JP2015206665A - Sound field three-dimensional image measurement method by digital holography, and sound reproduction method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sound field image measurement method/device and a sound reproduction method/device that records a sound field as a three-dimensional field as a hologram and can perform reproduction of a sound field (reproduction of sound).SOLUTION: Object light passing a sound field and reference light are superimposed non-coaxially to be made interference light, the interference light is imaged time-serially, the object light is reconfigured by each interference intensity distribution, time serial phase distribution data is acquired from a time serial reconfiguration image, and sound information in a three-dimensional field is reconfigured. Imaging of the interference light is performed in a sampling cycle by twice or more frequency of sound to be measured. Reconfiguration of the sound information is performed by acquiring phase time waveform from the time serial phase distribution data. It is possible to identify a sound source position from the three-dimensional sound field data as well. Moreover, the phase time waveform is available for speech recognition and extraordinary noise measurement by acquiring a frequency spectrum of the sound field by Fourier transformation.

Description

  The present invention relates to a sound field three-dimensional image measurement method in which a state in which sound propagates through a three-dimensional space using digital holography is measured in a non-contact manner using light, and the three-dimensional sound field is reproduced by a computer, and The present invention relates to a playback device.

  Usually, a microphone is used to measure sound. However, it is necessary to arrange a large number of microphones in an array for sound field measurement to grasp the spatio-temporal behavior of sound waves. When a microphone array is used, there is a problem that an accurate distribution cannot be measured with high resolution because the microphone installation itself becomes an obstacle and sound reflection occurs to disturb the sound field. In addition, since physical microphones are arranged in an array, there is a problem that spatial resolution is limited.

  On the other hand, research on three-dimensional measurement techniques has been actively conducted in recent years, and digital holography capable of instantaneously measuring three-dimensional information has attracted attention. In the holography, as shown in FIG. 19, when the object light 2 (reflected light or transmitted light) of the three-dimensional object 50 interferes with the reference light 4 to record the interference fringes on the film 7, when reproducing, The same reference light 4 is irradiated onto the interference fringes to project a stereoscopic image. Digital holography is a technique for recording light wave information (complex amplitude distribution) from a three-dimensional object on an image sensor by interference and reconstructing the object quantitatively by light propagation calculation using a computer. As a result, instantaneous recording of the three-dimensional spatial information becomes possible, so that dynamic events can be recorded.

FIG. 20 shows a configuration example of an optical measurement system using digital holography.
The intensity of the laser light 6 emitted from the laser light source 10 is adjusted by the amplitude modulation plate 11 and then separated into the object light 2 and the reference light 4 by the first beam splitter 12. The beam diameter of the laser light is enlarged by a beam expander, and the object light 2 is irradiated onto the three-dimensional object 50. Then, the object light 3 and the reference light 4 that have passed through the three-dimensional object 50 are overlapped by the second beam splitter 19. The object light 3 and the reference light 4 are overlapped to become interference light, and interference fringes are recorded by the CCD image sensor 20. Then, the hologram imaged by the CCD image sensor 20 is calculated for light propagation in the computer, and a reconstructed image of the three-dimensional object 50 is generated. At this time, the object beam 3 and the reference beam 4 are overlapped as non-coaxial with the same axis or an angle.

  Conventionally, sound field information is visualized by interference between two light waves of measurement light and reference light, that is, a device for measuring sound by visualizing the directionality and density of the sound field by using light interference. And measurement methods are known (see, for example, Patent Documents 1 and 2 and Non-Patent Document 1).

  As shown in FIG. 22, a sound field visualization measuring device disclosed in Patent Document 1 includes a laser light generation device 101, a lens 102 that makes a laser point light source emitted from the laser light generation device parallel light, and a lens passing through the lens. A beam splitter 103 that divides the laser light into measurement light and reference light, and a sound field measurement unit that measures the sound field so that the divided measurement light 114 passes through the sound field generated by the sound source 107 108, a beam splitter 109 that superimposes the divided measurement light 114 and the reference light 115 to make interference light, and an imaging unit 112 that images the interference light, and the measurement light or reference of the divided laser light A half-wave plate 104 that converts light into an opposite phase is provided on one of the light paths.

  The phase of the measurement light is modulated in accordance with the density change amount when passing through the air density change portion due to the sound field from the sound source 107. When the measurement light and the reference light interfere with each other, the light intensity is slightly lower in the phase-modulated portion due to density change than in the same-phase portion, but visualization and measurement are difficult because the difference is small. Therefore, in the sound field visualization measurement device of Patent Document 1, by making the reference light in reverse phase by the half-wave plate 104, the part not affected by the density change, that is, the length of the reference optical path and the measurement optical path are the same. Alternatively, a portion that differs by one wavelength of light is darkened, and a luminance difference is generated so that the portion that is phase-modulated by the density change due to the sound field from the sound source 107 becomes brighter than the portion that is not phase-modulated. Yes. Since the light intensity of the phase-modulated part is slight, the light intensity of the bright part is greatly increased by amplifying the interference light by the optical multiplier 110, and the difference from the dark part is amplified and imaged by the camera.

As described above, the sound field visualization measuring device of Patent Document 1 is to measure the phase of a sound and visualize the sound field. However, the region where the sound field exists (sound field measurement through the imaging action by the lens). Part 108) is for measuring the vicinity, and cannot measure a three-dimensional sound field having a deep depth of field.
Further, although the interference light is imaged with a camera and the sound field is visualized, the sound field from the sound source 107 cannot be reproduced (sound reproduction).

  The sound field visualization device disclosed in Patent Document 2 visualizes a sound field using interference of a speckle image of laser light, but is similar to the sound field visualization measurement device of Patent Document 1. It was not possible to measure a three-dimensional sound field, and it was not possible to reproduce the sound field (sound reproduction).

  Non-Patent Document 1 discloses a method of performing interference measurement using digital holography as a method of observing a standing wave when an object is levitated by sound waves. As shown in FIG. 23, the observation apparatus disclosed in Non-Patent Document 1 uses a laser point light source as parallel light, as in the sound field visualization measurement apparatus of Patent Document 1, and the presence of a sound field due to the imaging action of the lens. However, it cannot measure a three-dimensional sound field with a deep depth of field. In addition, the observation apparatus of Non-Patent Document 1 captures interference light with a CCD image sensor and performs image processing with a computer to visualize standing waves. However, standing waves are temporally stable. For this reason (in FIG. 23A, the sound wave emitted from the Emitter is reflected by the reflector to form a standing wave), the CCD image sensor can be observed even at a low imaging speed. However, in the case of normal sound, a propagating three-dimensional sound field is formed instead of a standing wave, and it is difficult to shoot with a CCD image sensor for shooting a standing wave.

JP 2005-241348 A JP-A-61-148327

Optics Communications, 282 (2009) pp4339-4344

  In view of the above situation, the present invention provides a sound field image measurement method / device and a sound reproduction method / device capable of recording a sound field as a three-dimensional field as a hologram and restoring the sound field (sound reproduction). For the purpose.

In order to solve the above-described problem, in the sound field three-dimensional image measurement method according to the first aspect of the present invention, the object light passing through the sound field and the reference light are superposed non-coaxially to form interference light, and the interference light is Images are taken in time series, object light is reconstructed from the respective interference intensity distributions, time series phase distribution data is acquired from the time series reconstructed images, and sound information in a three-dimensional field is reconstructed.
According to such a configuration, it is possible to capture the interference light in time series, measure the phase distribution in time series from the respective interference intensity distributions, and record the sound field as a three-dimensional field as a hologram. The sound field can be restored (sound reproduction) in a three-dimensional field.

  Here, superimposing in a non-coaxial direction means shifting the axis or removing the axis. The method of reconstructing the object light from the interference intensity distribution is the same as the method used in the interference measurement using digital holography. The interference intensity distribution is used for filtering in the spatial frequency space, and the complex amplitude distribution of the object light is obtained. After extraction, the object light is reconstructed by performing light propagation calculation (back propagation calculation) in the computer.

The sound is a sparse wave, and when the air is thin (sparse) and when the air is dark (dense), the refractive index when light passes through is different, so the object light passing through the sound field is temporal The phase of the light has changed. Therefore, a sound wave (dense wave) is detected as a time distribution of the phase of the object light passing through the sound field. In order to measure how the phase of the object light changes over time, the interference light is imaged in time series, the object light is reconstructed from each interference intensity distribution, and the time-series phase distribution data from the time-series reconstructed image To get. Thereby, the sound in a three-dimensional field (sound field) can be measured and the sound can be reproduced.
That is, by making object light that has passed through the sound field interfere with reference light that does not pass through the sound field, sound field information can be recorded as interference fringes, and a three-dimensional sound field can be recorded in a computer using digital holography technology. Can be reconfigured.

  In the sound field three-dimensional image measurement method of the present invention, since the sound field distribution can be measured simply by irradiating light to the three-dimensional field to be measured, there is an unnecessary obstacle that becomes a problem when measuring using a microphone. do not do. In addition, since the spatial resolution is determined by the resolution and size of the image sensor that captures the interference light, the resolution can be increased by increasing the resolution of the sensor or by increasing the size of the sensor. Further, it is not necessary to perform focusing during recording by the digital holography technique, and a three-dimensional sound field can be reconstructed in a computer.

In the sound field three-dimensional image measurement method according to the second aspect of the present invention, an electromagnetic wave is allowed to pass through an object that is a sound field, and an object wave that passes through the sound field and a direct wave that is a reference are coaxial or non-shared. Axes are superimposed on the axis and received in time series as interference waves, or the phase difference between the object wave and direct wave is detected in time series in the detector to obtain complex amplitude information of the object wave, and each interference An object wave is reconstructed from intensity distribution or complex amplitude information, time-series phase distribution data is acquired from a time-series reconstructed image, and sound information in a three-dimensional field is reconstructed.
According to such a configuration, the interference wave is received in time series, or the phase difference is detected in time series, and the phase distribution is reproduced in time series from each interference intensity distribution or complex amplitude information. A sound field as a three-dimensional field can be recorded as a hologram. The sound field can be restored (sound reproduction) in a three-dimensional field.

  In general, electromagnetic waves having a wavelength of about millimeters (mm) or more are radio waves, shorter than that, infrared rays are used up to about 1 μm, visible light is about 0.7 to 0.4 μm, shorter are several nm to pm ultraviolet rays, and X-rays. , Γ rays. When the frequency of the electromagnetic wave is lowered, it is also possible to directly detect the amplitude and phase of the electromagnetic wave. When the frequency is high, the electromagnetic wave (object wave) that passes through the sound field is obtained from the interference intensity distribution obtained by superimposing the object wave and the direct wave to be referenced in a coaxial or non-coaxial manner and causing interference. Can be reconfigured. Further, the phase difference between the object wave and the direct wave is detected in the detector, the complex amplitude information of the object wave is acquired, and the object wave can be reconstructed from the complex amplitude information.

  In the sound field three-dimensional image measurement method according to the first or second aspect of the present invention, it is preferable that the imaging of the interference light is performed at a sampling period that is twice or more the frequency of the sound to be measured. By using a super-resolution method by numerical calculation, reconstruction is possible even with a sampling period less than twice the frequency of the sound to be measured. However, according to the sampling theorem, it is not necessary to use a super-resolution method by sampling data at a sampling period that is at least twice the frequency of the sound to be measured, so that the reconstruction process is simple. Can be achieved.

  In the sound field three-dimensional image measurement method of the present invention, sound information is reconstructed by acquiring a phase time waveform from time-series phase distribution data and reproducing the phase time waveform as audio data. Furthermore, by acquiring the frequency spectrum of the sound field by Fourier transform of the phase time waveform, it can be used for applications such as recognition.

Moreover, in the sound field three-dimensional image measurement method of the present invention, it is preferable to detect a sound that does not occur in the steady state based on the sound data or the frequency spectrum in the steady state.
By detecting a sound that does not occur in a steady state, it is possible to detect an abnormality of the device or equipment in a non-contact manner.

  In the sound field three-dimensional image measurement method of the present invention described above, it is preferable that the three-dimensional relative position of the sound source from the imaging position or the receiving position can be measured when a sound source exists in the sound field.

  The sound reproduction method of the present invention records the sound field as a three-dimensional field as a time-series reconstructed image using the sound field three-dimensional image measurement method described above, and reproduces the sound based on the phase time waveform.

Next, the sound field three-dimensional image measurement apparatus of the present invention will be described.
The sound field three-dimensional image measurement apparatus according to the first aspect of the present invention includes the following 1) to 6).
1) An optical measurement system in which object light passing through a sound field and reference light are superposed non-coaxially to form interference light 2) imaging means for imaging interference light in time series 3) object light from each interference intensity distribution And time series phase distribution acquisition means for acquiring time series phase distribution data from time series reconstructed images 4) phase time waveform acquisition means for acquiring phase time waveform from time series phase distribution data 5) phase time waveform Audio data acquisition means for acquiring the frequency spectrum of the sound field by Fourier transform of the phase time waveform.

A sound field three-dimensional image measurement apparatus according to a second aspect of the present invention includes the following a1) or a2) and b) to e).
a1) An electromagnetic wave measurement system that passes an electromagnetic wave through an object that is a sound field and superimposes the object wave and a reference direct wave in a coaxial or non-coaxial manner to generate an interference wave and receives the interference wave in time series Receiving means or
a2) Means for passing electromagnetic waves through an object as a sound field, detecting a phase difference between the object wave and a reference direct wave in a detector in time series, and acquiring complex amplitude information of the object wave b) Time series phase distribution acquisition means for reconstructing object light from interference intensity distribution or complex amplitude information and obtaining time series phase distribution data from a time series reconstructed image c) obtaining a phase time waveform from time series phase distribution data Phase time waveform acquisition means d) audio data acquisition means for acquiring the phase time waveform as audio data e) frequency spectrum acquisition means for acquiring the frequency spectrum of the sound field by Fourier transform of the phase time waveform

  In the sound field three-dimensional image measurement apparatus according to the first or second aspect of the present invention, it is preferable that imaging of interference light is performed at a sampling period that is twice or more the frequency of the sound to be measured.

  The sound reproduction device of the present invention records a sound field as a time-series reconstructed image using the sound field three-dimensional image measurement device according to the first or second aspect, and generates a sound based on the phase time waveform. Reproduce.

  According to the present invention, there is an effect that a three-dimensional sound field is recorded as a hologram and the sound field can be reproduced (sound reproduction).

Illustration of the sound field 3D image measurement method Configuration example of optical measurement system in sound field three-dimensional image measurement method Explanatory drawing of reproduction of phase time waveform in sound field 3D image measurement method Explanatory diagram of the tuning fork sound field 3D image measurement method Waveform diagram by tuning fork measured with microphone Tuning fork frequency spectrum measured with a microphone Tuning fork phase time distribution measured by sound field 3D image measurement method Tuning fork frequency spectrum measured by sound field 3D image measurement method Hologram and reconstructed image of interference light of object light that passed through the sound field of human voice Diagram showing phase time change of reconstructed image Phase time distribution of sound field “a” Frequency spectrum of sound field “a” (A) Phase time distribution of sound field of “i” (ii) Frequency spectrum of the sound field of “i” (ii) Correlation diagram of frequency spectrum of “a” (a) and formant frequency Correlation diagram of frequency spectrum of “i” (ii) and formant frequency "A" (A) frequency spectrum Frequency spectrum of “i” (ii) Illustration of the principle of holography Configuration example of optical measurement system for digital holography Configuration example using millimeter wave Prior art block diagram Illustration of prior art

  Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings. The scope of the present invention is not limited to the following examples and illustrated examples, and many changes and modifications can be made.

Sound is vibration transmitted through gas, liquid, solid, etc. When the substance (medium) that transmits sound is air (gas), sound is a phenomenon in which pressure fluctuations propagate. A sound in the air is a pressure that can be regarded as not changing like atmospheric pressure, that is, a pressure fluctuation applied in a form superimposed on a static pressure, and a minimum sound pressure change that a human can hear is about 2 × 10 ^−5. (Pa), since the normal conversational sound is approximately 10 ⁻² (Pa), the pressure fluctuation of the sound in the air is a very small vibration compared to about 1.013 × 10 ⁵ (Pa) which is atmospheric pressure. is there.
Sound propagates in the air as dense waves. Since the atmospheric pressure is always applied to the air, the pressure is lower than the atmospheric pressure in the sparse area, and the pressure is higher in the dense area. This variation is the sound pressure.

  In the case of a microphone that is a conventionally known sound observation method, the diaphragm inside the microphone swells or dents depending on the sound pressure, and this is electrically detected and output as an electrical signal. Laser microphones that detect sound with a laser do not directly measure the sound pressure. Sounds that are sparse and dense waves vary in phase because the refractive index differs between the sparse and dense parts. The light intensity is detected by the light receiving element, and the sound is detected as an electrical signal.

  On the other hand, in the present invention, the sound field is measured by digital holography. By measuring the sound field using digital holography, unlike a microphone, the sound can be observed remotely without disturbing the sound field, and the sound spreading can be visualized by reconstructing the sound field hologram in the computer. can do.

Since sound propagates in the air as a sparse and dense wave, as shown in FIG. 1, when the sound field (1A, 1B) is irradiated with the laser 2, the refractive index is high when the air density is high (dense) and low (sparse). Are different, the phase of the light changes with time. When the sound frequency is f, the sound period is T, the sound wavelength λ, and the sound speed is v (= 340 m / sec), the relationship f = 1 / T and v = f × λ holds. For example, in a 200 Hz sound, 1/200 second is one period (T) of the sparse / dense wave, and its wavelength is 1.7 m. That is, since the phase of light changes with time every T / 2 seconds, sound waves (dense waves) can be detected as a time distribution of phases.
In the present invention, interference fringes are continuously photographed by the CCD image sensor 20, the interference fringe images are acquired in time series, and a three-dimensional sound field is recorded as a hologram. The computer 30 performs a light propagation calculation and acquires reconstructed images (40A, 40B) of the object light. Further, different phases are detected in the pixels (41A, 41B) at the same position in the reconstructed image (40A, 40B). By capturing a time-series phase change as a phase waveform, it is possible to reproduce a sound field (sound reproduction) as a three-dimensional field.

FIG. 2 shows a configuration example of an optical measurement system in the sound field three-dimensional image measurement method.
As shown in FIG. 2, the intensity of the laser light 6 emitted from the laser light source 10 is adjusted by the amplitude modulation plate 11, and then divided into the object light 2 and the reference light 4 by the first beam splitter 12. In both cases, the beam expander (13, 14, 16, 17) is used to expand the beam diameter of the laser beam, and the object field 2 is irradiated onto the sound field 1 to be observed. Then, the object beam 3 and the reference beam 4 that have passed through the sound field 1 are superposed by the second beam splitter 19. By tilting the reference beam 4 slightly, interference fringes having a carrier frequency are recorded by the CCD image sensor 20.

  As shown in FIG. 3, a hologram captured in time series by the CCD image sensor 20 is subjected to a band-pass filter in a computer to extract a complex amplitude distribution of object light, and then a light propagation calculation is performed to obtain a sound field. The object light 3 that has passed through 1 is reconstructed. The reconstructed image includes information on the amplitude and phase of the object light 3 that has passed through the sound field 1. By detecting the phase information therefrom, the phase of the object light 3 that is fluctuating due to the change in air density due to the sound field 1 is detected. One reconstructed image has only instantaneous phase information. In order to detect phase fluctuations to the last, holograms are continuously photographed by the high-speed CCD image sensor 20. Then, by detecting the phase of the same point one by one from the reconstructed image of the hologram, the phase time waveform becomes a waveform of a sound wave.

  The laser wavelength used in Example 1 was 532 nm, the CCD image sensor used had a resolution of 512 × 512 (pixels), a pixel size of 16 × 16 μm, and a frame rate of 2000 (fps). From the sampling theorem, this CCD image sensor can observe sound having a frequency of 1000 Hz or less.

(Tuning fork sound field 3D image measurement experiment)
A tuning fork capable of generating a single frequency sound is used as a sound source for the sound field to be observed. A pure tone is a sound represented by a sine wave, and a natural sound has a harmonic that is a frequency component that is an integral multiple of the fundamental frequency, but a pure tone has no harmonics. A tuning fork can generate a sound that is almost pure, although it contains slightly overtones.

In this experiment, a tuning fork that generates a pure tone of 440 Hz was used. Immediately after hitting the tuning fork, overtones of 440 Hz or higher were included, so the subsequent sound was used without measuring for 1-2 seconds immediately after hitting. Since the sound of the tuning fork itself is extremely weak, instead of irradiating the object light around the tuning fork, the object light is directly irradiated to the tuning fork to reconstruct the sound field in a space closer to the tuning fork.
In FIG. 4 (1), the tuning fork is directly irradiated with object light, the interference light is imaged as shown in FIG. 4 (2), and a hologram is obtained. As shown in FIG. 257, 100) at the position of the pixel (pixel) is acquired, time-series phase distribution data is acquired, and sound information in the three-dimensional field is reconstructed.

A waveform of a tuning fork measured with a general microphone is shown in FIG.
FIG. 6 shows the result of performing Fourier transform on the waveform shown in FIG. 5 and analyzing the spectrum of this sound wave. It can be seen from FIG. 6 that no peaks other than approximately 440 Hz are observed.
The tuning fork where the sound is generated is installed in the optical system, the frame rate of the CCD image sensor is set to 2000 (fps), the object light is irradiated, the reference light is interfered, and 4000 holograms for 2 seconds. Were continuously photographed with a CCD image sensor. FIG. 7 shows a graph showing the time distribution of the phase for 2 seconds in terms of time detected at the position (257, 100) in the reconstructed image (512, 512) of the hologram. FIG. 8 shows the result of Fourier transform of the time distribution of the phase in FIG. 7 in order to obtain frequency characteristics.

  FIG. 7 shows that the average value of the phase decreases with time, but a sine wave exists. Further, FIG. 8 shows a peak at a position of 440 Hz as in FIG. From these, it was found that recording and reconstruction of the sound field can be performed using the phase distribution.

(Experiment for 3D image measurement of human voice)
The time of one period of the speech waveform is called a basic period, and its reciprocal is called a basic frequency. The average fundamental frequency for men is about 120 Hz, and the average fundamental frequency for women is about 240 Hz. By setting the frame rate of the CCD image sensor to 2000 (fps), the sampling theorem is sufficiently satisfied. The observation voice was made into one word. Observe the Japanese vowels “a” (a) and “i” (i). As an observation method, “a” (a) and “i” (i) are uttered from the side toward the object light during 2 seconds of photographing. Unlike the tuning fork experiment described above, the target object is not a sound source but a space in which a sound field is generated. An example of a photographed hologram and a reconstructed image are shown in FIG.

Since the sound field is invisible, no object or the like is shown in the hologram and the reconstructed image shown in FIG. However, a sound field exists. FIG. 10 shows the phase change at the center (257, 257) of the reconstructed image shown in FIG.
The sine wave of FIG. 11 is a phase time distribution by the sound field “a” (A), and FIG. 12 shows a result of Fourier transform of the phase time distribution of FIG. Moreover, the sine wave of FIG. 13 is a phase time distribution by the sound field of “i” (ii), and FIG. 14 shows the result of Fourier transform of FIG. It can be seen from the frequency spectra of FIGS. 12 and 14 that the measured sound field has a fundamental frequency of about 260 Hz.

  In the above experiment, Japanese vowels “a” (a) and “i” (i) could be reconstructed by digital holography. This “a” (a) and “i” (i) are evaluated from the aspect of phoneme recognition. The waveform of speech is complex, and its characteristics are difficult to understand by looking at the waveform. Even if you hear the same voice “a” (a), the shape and frequency of the waves differ greatly depending on the volume of the voice and the person. Therefore, there is a formant frequency that characterizes the speech waveform. The characteristics of the speech waveform appear in the frequency spectrum. The frequency spectrum of speech is formed by superimposing frequency components with periodic fine peaks and the general shape (rough shape) with some peaks.

  The periodic peak is a peak related to the fundamental period of speech, and the interval corresponds to the fundamental frequency. Moreover, the peak seen in the outline of the frequency spectrum is called formant, and the frequency is called formant frequency. The formant frequencies are called the first formant (F1), the second formant (F2),. These formant frequencies correspond to the resonance frequency of the vocal tract as an acoustic tube. In Japanese vowels, F1 and F2 are important among formant frequencies, and vowels can be distinguished by F1 and F2.

For example, FIG. 15 shows the relationship between the frequency spectrum of the vowel “a” (A) recorded by the microphone and the formant frequency.
Next, FIG. 16 shows the relationship between the frequency spectrum of the vowel “i” (ii) recorded by the microphone and the formant frequency.
From these, it can be seen that the basic frequency of both “a” (a) and “i” (i) is equal to about 120 Hz, but the outline of the frequency spectrum is greatly different. “A” (A) has the formant frequency with the closest values of F1 and F2 among vowels, while “i” (I) has the feature that the values of F1 and F2 are the farthest among vowels. Have. In addition, if the fundamental frequency is different for the same vowel, the outline of the frequency spectrum is similar. FIGS. 17 and 18 show frequency spectra of “a” (A) and “i” (I) having a fundamental frequency of about 240 Hz recorded by the microphone, respectively.

17 and 18 are compared with FIGS. 15 and 16, it can be seen that when the fundamental frequency is increased, the outline is the same, but the formant frequency is higher.
Here, when the frequency spectrum diagrams 12 and 14 of the sound field (basic frequency 260 Hz) measured by digital holography are confirmed, the frequency spectrum diagrams of “a” (a) and “i” (i) at 240 Hz measured by the microphone. 17, it can be seen that the shape is almost the same as FIG.
Therefore, it can be seen that in the sound field measured by digital holography, the characteristic of formant frequency appears in the same manner as when recording with a microphone. From this, even with digital holography, it is possible to measure sound that is accurate enough to be recognized as phonemes in the same way as a microphone.

Next, a method of acquiring the complex amplitude information of the object wave and measuring the sound field three-dimensionally using millimeter waves, which are an example of electromagnetic waves, will be described.
The millimeter wave is passed through the object that becomes the sound field, the phase difference between the object wave and the direct wave is detected in time series in the detector to obtain the complex amplitude information of the object wave, and the object wave is obtained from each complex amplitude information. A configuration example in the case of reconfiguration is shown in FIG.
As shown in FIG. 21, the millimeter wave oscillated from the millimeter wave generating source 60 passes through a beam diameter expanding system 61 that expands the millimeter wave beam diameter, and then is split by a beam splitter 62. It passes through the sound field 1 and is received by the millimeter wave detector array 63 as an object wave. The other millimeter wave does not pass through the sound field 1 and is received by the millimeter wave detector array 63 as a direct wave. Both millimeter wave signals received are received by the phase comparator 64, and the phase difference between the object wave and the direct wave is detected. The phase comparator 64 serves as a detector, and the phase difference between the object wave and the direct wave is detected in time series in the detector to obtain complex amplitude information of the object wave, and a computer (not shown) receives each complex amplitude information. The object wave is reconstructed from Further, instead of using the millimeter wave detector array, a single detector can be substituted for the phase detection of the direct wave as a reference. Furthermore, when the value is spatially constant, direct wave phase measurement can be omitted.

  The present invention is useful as a design tool for living spaces and concert halls. In addition, visualization of sound field formation in artificial vocal cords and musical instruments becomes possible, which is useful as a design tool for improvement and commercialization.

1, 1A, 1B Sound field 2, 3, 3A, 3B Object light 4 Reference light 5 Interference light 6 Amplitude modulation plate 7 Film 8 Hologram 9 Transmitted light 10 Laser light source 12, 19 Beam splitter 13, 14, 16, 17 Beam x Pander 15, 18 Mirror 20 CCD image sensor 30 Computer 40A, 40B, 51 Reconstructed image 41A, 41B Pixel (pixel)
50 Three-dimensional object 60 Millimeter wave source 61 Beam diameter expansion system 62 Beam splitter 63 Millimeter wave detector array 64 Phase comparator

Claims (11)

The object light passing through the sound field and the reference light are superposed non-coaxially to form interference light,
The interference light is imaged in time series, the object light is reconstructed from the respective interference intensity distributions, time series phase distribution data is acquired from the time series reconstructed images, and sound information in a three-dimensional field is reconstructed. A sound field three-dimensional image measurement method characterized by the above. An electromagnetic wave is passed through an object that is a sound field, and the object wave that passes through the sound field and a direct wave that is a reference are superimposed in a non-coaxial or coaxial manner and received in time series as an interference wave, or In the detector, the phase difference between the object wave and the direct wave is detected in time series to obtain complex amplitude information of the object wave,
The object wave is reconstructed from each interference intensity distribution or the complex amplitude information, time-series phase distribution data is acquired from a time-series reconstructed image, and sound information in a three-dimensional field is reconstructed. Sound field 3D image measurement method.   3. The sound field three-dimensional image measurement method according to claim 1, wherein the imaging of the interference light is performed at a sampling period that is twice or more the frequency of the sound to be measured.   The sound information is reconstructed by acquiring a phase time waveform from the time-series phase distribution data, acquiring the phase time waveform as sound data, and acquiring a frequency spectrum of the sound field by Fourier transform of the phase time waveform. The sound field three-dimensional image measurement method according to any one of claims 1 to 3.   5. The sound field three-dimensional image measurement method according to claim 4, wherein a sound that does not occur in a steady state is detected based on the sound data or the frequency spectrum at a constant time.   The three-dimensional sound field according to any one of claims 1 to 5, wherein when a sound source is present in the sound field, a three-dimensional relative position of the sound source from an imaging position or a receiving position can be measured. Image measurement method. Using the sound field three-dimensional image measurement method according to claim 1,
A sound reproduction method for recording the sound field as a time-series reconstructed image and reproducing the sound based on the phase time waveform. An optical measurement system in which object light passing through the sound field and reference light are superposed non-coaxially to form interference light;
Imaging means for imaging the interference light in time series;
Reconstructing the object light from each interference intensity distribution, time series phase distribution acquisition means for acquiring time series phase distribution data from a time series reconstructed image;
Phase time waveform acquisition means for acquiring a phase time waveform from the time-series phase distribution data;
Audio data acquisition means for acquiring the phase time waveform as audio data;
A frequency spectrum acquisition means for acquiring a frequency spectrum of the sound field by Fourier transform of the phase time waveform;
A sound field three-dimensional image measurement apparatus comprising: An electromagnetic wave measurement system that passes an electromagnetic wave through an object to be a sound field and superimposes the object wave and a reference direct wave on a non-coaxial or coaxial axis to form an interference wave, and receives the interference wave in time series Receiving means;
Or
Means for detecting a phase difference between the object wave and the direct wave in a detector in time series, and acquiring complex amplitude information of the object wave;
Time series phase distribution acquisition means for reconstructing the object light from each interference intensity distribution or the complex amplitude information and acquiring time series phase distribution data from a time series reconstructed image;
Phase time waveform acquisition means for acquiring a phase time waveform from the time-series phase distribution data;
Audio data acquisition means for acquiring the phase time waveform as audio data;
A frequency spectrum acquisition means for acquiring a frequency spectrum of the sound field by Fourier transform of the phase time waveform;
A sound field three-dimensional image measurement apparatus comprising:   The sound field three-dimensional image measurement apparatus according to claim 8 or 9, wherein the imaging of the interference light is performed at a sampling period that is twice or more the frequency of the sound to be measured. Using the sound field three-dimensional image measurement device according to any one of claims 8 to 10,
A sound reproducing apparatus for recording the sound field as a time-series reconstructed image and reproducing the sound based on the phase time waveform.