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FIELD OF THE INVENTION The present invention relates to a sound field display device used
when measuring or monitoring a sound field by electroacoustic reproduction such as a real
sound source such as a hall or stereo. [Conventional Technique 1 Conventionally, there are the
following techniques for measuring or visualizing sound image localization and a sense of sound
spreading. (1) In stereo audio signals, the audio signals of the left and right channels are input to
an oscilloscope and the Lissajous waveform is observed. (2) Observe the shape of the crosscorrelation function of the sound pressure at two points in space (corresponding to the positions
of both ears) (For example, R. Suzuki, About the inter-ear correlation coefficient in the stereo
reproduction sound field J JAS Jurna 11985 .4). (3) Measure the intensity vector (particle
velocity × time average of sound pressure) to estimate the sound source direction. [Problems to
be Solved by the Invention] Although the method described by the item (1) or the method of
using a sarge waveform is widely used in recording studios and the like (suitable for monitoring
the electrical signal itself), the sound field itself is It does not monitor the The correlation method
described as the item (2) is effective to know the diffusion degree of the sound field, but there is
a drawback that the sound image localization can not be distinguished between the front and the
rear. Also, it is difficult to display transient sound. The intensity vector method described in
section (3) is effective for steady-state sound analysis because it can measure only components in
one direction at a time, while displaying transient sounds. Has the disadvantage of being unable
to Therefore, in view of the above-described point, an object of the present invention is to
provide a sound field display device capable of displaying a sound image in any direction in front,
rear, left, and right in real time. [Means for Solving the Problems 1 In order to achieve the object,
in the present invention, a first measuring means for measuring the motion velocity of the
medium in at least two directions, and a second measuring means for measuring the sound
pressure, Arithmetic means for obtaining a particle velocity component in phase with sound
pressure at a predetermined frequency or a predetermined frequency band by introducing
output signals from the first and second measuring means, and a localization direction of a sound
image based on the particle velocity component And display means for displaying. [Operation]
The present invention measures the sound pressure and particle velocity at the listening position
two-dimensionally or three-dimensionally, and observes the wave front state of the sound field in
real time by performing predetermined calculations. . That is, the real part (and imaginary part)
of the mutual spectrum of the sound pressure and particle velocity is determined from the sound
pressure and particle velocity at one point in the sound field, or the particle velocity component
in phase with the sound pressure is determined for each band It is displayed on one screen.
EXAMPLES The present invention will be described in detail based on the following examples.
FIG. 1 is a block diagram showing an embodiment of a sound field display device to which the
present invention is applied. In the illustrated microphone unit 1, one pressure-type microphone
(nondirectional) M2 and two main axis directions orthogonal to each other in a predetermined
plane (hereinafter, two main axis directions are referred to as X direction and X direction) The
velocity type microphones (bidirectional) M1 and M3 are disposed close to each other. また、バ
ンドパスフィルタ(BPF)2−1〜2−N、4−1〜4−N。 Each of 6-1 to 6-N includes a
band pass filter of 1/3 octal width. Further, two sets of arithmetic units 8-1 and 8-N and 10-1 to
10-N are provided corresponding to the output signals of these 8 PFs. The multiplexer 12.14
selects one of the output signals obtained from these operation units and applies it to a CRT (not
shown) of the display unit 16. Next, the operation of this embodiment will be described. First, a
signal proportional to the sound pressure is obtained by the pressure microphone M2, and a
signal proportional to the velocity of one particle, which is the motion velocity of the medium in
each of the Xr y directions, is obtained by the velocity microphones Ml and M3. Next, these
signals are introduced into band pass filters (BPFs) 2-1 to 2-N, 4-1 to 4-N, and 6-1 to 6-N to be
decomposed into frequency components. As the bandwidth of these BPFs, a 1/3 octal width
corresponding to the nature of hearing is appropriate, but it is determined appropriately
according to the purpose of use. In addition, it is also possible to obtain ¦ require a pressure
gradient from the difference using several pressure microphones, and to obtain ¦ require a
particle velocity from the derivative value. In the arithmetic units 8-1 to 8-N and 10-1 to 10-H,
the sound pressure p (L) and the particle velocity u in the X direction and in the X direction (t).
The direction of the particle velocity in phase with the sound pressure (function of time) is
determined as vector component i- (t), Ly (t) by T-time integration of the product of u, (t) (ie, dt '
). In the display unit 16, the components of the vector determined by the operation unit
corresponding to each frequency region are manually input as vertical and horizontal axis signals
of the CRT, and are displayed as X components and X components. As a result, vectors (tx (t), 1y
(t)) are displayed on the screen. The integration time T is determined for each band according to
the speed of fluctuation of each frequency component and the length of the response time of
hearing. In general, several tens of milliseconds may be sufficient. Next, specific modes of display
on the display unit 16 will be described. FIG. 2 is a view showing the relationship between the
main axis directions x and y of the velocity type microphones M1 and M3 and the localization
direction of the sound image.
Now, as shown in the figure, it is assumed that the sound source is in the direction of the angle
α from the main axis X, and emits a sound including a plurality of frequency components.
Further, in the embodiment shown in FIG. 1, it is assumed that six BPFs are provided. Then, i (t) if
the sound source is stationary. Since 1x (t) is constant regardless of time, six bright spots are
displayed in a line in one display portion 16 as shown in FIG. A line segment represented by
these six bright spots represents the direction α of the sound source and the intensity in each
frequency component. Further, when only the power of the sound source changes (the direction
is unchanged), only the length of the line segment changes as shown in FIG. Next, the reason why
the localization direction of the sound image can be known by the display of the display unit 16
will be described. Since the direction of the particle velocity vector in phase with the sound
pressure coincides with the normal direction of the wave front, the direction of the displayed
vector indicates the direction of arrival of the sound wave and approximates the localization
direction of the sound image. Here, it is clear from the following description that the direction of
the particle velocity vector in phase with the sound pressure coincides with the normal direction
of the wavefront. Now, assuming that the velocity potential φ (r) at one point of the sine wave
sound field is A (r) exp J (cc + t−θ ( )), the sound pressure and the particle velocity can be
obtained by the following equations. Particle velocity u (r) = − [7φ (2) = − (V! -J (7θ) φ (3)
where r is a position vector, ρ. Is the density of the medium at static pressure. Since the normal
direction of the wavefront is given by gradθ, that is, 7θ, an amount proportional to θ can be
determined from the term of J (17θ) φ of the particle velocity, that is, the term in phase with
the sound pressure. If the signal is not a sine wave, the wave front can not be defined strictly
speaking, but it can be treated as a sine wave whose amplitude 1 phase changes gradually by
cutting out with a narrow band pass filter, so the above concept can be applied . FIG. 5 is a block
diagram showing another embodiment of the present invention. In the figure, 20 ^ and 20B are
mutual spectrum operation units for introducing the output signals of the pressure type
microphone M2 and the velocity type microphones M1 and M3 respectively shown in FIG.
Reference numeral 22 denotes a display unit having a CRT capable of three-dimensional display.
In the second embodiment shown in FIG. 5, mutual spectrum operation units 20A and 20B are
included instead of the band pass filter (BPF) and the operation unit in FIG. In the calculation
units 20 ^ and 20B, a mutual spectrum of sound pressure and particle velocity is calculated.
That is, assuming that the Fourier transform of sound pressure is P (ω) and the Fourier
transform of particle velocity is Ux (ω), U, (ω), the real parts R, (ω), R 2 (ω) of the respective
mutual spectra 11. Rx (ω) −Real (P at ω) Ox (ω) = (4) Ry (ω) −Real (P at 11) 11. Calculated as
((L)))-(s) (* indicates complex conjugate). Since these real parts correspond to obtaining the
amount proportional to 70 from the equations (1) and (3), they represent the normal direction
component of the wave front by the ω component of the signal. Moreover, since these real parts
are functions of frequency, the display unit 22 needs to perform three-dimensional display
having the frequency axis f in addition to the main axis directions x and y. That is, the display
unit 22 displays the result obtained from the particle velocity in the X direction as the X
component and the result obtained from the particle velocity in the X direction as the y
component for each frequency component. It becomes dimensional. 6 (A) to 6 (C) are diagrams
showing specific display modes in the second embodiment shown in FIG. Now, assuming that the
sound source is at the position (direction α) as shown in FIG. 6 (A) and the power spectrum of
the sound source is as shown in FIG. 6 (B), the display unit 22 A three-dimensional display as
shown in FIG. 6 (C) is obtained. In the second embodiment, perfect real-time display is difficult,
but quasi-real-time display is possible if averaging with exponential weighting is used in Fourier
transform. Also in the first embodiment (see FIG. 3), the three-dimensional display shown in FIG.
6 (C) can be performed by shifting the origin for each bright point and changing the color of the
bright point. It is possible to make it an equivalent display mode. Further, although only the real
part of the mutual spectrum is used in the second embodiment shown in FIG. 5, the imaginary
part is also a significant amount. Now, the relationship expressed by the particle velocity u (r)(7φ) is expanded to the Fourier velocity mU 8 (ω), uy (ω), P (ω) of the particle velocity and
sound pressure of the signal having bandwidth. If applicable, it is as stated before that the
orientation of the vector represents the orientation of 7θ at each ω. On the other hand, the
imaginary part is considered to represent the direction of 7 ^ / A from Equation (3), that is, the
maximum inclination direction of the amplitude. In other words, it can be interpreted as the
normal direction of the vector direction by the real part.
Next, how to interpret this physically will be described with an example. For example, if there is a
point sound source emitting a sine wave in free space, the isophase lines are concentric as shown
in FIG. 7 (^). Also, as shown in FIG. 7 (B), the equal amplitude lines are also concentric circles.
That is, in such a sound field, the normal directions of both lines coincide at two points. However,
in a general sound field (a sound field having reflection or interference by a plurality of sound
sources), the shapes of the equal phase line and the equal amplitude line are different, so the two
do not necessarily match. Since the sound image localization direction has a strong correlation
with the isophase line, the present invention focuses on the isophase line, but the iso-amplitude
line is also general as a representation method of the sound field. In particular, it is useful for
detecting the presence or absence of a standing wave. The sound field where the direction of the
vector by the real part and the vector by the imaginary part differ greatly is a sound field by
interference, so unnaturalness occurs in sound image localization. Therefore, it is possible to
obtain the naturalness of sound image localization by simultaneously displaying the vectors of
the imaginary part. In the first embodiment, it is obvious that the amount corresponding to the
imaginary part can be obtained by applying a Phase shift circuit to the sound pressure
signal. [Effects of the Invention] By implementing the present invention, it becomes possible to
directly display sound image localization from the sound field, which was conventionally difficult.
In particular, it has a new function in that front and back judgment of a sound image is possible,
and can be applied to multi-channel stereo sound fields. Examples of application of the present
invention include l) sound field monitor of multi-channel stereo (including pseudo 4ch such as
Dolby); 2) monitor of PA sound field such as hall; 3) room acoustic design such as studio etc.
Such as measuring instruments;
Brief description of the drawings
FIG. 1 is a block diagram showing the first embodiment of the present invention, FIGS. 2 to 4 are
diagrams for explaining the display mode in the first embodiment, and FIG. 5 is the second
embodiment of the present invention 6 is a block diagram showing an example. FIGS. 6 (A) to 6
(C) are diagrams explaining the display mode in the second embodiment, and FIGS. 7 (A) and 7
(B) are equiphases formed by a sound source It is a figure shown about a line and an equal
amplitude line.
1: Microphone unit, M1, M3: Speed-type microphone, M1: Pressure-type microphone, 2-1 to 2-N,
4-1 to 4-N, 6-1 to 8-N.・ Bandpass filter, 8-1 to 8-N, 10-1 to 10-N ・ ・ ・ Arithmetic part, 12.14
・ ・ ・ Multiplexer, 16 ・ ・ ・ Display part, 20 ^, 20B ... mutual spectrum Operation unit, 22 ...
display unit. 2 2 Figure 5 (A) (B) Figure 6