Patent Publication Number: US-8526633-B2

Title: Acoustic apparatus

Description:
This application is a U.S. National Phase Application of PCT International Application PCT/2008/059814 filed on 28 May 2008, which is based on and claims priority from JP 2007-147997 filed on 4 Jun. 2007, the contents of which are incorporated herein by reference in their entirety. 
     TECHNICAL FIELD 
     This invention relates to an acoustic apparatus for collecting a sound mainly, and particularly to an acoustic apparatus having plural directional microphones. 
     BACKGROUND ART 
     In recent years, an audio conference apparatus provided with a speaker and a microphone integrally in order to conduct audio conference (communication conference) becomes widespread. The audio conference apparatus sends a sound collected by a microphone to a connection destination and emits a sound received from the connection destination by the speaker. In the case of conducting conference by plural persons, such an audio conference apparatus is often installed in the center (for example, the center of a conference desk) of conference participants. Therefore, it is desirable to miniaturize such an audio conference apparatus and, for example, as shown in Patent Reference 1, an audio conference apparatus miniaturized by omitting a case for speaker is proposed. 
     Also, an apparatus in which plural directional microphones are installed so as to be directed to the periphery around the apparatus is provided in consideration that the apparatus is placed in the center of a conference desk.
     Patent Reference 1: JP-A-8-204803   

     DISCLOSURE OF THE INVENTION 
     Problems that the Invention is to Solve 
     However, in a configuration of Patent Reference 1, the configuration is a compact configuration, but a speaker is near to a microphone, therefore diffraction sound volume becomes large. 
     On the other hand, in the apparatus in which the plural directional microphones are mounted so as to be directed to the periphery around the apparatus, sounds emitted at positions (or regions near to the positions) of the same distance from all the directional microphones are collected in the same phase, therefore there is a problem that a sound collected from a particular region becomes a very large level. As a result of this, for example, noise etc, generated from an air-conditioning equipment installed in a ceiling are collected at a particularly large level and are harsh on the ear. 
     Hence, an object of the invention is to provide an acoustic apparatus without increasing noise etc, even when plural directional microphones collect sounds from positions located at the same distance. 
     Means for Solving the Problems 
     In this invention, there is provided an acoustic apparatus, comprising: 
     a plurality of sound collection sections arranged on a circumference around one axis, wherein sound collection directions of the sound collection sections are set toward normal directions of the circumference in a plane orthogonal to the axis; and 
     a sound signal processing section that delays a phase of a sound signal output from each of the sound collection sections by an angle on the circumference at an installation position of each of the sound collection sections and combines the sound signals. 
     In this configuration, the plurality of sound collection sections are respectively provided on the circumference around the axis. The sound collection sections are provided toward normal directions (for example, when a case has a disk shape, the normal directions are directions toward a case side face) of the circumference in the plane orthogonal to the axis. Sound signals output from the sound collection sections are subjected to the phase shifts according to the installation position (an angle on the circumference) of each of the sound collection sections. For example, when an installation position is positioned at 180 degrees, a phase is also shifted 180 degrees. Sounds emitted at positions (axis direction) extending toward an upper face and a lower face from a center position of a case are collected with substantially the same level by all the sound collection sections, but are combined after phase shifts. As a result, the sounds are canceled. On the other hand, sounds emitted from a side face are collected with a high level by the sound collection section nearest to its position, so that the sounds are not canceled after combination. 
     Also, in this invention, each of the sound collection sections includes a microphone array in which a plurality of microphone units are arranged, and a delay processing portion which delays and combines sound signals collected by the microphone units to provide directivity for the sound collection section. 
     The sound collection section has a microphone array in which the microphone units are arranged, and a delay processing portion. The directivity great in a predetermined direction is set by delaying and combining the sound signals collected by the microphone units. 
     Also, in this invention, the acoustic apparatus further includes a speaker in which a sound emission direction is set in an extending direction of the axis. 
     In this configuration, the speaker is provided so that a sound emission face of the speaker is directed in an extending direction of the axis from the center position of the case. The extending direction of the axis includes an upper face direction, a lower face direction of the case or both the directions. A sound may be emitted toward the upper face direction or the lower face direction of the case. Also, a sound may be emitted toward both the directions. Even when sounds are collected by the sound collection sections, the sounds emitted in the sound emission directions are canceled, so that occurrence of echo can be suppressed. 
     Also, in this invention, the acoustic apparatus further includes an adaptive echo canceller that subtracts a pseudo feedback signal in which a sound signal input to the speaker is filtered from an output signal of the sound signal processing section to output a signal. 
     In this configuration, an echo component is eliminated by estimating a diffraction component emitting from the speaker to the sound collection section and subtracting the estimated diffraction component from the output signal of the sound signal processing section. 
     Advantage of the Invention 
     According to the invention, even in the case of collecting sounds emitted in a position away from the directional microphones (sound collection sections) by the same distances, the sounds are canceled by being combined after phase shifts are performed, so that noise etc. occurring in the position are not collected with a high level. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram showing an external appearance of an audio conference apparatus. 
         FIG. 2  is a block diagram showing a configuration of the audio conference apparatus. 
         FIG. 3  is a block diagram showing a configuration of a microphone signal processing circuit. 
         FIG. 4  is a diagram showing a sound signal after a phase shift is performed. 
         FIG. 5  is a diagram illustrating a situation in which a sound is collected. 
     
    
    
     DESCRIPTION OF REFERENCE NUMERALS AND SIGNS 
     
         
           1  AUDIO CONFERENCE APPARATUS 
           10 A˜ 10 H MICROPHONE ARRAY 
           13  SPEAKER 
           21  MICROPHONE SIGNAL PROCESSING CIRCUIT 
           22  ECHO CANCELLER 
           23  INPUT-OUTPUT I/F 
       
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     An audio conference apparatus will be described as an embodiment of an acoustic apparatus of the invention,  FIG. 1  is an external appearance diagram of the audio conference apparatus according to this embodiment, and  FIG. 1(A)  is a plan diagram, and  FIG. 1(B)  is a side diagram. In  FIG. 1(A) , using a center position in the case of viewing an audio conference apparatus  1  from an upper side as the center of rotation, the paper surface lower side (a sound collection direction of a microphone array  10 A) is set at 0 degree and an angle increasing clockwise is set at θ. 
     The audio conference apparatus  1  includes a disk-shaped case  11 . In the case  11 , a shape viewed from an upper side is a circular shape with a diameter of about 30 cm. Areas of an upper face and a lower face of the case  11  become narrower than an area of the halfway portion of a vertical direction. In the case  11 , a shape viewed from the side of a side face of the case  11  becomes narrow from a predetermined position of a height direction toward the upper face and also becomes narrow toward the lower face. That is, the case  11  includes a shape having respectively inclined faces from the predetermined position to an upper side and an lower side of the case  11 . 
     The eight microphone arrays  10 A to  10 H are respectively installed inside the upper face side of the case  11  toward a side face of the case  11 . Each of the microphone arrays  10 A to  10 H is placed at an equiangular pitch (an interval of about 45 degrees in this case) using a center position of the case  11  as the center of rotation in the case of being viewed from the upper side. In this case, the sound collection direction of the microphone array  10 A is set in a direction of θ=0 degree and each of the microphone arrays  10 A to  10 H is placed along a direction in which θ increases sequentially by 45 degrees. 
     The microphone arrays  10 A to  10 H respectively have plural (four in  FIG. 1(A) ) microphone units. For example, the microphone array  10 A has four microphone units  101 A to  104 A. Sounds collected by these microphone units  101 A to  104 A are combined (see  FIG. 2 ) after delay processing is performed by a delay processing portion (see  FIG. 2 ). The combined sound has directivity in a particular direction since the sound are combined after the delay processing is performed. The microphone array  10 A has directivity in the direction of θ=0 degree, and the direction of θ=0 degree becomes the sound collection direction. In addition, the number of microphone units is not limited to this embodiment, and could be set properly according to specifications. Also, a unidirectional microphone may be used for the apparatus instead of the microphone array. 
     A speaker  13  is installed so that a sound emission direction of the speaker  13  is directed to the lower face of the case  11 . In addition, a configuration (configuration of a sound emission system) of the speaker  13  is not essential portion when the audio conference apparatus is simply used as a sound collection apparatus. 
       FIG. 2  is a block diagram showing a configuration of the audio conference apparatus  1 . The audio conference apparatus  1  includes a microphone signal processing circuit  21  connected to the microphone arrays  10 A to  10 H, an echo canceller  22  connected to the microphone signal processing circuit  21 , and an input-output I/F  23  connected to the echo canceller  22 . In addition, a front-end amplifier for amplifying a sound signal collected by a microphone unit, an A/D converter for making digital conversion of an analog sound signal, a D/A converter for making analog conversion of a digital sound signal and a power amplifier for amplifying a sound signal supplied to a speaker, etc. are omitted in  FIG. 2  and unless otherwise specified, a sound signal transferred in the audio conference apparatus  1  shall be a digital sound signal. 
     The input-output I/F  23  is provided on any face of the case  11 , and includes a network connection terminal, a digital audio terminal, and an analog audio terminal (not shown), etc. The audio conference apparatus  1  can be connected to other apparatus by connecting a network cable etc. to the input-output I/F  23 . 
     The microphone arrays  10 A to  10 H respectively have plural microphone units as described above and delay processing portions for performing delay processing of sound signals collected by each of the microphone units and combining the delayed sound signals and then outputting the sound signals to a subsequent stage. For example, the microphone array  10 A has four microphone units  101 A to  104 A and performs delay and combination processing by the delay processing portion  111 A. The signal combined by the delay processing portion of each of the microphone arrays  10 A to  10 H is input to the microphone signal processing circuit  21 . 
     The microphone signal processing circuit  21  performs a phase shift to sound signals output from the microphone arrays  10 A to  10 H respectively and combines the sound signals to output a combined sound signal to The echo canceller  22  of a subsequent stage.  FIG. 3  shows a detailed block diagram of the microphone sign&amp; processing circuit  21 . The microphone signal processing circuit  21  includes phase shift circuits  211 A to  211 H and an adder  212 . 
     The sound signals output from the microphone arrays  10 A to  10 H are respectively input to the phase shift circuits  211 A to  211 H. Output signals of the phase shift circuits  211 A to  211 H are respectively input to the adder  212 . The adder  212  combines the output signals of the phase shift circuits  211 A to  211 H and outputs an output signal to the echo canceller  22  of the subsequent stage. 
     The echo canceller  22  eliminates an echo component by estimating a diffraction component emitting from the speaker  13  to the microphone arrays  10 A to  10 H and subtracting the estimated diffraction component from the output signal of the microphone signal processing circuit  21 . The echo canceller  22  has an adaptive filter for filtering a signal supplied to the speaker  13 , and generates a simulated signal of a diffraction component emitted from the speaker to a microphone by estimates a transfer function of an acoustic transfer system (an acoustic propagation path extending from the speaker to the microphone arrays). The simulated signal is subtracted from the output signal of the microphone signal processing circuit  21 . In addition, the transfer function is updated by using a residual signal generated after the echo component is subtracted. A signal in which the echo component is eliminated is input to the input-output I/F  23  and is sent to other apparatus. 
     In  FIG. 3 , the phase shift circuits  211 A to  211 H are constructed of FIR filters etc. and phase shift calculation is performed at the entire frequency band (broad frequency band, for example, several tens of Hz to several kHz) so that a phase of a sound signal is shifted. Here, the phase shift circuits  211 A to  211 H rotate phases of the signals according to angles corresponding to sound collection directions of the microphone arrays. 
     The phase shift circuit  211 A sets an angle of 0 degree in a sound collection direction of the microphone array  10 A as a rotational angle. In other words, the phase shift circuit  211 A does not perform a phase shift. The phase shift circuit  211 B sets an angle of 45 degrees in a sound collection direction of the microphone array  10 B as a rotational angle. In other words, a phase of the signal is delayed 45 degrees. Similarly, the phase shift circuit  2110  delays a phase 90 degrees, and the phase shift circuit  211 D delays a phase 135 degrees, and the phase shift circuit  211 E delays a phase 180 degrees. Also, the phase shift circuit  211 F delays a phase 225 degrees, and the phase shift circuit  211  delays a phase 270 degrees, and the phase shift circuit  211 H delays a phase 315 degrees. 
       FIG. 4  is a diagram showing signals output from the phase shift circuits  211 A to  211 H as a result of performs phase shifts to sound signals of the microphone arrays  10 A to  10 H.  FIG. 4(A)  shows the case of collecting sounds from a region where distances are equal from all the microphone arrays. The region in which the distances from all the microphone arrays become equal is a region in the vicinity of a center position (central axis) of the audio conference apparatus  1  in the case of viewing the audio conference apparatus  1  from an upper side. For example, as shown in  FIG. 5(A) , it is the case of collecting a sound emitted from a region  50  positioned at an above area (zenith direction) of the audio conference apparatus  1 . 
     Also,  FIG. 4(B)  shows the case of collecting sounds emitted from a region near to any one of the microphone arrays. For example, as shown in  FIG. 5(B) , it is the case of collecting a sound emitted from a region  51  near to the microphone array  10 D. 
     In  FIGS. 4(A) and 5(A) , all the sounds collected by the microphone arrays  10 A to  10 H are the same component. Therefore, when the collected sound signals are combined after phase shifts are performed to the collected sound signals by the phase shift circuits  211 A to  211 H, the sound signals are canceled out For example, a phase of a sound signal collected by the microphone array  10 A is shifted 180 degrees with respect to a phase of a sound signal collected by the microphone array  10 E, so that the sound signals cancel out mutually. 
     Thus, the sound signals collected from the region in the vicinity of the central axis of the apparatus by the microphone arrays  10 A to  10 H are canceled out after combination, so that a level of the sound signal becomes extremely small. As a result of that, for example, a situation in which noise etc. of air-conditioning equipment installed in the ceiling is collected at a high level is eliminated. Also, the speaker  13  is mounted in a center position of the audio conference apparatus  1 , so that a situation in which an emitted sound from the speaker  13  is diffracted and is collected with a high level is eliminated. As a result of that, occurrence of howling or echo can be suppressed. Also, a processing load of the echo canceller  22  can be reduced. In addition, a sound emission direction of the speaker  13  may be an upper face direction or a lower face direction. The speaker  13  may emit the sound toward both of the upper face direction and the lower face direction. 
     On the other hand, in  FIGS. 4(B) and 5(B) , the sound emitted from the region  51  is collected with a high level by the nearest microphone array  10 D, and the microphone arrays collects the sound with a low level as the microphone arrays are distant from the region  51 , A sound collected in the most distant microphone array  10 H becomes the lowest level. Therefore, a sound signal collected by the microphone array  10 D and a sound signal collected by the microphone array  10 H do not completely cancel out to each other even when the sound signals are combined. Also, sounds collected by the microphone array  10 C and the microphone array  10 E are near to a level of the sound collected by the microphone array  10 D. However, the sounds collected by the microphone array  10 C and the microphone array  10 E are not completely canceled out even when the sounds are combined since the phases of the sounds are near (a difference is 45 degrees). Therefore, the sound emitted from the region  51  is collected with the high level. 
     According to the audio conference apparatus  1  of this embodiment as described above, noise of a zenith direction of the audio conference apparatus  1  is not collected and a sound from a horizontal direction can be collected with a high level, so that a stable sound collection environment can be achieved with respect to all the directions. 
     Also, filter factors of the phase shift circuits  211 A to  211 H are not changed dynamically, so that a stable sound collection environment can be achieved. 
     The invention is based on Japanese patent application (patent application No. 2007-147997) filed on Jun. 4, 2007, and the contents of which are hereby incorporated by reference.