control signal generating section  100  and a controlling section  300 . The active noise control apparatus is configured such that the active noise control apparatus divides a reference signal and a residual noise signal into multiple bands, and performs adaptive learning of a filtering coefficient in each divided band. The active noise control apparatus evaluates a generation state of harmonic distortion in each divided band, and if the harmonic distortion is likely generated, the learning operation of the filtering coefficient with respect to that band is interrupted or reset so that an excessive input to a speaker is avoided. 
       FIG. 6  is an explanatory diagram of operation of the active noise control apparatus of the first embodiment illustrated in  FIG. 5 . 
     According to the active noise control apparatus illustrated in  FIG. 5 , the active noise control apparatus illustrated in  FIG. 5  evaluates the generation state of the harmonic distortion for each of the multiple divided bands and control the learning operation of the filtering coefficient. As a result, it is possible to avoid a deterioration of the noise control performance caused by a harmonic distortion and to enhance the sound control effect. 
       FIG. 7  is a detailed block diagram of the control signal generating section of the active noise control apparatus of the first embodiment illustrated in  FIG. 5 .  FIG. 8  is a detailed block diagram of a controlling section of the active noise control apparatus of the first embodiment illustrated in  FIG. 5 . 
     The reference signal detecting section  10  detects a signal (reference signal) concerning the generation state of noise,
 
 x ( t ),
 
     and divides the detected reference signal by six band-pass filters  101 _ 1 ,  101 _ 2 , . . . ,  101 _ 6  which divides a band into predetermined six bands. 
     The control sound generating section  30  is arranged to direct to a region where it is desired to control a noise, and outputs a control sound which interferes with a noise. 
     The residual noise detecting section  40  detects a residual noise which remains after a control sound generated by the control sound generating section  30  interferes with the noise
 
 e ( t ),
 
     and divides the detected residual noise signal by the band-pass filters  201 _ 1 ,  201 _ 2 , . . . ,  201 _ 6  which divides a band into six bands. 
     The controlling section  300  includes six harmonic component calculating sections  301 _ 1 ,  301 _ 2 , . . . ,  301 _ 6  which calculate harmonic components with respect to outputs of the six adaptive filters  102 _ 1 ,  102 _ 2 , . . . ,  102 _ 6  for the respective divided bands of the control signal generating section  100 ; error path correction filters  302 _ 1 ,  302 _ 2 , . . . ,  302 _ 6  which convolute transmission characteristics of the error path from the control sound generating section  30  to the residual noise detecting section  40  into each of the harmonic components, thereby correcting each of the harmonic components; six band-pass filters  303 _ 1 ,  303 _ 2 , . . . ,  303 _ 6  which divide a residual noise signal detected by the residual noise detecting section  40  into six bands respectively corresponding to bands of the harmonic components; and six correlation calculating sections  304 _ 1 ,  304 _ 2 , . . . ,  304 _ 6  which calculate correlations between the residual noise signals divided by the band-pass filters  303 _ 1 ,  303 _ 2 , . . . ,  303 _ 6  and the harmonic components. 
     The control signal generating section  100  includes six adaptive filters  102 _ 1 ,  102 _ 2 , . . . ,  102 _ 6  which perform filtering operations for reference signals in each of the bands divided by the reference signal detecting section  10 , and an adder  103  which adds outputs of the six adaptive filters  102 _ 1 ,  102 _ 2 , . . . ,  102 _ 6 . Further, the control signal generating section  100  includes a threshold value storing section  202  which stores a threshold value, and 
     a switch group  203  which compares correlation values calculated by the correlation calculating sections  304 _ 1 ,  304 _ 2 , . . . ,  304 _ 6  of the distortion evaluating section  300 
 
corr 1 ( t ),corr 2 ( t ), . . . corr 6 ( t )
 
with corresponding threshold values of the multiple threshold values TH 1  to TH 6  stored in the threshold value storing section  202  respectively, thereby selecting a band of the divided bans which is to be used for renewing a filter coefficient.
 
       FIG. 9  is a flowchart illustrating operations of the active noise control apparatus of the first embodiment. 
     The operations of the active noise control apparatus of the first embodiment will be explained with reference to block diagrams in  FIGS. 7 and 8  and a flowchart in  FIG. 9 . 
     In the active noise control apparatus of the first embodiment, an operation of processing both the residual noise signal and reference signal corresponding to a noise detected by the reference signal detecting section  10  by the control signal generating section  100 , and an operation of processing both the control signal and residual error signal by the Controlling section  300  are executed in parallel. However, if a filtering coefficient is renewed in the adaptive filters  102 _ 1 ,  102 _ 2 , . . . ,  102 _ 6 , corresponding frequency components of the reference signal and the residual noise signal detected at the same time are used for the calculation. 
     In the block diagrams in  FIGS. 7 and 8 , the current time is defined as
 
 t  
 
     and the following processes (1) to (12) are carried out repeatedly. 
     (Reference Signal Detecting Section) 
     (1) The reference signal detecting section detects
 
 x ( t )
 
     a reference signal. 
     (2) The band-pass filters  101 _ 1 ,  101 _ 2 , . . . ,  101 _ 6  are applied to
 
 x ( t )
 
     the detected reference signals, and the reference signals divided into the six bands
 
 x   i ( t )( i= 1,2, . . . ,6)
 
     are calculated.
 
 x   i ( t )= bpf   i   *x ( t )( i= 1,2, . . . ,6)
 
     (The control signal generating section) 
     (3) Filtering coefficient of adaptive filter
 
 h   i ( t )( i= 1,2, . . . ,6)
 
     Using the equation 23, from the divided reference signals
 
 x   i ( t )( i= 1,2, . . . ,6)
 
     control signals in the respective bands
 
 y   i ( t )( i= 1,2, . . . ,6)
 
     are produced.
 
 y   i ( t )= h   i ( t )* x   i ( t )( i= 1,2, . . . ,6)
 
     (4) Control signal in respective bands
 
 y   i ( t )( i= 1,2, . . . ,6)
 
     are added, the control signal,
 
 y ( t )
 
     is produced and is output as a control sound from the control sound generating section  30 . 
     
       
         
           
             
               y 
               ⁡ 
               
                 ( 
                 t 
                 ) 
               
             
             = 
             
               
                 ∑ 
                 
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                   1 
                 
                 6 
               
               ⁢ 
               
                   
               
               ⁢ 
               
                 
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                   t 
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     (Controlling Section) 
     (5) A residual noise signal
 
 e ( t )
 
     is detected by the residual noise detecting section. 
     (6) For outputs of the adaptive filters in the respective divided bands
 
 y   i ( t )( i= 1,2, . . . ,6)
 
     harmonic components
 
 y   i ( t ) 3 ( i= 1,2, . . . ,6)
 
     are calculated. Odd-order (third, fifth, . . . ) harmonics are generated due to an excessive large input to a speaker, but since the influence of third component specifically is relatively large, the fifth or higher order harmonics are omitted here. 
     (7) For respective harmonic components
 
 y   i ( t ) 3 ( i= 1,2, . . . ,6)
 
     error path corrections are performed, and corrected harmonic components
 
 hm   i ( t )( i= 1,2, . . . ,6)
 
     are calculated.
 
 hm   i ( t )= ĉ*y   i ( t ) 3 ( i= 1,2, . . . ,6)
 
     (wherein
 
 ĉ 
 
     represents a transfer function of an error path from the control sound generating section  30  to the residual noise detecting section  40 ) 
     (8) A residual noise signal
 
 e ( t )
 
     is divided into six bands corresponding to the respective bands of the harmonic components.
 
 e′   i ( t )= bpf′   i   *e ( t )( i= 1,2, . . . ,6)
 
     (9) For harmonic components for the individual divided bands
 
 hm   i ( t )( i= 1,2, . . . ,6)
 
     and the residual noise signals,
 
 e′   i ( t )( i= 1,2, . . . ,6)
 
     harmonic distortions
 
corr i ( t )( i= 1,2, . . . ,6)
 
     are calculated. 
     
       
         
           
             
               
                 corr 
                 i 
               
               ⁡ 
               
                 ( 
                 t 
                 ) 
               
             
             = 
             
               
                 
                   max 
                   
                     k 
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                         j 
                         = 
                         0 
                       
                       L 
                     
                     ⁢ 
                     
                         
                     
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                           hm 
                           i 
                         
                         ⁡ 
                         
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                             t 
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                           ) 
                         
                       
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     (wherein
 
 T  
 
     represents a correlation calculation range, and
 
 L  
 
     represents a correlation calculation length) 
     (Residual Noise Detecting Section) 
     (10) For the detected residual noise signal
 
 e ( t )
 
     a band-pass filter
 
 bpf   i ( i= 1,2, . . . ,6)
 
     is applied, 
     thereby dividing the band into six, and the residual noise signal after dividing
 
 e   i ( t )( i= 1,2, . . . ,6)
 
     are calculated.
 
 e   i ( t )= bpf   i   *e ( t )( i= 1,2, . . . ,6)
 
     (Control Signal Generating Section) 
     (11) For a band where harmonic distortions
 
corr i ( t )( i= 1,2, . . . ,6)
 
     become greater than predetermined threshold values for the adaptive learning control,
 
 TH   i ( i= 1,2, . . . ,6),
 
     the band-divided residual noise signals are set to 0, thereby selecting a band to be used for renewing a filtering coefficient of the adaptive filter. 
     
       
         
           
             
               
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     (Renewal of Filtering Coefficient of Adaptive Filter) 
     (12) By the reference signals after the band is divided
 
 x   i ( t )
 
     and the residual noise signals,
 
 e″   i ( t )
 
     the filtering coefficient of the adaptive filter
 
 h   i ( t )( i= 1,2, . . . ,6)
 
     are renewed.
 
 h   i ( t+ 1)= h   i ( t )+μ· e″   i ( t )· ĉ*x   i ( t )( i= 1,2, . . . ,6)
 
(wherein
 
μ
 
     represents a step size parameter, and
 
 ĉ 
 
     represents a transfer function of an error path from the control sound generating section to the residual noise detecting section.) 
     The active noise control apparatus of the first embodiment is operated as described above, evaluates a generation state of a harmonic distortion in each of multiple divided bands to control the learning operation of the filtering coefficient, so that it is possible to avoid a deterioration of the noise control performance by a harmonic distortion, and to enhance the sound control effect. 
       FIG. 10  is a block diagram of a second embodiment of the active noise control apparatus of the present invention. 
     In  FIG. 10 , a threshold value changing section  400  is added to the structure illustrated in  FIG. 5 . The threshold value changing section  400  dynamically changes a threshold value to be used for controlling whether adaptive learning operation is carried out. In the following description, a redundant explanation will be omitted, and the threshold value changing section  400  will be explained. 
       FIG. 11  is a detailed block diagram of the threshold value changing section of the active noise control apparatus of the second embodiment illustrated in  FIG. 10 . 
     In  FIG. 10 , the threshold value changing section  400  includes six band-pass filters  401 _ 1 ,  401 _ 2 , . . . ,  401 _ 6  for dividing a band into six bands, six level calculating sections  402 _ 1 ,  402 _ 2 , . . . ,  402 _ 6 , and six threshold value estimating sections  403 _ 1 ,  403 _ 2 , . . . ,  403 _ 6 . 
     The band-pass filters  401 _ 1 ,  401 _ 2 , . . . ,  401 _ 6  are the same as the band-pass filters  303 _ 1 ,  303 _ 2 , . . . ,  303 _ 6  of the controlling section  300  illustrated in  FIG. 8 . The band-pass filters  401 _ 1 ,  401 _ 2 , . . . ,  401 _ 6  divide a residual noise signal from the residual noise detecting section  40 
 
 e ( t )
 
     into six bands corresponding to harmonic components. 
     The level calculating sections  402 _ 1 ,  402 _ 2 , . . . ,  402 _ 6  input band components e 1 ′( t ), . . . , e 6 ′( t ) of the residual noise signal, respectively, calculate mean values for a predetermined time (Te) for respective band components, and obtains mean values of sound pressure levels of the respective bands. 
     A level calculating section i which processes the i-th ( i= 1, . . . , 6) band component ei′(t) carries out, for example, the following action. 
     The square of ei′(t) (ei′(t)) 2  is calculated from the input ei′(t). A total sum of values of each time of the current time and a past time which are latched in delaying devices (not illustrated), i.e., {ei′(t)} 2 , {ei′ (t−1)} 2 , . . . , {ei′ (t−Te)} 2 , thereby obtaining outputs bli of the level calculating sections  402   —   i  by the following equation. 
     
       
         
           
             
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     The threshold value estimating sections  403 _ 1 ,  403 _ 2 , . . . ,  403 _ 6  input outputs bl 1 , . . . , bl 6  of the six level calculating sections  402 _ 1 ,  402 _ 2 , . . . ,  402 _ 6  as sound pressure levels of the respective bands, change the threshold values TH 1 , TH 2 , . . . for controlling adaptive learning operation, and output the same to the threshold value storing section  202  (see  FIG. 7 ) in the control signal generating section  100  in  FIG. 10 . 
     Next, two methods of changing threshold value by the threshold value estimating sections  403 _ 1 ,  403 _ 2 , . . . ,  403 _ 6  will be explained. 
     According to a first method of changing threshold value, a threshold value is changed in the following manner.
     1. Second threshold values for determining whether sound pressure levels in six bands corresponding to harmonic components are large provided independently from threshold values for the adaptive learning operation control.   2. When the sound pressure levels in the respective band are greater than the second threshold values, the adaptive learning operation control threshold values are set to greater values. With this, when a residual noise in a band corresponding to a harmonic component is large and a harmonic distortion is unremarkable, it is possible to control renewing filtering coefficients in respective divided bands such that a control of discontinuing the adaptive learning to enhance the noise control performance.   3. When the sound pressure levels in the respective bands are not greater than the second threshold values, the threshold values for the adaptive learning operation control are set to small values. With this, when a residual noise of the band corresponding to the harmonic component is small and a high harmonic distortion is remarkable, it is possible to control renewing filtering coefficients in the respective divided bands such that an influence of the harmonic distortion becomes small.   

     The control based on the first method of changing threshold value is carried out, so that it is possible to enhance the noise control performance without generating a harmonic distortion (unusual sound), even when a spectrum after sound control is changed due to a surrounding noise or an environment of the active noise control apparatus. 
     According to a second method of changing threshold value, a threshold value is changed in the following manner. 
     When a band corresponding to a harmonic component is a band where a sensitivity of a near is high, the adaptive learning operation control threshold value is set to a small value. With this, when a high harmonic distortion is easily sensed, it is possible to control such that a noise control performance is enhanced without generating a high harmonic distortion (unusual sound). 
     Although Filtered-X LMS algorithm is used as the adaptive algorithm in the embodiments described above, another adaptive algorithm may be used. 
     According to the present invention, a generating state of a harmonic distortion is evaluated and learning of a filtering coefficient in the control sound generating section is controlled so that deterioration of the noise control performance caused by the harmonic distortion can be avoided, and the sound control effect can be enhanced. 
     All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the principles of the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiment(s) of the present invention(s) has(have) been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.