JP2009188858A - Audio output device, audio output method, and program - Google Patents

Abstract

An audio output device capable of removing noise superimposed on speech uttered by a speaker is provided.
A first microphone 11 that acquires voice uttered by a speaker, a second microphone 12 that acquires noise, a voice signal acquired by the first microphone 11, and a second microphone 12 acquire the voice. The noise cancellation unit 13 cancels the noise signal from the audio signal using the noise signal thus generated, and the output unit 14 outputs the audio signal whose noise is canceled by the noise cancellation unit 13.
[Selection] Figure 1

Description

  The present invention relates to an audio output device that cancels and outputs noise in speech uttered by a speaker.

  2. Description of the Related Art Conventionally, technology development has been performed so that speech uttered by a speaker can be clearly captured even under noisy conditions. For example, in an MRI apparatus (nuclear magnetic resonance imaging apparatus), a communication system has been developed that allows an operator to clearly hear the voice of a subject using a limiter and a low-pass filter in order to clearly communicate with the subject. (For example, refer to Patent Document 1).

In addition, a mask that is used for a call in excavation work or the like and has a built-in microphone that can cancel construction noise or the like has been developed (for example, see Patent Document 2).
JP 2000-339000 A JP 2003-19218 A

  Although the technique disclosed in Patent Document 1 has a merit that it has a simple configuration, it can only limit an extremely loud noise level to the voice level of the subject and is superimposed on the voice of the subject. There is a problem that it is not possible to cancel the noise. That is, there is a problem that it is not effective for clarifying the voice of the subject with high S / N.

  In addition, the technique disclosed in Patent Document 2 includes a microphone inside the mask, thereby canceling noise from outside the mask that is superimposed on the voice spoken by the speaker. It is. Therefore, there is a problem that it cannot be used in an environment where the speaker does not mask. Especially, it is configured to enhance the voice uttered in the mask and cancel the noise from outside the mask, so if the speaker is not wearing the mask, noise cancellation for the voice of the speaker May not be performed properly, and for example, the voice itself spoken by the speaker may be canceled in the same manner as noise. There is also a problem that electromagnetic induction noise generated in an MRI environment cannot be removed appropriately.

  The MRI apparatus is one of medical image diagnosis apparatuses, and is highly useful. Recently, the MRI apparatus is often used for brain research. However, since a strong pulsed current is passed through the magnetic field coil and the magnetic field is changed abruptly to capture images, electromagnetic induction noise, noise noise, vibration noise, and noise including electromagnetic induction noise caused by the vibration are generated. To do. For this reason, when an actual high magnetic field MRI apparatus is in operation, intense noise exceeding 100 dB (noise level under the overhead wire guard) is generated, and a call between the inspector and the subject (patient) occurs. Is impossible. In the brain research using the MRI apparatus, it is necessary to record the voice uttered by the subject. However, when the MRI apparatus is in operation, the voice of the subject cannot be clearly recorded.

  Further, an apparatus for performing an operation while viewing an image under an MRI apparatus has been developed (for example, a document “Morikawa et al., Journal of Magnetics of Japan, Vol. 21, No. 2, p. 41-47, 2001). Etc.)). When an operation is performed under a high-noise MRI apparatus, it is very difficult to make a call between the operators during the operation. Up to now, there has been no communication device that is highly useful for calls between surgeons during surgery performed under the supervision of a noisy MRI device.

  The present invention has been made to solve the above-described problems, and one object of the present invention is to provide an audio output device and the like that can effectively remove noise superimposed on the voice uttered by the speaker. Is to provide.

  Another object of the present invention is to provide an audio output device that can effectively remove electromagnetic induction noise caused by MRI or the like.

  In order to achieve at least one of the above objects, an audio output device according to the present invention includes a first microphone that acquires a voice uttered by a speaker, a second microphone that acquires noise, and the first microphone. Using the acquired audio signal and the noise signal acquired by the second microphone, a noise cancellation unit that cancels the noise signal from the audio signal, and an audio signal in which noise is canceled by the noise cancellation unit are output And an output unit.

  With such a configuration, noise mixed in the first microphone can be removed by the noise signal acquired by the second microphone, and an audio signal with reduced noise can be obtained. Therefore, for example, noise that becomes an obstacle during the call or voice recording can be removed, and a good call system, a good voice recording system, and the like can be realized.

  In the audio output device according to the present invention, the second microphone may be a dummy microphone that has the same electrical characteristics as the first microphone and does not capture air vibrations.

  With such a configuration, noise mixed in the first microphone, for example, electromagnetic induction noise can be captured by the dummy microphone, and by using the noise captured by the dummy microphone, an audio signal with reduced noise can be obtained. Obtainable.

  In the audio output device according to the present invention, the noise acquired by the second microphone may be any one or more of electromagnetic induction noise, high noise noise, vibration noise, and electromagnetic induction noise caused by vibration. Good.

  With such a configuration, for example, electromagnetic induction noise, high noise noise, vibration noise, electromagnetic induction noise caused by vibration, and the like can be removed.

  In the audio output device according to the present invention, the electromagnetic induction noise, the high noise noise, the vibration noise, and the electromagnetic induction noise caused by the vibration may be caused by an MRI apparatus.

  With such a configuration, it is possible to reduce electromagnetic induction noise and the like caused by the MRI apparatus in an MRI environment.

  In the audio output device according to the present invention, the audio signal storage unit that stores the audio signal acquired by the first microphone and the noise signal storage unit that stores the noise signal acquired by the second microphone are further provided. The noise cancellation unit may cancel the noise signal from the audio signal using the audio signal accumulated by the audio signal accumulation unit and the noise signal accumulated by the noise signal accumulation unit.

  With such a configuration, it is possible to accumulate data that has not been processed in advance such as noise cancellation processing, so it is possible to perform noise cancellation processing, etc. many times while changing various settings, and noise removal processing. It is possible to perform noise removal processing at a setting with high efficiency and little change in the voice of the subject.

In the audio output device according to the present invention, the first microphone is bi-directional, and when the second microphone captures air vibration, the second microphone is bi-directional. It may be.
With such a configuration, since the microphone is bidirectional, the influence of noise can be reduced.

In the audio output device according to the present invention, the shape of the first microphone may match the shape of the mouth of the speaker.
With such a configuration, it is possible to efficiently acquire the voice to be output.

  In the audio output device according to the present invention, the first microphone and the second microphone may be composed of a composite piezoelectric body in which a piezoelectric element is disposed in an organic substance.

  With such a configuration, a microphone having an arbitrary size and shape suitable for the application can be realized. As a result, an audio output device with high noise removal efficiency can be realized.

  In the audio output device according to the present invention, the piezoelectric element may be polarized.

  In the audio output device according to the present invention, the dummy microphone is configured by a composite piezoelectric body in which a piezoelectric element is disposed in an organic material, and the composite piezoelectric body may not be polarized.

  In the audio output device according to the present invention, the sample number information storage unit storing the sample number information indicating the number of samples used in the averaging process, and the audio signal before or after the noise cancellation process by the noise cancellation unit And an average processing unit that performs an averaging process with the number of samples indicated by the number-of-samples information for the noise signal or only for the audio signal after the noise cancellation process.

  With such a configuration, it is possible to output an audio signal at a higher S / N by using the averaging process together with the noise cancellation process.

  In the audio output device according to the present invention, a change information receiving unit that receives change information that is information indicating that the number of samples is changed, and the sample number information is changed according to the change information received by the change information receiving unit. And a changing unit.

  With such a configuration, the number-of-samples information can be appropriately changed so as to obtain a high S / N.

  According to the voice output device or the like according to the present invention, noise superimposed on the voice uttered by the speaker can be canceled.

  Hereinafter, an audio output device according to the present invention will be described using embodiments. In the following embodiments, components and steps denoted by the same reference numerals are the same or equivalent, and repetitive description may be omitted.

(Embodiment 1)
An audio output device according to Embodiment 1 of the present invention will be described with reference to the drawings. The voice output device according to the present embodiment cancels noise superimposed on the voice uttered by the speaker.

  FIG. 1 is a block diagram showing a configuration of an audio output device 1 according to the present embodiment. The audio output device 1 according to the present embodiment includes a first microphone 11, a second microphone 12, a noise cancellation unit 13, an output unit 14, a sample number information storage unit 15, an average processing unit 16, A change information receiving unit 17 and a change unit 18 are provided.

  The first microphone 11 acquires the voice uttered by the speaker and converts it into a voice signal. Note that the first microphone 11 also acquires noise other than the voice uttered by the speaker. Therefore, the audio signal obtained from the first microphone 11 includes a noise signal. For example, as shown in FIG. 2, the first microphone 11 may include a frame 31 and a composite piezoelectric body 32 having a peripheral portion fixed by the frame 31. When the audio output device 1 according to the present embodiment is used in MRI, the frame 31 is placed in a magnetic field, and therefore is not made of a ferromagnetic material (for example, iron), such as resin or ceramic. Is preferred. The resin may be, for example, polypropylene (PP) or vinyl chloride. The frame 31 can be fixed directly or indirectly to a floor, a wall, an MRI apparatus or the like. The composite piezoelectric body 32 can constitute an acoustic device such as a speaker or a microphone. The composite piezoelectric body 32 is suitable for use in MRI because a piezoelectric element is disposed in an organic material and is non-magnetic without containing a ferromagnetic material. FIG. 3 is a diagram showing the structure of the composite piezoelectric body. The composite piezoelectric body 60 is composed of, for example, a large number of PZTs 61 arranged on the organic material 61. PZT 61 is a piezoelectric element made of lead zirconate titanate. The composite piezoelectric body 32 is already known and will not be described in detail. The composite piezoelectric material is described in, for example, JP-A-63-4799. The piezoelectric element is preferably polarized. Further, the polarization direction may be clearly shown on the piezoelectric element. Since the polarization direction is clearly indicated on the piezoelectric element, the first microphone 11 can be easily configured. When the audio output device 1 according to the present embodiment is used other than MRI, the first microphone 11 is not limited to such a configuration, and a microphone using a ferromagnetic material, for example, A dynamic microphone, a condenser microphone, or the like may be used.

  Further, it is preferable that the shape of the first microphone 11 matches the shape of the mouth of the speaker. The shape that matches the shape of the speaker's mouth is a shape that can effectively capture the voice uttered by the speaker. For example, as shown in FIG. 2, the position of the mouth of the speaker is the center. In this case, it may be a belt having a circular arc shape (cylindrical surface), or a parabolic curved surface such as a parabolic antenna (in this case, the position of the speaker's mouth is a parabolic curved surface). It may be a focal point), hemispherical (in this case, the position of the mouth of the speaker is preferably the center of the sphere), An elliptical surface may be used. Needless to say, other shapes may be used as long as the voice uttered by the speaker can be effectively captured. Moreover, it is preferable that the 1st microphone 11 is a magnitude | size which can catch the audio | voice which the speaker uttered effectively. Further, the first microphone 11 is preferably arranged at a position close to the mouth of the speaker when used. This is because the voice uttered by the speaker can be acquired effectively.

  Further, the first microphone 11 may be bi-directional as shown in FIG. For example, when the audio output device 1 according to the present embodiment is used in MRI, in MRI, noise is generated from the inner wall of a cylindrical container that stores a human body at the time of photographing, which is called a gantry, toward the center of the container. Moreover, although reflected sound is generated in the reverse direction, the sensitivity to noise can be reduced because the first microphone 11 is bidirectional. FIG. 4 shows a side view of a bidirectional microphone. MRI noise traveling in the radial direction of the gantry enters the first microphone 11 attached to the subject's mouth from the side of the first microphone 11 as shown in the figure. As a result, if the first microphone 11 is bi-directional, noise entering from the entire surface and the back surface of the first microphone 11 cancels out, so that the sensitivity to noise decreases.

  The second microphone 12 acquires noise and converts it into a signal. This signal is called a noise signal. Similar to the first microphone 11, the second microphone 12 may be one that captures air vibrations, that is, one that can detect sound, or the same electric power as the first microphone 11. It may be a dummy microphone that has special characteristics and does not capture air vibrations. Here, the electrical characteristic may be, for example, an electrostatic capacity, or an electrical impedance in the vicinity of a frequency of 1 kHz. The similar electrical characteristics may be that the electrical characteristics match, or that the electrical characteristics are close. For example, when the difference between the two electrical characteristics is ± 15% or less of one of the electrical characteristics, it may be considered that the electrical characteristics of the two are close. The second microphone 12 is preferably arranged in the vicinity of the first microphone 11. To be close, the microphone positions of each other are preferably within 20 mm, and more preferably within 5 mm. Furthermore, when a composite piezoelectric body is used for the first microphone 11 and the second microphone 12, a flat structure is possible, and thus there is an advantage that the proximity can be increased more easily. Even when the second microphone 12 is a dummy microphone, the second microphone 12 can acquire any one or more of electromagnetic induction noise, vibration noise, and electromagnetic induction noise caused by vibration. Such electromagnetic induction noise, vibration noise, and electromagnetic induction noise caused by vibration may or may not be due to MRI. In the former case, the second microphone 12 as a dummy microphone is close to the first microphone 11, and therefore captures MRI induced noise that is substantially the same as the MRI induced noise generated in the first microphone 11. Can do. Here, noise caused by the MRI apparatus will be described. In the MRI apparatus, three types of magnetic fields, that is, a static magnetic field, a gradient magnetic field, and a high-frequency magnetic field are roughly used. The application procedure of the gradient magnetic field and the high-frequency magnetic field is called a pulse sequence. At this time, since a strong current pulse periodically flows in the magnetic field coil, a large noise is generated due to electromagnetic induction noise and vibration generated in the coil. Thus, electromagnetic induction noise, noise, vibration, and induction noise due to vibration in a static magnetic field are generated in the MRI apparatus. Needless to say, when the second microphone 12 is a dummy microphone, noise other than the above may be acquired.

  When the second microphone 12 is not a dummy microphone, the second microphone 12 may be the same as the first microphone 11. That is, as shown in FIG. 2, the second microphone 12 may be constituted by a frame and a composite piezoelectric material, and the piezoelectric element included in the composite piezoelectric material may be polarized. Also, it may be bi-directional. Further, when not used in MRI, the second microphone 12 may be a microphone using a ferromagnetic material. However, since it is preferable that the second microphone 12 does not capture the voice uttered by the speaker, the shape may or may not match the shape of the mouth of the speaker. Even when the shape of the second microphone matches the shape of the speaker's mouth, it is preferable that the second microphone 12 does not acquire the voice spoken by the speaker. Needless to say, the second microphone 12 is preferably arranged close to the first microphone 11. In addition, when the microphone is constituted by a frame and a composite piezoelectric body, there is an advantage that a structure close to the target shape can be easily made. Therefore, in this case, the second microphone 12 can catch almost the same noise as the noise acquired by the first microphone 11, but the voice uttered by the speaker acquired by the first microphone 11 is taken. It is preferable to be arranged at a position where it cannot be done. When the second microphone 12 is not a dummy microphone, the second microphone 12 acquires at least one of electromagnetic induction noise, high noise noise, vibration noise, and electromagnetic induction noise caused by vibration. Can be.

  When the second microphone 12 is a dummy microphone, the dummy microphone may be composed of a composite piezoelectric body in which a piezoelectric element is disposed in an organic substance, and the piezoelectric element is polarized. Or it may not be polarized. Even when the piezoelectric element is polarized, the dummy microphone does not catch air vibrations, that is, does not detect sound (or has almost no function for detecting sound). When the second microphone 12 is a dummy microphone, the second microphone 12 may be disposed in the vicinity of the first microphone 11 because there is no function for detecting sound. Also good. FIG. 5 is a diagram illustrating an example of a positional relationship among the first microphone 11, the second microphone 12, and the position of the speaker's mouth 41 when the second microphone 12 is a dummy microphone. As shown in FIG. 5, the voice 42 emitted from the speaker's mouth 41 is acquired by the first microphone 11. On the other hand, the second microphone 12 is arranged on the back side of the first microphone 11, but does not capture air vibrations, and therefore does not acquire the sound 42 itself. On the other hand, since the second microphone 12 has the same electrical specification as that of the first microphone 11, it is possible to acquire electromagnetic induction noise captured by the first microphone 11 and noise similar to vibration noise.

  In addition, the first microphone 11 and the second microphone 12 are generally separate microphones, but both may be configured as an integrated microphone.

  The noise cancellation unit 13 cancels the noise signal from the audio signal using the audio signal acquired by the first microphone and the noise signal acquired by the second microphone. FIG. 6 is a diagram for explaining an example of noise cancellation. As shown in FIG. 6, the processing circuit 51 receives the audio signal acquired by the first microphone 11 and the noise signal acquired by the second microphone 12, and adds the inverted signal to the audio signal. By doing so, noise can be removed. A noise canceling method will be described later.

  The output unit 14 outputs the audio signal whose noise has been canceled by the noise canceling unit 13. Here, the output may be, for example, transmission via a communication line to a predetermined device, audio output by a speaker, accumulation in a recording medium, or delivery to another component. The output unit 14 may or may not include a device that performs output (for example, a speaker or a communication device). The output unit 14 may be realized by hardware, or may be realized by software such as a driver that drives these devices.

  The sample number information storage unit 15 stores sample number information indicating the number of samples used in the averaging process performed by the average processing unit 16 described later. The process of storing information in the sample number information storage unit 15 does not matter. For example, information may be stored in the sample number information storage unit 15 via a recording medium, and information transmitted via a communication line or the like is stored in the sample number information storage unit 15. Alternatively, the information input via the input device may be stored in the sample number information storage unit 15. Note that the sample number information stored in the sample number information storage unit 15 can be changed by the changing unit 18 described later. Storage in the sample number information storage unit 15 may be temporary storage in a RAM or the like, or may be long-term storage. The sample number information storage unit 15 can be realized by a predetermined recording medium (for example, a semiconductor memory, a magnetic disk, an optical disk, etc.).

  The average processing unit 16 is a sample indicated by the number-of-samples information for the audio signal and the noise signal before or after the noise cancellation processing by the noise cancellation unit 13 or only for the audio signal after the noise cancellation processing. Averaging with numbers. The averaging process can be realized by a moving average process, for example. In the present embodiment, a case where a moving average process is performed as the averaging process will be described. FIG. 7 is a diagram illustrating an example of a circuit that performs moving average processing when the number of samples indicated by the number-of-samples information is “4”. By being delayed by one sample time by each delay element, four consecutive samples are added, and finally four quarters are averaged by being ¼. This process is performed every time a new sample of the audio signal is input. Note that the moving average process is similarly performed on the noise signal. It goes without saying that the processing shown in FIG. 7 is changed according to the number of samples indicated by the sample number information.

  The change information receiving unit 17 receives change information which is information indicating that the number of samples is changed. This change information may be information indicating the number of samples after the change or information indicating a difference in the number of samples.

  For example, the change information receiving unit 17 may receive information input from an input device (for example, a keyboard, a mouse, a touch panel, etc.), or may receive information transmitted via a wired or wireless communication line. Alternatively, information read from a predetermined recording medium (for example, an optical disk, a magnetic disk, a semiconductor memory, etc.) may be received. Note that the change information receiving unit 17 may or may not include a device (for example, a modem or a network card) for receiving. The change information receiving unit 17 may be realized by hardware, or may be realized by software such as a driver that drives a predetermined device.

  The changing unit 18 changes the sample number information according to the change information received by the change information receiving unit 17. When the change information is information indicating the number of samples after the change, the change unit 18 may overwrite the sample number information stored in the sample number information storage unit 15 using the change information. When the change information is information indicating the difference in the number of samples, the change unit 18 uses the change information and the sample number information stored in the sample number information storage unit 15 to change the change information. The sample number information stored in the sample number information storage unit 15 may be overwritten with the sample number information.

  Although not explicitly shown in FIG. 1, an audio signal or a noise signal may be temporarily stored in a recording medium (not shown) during various processes in the audio output device 1.

  Although not explicitly shown in FIG. 1, the audio signal and the noise signal may be converted into a digital signal by A / D conversion or D / A conversion as appropriate, or converted into an analog signal. It goes without saying that it may be done.

  The audio output device 1 can also be used as an audio communication system or an audio recording system, and the use of the audio output device 1 is not limited.

  Next, the operation of the audio output device 1 according to the present embodiment will be described with reference to the flowchart of FIG. In the flowchart of FIG. 8, a case where the moving average process is performed before noise cancellation will be described.

  (Step S101) The control unit (not shown) of the audio output device 1 determines whether or not to start the noise canceling process. And when starting, it progresses to step S102, and when that is not right, it repeats the process of step S101 until it starts. For example, when a user inputs an instruction to start noise cancellation processing, the control unit (not shown) may determine to start noise cancellation processing, or the first microphone 11 or the second microphone may be started. When an audio signal or noise signal having a predetermined level or higher is input from the microphone 12, it may be determined that the noise canceling process is started.

  (Step S <b> 102) The average processing unit 16 takes in an audio signal from the first microphone 11 and takes in a noise signal from the second microphone 12.

  (Step S103) The average processing unit 16 performs moving average processing on the acquired audio signal and noise signal with the number of samples indicated by the sample number information stored in the sample number information storage unit 15, and performs the average processing. The resulting audio signal and noise signal are passed to the noise cancellation unit 13.

  (Step S104) The noise cancellation unit 13 removes a noise component from the audio signal using the audio signal and the noise signal.

  (Step S <b> 105) The output unit 14 outputs the audio signal whose noise has been canceled by the noise canceling unit 13.

(Step S106) The control unit (not shown) determines whether or not to end the noise canceling process. If the process is to end, the process returns to step S101; otherwise, the process returns to step S102. Note that the control unit (not shown) may determine that the noise canceling process is to be ended, for example, when the user inputs an instruction to end the noise canceling process, or the first microphone 11 or the first microphone When an audio signal or noise signal is no longer input from the second microphone 12 or when the time during which the audio signal output from the output unit 14 is at a level equal to or lower than a threshold value exceeds a predetermined time (this In this case, it may be determined that the noise canceling process is finished when the speaker has not made a speech for a predetermined time).
In the flowchart of FIG. 8, the process ends when the power is turned off or the process is terminated.

  Further, as described above, the moving average process may be performed after noise cancellation. In that case, instead of the flowchart of FIG. 8, the processing is executed as shown in the flowchart of FIG. In the flowchart of FIG. 9, processes other than steps S201 to S203 are the same as those in the flowchart of FIG.

  (Step S <b> 201) The noise cancellation unit 13 takes in an audio signal from the first microphone 11 and takes in a noise signal from the second microphone 12.

  (Step S202) The noise cancellation unit 13 removes a noise component from the audio signal using the audio signal and the noise signal.

  (Step S203) The average processing unit 16 performs a moving average process on the audio signal after noise cancellation with the number of samples indicated by the sample number information stored in the sample number information storage unit 15, and the result of the average process Is delivered to the output unit 14.

  Further, as described above, the moving average process may be performed before and after the noise cancellation. In that case, instead of the flowcharts of FIGS. 8 and 9, the process is executed as shown in the flowchart of FIG. In the flowchart of FIG. 10, processes other than step S301 are the same as those of the flowchart of FIG.

  (Step S301) The average processing unit 16 performs moving average processing on the audio signal after noise cancellation with the number of samples indicated by the sample number information stored in the sample number information storage unit 15, and the result of the average processing Is delivered to the output unit 14.

  The process of the change information receiving unit 17 and the change unit 18 is such that when the change information receiving unit 17 receives the change information, the change unit 18 changes the sample number information. Therefore, description of the flowchart of the process is omitted.

  Next, the operation of the audio output device 1 according to the present embodiment will be described using a specific example. In this specific example, the case where the audio output device 1 is used in MRI will be described. In that case, as shown in FIG. 11, only the first microphone 11 and the second microphone 12 are arranged in the shielded MRI room, and other components are arranged in the sound processing room. Will be. This is to prevent the noise cancellation unit 13, the output unit 14, and the like from being affected by a strong magnetic field caused by MRI. Further, it is assumed that the second microphone 12 is a dummy microphone.

  In such a situation, when a test subject as a speaker speaks, the first microphone 11 collects and acquires the voice and converts it into a voice signal. The primary purpose of the first microphone 11 is to capture spoken voice, but as a result, noise generated in the MRI room is also captured. Further, the second microphone 12 captures electromagnetic induction noise or vibration noise caused by MRI and converts it into a noise signal. Since the second microphone 12 is a dummy microphone, it does not capture the voice spoken by the subject.

  Thereafter, noise cancellation by the noise cancellation unit 13, moving average processing by the average processing unit 16, and the like are performed, and an audio signal in which noise is suppressed is output by the output unit 14.

  FIG. 12 is a diagram illustrating a comparison result between the waveform 1202 when noise cancellation is performed and the waveform 1201 when noise cancellation is not performed. In FIG. 12, the noise of the actual MRI machine is recorded at a position away from the MRI apparatus and not affected by electromagnetic induction noise, and the recorded MRI noise is output by a radio cassette recorder, and a cancellation experiment is performed with the apparatus of FIG. In this example, the voice uttered by the speaker is not captured. As shown in FIG. 12, it can be seen that a good noise canceling effect is obtained by the audio output device 1 according to the present embodiment.

  Next, the effect of the averaging process described in this embodiment will be described. FIG. 15 shows waveforms in a field where the influence of electromagnetic induction noise or vibration is strong, and the experimental results of the cancellation process. An original waveform 1501 is an MRI noise waveform in which electromagnetic induction noise or the like is strongly mixed, and a waveform 1502 after noise cancellation is a result of performing only a cancellation process on the original waveform. At this stage, spike-like noise remains, but in the waveform 1503 with the averaging process after the noise cancellation, the noise is finally reduced, and the effect of the averaging process is shown.

  FIG. 13 and FIG. 14 show an example in which the subject enters the gantry and the subject's voice is taken and noise is canceled by the apparatus of FIG. FIG. 13 and FIG. 14 are experimental results showing the result of noise cancellation processing for a signal including the voice uttered by the speaker. As shown in FIG. 13, it can be seen that the level of the voice uttered by the speaker is sufficiently higher than the level of the canceled noise. Therefore, the voice uttered by the speaker can be clearly heard by the voice signal from which noise is removed.

  As shown in FIG. 14, the MRI trigger signal may be measured, recorded, and displayed simultaneously with the voice signal of the speaker. In each experiment, a normal microphone was used as the second microphone 12 instead of a dummy microphone.

  As described above, the voice output apparatus 1 according to the present embodiment can output the voice of the subject in the MRI room at a high S / N, and as a result, it can be expected that a free call with the examiner can be performed.

  Note that the audio output device 1 according to the present embodiment may not be used in MRI. For example, it may be used in a place where noise or electromagnetic induction noise is intense. Specifically, the audio output device 1 according to the present embodiment may be used in a power plant, an airport, a helicopter, an aircraft, a ship, an auto racing field, and the like.

  As described above, according to the audio output device 1 according to the present embodiment, the noise that is acquired by the first microphone 11 and superimposed on the voice uttered by the speaker is acquired by the second microphone 12. It can be removed using the signal. Therefore, a clear voice with a high S / N (SN ratio) can be output.

  Under the conventional MRI environment, strong MRI induction noise and MRI noise are input to the microphone, and sound is also input. Therefore, in order to prevent the microphone amplifier from being saturated, the gain of the amplifier has to be set low. For this reason, the sensitivity to the desired sound is low. On the other hand, by using the audio output device 1 according to the present embodiment, the MRI induced noise can be canceled and the sensitivity to the MRI noise can be reduced. It becomes possible to raise the level suitable for output, and high S / N can be realized.

  In MRI, there are cases where it is desired to take an MRI image while interacting with a subject. In such a case, since it is required that the subject does not move so much, there is a request that the movement of the subject in utterance should be reduced (that is, the subject need not make a loud voice). In such a situation, by using the voice output device 1 according to the present embodiment, noise can be efficiently removed from the voice uttered by the subject under the strong noise environment of MRI even if the subject does not speak loudly. And clear voice of the subject can be acquired. As a result, for example, it is possible to satisfactorily measure the brain activity of the subject during conversation.

  Further, by using the moving average process together with the noise cancellation process, the effect of the cancellation process for electromagnetic induction noise and noise can be improved, and the voice uttered by the speaker can be acquired at a higher S / N. It becomes like this.

  In the present embodiment, the case where the audio output device 1 includes the change information receiving unit 17 and the changing unit 18 in order to change the sample number information stored in the sample number information storage unit 15 will be described. However, if the sample number information is not changed, the audio output device 1 may not include the change information receiving unit 17 and the changing unit 18.

  Further, in the present embodiment, the case where the audio output device 1 performs the moving average process has been described. However, when the audio output device 1 does not perform the moving average process, the audio output device 1 includes the sample number information storage unit. 15 and the average processing unit 16 may not be provided.

  Further, in the present embodiment, a case where a series of processes from the acquisition of the audio signal and the noise signal by the first microphone 11 and the second microphone 12 to the output of the audio signal from which noise has been canceled is executed. As described above, the audio signal acquired by the first microphone 11 and the noise signal acquired by the second microphone 12 are first accumulated, and thereafter processing such as noise cancellation and moving average processing is executed. May be. In this case, after monitoring the audio signal after noise cancellation and determining the appropriateness of the audio signal, if it is not appropriate, repeatedly canceling noise while changing the setting of noise cancellation or moving average processing, etc. It becomes possible to execute the process. FIG. 16 is a block diagram illustrating a configuration of the audio output device 2 in a case where an audio signal and a noise signal are accumulated. As shown in FIG. 16, the audio output device 2 includes a first microphone 11, a second microphone 12, a noise cancellation unit 13, an output unit 14, a sample number information storage unit 15, and an average processing unit. 16, a change information receiving unit 17, a change unit 18, an audio signal storage unit 21, and a noise signal storage unit 22. The configurations and operations other than the audio signal storage unit 21 and the noise signal storage unit 22 are the same as those described above, and the description thereof is omitted.

  The audio signal storage unit 21 stores the audio signal acquired by the first microphone 11 in a predetermined recording medium. This recording medium is, for example, a semiconductor memory, an optical disk, a magnetic disk, or the like, and may be included in the audio signal storage unit 21 or may exist outside the audio signal storage unit 21. Further, this recording medium may or may not temporarily store an audio signal.

  The noise signal storage unit 22 stores the noise signal acquired by the second microphone 12 in a predetermined recording medium. The recording medium is, for example, a semiconductor memory, an optical disk, a magnetic disk, or the like, and may be included in the noise signal storage unit 22 or may exist outside the noise signal storage unit 22. The recording medium may or may not temporarily store the captured image.

  In addition, when the audio signal acquired by the first microphone 11 and the noise signal acquired by the second microphone 12 are stored in the recording medium, they are stored so that the time correspondence between them can be taken. It is suitable to leave. This is because both can be synchronized in subsequent processing such as noise cancellation. For example, by assigning and accumulating the same time code, it may be possible to take a temporal correspondence between the two, or audio signals and noise signals are accumulated in two tracks of the same file. By doing so, you may be able to take time correspondence of both.

  Here, the noise cancellation will be briefly described. In noise cancellation, an FIR (Finite Impulse Response) filter is often used. FIG. 17 is a diagram for explaining noise cancellation. In FIG. 17, the audio signal measured by the first microphone 11 is Dk, and the noise signal measured by the second microphone 12 is Uk. Noise also enters Dk. In noise cancellation, noise mixed in Dk must be accurately estimated and canceled using Uk. Specifically, the digital filter 31 outputs an estimated value Xk of noise mixed in Dk. Then, the subtractor 32 subtracts the estimated value Xk from the audio signal Dk to obtain an estimated error Ek. The filter parameter calculation processing unit 33 calculates the parameters of the digital filter 31 so as to minimize the estimation error Ek, and sets the calculated parameters in the digital filter 31. This estimated error Ek becomes the output of the noise canceling unit 13.

In the FIR filter, calculation for estimating Xk is performed using _m filter parameters W ₀ ,..., W _m−1 as in the following equation. For the calculation of the filter parameter W, various calculation methods such as a least square estimation method and an LMS (Least Mean Square) method are known.
Xk = θ ^T U _k
θ = [W ₀ ,..., W _m−1 ] ^T
U _k = [U _k ,..., U _{k−m + 1} ] ^T

For waveform processing such as noise cancellation, refer to the following document, for example.
Literature: Adachi, Sano, “Role of System Identification in Active Noise Control”, System / Control / Information, Vol. 41, no. 2, p. 64-72, 1997

  In the noise cancellation unit 13 according to the above embodiment, only the subtraction process shown in FIG. 6 may be performed, or only the noise cancellation process using the FIR filter shown in FIG. 17 may be performed, or Both may be performed. When both the subtraction process and the noise cancellation process using the FIR filter or the like are used, the noise may be canceled by the FIR filter or the like after the subtraction process is performed first. In that case, a filter for predicting and estimating the noise waveform is configured from a plurality of (for example, about 20) past signals after the subtraction process, and the estimated value is subtracted from the current signal after the subtraction process. Thus, noise may be canceled. In that case, you may perform AD conversion, DA conversion, etc. before, during and during the process suitably. Further, as described above, the averaging process may be performed before, after, or during these processes.

  In the above embodiment, the case where the audio output device is stand-alone has been described. However, the audio output device may be a stand-alone device or a server device in a server / client system. In the latter case, the output unit outputs information via a communication line. In addition, the noise cancellation unit 13 and the average processing unit 16 may also receive an audio signal from the first microphone 11 and a noise signal from the second microphone 12 via a communication line.

  In the above embodiment, each process or each function may be realized by centralized processing by a single device or a single system, or may be distributedly processed by a plurality of devices or a plurality of systems. It may be realized by doing.

  In the above embodiment, information related to processing executed by each component, for example, information received, acquired, selected, generated, transmitted, or received by each component In addition, information such as threshold values, mathematical formulas, addresses, etc. used by each component in processing is retained temporarily or over a long period of time on a recording medium (not shown) even when not explicitly stated in the above description. It may be. Further, the storage of information in the recording medium (not shown) may be performed by each component or a storage unit (not shown). Further, reading of information from the recording medium (not shown) may be performed by each component or a reading unit (not shown).

  In the above embodiment, when two or more components included in the audio output device include a communication device or an input device, the two or more components may physically include a single device. Alternatively, it may have a separate device.

  In the above embodiment, each component may be configured by dedicated hardware, or a component that can be realized by software may be realized by executing a program. For example, each component can be realized by a program execution unit such as a CPU reading and executing a software program recorded on a recording medium such as a hard disk or a semiconductor memory. The software that realizes the audio output device in the above embodiment is the following program. That is, the program uses the audio signal acquired by the first microphone that acquires the voice uttered by the speaker and the noise signal acquired by the second microphone that acquires the noise, to the computer. To function as a noise canceling unit that cancels the noise signal and an output unit that outputs an audio signal in which noise is canceled by the noise canceling unit.

  In the program, the functions realized by the program do not include functions that can be realized only by hardware. For example, a function that can be realized only by hardware such as a modem or an interface card in an output unit that outputs information is not included in at least the function realized by the program.

  Further, this program may be executed by being downloaded from a server or the like, and a program recorded on a predetermined recording medium (for example, an optical disk such as a CD-ROM, a magnetic disk, a semiconductor memory, or the like) is read out. May be executed by

  Further, the computer that executes this program may be singular or plural. That is, centralized processing may be performed, or distributed processing may be performed.

  FIG. 18 is a schematic diagram showing an example of the appearance of a computer that executes the program and realizes the audio output device according to the embodiment. The above-described embodiment is realized by computer hardware and a computer program executed on the computer hardware.

  In FIG. 18, a computer system 100 includes a computer 101 including a CD-ROM (Compact Disk Read Only Memory) drive 105 and an FD (Flexible Disk) drive 106, a keyboard 102, a mouse 103, and a monitor 104.

  FIG. 19 is a diagram illustrating a computer system. In FIG. 19, in addition to the CD-ROM drive 105 and the FD drive 106, a computer 101 includes a CPU (Central Processing Unit) 111, a ROM (Read Only Memory) 112 for storing a program such as a bootup program, A CPU (Random Access Memory) 113 that is connected to the CPU 111 and temporarily stores application program instructions and provides a temporary storage space, a hard disk 114 that stores application programs, system programs, and data, a CPU 111 and a ROM 112. Etc. to each other. The computer 101 may include a network card (not shown) that provides connection to the LAN.

  A program that causes the computer system 100 to execute the functions of the audio output device according to the above-described embodiment is stored in the CD-ROM 121 or FD 122, inserted into the CD-ROM drive 105 or FD drive 106, and transferred to the hard disk 114. May be. Instead, the program may be transmitted to the computer 101 via a network (not shown) and stored in the hard disk 114. The program is loaded into the RAM 113 at the time of execution. The program may be loaded directly from the CD-ROM 121, the FD 122, or the network.

  The program does not necessarily include an operating system (OS) or a third-party program that causes the computer 101 to execute the functions of the audio output device according to the above-described embodiment. The program may include only a part of an instruction that calls an appropriate function (module) in a controlled manner and obtains a desired result. How the computer system 100 operates is well known and will not be described in detail.

  Further, the present invention is not limited to the above-described embodiment, and various modifications are possible, and it goes without saying that these are also included in the scope of the present invention.

  As described above, according to the audio output device or the like according to the present invention, an effect that noise can be removed from the audio signal acquired by the microphone is obtained, and the audio uttered by the speaker under the noise is effectively acquired. It is useful as an output device.

The block diagram which shows the structure of the audio | voice output apparatus by Embodiment 1 of this invention. The figure which shows an example of the microphone in the embodiment The figure for demonstrating the composite piezoelectric material in the embodiment The figure for demonstrating the bidirectionality of the microphone in the embodiment The figure for demonstrating arrangement | positioning of the 1st and 2nd microphone in the same embodiment The figure for demonstrating the cancellation of the noise in the same embodiment The figure for demonstrating the moving average process in the embodiment The flowchart which shows the operation | movement of the audio | voice output apparatus by the embodiment The flowchart which shows the operation | movement of the audio | voice output apparatus by the embodiment The flowchart which shows the operation | movement of the audio | voice output apparatus by the embodiment The figure which shows an example of use of the audio | voice output apparatus by the embodiment The figure which shows the experimental result in the same embodiment The figure which shows the experimental result in the same embodiment The figure which shows the experimental result in the same embodiment The figure which shows the experimental result for demonstrating the effect of the averaging process in the embodiment The block diagram which shows another example of the audio | voice output apparatus by the embodiment Diagram for explaining noise cancellation Schematic diagram showing an example of the appearance of the computer system in the embodiment The figure which shows an example of a structure of the computer system in the embodiment

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 2 Audio | voice output apparatus 11 1st microphone 12 2nd microphone 13 Noise cancellation part 14 Output part 15 Sample number information storage part 16 Average processing part 17 Change information reception part 18 Change part 21 Audio | voice signal storage part 22 Noise signal storage Part

Claims (14)

A first microphone that captures the voice spoken by the speaker;
A second microphone for acquiring noise;
A noise cancellation unit that cancels the noise signal from the audio signal using the audio signal acquired by the first microphone and the noise signal acquired by the second microphone;
An audio output device comprising: an output unit that outputs an audio signal from which noise has been canceled by the noise cancellation unit. The audio output device according to claim 1, wherein the second microphone is a dummy microphone that has the same electrical characteristics as the first microphone and does not capture air vibrations. The audio output according to claim 1 or 2, wherein the noise acquired by the second microphone is at least one of electromagnetic induction noise, high noise noise, vibration noise, and electromagnetic induction noise caused by vibration. apparatus. The audio output device according to claim 3, wherein the electromagnetic induction noise, the high noise noise, the vibration noise, and the electromagnetic induction noise caused by the vibration are caused by an MRI apparatus. An audio signal storage unit for storing the audio signal acquired by the first microphone;
A noise signal storage unit that stores a noise signal acquired by the second microphone;
The noise cancellation unit cancels the noise signal from the audio signal using the audio signal accumulated by the audio signal accumulation unit and the noise signal accumulated by the noise signal accumulation unit. 5. The audio output device according to any one of 4. The first microphone is bi-directional;
The audio output device according to any one of claims 1 to 5, wherein when the second microphone captures vibrations of air, the second microphone is bi-directional. The voice output device according to any one of claims 1 to 6, wherein a shape of the first microphone matches a shape of a mouth of a speaker. 8. The audio output device according to claim 1, wherein each of the first microphone and the second microphone is configured by a composite piezoelectric body in which a piezoelectric element is disposed in an organic substance. . The audio output device according to claim 8, wherein the piezoelectric element is polarized. The dummy microphone is composed of a composite piezoelectric body in which a piezoelectric element is disposed in an organic material,
The audio output device according to claim 2, wherein the composite piezoelectric body is not polarized. A sample number information storage unit in which sample number information indicating the number of samples used in the averaging process is stored;
Averaging with the number of samples indicated by the number-of-samples information before or after noise cancellation processing by the noise canceling unit, with respect to the audio signal and the noise signal, or with respect to only the audio signal after the noise cancellation processing The audio output device according to claim 1, further comprising: an average processing unit that performs. A change information receiving unit that receives change information that is information indicating that the number of samples is changed;
The audio output device according to claim 11, further comprising: a changing unit that changes the sample number information according to the change information received by the change information receiving unit. Noise cancellation for canceling the noise signal from the audio signal using the audio signal acquired by the first microphone that acquires the voice uttered by the speaker and the noise signal acquired by the second microphone that acquires the noise Steps,
An audio output method comprising: outputting an audio signal whose noise has been canceled in the noise cancellation step. Computer
Noise cancellation for canceling the noise signal from the audio signal using the audio signal acquired by the first microphone that acquires the voice uttered by the speaker and the noise signal acquired by the second microphone that acquires the noise And
A program for functioning as an output unit that outputs an audio signal from which noise has been canceled by the noise cancellation unit.