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Specification I Title of Invention
Sound image position elevation suppressor in one-dimensional sound reproduction
3) Detailed Description of the Invention The present invention relates to a signal processing
apparatus for performing stereophonic sound reproduction using a head phone or a speaker /
stem, and in particular: It is intended to suppress the rising of the synthesized sound image by
the speaker / stem relative to the front horizontal surface, and to obtain a natural sound field
feeling of uniform spread in the front horizontal surface. Conventionally, at the time of Hendofon
playback of a pinaural source, or at the time of playback by a speaker / stem of a general audio
source, for example, the sound image in the vicinity of the 1-front is forward when approaching
very close to the sound source or listening in an anechoic chamber An unusual hearing
phenomenon such as rising above the horizontal plane occurs. EndPage: The occurrence of such
a phenomenon is well known in the prior art, but generally an image of a sound such as a
musical tone in stereophonic sound reproduction. Considering that it is natural and desirable to
spread in the horizontal plane in front of the bamboo and the listener, it is a fatal defect such as
the phenomenon 1d described above. The present invention provides the effect of suppressing
the rise of the above-mentioned reproduced sound image by providing a band elimination filter
such as a notch filter having an amplitude characteristic under the condition of Q =-,-in the threedimensional sound pickup-reproduction system path The dummy head microphone sound pickup
reproduction can be mentioned as a means to realize the original sound field reproduction
relatively easily based on the drawings. In fact, even with a dummy head microphone, it is
possible to obtain a winning presence by playing back and listening to the recording source with
henotofon, but in such a reproduction method, a peculiar phenomenon that the sound image
rises above the front horizontal surface generally occurs . Such anomalous phenomena occur
remarkably in particular in the front, and such anomalous phenomena are often seen in synthetic
sound images in stereophonic reproduction such as 2-channel and 4-channel, etc. The reason is
that the sound supplied to the listener's ears via the three-dimensional sound collectionreproduction system and the sound provided at the time of actual sound field listening are not
exactly one. Therefore, it is conceivable to insert an appropriate equalizer in the abovementioned system so that the transfer characteristic of the three-dimensional sound collectionreproduction system matches the head sound transfer characteristic of the listener. However, it is
technically difficult to manufacture the above-mentioned equalizer in a strict sense because the
head acoustic transfer characteristics are extremely complicated and individual differences can
not be ignored.
However, if the sole purpose is to improve the drawback that the sound image rises above the
horizontal plane, it can be made possible in a relatively simple way by utilizing the aural
attributes. The main point is to remove the physical factor that makes the sound image feel
upwards The main physical factor of the sense of front and back and up and down in the
perception of the direction of the 6 sounds in 1 direction, the sound is incident on the head and
reaches the tympanist It is a spectral change that occurs in the process, and there is a close
relationship between the frequency component of sound and the sense of localization. For
example, when listening to various 1⁄3 octave hand noises using a speaker / stem or
hesothophon or the like without any interaural difference, the following facts have been clarified
by sensory experiments: Sound image direction (front, back, elevation) (di, depends only on the
center frequency f / i 7 of the noise, 8 kt (only upwards in the case of z, all before or after for
other frequencies 3, ('1st (Refer to [A) and [13)] (When white noise through a 2-band elimination
filter is listened to by a speaker / stem or hesotophon placed on overhead, the center frequency
of that filter is 7 to 9 kHz. The sound image is the lowest, and the elevation of the sound image
tends to gradually increase as the frequency rises. (Refer to FIG. 2.) From the above-mentioned σ
and σ, the factor that makes the sound image feel upward is the frequency component near 8
kHz, and the elevation angle θ of the sound image is determined by the ratio of that component
and other frequency components. Can be thought of as It is valid that such an idea is appropriate
(the ear shell as an acoustic filter having different characteristics depending on the d incident
direction has a strong characteristic as a band elimination filter near 8kl-1z at 1 when the
incident elevation angle of sound is small This is also supported by the fact that the band
becomes softer with the increase of the incident elevation angle. (See FIG. 3) Therefore, it can be
understood that it is better to remove only the frequency component near 8 kHz among the
frequency components included in the signal source so as not to make the sound image as shown
in FIG. FIG. 5 shows the amplitude characteristics of the band elimination notch filter for
specifically realizing the sound image position elevation suppressor according to the present
invention, and each variable defining the shape of the notch, ie, the center frequency J. 7-9 kl-12,
bandwidth Δf: 0.3 to 15 octaves, depth lL1;] sound image position EndPage: 2 ascend
suppression function is effectively performed by selecting a value of O dB or more, I − If the
bandwidth of the notch is narrow, the test band removal non-notch filter can not obtain a good
effect, but on the contrary, if the bandwidth of the notch can not be broadened too much, the
sound quality may be deteriorated.
Therefore, it is desirable that the bandwidth of the band elimination notch filter be variably
adjusted arbitrarily at the stage of actual use, and that the bandwidth can be set to the maximum
bandwidth within the range that does not impair the sound quality. FIGS. 6, 7 and 8 are block
diagrams and a circuit diagram showing an embodiment of the band elimination filter having the
notch characteristic as described above (1) FIG. 6 is the case where the delay element Δt is used
Since Sumo is shown, the characteristics when the attenuator 9 = I is shown in FIG. This band
elimination filter has a delay element Δ! The center frequency can be set within 7 to 9 kHz by
selecting the tile time 56 to 71 (.mu.5 ec) K, and a notch characteristic having a bandwidth of 15
octaves and a depth of 0 O (dB) can be obtained. (11) FIG. 7 shows the case where an RC parallel
T-type filter is used. Arbitrary notch characteristics can be obtained by appropriately selecting
each constant of the resistor R1 capacitor C. (Iiii 'Figure 8 shows the case where CR and Brino /
are used, the center frequency is changed by changing the time constant of the CR bridge, and
the level and the bandwidth are selected by combining the gains of the attenuators g6 and g2.
Can be varied. For example, assuming that the time constant is 17.7 to 22.7 (μsec), and the two
attenuators y and g2 can be gl-09 and g2-05, the center frequency is approximately 15 in a
bandwidth range of 7 to QkIiz. Octave, depth] 6cl13 notch characteristics can be obtained. FIG.
10 shows a dummy head microphone sound collecting and reproducing system, in which a
pseudo-cephalitis acoustically equivalent to an actual human head is arranged in the sound field
1, and a microphone λ3 built in at both bins is provided. The sound is picked up, and the output
thereof is reproduced by the headphone 6 through the recording / reproducing device 4, the
amplifier 5 and the like to be listened to. The present invention inserts a band elimination filter
having a notch characteristic as described in (1) to (fiii) in (2), (1), (2) or (3) of such a dummy
head microphone sound collecting and reproducing system. Thus, it is possible to suppress the -L
rise of the reproduced sound image. FIG. 11 shows a stereophonic sound pickup reproduction
system, in which a microphone group 71 (a sound is picked up with fi and its output is output
through a mixer 8 etc.) arranged in a music hall or one other sound field 1 It is comprised so that
it may reproduce | regenerate by 7 stem 9 and listen. When the device of the present invention
having the notch characteristic as described above in (1) to (iii) is inserted into such a sound
collecting and reproducing system, it is arranged at the center of the output system of the
microphone group 7 The speaker / stem 9 can suppress the rise of the reproduced sound image
by inserting it at the position of Φ in the output system path of the microphone group.
The same effect can be obtained by inserting it at the position of the regeneration system.
Therefore, in the present invention, at the time of three-dimensional sound reproduction, a band
elimination filter having an amplitude characteristic with a center frequency of 7 to 9 k), a
bandwidth of O3 to 15 octaves and a depth of 10 dB or more is provided in the reproduction
system. It is possible to suppress rising of the reproduced sound image from the horizontal plane
at the time of three-dimensional sound reproduction, spread uniformly in the horizontal plane to
obtain a natural sound field feeling, and improve the clarity of the sound image to facilitate
listening? ),
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 [A] is a perspective view showing the spill force
arrangement of the front and back upper determination experiment, FIG. 1 (B) Itd, a
characteristic view showing the relationship between front and back determination and
frequency, FIG. Is a characteristic diagram showing the relationship between the sound image
elevation angle and the band removal frequency, FIG. 3 is a characteristic diagram showing the
measurement result of head transfer function (cut value) in the central area, and FIG. 4 is the
incident elevation angle of sound. The explanatory diagram shown in FIG. 5 is a characteristic
diagram of the band elimination filter used in the present invention, and FIGS. 6, 7 and 8 are
block diagrams and circuit diagrams of the band elimination filter used in the present invention.
Fig. 9 is a dip filter using a delay circuit and its amplitude characteristic diagram, Fig. 10 is a
configuration diagram showing a dummy head microphone sound collecting and reproducing
system, and Fig. 11 is Sdereo Foniso EndPage: 33OMK'R (kHz) Fig. Fig. 7 Fig. 8 Attenuator
EndPage: 4
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