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■ Multi-channel stereo reproduction system App. No. 50-1877 ■ Japanese Patent Application
No. 45-114478 [Phase] Application No. 45 (1970 ') Dec. 18 @ For Kamifukushi Hamamatsu City
Nakazawa-cho 7-5 No. 0 Applicant Japan No. 10 No. 1 Nakazawacho, Hamamatsu Co., Ltd.
Attorney Attorney Attorney Attorney Fudan Robe Part 1 [Phase] Cited Reference Journal 3921645 (JP, Yl)
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of a
multi-channel stereo reproduction system according to the present invention, and FIGS. 2 and 3
are diagrams showing a concrete example of the phase conversion device of FIG.
DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a multi-channel
stereo reproduction system in which natural presence is obtained by reproducing an indirect
sound component also from the front when reproducing a stereo-recorded program source. .
There are two ways to create sound behavior in a room: one based on wave acoustics and the
other based on geometric acoustics. There are many difficult factors in setting boundary
conditions etc. based on wave acoustics, so the analysis of the sound in the room currently relies
mainly on the geometric acoustic theory that sees the sound as a mass of energy. According to it,
the sound pressure level SPL of the point which is rCm'l away from the sound source of the
sound source output PWLC dB) and the directivity factor Q in the room] dB is [111111]. (R is
called a room constant, and is a parameter determined from the average sound absorption in the
room, and the larger the room, the larger the total sound absorption in the room. In short, the
first term in parentheses in the equation (1) represents a direct sound component in the room,
and the second term is a sound other than the direct sound, that is, an indirect sound (reflected
sound, diffuse sound, scattered sound, dispersed sound, reverberation sound Represents an
ingredient). Here, a point at which the energy of the direct sound and the indirect sound is equal
is called the critical distance re, and rc is obtained. From equation (1), the critical distance re is
the front seat of the audience in the case of a regular performance venue. That is, the indirect
sound contributes more than the direct sound in most of the seats. Therefore, in multi-channel
stereo, it is more reasonable to think of indirect sound = main, direct sound = follow, rather than
the idea of direct sound = main, indirect sound = follow, including recording and reproduction. In
addition, it is necessary for the establishment of the above equation (1) that once the direct
sound is reflected on the wall once, it becomes diffuse sound without phase correlation with each
other and uniformly distributed in the room. There is, however, this assumption is not
inconvenient as it holds in any room, in view of the fact that the sound pressure distribution in a
normal hall or sunning room follows most of the equation (1). Therefore, conversely, it can be
said that diffuse sound in a room has no topological correlation with each other. Even when the
diffuse sound component is actually analyzed in the hole, the result is that the diffuse sound, that
is, the indirect sound has almost no topological correlation. That is, these sounds are phaserandomly random, and sound image localization does not occur. However, with regard to
conventional multi-channel stereo recording and reproduction, the relationship as described
above has been clarified [111111] EndPage: 1 without relying on experience and trial and error.
Therefore, for example, when recording the forward signal, a microphone with high directivity is
placed in the vicinity of the sound source on the stage to record only direct sound, or the
recording of the backward signal aims for a space-friendly effect. The arrangement of
microphones during recording is also the recording sense of the mixer, as recorded at a position
extremely distant from the stage, etc. In terms of sound field reproduction, recording and
reproduction faithful to the original sound field are made It has not reached The present
invention was made in view of the above-mentioned point, and aims to provide a multi-channel
stereo reproduction system rich in natural presence, and capable of obtaining a Hall effect close
to the original sound field, Is electrically or acoustically subjected to phase modulation or other
phase conversion treatment, converted to a signal having no topological correlation so as not to
cause sound image localization during reproduction, and is also reproduced from the front.
Hereinafter, the present invention will be described in detail with reference to illustrated
embodiments. FIG. 1 shows an embodiment of the multi-channel stereo reproduction system
according to the present invention, in which 1 and 2 indicate front left and right signal input
terminals, 3 and 4 indicate rear left and right signal input terminals, and 5.6 indicate respective
ones. A phase conversion device including a phase modulation circuit or the like for phaseconverting each input signal to eliminate phase correlation between each input signal and output
signal and preventing sound localization due to these sounds during reproduction. 7, 8 are
mixing circuits for mixing the front signal and the converted rear signal, 10 is a listening room,
and 11 12, 14 are speakers. The front left and right signals F, L, F and R introduced to the front
left and right signal input terminals 1 and 2 are the front left of the listening room 10 through
the mixing circuits (amplifier circuits) 7 and 8 respectively. , Supply to the speaker lL12 arranged
on the right and reproduce. On the other hand, the rear left and right signals R, L, R and R
introduced to the rear left and right signal input terminals 3 and 4 are supplied as they are to the
speakers 13 and 14 disposed on the rear left and right of the swing room 10 respectively. Of the
signals R, L ', R, R1' after passing through the phase conversion devices 5, 6, respectively, and the
above-mentioned backward signals R, L, R, R After making sure that there is no regular
relationship, they are supplied to the mixing cycles [111111] path γ and 8, respectively, and the
front left and right signals F. The L, F and R are mixed and reproduced from the front left and
right speakers 11.12. Thus, the front left and right signals F, L, F and R are reproduced from the
front speaker lL12, and the rear left and right signals R, L, R and R are signals R, L, which have
no phase correlation, respectively. After conversion into R, R, R, L 'and R9R, reproduction is
performed from the rear and front speakers 13, 14 11.12.
Therefore, while reproducing from the front the signals for the front (which are usually in the
immediate vicinity of the sound source on the stage and consist only of direct sound components
and hardly contain indirect sound components), they have no topological correlation with each
other The back signal sound (indirect sound) is used for sound image localization because the
back signal (normally recorded at a distance from the stage and mostly composed of indirect
sound components) is also reproduced from the back and the front. It is possible to perform
sound reproduction that can produce a more natural presence that does not occur and that
corresponds to the above-described sound theory. As the phase conversion devices 5 and 6, the
signals R9L ', R, R1 and the backward signals R, L, R, R after passing through this device can be
signals which do not cause sound image localization during reproduction. The phase modulation
circuit does not necessarily have to perform random phase conversion. For example, in the case
where the phases of the two signals are largely shifted, eg, 90 °, these reproduced sounds
hardly localize the sound image and are similar to the case where the phase correlation is
substantially eliminated. You can get the effect. If such a method is used, the configuration can
be simpler and cheaper than using a phase modulation circuit. Examples of these are a phase
shift circuit as illustrated in FIG. 2 and a rear left and right signals are recorded on a two track
magnetic tape 16 by a two channel recording head 15 as illustrated in FIG. There is a method of
performing phase shift by immediately reproducing with the two channel reproduction head 17
of the stagger method, or a method of using coil springs having slightly different characteristics,
with the reverberation time and the delay time being as small as possible. In the above
embodiment, the case of the so-called 2-2 system 4-channel stereo reproduction system has been
described, but the invention is not limited to the 2-2 system and can be applied to all other
systems such as the case of other 3-1 system. . Furthermore, after passing the signal for the rear
to the phase conversion device, do not mix it with the signal for the front by the mixing circuit
[111111] EndPage: 2, and place another speaker on the front piece of the listening room and on
the right , May be reproduced from the speaker. In this case, it is possible to obtain a more
realistic spread effect by the action of space synthesis of the indirect sound component. As
described above, according to the present invention, the direct sound component of the program
source is reproduced from the front and, at the same time, each indirect sound component
without topological correlation is also reproduced from the back and the front. The sound image
localization of the direct sound does not shift from the front side in conjunction with the method
[IJ, and the indirect sound component does not sound image localization, and performs stereo
reproduction richer in natural presence as in the front [111111] be able to.
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