Patent Publication Number: US-10327070-B2

Title: Sound pickup device and imaging device using same

Description:
BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a sound pickup device that picks up a sound and an imaging device using the sound pickup device. 
     2. Description of the Related Art 
     Conventionally, an audio processing device having an auto level control (ALC) function for controlling input audio so that the sound has an appropriate level has been known (for example, see PTL 1). 
     A microphone device in PTL 1 includes a mechanism part that causes a noise at a time of operation in a device housing. This microphone device reduces mixing of a noise which is caused inside when picking up an external sound. The microphone device includes a main microphone, a noise reference microphone, an adaptive filter unit, a signal subtracting unit, a signal level comparison unit, and a filter coefficient updating control unit. The main microphone picks up an external sound that has arrived from outside the device housing. The noise reference microphone is provided inside the device housing. The adaptive filter unit receives a detection signal from the noise reference microphone, and generates a control sound signal using an updated filter coefficient. The signal subtracting unit subtracts the control sound signal of the adaptive filter unit from an output signal from the main microphone. The signal level comparison unit compares levels between an output signal from the main microphone and a detection signal of the noise reference microphone. The filter coefficient updating control unit receives a compared result of the signal level comparison unit, a subtracted result of the signal subtracting unit, and the detection signal of the noise reference microphone. When an output level of the noise reference microphone is larger than an output level of the main microphone, the filter coefficient updating control unit updates a filter coefficient of the adaptive filter unit such that the subtracted result of the signal subtracting unit becomes minimum. 
     With this microphone device, a signal is given from the noise reference microphone to the adaptive filter unit, thus a control sound signal is generated, and the control sound signal cancels a noise. As a result, mixing of an internal noise can be reduced when an external sound is picked up. 
     CITATION LIST 
     Patent Literature 
     PTL 1: Unexamined Japanese Patent Publication No. 2000-4494 
     SUMMARY 
     The present disclosure provides a sound pickup device that includes a housing having a porous exterior surface provided with a plurality of holes, a main microphone that receives sound pressure from an outside of the housing via the plurality of holes to generate a first audio signal and is disposed on an inside of the housing, a reference microphone that generates a second audio signal and is disposed near the main microphone on the inside the housing, a first support member that supports the main microphone and is disposed on the inside of the housing, a second support member that supports the reference microphone and is disposed on the inside of the housing, a first blocking member that blocks between the inside of the housing and an inside of the main microphone, a second blocking member that blocks between the outside of the housing and an inside of the reference microphone, and a third blocking member that blocks the inside of the housing and the inside of the reference microphone. 
     Further, the present disclosure provides an imaging device that includes an imaging unit that images a subject and generates an image signal, the sound pickup device that generates a third audio signal based on the first audio signal and the second audio signal, and a controller that records the image signal as well as the third audio signal in a predetermined recording medium. 
     With the sound pickup device of the present disclosure, even if the exterior surface has a porous shape, a noise included in an audio signal can be reduced when audio from an outside of an electronic device is picked up and thus an audio signal is generated. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating a configuration of an imaging device of the present disclosure; 
         FIG. 2A  is a front view of the imaging device of the present disclosure, and illustrates positions of punching metal plates; 
         FIG. 2B  is a top view of the imaging device of the present disclosure, and illustrates the positions of the punching metal plates; 
         FIG. 3  is a perspective view illustrating a configuration of a main microphone of the present disclosure; 
         FIG. 4  is a diagram schematically illustrating a cross-section of the main microphone taken along line  4 - 4  of  FIG. 3 ; 
         FIG. 5  is a diagram describing a disposition configuration of the main microphone and a reference microphone of the present disclosure; 
         FIG. 6A  is a pattern diagram illustrating a cross section of sponge C  133  in the imaging device of the present disclosure; 
         FIG. 6B  is a pattern diagram illustrating a cross section of sponge D  134  in the imaging device of the present disclosure; 
         FIG. 7  is a diagram describing a configuration of a noise suppressing function in a digital image/audio processor; 
         FIG. 8  is a diagram illustrating a measured result of a noise level in various disposition configurations of the reference microphone; 
         FIG. 9  is a diagram illustrating positions of the main microphone and the reference microphone in an imaging device of a modified example; and 
         FIG. 10  is a diagram illustrating a list of a first blocking member to a third blocking member in a first exemplary embodiment and the modified example. 
     
    
    
     DETAILED DESCRIPTION 
     Development of the Disclosure 
     The inventor of the present disclosure proposed a sound pickup device that, when picking up a sound outside an electronic device to generate an audio signal, can reduce a noise included in the audio signal in Unexamined Japanese Patent Publication No. 2016-243909. This sound pickup device is preferable for dust-proof and drip-proof digital cameras. 
     It is generally preferable for heightening sound quality to provide a sufficient pathway for allowing a sound to reach a main microphone to an exterior surface of an electronic device (a sound pickup device). Therefore, for an exterior surface of an electronic device, a porous member such as a punching metal plate is more desirable than a member in which small holes are provided locally on a position opposing a main microphone. When the exterior surface is made of a porous member such as a punching metal plate or when the punching metal plate does not have a horizontal face but has a slant face, a reference microphone that picks up a noise should be disposed near a main microphone and should be blocked from sound pressure from the outside of the electronic device. An object of the present disclosure is to, when audio from an outside of an electronic device is picked up and an audio signal is generated, reduce a noise included in the audio signal even if an exterior surface has a porous shape. 
     Hereinafter, exemplary embodiments will be described in detail with reference to the drawings appropriately. However, descriptions in more detail than necessary may be omitted. For example, a detailed description of a matter which is already well-known, or an overlapped description for a substantially identical configuration may be omitted. This is intended to prevent the following description from becoming unnecessarily redundant and to facilitate understanding by those skilled in the art. 
     Here, the inventor provides the attached drawings and the following description such that those skilled in the art can sufficiently understand the present disclosure, and therefore, they do not intend to restrict the subject matters of claims. 
     First Exemplary Embodiment 
     A first exemplary embodiment will now be described herein with reference to the drawings. 
     The first exemplary embodiment will exemplify a digital camera that can output an audio signal as one exemplary embodiment of an imaging device. A sound pickup device is incorporated into and integral with a digital camera. As resolution of a digital camera becomes higher, a taken image is influenced by camera shake more easily. Therefore, it is desirable to mount a camera shake correcting mechanism of high performance to a digital camera, but a noise is easily caused by driving of the camera shake correcting mechanism. That is, a high-resolution digital camera has a problem such that a noise is caused in the digital camera more easily. In general, it is desirable for heightening sound quality to provide a larger number of pathways for allowing a sound to reach a main microphone. That is, as an exterior surface of a digital camera, a porous exterior surface made of a punching metal plate or the like is more desirable than an exterior surface locally having small holes as sound pathways. However, when an exterior surface is made of a porous member such as a punching metal plate, it is substantially impossible to mount a main microphone and a reference microphone such that these microphones are enclosed in an exterior member (housing). That is, since it is difficult to mold a porous member by an injection molding method, it is difficult to mold a recessed portion (supporting member) that fixes a microphone integrally with a housing, and the like. Further, when a punching metal plate does not have a horizontal face but a slant face or a curved face, it is more difficult to mount a microphone such that the microphone is enclosed in an exterior member (housing). 
     Therefore, even when a main microphone and a reference microphone cannot be mounted to be enclosed in an exterior member, the first exemplary embodiment easily achieves a configuration such that the reference microphone can be disposed near the main microphone, and the reference microphone is blocked from sound pressure from outside. 
     1-1. Configuration 
     1-1-1. Entire Configuration 
       FIG. 1  is a diagram illustrating a configuration of digital camera  100  that is one exemplary embodiment of an imaging device having a sound pickup device of the present disclosure. Digital camera  100  images a subject and generates image data (still image, moving image) to record the image data on a recording medium. Digital camera  100  includes camera body  102 , and interchangeable lens  301  attached to camera body  102 . Digital camera  100  receives audio during taking a moving image, and can record audio data as well as the image data on the recording medium. 
     1-1-2. Configuration of Interchangeable Lens 
     Interchangeable lens  301  has an optical system including focus lens  310 , correcting lens  318 , and zoom lens  312 . Interchangeable lens  301  further includes lens controller  320 , lens mount  330 , focus lens driver  311 , zoom lens driver  313 , diaphragm  316 , diaphragm driver  317 , operating ring  315 , optical image stabilizer (OIS) driver  319 , dynamic random access memory (DRAM)  321 , flash memory  322 , and the like. 
     Lens controller  320  controls entire operation of interchangeable lens  301 . Lens controller  320  accepts an operation of operating ring  315  performed by a user, and can control zoom lens driver  313  such that zoom lens  312  is driven. Lens controller  320  can control focus lens driver  311 , OIS driver  319 , and diaphragm driver  317  such that focus lens  310 , correcting lens  318 , and diaphragm  316  are driven. 
     OIS driver  319  includes a drive mechanism configured with, for example, a magnet and a flat coil. OIS driver  319  controls the drive mechanism based on a detection signal of a gyro sensor that detects unsteadiness of interchangeable lens  301 , and shifts correcting lens  318  in a plane vertical to an optical axis of the optical system in accordance with the unsteadiness of interchangeable lens  301 . As a result, an influence of unsteadiness caused by camera shake in a picked up image can be reduced. 
     Lens controller  320  is connected to DRAM  321  and flash memory  322 , and writes or reads information in or from these memories as necessary. Further, lens controller  320  can communicate with controller  130  via lens mount  330 . Lens controller  320  may be configured with a hard-wired electronic circuit, or a microcomputer using a program, or the like. 
     Lens mount  330  is connected to body mount  340  of camera body  102 , and mechanically and electrically connects interchangeable lens  301  and camera body  102 . When interchangeable lens  301  is connected with camera body  102 , lens controller  320  and controller  130  can communicate with each other. Body mount  340  can transmit a signal received from lens controller  320  via lens mount  330  to controller  130  of camera body  102 . 
     1-1-3. Configuration of Camera Body 
     Camera body  102  includes charge coupled device (CCD) image sensor  143 , and analog front end (AFE)  144 . An exterior member (housing) of camera body  102  includes case  105  illustrated in  FIG. 2A  and punching metal plates  119   a ,  119   b , and  119   c  illustrated in  FIG. 2B . 
     CCD image sensor  143  picks up a subject image formed through interchangeable lens  301  to generate image information. As the image sensor, another kind of image sensor (for example, complementary metal oxide semiconductor (CMOS) image sensor) may be used. 
     With respect to image information read from CCD image sensor  143 , AFE  144  suppresses a noise through correlated double sampling, causes an analog gain controller to perform amplification to an input range width for an analog/digital (A/D) converter, and causes the A/D converter to perform A/D conversion. 
     Camera body  102  further includes audio input unit  111  and analog audio processor  115 . Audio input unit  111  includes two main microphones (main microphone  111 R, main microphone  111 L) that separately pick up main audio (audio to be recorded) from left and right directions. In the first exemplary embodiment, one example of a first direction is the left direction, and one example of a second direction is the right direction. A first main microphone is main microphone  111 R, and a second main microphone is main microphone  111 L. 
     Further, audio input unit  111  includes reference microphone  111 N that acquires information about a noise inside camera body  102 . That is, reference microphone  111 N receives at least one of a noise caused by vibration of camera body  102  and various noises generated in camera body  102 . The information acquired by reference microphone  111 N is used for generating a signal for suppressing a noise included in the main audio (noise component). 
     Each of the microphones (main microphone  111 R, main microphone  111 L, and reference microphone  111 N) converts the audio signal into an electric signal (analog audio signal). The analog audio signal from each of the microphones (main microphone  111 R, main microphone  111 L, and reference microphone  111 N) is transmitted to analog audio processor  115 . 
     Analog audio processor  115  executes a predetermined signal process on the analog audio signals. Analog audio processor  115  converts the processed analog audio signals into digital audio signals through the A/D converter, and outputs the digital audio signals to digital image/audio processor  120 . Analog audio processor  115  is one example of the audio signal processor. Analog audio processor  115  is configured with an electronic circuit including an analog circuit, namely, one or a plurality of semiconductor integrated circuit(s). Analog audio processor  115  has an automatic level control (ALC) function. The automatic level control function is for automatically adjusting a gain such that a level of a digital audio signal to be output does not exceed a predetermined upper limit threshold regardless of a level of a received analog audio signal. 
     Digital image/audio processor  120  executes various processes on image information output from AFE  144  and an audio signal output from analog audio processor  115 . For example, digital image/audio processor  120  performs gamma correction, white balance correction, flaw correction, a coding process, and the like on the image information in accordance with an instruction from controller  130 . Further, digital image/audio processor  120  executes various processes on the audio signals in accordance with the instruction from controller  130 . Digital image/audio processor  120  may be achieved by a hard-wired electronic circuit, or a microcomputer that executes a program, or the like. Digital image/audio processor  120  may be achieved as one semiconductor chip integrally with controller  130  or the like. For example, digital image/audio processor  120  can be configured with a device, such as a central processing unit (CPU), a field-programmable gate array (FPGA), an application specific integrated circuit (ASIC), a digital signal processor (DSP), or the like. 
     Digital image/audio processor  120  performs a computing process on an audio signal output from audio input unit  111 , and performs a directivity synthesis process and a noise suppressing process. A circuit that achieves digital image/audio processor  120  may be integrated into one or a plurality of semiconductor integrated circuit(s). 
     Display unit  190  is disposed on a back face of digital camera  100 . Display unit  190  can be configured with a liquid crystal display or an organic electro luminescence (EL) display. Display unit  190  displays an image based on the image information processed by digital image/audio processor  120 . 
     Controller  130  integrally controls entire operation of digital camera  100 . Controller  130  may be achieved by a hard-wired electronic circuit, or a microcomputer that performs a program, or the like. Further, controller  130  may be achieved as one semiconductor chip integrally with digital image/audio processor  120 . Further, read only memory (ROM)  170  does not have to be present outside controller  130  (as a member separated from controller  130 ), and may be incorporated in controller  130 . For example, controller  130  can be configured with a CPU, an FPGA, an ASIC, or a DSP. 
     ROM  170  stores programs relating to automatic focus control (AF control), automatic exposure control (AE control), and strobe light emission control to be made by controller  130 , as wells as programs for generally controlling the entire operation of digital camera  100 . ROM  170  stores various conditions and settings relating to digital camera  100 . In the first exemplary embodiment, ROM  170  is a flash ROM. 
     Random access memory (RAM)  150  functions as work memories of digital image/audio processor  120  and controller  130 . RAM  150  can be achieved by a synchronous dynamic random access memory (SDRAM) or a flash memory, for example. RAM  150  functions also as an internal memory in which image information and an audio signal are recorded. 
     External storage medium  160  is a memory device containing a nonvolatile storage cell such as a flash memory therein. External storage medium  160  is detachable from camera body  102 . External storage medium  160  records image data and audio data to be processed by digital image/audio processor  120  in accordance with control of controller  130 . 
     Operation unit  180  is a general name of an operation interface such as an operation button and an operation dial disposed on an exterior of digital camera  100 . Operation unit  180  accepts an operation to be performed by a user. For example, operation unit  180  includes a release button, a power switch, and a mode dial provided to an upper face of digital camera  100 , and includes a center button, a cross button, and a touch panel provided to a rear face of digital camera  100 . When operation unit  180  receives an operation performed by a user, operation unit  180  informs controller  130  of various operation instruction signals. 
     Further, camera body  102  shifts CCD  143  in accordance with unsteadiness of camera body  102 , and therefore reduces an influence of unsteadiness caused by camera shake in a captured image. As a configuration that achieves this function, camera body  102  includes body image stabilizer (BIS) driver  181  that moves CCD  143  based on the unsteadiness of camera body  102 . BIS driver  181  includes a drive mechanism that is configured with, for example, a magnet and a flat coil. BIS driver  181  controls the drive mechanism based on signals from the gyro sensor and a position sensor, and shifts CCD  143  in a plane vertical to the optical axis such that the unsteadiness of camera body  102  is canceled. 
     1-1-4. Configuration of Microphones 
     Main microphone  111 R, main microphone  111 L, and reference microphone  111 N are disposed inside camera body  102  as illustrated in  FIG. 2A . Positions and detailed disposition of main microphone  111 R, main microphone  111 L, and reference microphone  111 N in camera body  102  will be described in detail later. 
     A configuration of main microphone  111 R will be described below. Since configurations of main microphone  111 L and reference microphone  111 N are similar to the configuration of main microphone  111 R, description thereof will be omitted. 
     Main microphone  111 R has a circular cylindrical shape as illustrated in  FIG. 3 . Main microphone  111 R includes, as illustrated in  FIG. 4 , case  401 , vibrating membrane  402 , vibrating membrane ring  403 , spacer  404 , back polar plate  405 , electrode  406 , insulator  407 , printed board  408 , and field effect transistor (FET)  409 . 
     Case  401  partially configures an exterior portion of main microphone  111 R. Tone holes  410  are formed on a face on an opposite side to printed board  408 , of case  401 . A material of case  401  is metal. The material of case  401  is particularly steel use stainless (SUS) or aluminum. 
     Vibrating membrane  402  has a disc shape. Vibrating membrane  402  is formed by coating a surface of a thin film that has a thickness of about several microns to several dozen microns and is made of a polymeric material such as polyethylene terephthalate (PET) with metal such as gold or nickel through sputtering or vapor deposition. Vibrating membrane  402  is disposed inside case  401 . Vibrating membrane  402  is bonded to ring-shaped vibrating membrane ring  403 , and is braced like a membrane of a drum. A material of vibrating membrane ring  403  is metal, such as SUS or brass. Vibrating membrane  402  and vibrating membrane ring  403  each have an electric potential identical to an electric potential of case  401  through contact with case  401 . 
     Spacer  404  has a ring shape. Spacer  404  has a thickness of about several microns to several dozen microns. A material of spacer  404  is an insulating substance such as polyimide. 
     Back polar plate  405  has a disk shape. Back polar plate  405  is obtained by coating a substrate of metal such as SUS or brass with an electret material such as tetrafluoroethylene-hexafluoropropylene copolymer (FEP). The electret material is a polymeric material that semi-permanently holds electric charges. As a result, back polar plate  405  holds electric charges. Back polar plate  405  has some holes for allowing air passes therethrough. Back polar plate  405  opposes vibrating membrane  402  via spacer  404 . That is, a distance between back polar plate  405  and vibrating membrane  402  is approximately identical to a thickness of spacer  404 . 
     Electrode  406  has, for example, a pipe shape, namely, a cylindrical shape. Electrode  406  is disposed between back polar plate  405  and printed board  408 . Electrode  406  electrically connects back polar plate  405  with printed board  408 . 
     Insulator  407  has, for example, a pipe shape. Insulator  407  is disposed between back polar plate  405  and case  401  and between electrode  406  and case  401 . Insulator  407  prevents conduction of back polar plate  405  and electrode  406  with case  401 . 
     Printed board  408  configures a part of the exterior portion of main microphone  111 R. Printed board  408  is electrically connected to back polar plate  405  via electrode  406 . Further, printed board  408  is surface-mounted with a chip part such as FET  409 . A terminal ( 138  in  FIG. 5 ) is provided to an outside of printed board  408 , namely, a lower face in a sheet of  FIG. 4 . An electric output of main microphone  111 R can be taken from this terminal. 
     Note that one end of case  401  is caulked from a lower side of printed board  408 . That is, one end of case  401  is sealed without a gap between printed board  408  and case  401 . Further, one end of case  401  electrically connects case  401  and printed board  408 . 
     Operation of main microphone  111 R, main microphone  111 L, and reference microphone  111 N will be described below. 
     A sound is a compressional wave of air, and is a pressure fluctuation of air. When a sound passes through tone holes  410  and reaches vibrating membrane  402 , vibrating membrane  402  receives pressure. Vibrating membrane  402  displaces according to the pressure. That is, distance d between vibrating membrane  402  and back polar plate  405  changes. An amount of change is denoted by Δd. Further, an area of vibrating membrane  402  is denoted by S. Further, an amount of electric charges held by back polar plate  405  is denoted by Q. Vibrating membrane  402  and back polar plate  405  that oppose each other form a capacitor. When capacitance of the capacitor is denoted by C, and permittivity is denoted by ε, the following mathematical expression 1 holds. 
     
       
         
           
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     Further, when an electric potential formed between vibrating membrane  402  and back polar plate  405  is denoted by V, the following mathematical expression 2 holds in accordance with Coulomb&#39;s law. 
     
       
         
           
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     In accordance with the mathematical expressions 1 and 2, the following mathematical expression 3 holds. 
     
       
         
           
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     When vibrating membrane  402  displaces due to a sound, and the distance between vibrating membrane  402  and back polar plate  405  changes by Δd, change of an electric potential ΔV is expressed by the following mathematical expression 4. 
     
       
         
           
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     The mathematical expression 4 indicates that a displacement of vibrating membrane  402  due to a sound can be taken as a change in an electric potential. 
     Capacitance C of a capacitor formed by vibrating membrane  402  and back polar plate  405  is several pF to a dozen pF, and its impedance is high. Therefore, FET  409  to be mounted to printed board  408  is used for converting this impedance. 
     1-1-5. Disposition of Microphone 
       FIG. 2A  and  FIG. 2B  are diagrams illustrating positions of punching metal plates  119   a ,  119   b , and  119   c  in digital camera  100 . Punching metal plates  119   a ,  119   b , and  119   c  are metal plates obtained by molding a plate-shaped metal material that has undergone a punching process (punching) through pressing. Punching metal plates  119   a ,  119   b , and  119   c  each are provided with a lot of, namely, twenty or more tone holes  114 . In the first exemplary embodiment, a number of tone holes is about 100. A diameter of each of tone holes  114  is a range from 0.3 mm to 1.0 mm inclusive. Therefore, digital camera  100  in the first exemplary embodiment is further suitable as digital cameras that are not dust-proof and drip-proof. Punching metal plates  119   a ,  119   b , and  119   c  can be replaced by metal sheets obtained by molding sheet-shaped metal materials that have undergone a punching process through pressing, molded metal nets, or the like. Punching metal plates  119   a ,  119   b , and  119   c  are fitted so as to cover resin-made case  105 . In the first exemplary embodiment, punching metal plates  119   a ,  119   b , and  119   c  as well as case  105  configure the housing having a porous exterior surface. Punching metal plates  119   a ,  119   b , and  119   c  are curved, and are disposed obliquely with respect to a horizontal direction (left-right direction on a sheet of  FIG. 2A ) at a time of normal photography. 
     As illustrated in  FIG. 2B , main microphone  111 R is disposed below punching metal plate  119   a . Further, main microphone  111 L is disposed below punching metal plate  119   b . Note that an area of punching metal plate  119   a  is larger than an area of vibrating membrane  402  of main microphone  111 R. Therefore, punching metal plate  119   a  is disposed at not only a region opposing main microphone  111 R but also an outer circumference of that region. In a case of dust-proof and drip-proof digital cameras, a number of tone holes on the housing is small, namely, is one or more through less than 10 for one main microphone, and in general the tone holes are disposed locally only above the main microphone. On the other hand, punching metal plate  119   a  in the first exemplary embodiment has a lot of tone holes  114  uniformly on the region opposing main microphone  111 R and on the outer circumference of that region. Similarly, punching metal plate  119   b  has tone holes  114  uniformly on a region opposing main microphone  111 L and an outer circumference of that region. In  FIG. 2A  and  FIG. 2B , punching metal plate  119   c  is disposed also above reference microphone  111 N, but punching metal plate  119   c  does not have to be disposed above reference microphone  111 N. That is, a portion above reference microphone  111 N may be sealed by case  105 . 
     Main microphone  111 R, main microphone  111 L, and reference microphone  111 N are disposed on an upper portion of camera body  102  inside camera body  102 , namely, inside case  105 . A region where main microphone  111 R is disposed is within a region opposing punching metal plate  119   a , and is within region  112 R indicated by a dotted line. A region where main microphone  111 L is disposed is a region opposing punching metal plate  119   b , and is within region  112 L. A region where reference microphone  111 N is disposed is within a region opposing punching metal plate  119   c , and is within region  112 N. 
     Main microphone  111 L and main microphone  111 R are disposed side by side so as to be separated from each other by a predetermined distance in a longitudinal direction of camera body  102  (for example, about 15 mm). The longitudinal direction of camera body  102  is the left-right direction on the sheet of  FIG. 2A . 
     Reference microphone  111 N is disposed near main microphone  111 R and main microphone  111 L. Further, reference microphone  111 N is disposed such that a distance between reference microphone  111 N and main microphone  111 R is equal to a distance between reference microphone  111 N and main microphone  111 L. As a result, use of one reference microphone  111 N enables a noise suppressing process to be executed on main audio signals of left and right channels. Specifically, reference microphone  111 N is disposed such that the distance between reference microphone  111 N and main microphone  111 R and the distance between reference microphone  111 N and main microphone  111 L are in a range from 5 mm to 50 mm, inclusive (for example, 10 mm). 
       FIG. 5  is a diagram describing a disposition configuration of main microphone  111 R and reference microphone  111 N inside camera body  102 .  FIG. 5  schematically illustrates a cross section taken along line  5 - 5  of  FIG. 2B .  FIG. 5  illustrates only main microphone  111 R, but main microphone  111 L is disposed similarly to main microphone  111 R. In the first exemplary embodiment, main microphone  111 R and main microphone  111 L are disposed such that a surface of case  401  having tone holes  410  illustrated in  FIG. 3  faces outside (an upper side on a sheet of  FIG. 5 ), and printed board  408  faces inside camera body  102  (a lower side of the sheet in  FIG. 5 ). Reference microphone  111 N is disposed such that a surface of case  401  having tone holes  410  faces inside (the lower side on the sheet of  FIG. 5 ) and printed board  408  faces outside camera body  102  (the upper side on the sheet of  FIG. 5 ). That an orientation of reference microphone  111 N is opposite to orientations of main microphone  111 R and main microphone  111 L means that a sound pickup orientation of reference microphone  111 N is opposite to sound pickup orientations of main microphone  111 R and main microphone  111 L. That is, a sound pressure receiving orientation of vibrating membrane  402  of reference microphone  111 N is opposite to sound pressure receiving orientations of vibrating membranes  402  of main microphone  111 R and main microphone  111 L. 
     Further, as illustrated in  FIG. 5 , resin case  116  is disposed inside case  105 . Sponge A  131 , sponge B  132 , sponge C  133 , and sponge D  134  are disposed inside case  105  so as to fill gaps formed by case  105 , resin case  116 , main microphones  111 R,  111 L, and reference microphone  111 N, respectively. 
     Main microphone  111 R is disposed on resin case  116  and on sponge A  131  provided on resin case  116 . A space between an upper surface of main microphone  111 R and a rear face of case  105  (a face opposing the inside of the digital camera) is filled with sponge C  133 . Sponge C  133  enables sound pressure from the outside of case  105  to pass therethrough. An outer circumference face of main microphone  111 R (a side face vertical to vibrating membrane  402  in the faces of case  401 ) is surrounded by sponge B  132 . Sponge B  132  is provided with a cylinder-shaped hole such that cylinder-shaped main microphone  111 R can be fitted into the hole. 
     Reference microphone  111 N is disposed on a recessed portion formed by resin case  116  via rubber member  113 . 
     Rubber member  113  has a cylindrical shape having an end face. The end face of rubber member  113  has opening  113 H. However, opening  113 H may not be provided. One end on an opposite side to the end face, of rubber member  113 , is opened, and reference microphone  111 N is inserted through the open end. In the first exemplary embodiment, the end face of rubber member  113  comes to a lower end of the sheet of  FIG. 5 . Therefore, a face on the lower side of reference microphone  111 N is covered with the end face of rubber member  113 . Further, a side face of reference microphone  111 N is covered with a side face of rubber member  113 . Reference microphone  111 N is pressed into the recessed portion of resin case  116  by elastically deforming rubber member  113  (particularly a rib of rubber member  113 ) to be fixed into camera body  102 . This makes it difficult for sound pressure entering from the gap between resin case  116  and reference microphone  111 N to reach vibrating membrane  402  of reference microphone  111 N. In order to fix reference microphone  111 N to resin case  116 , instead of rubber member  113 , adhesive or clay may be used to fill the gap between resin case  116  and reference microphone  111 N so that sound pressure is blocked. 
     Further, a space between an upper face of reference microphone  111 N and the rear face of case  105  is filled with sponge D  134 . Sponge D  134  can block sound pressure applied from the outside of case  105 . 
     In the first exemplary embodiment, sponge A  131 , sponge B  132 , sponge C  133 , and sponge D  134  are used as a filling member that fills gaps inside case  105 , but a foam material such as foam plastic may be used instead. Further, sponge A  131 , sponge B  132 , sponge C  133 , and sponge D  134  have bubble structures that are categorized into two main types. One of the types is sponge having interconnected cell structure typified by urethane foam as illustrated in  FIG. 6A , and this sponge allows a sound to pass through a plurality of bubbles  118 . That is, the sponge having the interconnected cell structure (one example of the filling member) has a lot of sound pressure transmitting pathways which pierces from one end to the other end. In the first exemplary embodiment, sponge having an interconnected cell structure is used as sponge C  133 . The other one of the types is sponge having a closed cell structure typified by general-purpose polyethylene (PE) foam or rubber sponge as illustrated in  FIG. 6B . Since bubbles  118  of sponge having the closed cell structure each are independent, the sponge having the closed cell structure is extremely smaller in the number of sound pressure transmitting pathways than sponge having the interconnected cell structure, and thus hardly allows a sound to substantially pass. The closed cell structure is used for sponge A  131 , sponge B  132 , and sponge D  134 . However, the interconnected cell structure may be used for sponge A  131  and sponge B  132 . Further, it is desirable that the closed cell structure is used for sponge D  134  when possible, but the interconnected cell structure may be used. 
     In such a manner, when sponge A  131  to sponge D  134 , resin case  116 , and rubber member  113  are disposed for main microphones  111 R,  111 L, and reference microphone  111 N, in the first exemplary embodiment, resin case  116 , sponge A  131 , sponge B  132 , and sponge C  133  correspond to a first support member of the present disclosure. Resin case  116 , rubber member  113 , and sponge D  134  correspond to a second support member of the present disclosure. Sponge C  133  corresponds also to the first filling member of the present disclosure. Sponge A  131  and sponge B  132  correspond also to the second filling member of the present disclosure. 
     Further, sound pressure transmitting pathways from the outside or the inside of digital camera  100  to vibrating membranes  402  of main microphones  111 R,  111 L will be described below. Sound pressure caused by audio from the outside of digital camera  100  (air vibration) is transmitted via the plurality of tone holes  114  of punching metal plate  119   a , the plurality of bubbles  118  of sponge C  133 , and tone holes  410  of main microphone  111 R, to vibrating membrane  402  of main microphone  111 R. Similarly, sound pressure caused by audio from the outside of digital camera  100  is transmitted via the plurality of tone holes  114  of punching metal plate  119   b , the plurality of bubbles  118  of sponge C  133 , and tone holes  410  of main microphone  111 L, to vibrating membrane  402  of main microphone  111 L. 
     In the first exemplary embodiment, as illustrated in  FIG. 5 , an inside space between vibrating membrane  402  of main microphone  111 R and a center side of case  105  is blocked by printed board  408  of main microphone  111 R, sponge A  131 , sponge B  132 , and resin case  116 . Similarly, an inside of main microphone  111 L and an inside at the center side of case  105  are blocked by resin case  116 , sponge A  131 , sponge B  132 , and printed board  408  of main microphone  111 L. That is, resin case  116 , sponge A  131 , sponge B  132 , and printed board  408  make it difficult for sound pressure caused by a sound inside case  105  to be transmitted to vibrating membranes  402  of main microphones  111 R,  111 L. 
     Next, the sound pressure transmitting pathway from the outside and the inside of digital camera  100  to vibrating membrane  402  of reference microphone  111 N will be described below. In the first exemplary embodiment, sound pressure from the outside digital camera  100  passes through tone holes  114  of punching metal plate  119   c , but sponge D  134 , rubber member  113 , resin case  116 , and printed board  408  of reference microphone  111 N make it difficult for the sound pressure to be transmitted. Region  112 N where reference microphone  111 N is disposed does not have to be necessarily provided with tone holes  114  of punching metal plate  119   c  in case  105 , and partial transmitting of the sound pressure from the outside of camera body  102  to the inside of reference microphone  111 N may be blocked by case  105 . 
     The inside of reference microphone  111 N and the inside at the center side of case  105  are blocked by resin case  116  and rubber member  113 . 
     As a result, in the first exemplary embodiment, as summarized in a list of  FIG. 10 , printed boards  408  of main microphones  111 R,  111 L, sponge A  131 , sponge B  132 , and resin case  116  correspond to the first blocking member of the present disclosure that blocks the sound pressure transmitting pathways. Sponge D  134 , rubber member  113 , resin case  116 , and printed board  408  of reference microphone  111 N correspond to the second blocking member of the present disclosure. Further, resin case  116  and rubber member  113  correspond to a third blocking member of the present disclosure. 
     Respective terminals  138  of printed boards  408  of main microphone  111 R and main microphone  111 L, and printed board  408  of reference microphone  111 N are connected to printed circuit board (PCB)  135  via flexible printed circuit (FPC)  136  that passes through hole portion  11611 . 
     1-2. Operation of Sound Pickup Device 
     A noise suppressing process for an audio signal in digital image/audio processor  120  of digital camera  100  will be described. Digital image/audio processor  120  executes the noise suppressing process based on a signal received from reference microphone  111 N. 
     Main microphone  111 R and main microphone  111 L receive a main sound outside digital camera  100 , and convert the main sound into an electric signal as a first audio signal (hereinafter, referred to as a “main audio signal”). Reference microphone  111 N receives a noise inside digital camera  100 , and converts the noise into an electric signal as a second audio signal (hereinafter, referred to as a “noise signal”). 
     Analog audio processor  115  receives the main audio signals from main microphone  111 R and main microphone  111 L, receives the noise signal from reference microphone  111 N, and executes a predetermined process on these signals to output the processed signals to digital image/audio processor  120 . Digital image/audio processor  120  filters the noise signal to generate a noise component, and subtracts the noise component from the main audio signals. As a result, digital image/audio processor  120  generates the audio signals in which a noise is suppressed. 
       FIG. 7  is a diagram illustrating a main configuration that achieves the noise suppressing process for an audio signal in digital image/audio processor  120 .  FIG. 7  illustrates, for convenience of the description, the configuration for an audio signal from one microphone (main microphone  111 L) of two main microphone  111 R and main microphone  111 L on left and right sides. That is, digital image/audio processor  120  has the configuration illustrated in  FIG. 7  for each channel. The configuration and operation relating to the noise suppression for the audio signal from the microphone (main microphone  111 L) in one channel will be described below, but much the same is true on the microphone in the other channel (main microphone  111 R). 
     Digital image/audio processor  120  includes adaptive filter  117   a , coefficient setting unit  117   b , and subtractor  117   c.    
     Coefficient setting unit  117   b  sets a filter coefficient of adaptive filter  117   a  in accordance with a noise signal or the like. Adaptive filter  117   a  filters an output signal (noise signal) from reference microphone  111 N in accordance with the filter coefficient set by coefficient setting unit  117   b , and generates a noise component that is estimated to be included in an audio signal (main audio signal) picked up by main microphone  111 L. Subtractor  117   c  subtracts the noise component, which is output from adaptive filter  117   a , from the audio signal (main audio signal) picked up by main microphone  111 L. As a result, the audio signal in which the noise is suppressed is generated. 
     In  FIG. 7 , a transfer function relating to the noise suppressing function in digital image/audio processor  120  is defined as follows. Main audio signals input by main microphone  111 R and main microphone  111 L are denoted by S(ω,t), and a noise signal input by reference microphone  111 N is denoted by N(ω,t). The noise signal includes a signal of various noises caused in camera body  102 . For example, a noise represented by the noise signal includes a drive sound of the drive mechanism that is caused when BIS driver  181  drives CCD  143 . 
     Transfer functions for main audio signals S(ω,t) in main microphone  111 R and main microphone  111 L are denoted by H SM (ω,t). Transfer functions for noise signals N(ω,t) in main microphone  111 R and main microphone  111 L are denoted by H NM (ω,t). A transfer function for a noise signal N(ω,t) in reference microphone  111 N is denoted by H NR (ω,t). In this definition, output signals M(ω,t) of main microphone  111 R and main microphone  111 L, and output signal R(ω,t) of reference microphone  111 N can be obtain in accordance with mathematical expression (5) and mathematical expression (6), respectively.
 
 M (ω, t )= H   SM (ω, t )● S (ω, t )+ H   NM (ω, t )● N (ω, t )  (Mathematical expression 5)
 
 R (ω, t )= H   NR (ω, t )● N (ω, t )  (Mathematical expression 6)
 
     A signal component for a main audio signal included in output signal R (ω,t) of reference microphone  111 N is assumed to be negligibly small. 
     In output signals M(ω,t) of main microphone  111 R and main microphone  111 L, a noise component is H NM (ω,t)●N(ω,t). Therefore, the noise component H NM (ω,t)●N(ω,t) is estimated and is subtracted from output signals M(ω,t), and thus audio signals in which a noise is suppressed can be obtained. 
     For this reason, in digital image/audio processor  120 , coefficient setting unit  117   b  receives output signals M(ω,t) of main microphone  111 R and main microphone  111 L, and output signal R(ω,t) of reference microphone  111 N, and compares these output signals to estimate a noise component and sets a filter coefficient of adaptive filter  117   a  in accordance with the estimated noise component (H ENM (ω,t)●N(ω,t)). Adaptive filter  117   a  generates a noise component (H ENM (ω,t)●N(ω,t)) from output signal R(ω,t) and outputs the noise component. Subtractor  117   c  subtracts output signal (H ENM (ω,t)●N(ω,t)) of adaptive filter  117   a  from output signals M(ω,t). As a result, the audio signal in which a noise is suppressed is output from analog audio processor  115 . 
     1-3. Experimental Result 
       FIG. 8  is a diagram illustrating a measured result of a noise level in various disposition configurations of reference microphone  111 N. A lateral axis in  FIG. 8  represents a frequency (Hz) of an audio signal picked up by the sound pickup device, and a vertical axis represents a level (dB) of the audio signal. 
     In  FIG. 8 , a curved line S indicated by a thick line represents a waveform of each of audio signals picked up by main microphone  111 R and main microphone  111 L when digital image/audio processor  120  does not execute the above-described noise suppressing process. 
     In  FIG. 8 , a curved line indicated by a solid line (first exemplary embodiment) represents a waveform of an audio signal output from the sound pickup device in which main microphone  111 R (main microphone  111 L) and reference microphone  111 N are disposed as illustrated in  FIG. 5  as the first exemplary embodiment. 
     In  FIG. 8 , a curved line indicated by a broken line (modified example) represents a waveform of an audio signal output from the sound pickup device in which main microphone  111 R (main microphone  111 L) and reference microphone  111 N are disposed as illustrated in  FIG. 9 . 
     In the modified example, the following changes are given to the disposition configuration of main microphone  111 R (main microphone  111 L) and reference microphone  111 N illustrated in  FIG. 5  in the first exemplary embodiment. Specifically, as illustrated in  FIG. 9 , main microphone  111 R (main microphone  111 L) and reference microphone  111 N are disposed such that their orientations are identical to each other. That is, main microphone  111 R (main microphone  111 L) and reference microphone  111 N are disposed such that printed boards  408  face the inside of digital camera  100  on inner portions with respect to vibrating membranes  402  (a lower side on a sheet of  FIG. 9 ). Further, in the modified example, instead of rubber member  113  in  FIG. 5 , reference microphone  111 N is fixed between resin case  116  and sponge D  134  by using sponge E  131 A and sponge F  132 A. That is, in the modified example, reference microphone  111 N is disposed on resin case  116  via sponge E  131 A, and a bottom face of reference microphone  111 N is covered with sponge E  131 A. Further, a cylindrical hole is provided on sponge F  132 A such that cylindrical reference microphone  111 N is fitted into the hole. Therefore, sponge F  132 A is disposed so as to cover an outer circumferential face of reference microphone  111 N (on a side face vertical to vibrating membrane  402  in the faces of case  401 ). Sponge E  131 A is made of a material identical to the material of sponge A  131 . Sponge F  132 A is made of a material identical to the material of sponge B  132 . In the modified example, tape  137  is attached so as to block tone holes  410  at an upper portion of reference microphone  111 N. To wrap up, as shown in the list of  FIG. 10 , in the modified example, similarly to the first exemplary embodiment, resin case  116 , sponge A  131 , sponge B  132 , and printed board  408  of main microphone  111 R (main microphone  111 L) correspond to the first blocking member of the present disclosure. In the modified example, partially differently from the first exemplary embodiment, sponge D  134  and tape  137  correspond to the second blocking member of the present disclosure. In the modified example, partially differently from the first exemplary embodiment, resin case  116 , sponge E  131 A, sponge F  132 A, and printed board  408  of reference microphone  111 N correspond to the third blocking member of the present disclosure. 
     Also in the modified example, similarly to the first exemplary embodiment, sponge A  131 , sponge B  132 , sponge C  133 , and resin case  116  correspond to the first support member of the present disclosure. In the modified example, partially differently from the first exemplary embodiment, sponge D  134 , sponge E  131 A, sponge F  132 A, and resin case  116  correspond to the second support member of the present disclosure. Further, also in the modified example, similarly to the first exemplary embodiment, sponge C  133  corresponds to the first filling member of the present disclosure. Also in the modified example, similarly to the first exemplary embodiment, sponge A  131  and sponge B  132  correspond to the second filling member of the present disclosure. 
     From a result shown in  FIG. 8 , in the first exemplary embodiment and the modified example, the noise suppressing effect is higher than that effect in a case where the noise process is not executed. Further, when the first exemplary embodiment is compared with the modified example, the noise suppressing effect is higher in the first exemplary embodiment. In the configuration in the modified example, a part of sound pressure externally received is considered to be transferred to vibrating membrane  402  via sponge D  134  and tape  137  as the second blocking member. That is, as the second blocking member for blocking transmission of sound pressure, it is considered that a member obtained by combining sponge D  134  with a comparatively thicker member, such as at least any one of resin case  116  and printed board  408  which does not have sound transmitting pathways (holes) is more effective than a thin member such as sticking tape. 
     1-4. Effects 
     Digital camera  100  (one example of the imaging device) in the first exemplary embodiment has a sound pickup device. The sound pickup device includes case  105  (housing) having a porous (a plurality of tone holes  114 ) exterior surface of punching metal plate  119 , main microphone  111 R and main microphone  111 L that are disposed inside case  105 , receive sound pressure from outside case  105  via the plurality of tone holes  114  and generate first audio signals, reference microphone  111 N that is disposed near main microphone  111 R and main microphone  111 L inside case  105  and generates a second audio signal, a first support member that is provided in case  105  and supports main microphone  111 R and main microphone  111 L (resin case  116 , sponge A  131 , sponge B  132 , and sponge C  133 ), a second support member that is provided in case  105  and supports reference microphone  111 N (resin case  116  and rubber member  113 ), a first blocking member that blocks between the inside of case  105  and the insides of main microphone  111 R and main microphone  111 L (resin case  116 , sponge A  131 , sponge B  132 , and printed board  408 ), a second blocking member that blocks between the outside of case  105  and the inside of reference microphone  111 N (sponge D  134 , printed board  408 , rubber member  113 , and resin case  116 ), and a third blocking member that blocks between the inside of case  105  and the inside of reference microphone  111 N (resin case  116  and rubber member  113 ). 
     In the first exemplary embodiment, when the first blocking member, the second blocking member, and third blocking member are disposed, a noise caused inside digital camera  100  can be efficiently reduced from external main audio picked up by digital camera  100 . 
     Further, even when main microphones  111 R,  111 L, and reference microphone  111 N cannot be mounted to be enclosed in case  105 , the first exemplary embodiment easily achieves the configuration such that reference microphone  111 N can be disposed near main microphones  111 R,  111 L, and reference microphone  111 N is blocked from sound pressure from the outside. Therefore, a noise generated inside digital camera  100  can be prevented from being mixed into an audio signal output from the sound pickup device. For example, in the first exemplary embodiment, resin case  116  is combined with sponge A  131  to sponge C  133  that are also the filling member as the first support member, and resin case  116  and rubber member  113  are used as the second support member. As a result, also when a housing having a porous exterior surface is used, main microphones  111 R,  111 L can be easily disposed near reference microphone  111 N. When different materials are used between sponge C  133  and sponges A  131 , B  132 , and D  134 , sponges A  131 , B  132 , and D  134  can be used as a part of the blocking member. 
     In the first exemplary embodiment, since punching metal plates  119   a  to  119   c  are used as the housing having the porous exterior surface (a part of the housing), porous molding is easy. Further, since materials of punching metal plates  119   a  to  119   c  are metal, they are robust and produce an electric shield effect. 
     In the first exemplary embodiment, use of sponges A  131 , B  132 , and C  133  as the first filling member or the second filling member enables the housing to be easily molded using a cutting die along a shape of a rear face of the housing, even when the rear face is a slanted face or a curved face. The combination of a plurality of sponges (for example, sponge A  131 , sponge B  132 , and sponge C  133 ) makes it possible to easily configure a filling member into a complicated shape. When porous sponge A  131 , sponge B  132 , and sponge D  134  that are lower in rigidity than resin case  116  and printed board  408  are used as a part of the first blocking member or the second blocking member, wind pressure can be absorbed and mixing of a noise can be suppressed. 
     Further, in the first exemplary embodiment, the exterior surface (for example, punching metal plate  119   a , punching metal plate  119   b , or punching metal plate  119   c ) is a slant face or a curved face. In the first exemplary embodiment, since the first support member and the second support member are provided, even if the exterior surface is a slant face or a curved face, the main microphones can be easily disposed near the reference microphone. 
     In the first exemplary embodiment, the first support member and the second support member are configured with members separable from a portion of the housing (case  105 ) having the exterior surface (punching metal plates  119   a  to  119   c ). Therefore, even if the exterior surface is a slant face or a curved face, main microphones  111 R,  111 L can be disposed near reference microphone  111 N. 
     In the first exemplary embodiment, the first support member is configured by combining a member having a fixed shape (resin case  116 ) with a member that can be deformed in a compressed direction (for example, sponge C  133  as the first filling member, and sponge A  131  and sponge B  132  as the second filling member). As a result, main microphones  111 R,  111 L, and reference microphone  111 N can be easily disposed inside the housing having the porous exterior surface into a desired layout. Further, even if the exterior surface of case  105  for digital camera  100  is a slant face or a curved face, main microphones  111 R,  111 L, and reference microphone  111 N can be easily disposed into the desired layout. 
     Main microphones  111 R,  111 L in the first exemplary embodiment include a first main microphone that receives audio from a first direction (for example, main microphone  111 R), and a second main microphone that receives audio from a second direction different from the first direction (for example, main microphone  111 L). As a result, in the first exemplary embodiment, audio from more various directions can be picked up. 
     A distance between reference microphone  111 N and the first main microphone (for example, main microphone  111 R) in the first exemplary embodiment is equal to a distance between reference microphone  111 N and the second main microphone (for example, main microphone  111 L). As a result, in the first exemplary embodiment, a noise component can be suppressed for any audio signals from main microphones  111 R,  111 L. 
     Further, in the first exemplary embodiment, as illustrated in  FIG. 5 , at least a part of the second blocking member is an exterior portion of reference microphone  111 N (printed board  408 ), and at least a part of the third blocking member is resin case  116 . The disposition configuration is effective for a case where the orientations of main microphones  111 R,  111 L are desired to be set so as to be opposite to the orientation of reference microphone  111 N, or a case where rubber member  113  having opening  113 H is desired to be used, for example. 
     In the first exemplary embodiment, the first filling member (sponge C  133 ) is provided so as to fill the space between the surfaces of main microphones  111 R,  111 L and a rear face of case  105  and to allow sound pressure from the outside of case  105  to pass therethrough. As a result, the sound pressure from the outside can be transmitted to vibrating membranes  402  of main microphones  111 R,  111 L. 
     Further, in the first exemplary embodiment, at least a part of the first blocking member is a part of the first support member, and is the second filling member (sponge A  131  and sponge B  132 ) that is disposed on outer circumferences of main microphones  111 R,  111 L. As a result, a noise caused inside digital camera  100  can be blocked, and main microphones  111 R,  111 L can be easily disposed inside digital camera  100 . 
     The sound pickup device in the first exemplary embodiment further includes an audio processor that obtains a noise component based on an audio signal form reference microphone  111 N, and subtracts the noise component from main audio signals from main microphone  111 R and main microphone  111 L. As a result, the sound pickup device itself can suppress a noise component. 
     Other Exemplary Embodiments 
     As described above, the first exemplary embodiment has been described to exemplify a technique disclosed in the present application. However, the technique in the present disclosure is not limited to this, and can also be applied to an exemplary embodiment in which modification, replacement, addition, omission, or the like is performed appropriately. In addition, a new exemplary embodiment can be made by combining constituents described in the above first exemplary embodiment. 
     In the first exemplary embodiment, as illustrated in  FIG. 2A  and  FIG. 2B , reference microphone  111 N is disposed on a rearward side of the camera with respect to main microphone  111 R and main microphone  111 L, but reference microphone  111 N may be disposed on a frontward side of the camera (a side close to a subject) with respect to main microphone  111 R and main microphone  111 L. Further, main microphone  111 R, main microphone  111 L, and reference microphone  111 N are disposed on the upper portion of digital camera  100  (one example of electronic devices), but the positions of these microphones are not limited to this. For example, main microphone  111 R, main microphone  111 L, and reference microphone  111 N may be disposed on at least one of a side face and a front face of digital camera  100 . 
     In the above exemplary embodiment, reference microphone  111 N is fixed to the recessed portion of resin case  116  via rubber member  113 , but may be fixed to resin case  116  through another method. For example, reference microphone  111 N may be fixed directly to resin case  116  by using adhesive. 
     The above exemplary embodiment has described the noise suppressing process for suppressing noises in main audio signals generated by main microphones  111 R,  111 L by using a noise signal generated by reference microphone  111 N with reference to  FIG. 7 . However, the noise suppressing process is not limited to this, and thus various publicly-known methods can be applied. 
     In the first exemplary embodiment, the punching metal plate, the wire net, and the like have been illustrated as the housing (a part of the housing) having the porous exterior surface, but a member obtained by working a resin or carbon plate may be used as long as the plate can be molded into a porous shape. 
     In the first exemplary embodiment, the first support member is configured with resin case  116 , sponge A  131 , sponge B  132 , and sponge C  133 , but this configuration is only one example. For example, resin case  116  may be replaced by a metallic case. Further, for example, sponge A  131  and sponge B  132  may be integral sponge or integral rubber, for example. Alternatively, sponge A  131  or sponge B  132  may be further divided into a plurality of parts. In any cases, the member having a fixed shape such as resin case  116  is combined with a member that can be deformed in a compressed direction such as sponge A  131  to sponge C  133 , and thus main microphones  111 R,  111 L can be easily fixed into an internal space of the housing having a complicated shape. Even if the first support member is configured only with a member having a fixed shape such as resin case  116 , the first blocking member is separately disposed, and thus the noise suppressing effect can be produced. 
     In the first exemplary embodiment, the second support member is configured with resin case  116  and rubber member  113 , but this configuration is only one example. For example, like the modified example of  FIG. 9 , resin case  116 , sponge D  134 , sponge E  131 A, and sponge F  132 A may configure the second support member. Further, sponge E  131 A and sponge F  132 A, or sponge F  132 A and sponge D  134  may be integral sponge or integral rubber. Alternatively, sponge D  134  to sponge F  132 A may be further divided into a plurality of parts. In any cases, a member having a fixed shape such as resin case  116  is combined with a member that can be deformed in a compressed direction such as sponge D  134  to sponge F  132 A, and thus reference microphone  111 N can be easily fixed into an internal space of the housing having a complicated shape 
     The above exemplary embodiment has described an example in which the sound pickup device of the present disclosure is applied to the interchangeable lens type digital camera, but the sound pickup device of the present disclosure can be applied also to a digital camera in which a lens and a body are integral. 
     In the above exemplary embodiment, a digital camera that is not dust-proof and drip-proof is assumed as the digital camera, but when a fine porous shape can be provided to the exterior surface of the housing, a dust-proof and drip-proof digital camera may be used. 
     The above exemplary embodiment has described an example in which the sound pickup device of the present disclosure is applied to the digital camera, but the configuration of the sound pickup device of the present disclosure can be applied to other electronic devices. For example, the configuration of the sound pickup device of the present disclosure can be applied also to other electronic devices that receive audio (a video camera, an integrated circuit (IC) recorder, and the like). The configuration of the sound pickup device of the present disclosure is useful particularly for an electronic device containing a noise source therein. 
     As described above, the exemplary embodiments have been described to exemplify the technique disclosed in the present disclosure. For this reason, accompanying drawings and detail description are provided. 
     Therefore, the components described in the accompanying drawings and the detailed description include not only the components essential for solving the problem but also components that are not essential for solving the problem in order to illustrate the techniques. For this reason, even if these unessential components are described in the accompanying drawings and the detailed description, these unessential components should not be immediately approved as being essential. 
     Further, since the above exemplary embodiments illustrate the technique in the present disclosure, various modifications, substitutions, additions and omissions can be performed within the scope of claims and equivalent scope of claims. 
     The sound pickup device of the present disclosure can be applied to an electronic device that removes a noise component from a received audio signal to be capable of generating an audio signal in which a noise is suppressed, and converts audio into an electric signal to receive the electric signal (a video camera, an IC recorder), and is useful particularly for an electronic device containing a noise source therein.