JP2007081775A - Stereo reproducing method and stereo reproducing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To give a stable and clear position fixing property, irrespective of the listening position with a stereo reproduction system, while maintaining a small scale subject and under the assumption of application to two-way calls. <P>SOLUTION: A center speaker 15, having high directional characteristics with the sound pressure high in the front direction and low at both its sides, outputs a sum signal resulting from the addition of a right and left channel input stereo signals, while two side speakers 18a, 18b disposed on both sides of the center speaker 15 output the right and left channel signals delayed to the extent that preceding sound effects are generated in the sum signal. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a stereo reproduction method and a stereo reproduction device for reproducing a stereo signal, and more particularly to a stereo reproduction method and a stereo reproduction device that realize a good sense of localization with respect to a wide listening position.

  In general, in a two-channel audio signal reproduced using a stereo speaker, the listener's position is the apex of an isosceles triangle with the two speakers at the bottom, that is, the distance of the speakers as viewed from the listener is equal. The sound image is perceived at the correct position. On the other hand, when listening at a position away from the top of the isosceles triangle, the sound of the speaker closer to the listener reaches the listener earlier than the sound from the other speaker, or the sound from the near speaker. Due to the reason that the pressure level is greater than that from the other speaker, all sound images are perceived as being biased closer to the position of the speaker. Thus, when the sound is reproduced in stereo, the listening position for correctly perceiving the position of the sound image is limited. On the other hand, considering that a voice conference using communication is performed using stereo loudspeakers, the conference participants are not necessarily located at an equal distance from both speakers, and the benefits of stereophonic audio The number of people who can suffer is limited.

FIG. 6 is a conceptual diagram for explaining hearing during conventional stereo reproduction. FIG. 6 shows an example in which the listener listens to the sound output from the left and right speakers 101, 102 at the listening positions 21, 22, 23. Reference numerals 31, 32, and 33 denote positions of sound images to be reproduced. In the following, the sound during conventional stereo playback will be described with reference to FIG.
When the listener is at the center position, that is, the listening position 21, the distances from the left and right speakers 101, 102 to the listening position are equal. Therefore, the position of the sound image is correctly perceived without being different. On the other hand, at a position biased toward either the left or right speaker, for example, the listening position 22, the sound image position on the speaker 101 side (in this example, the sound image position 32) is perceived by being localized at an appropriate position. However, when the sound image is in the center, that is, at the sound image position 31, physically, the sound of the same sound pressure level is simultaneously emitted from the left and right speakers 101 and 102. Therefore, at the listening position 22, the sound output from the near speaker 101 arrives earlier than the sound output from the far speaker 102 and is observed at a high sound level. Therefore, the sound image is perceived as a different position at the listening position 22, that is, the sound image position 32. In addition, the sound image at the reverse speaker position (in this example, the sound image position 33) is perceived as a substantially correct position, but the sound image tends to be ambiguous, and any position between the sound image positions 31 to 33. Will be perceived.

In order to deal with this problem, for example, using three speakers for one channel and appropriately setting each delay, phase, or amplification amount, a method for properly locating the listener image over a wide range (patented) Document 1) and a method of expanding the listening position by operating the directivity of the left and right speakers so that the sound pressure levels from the left and right speakers are equal even in places that are not equidistant from both speakers (non-patent document) Document 1) has been proposed. Further, a loudspeaker having a sharp directivity is realized by using a speaker array, and a method of expanding a range in which a sound image can be heard at an appropriate position by using a multi-beam formed thereby (Non-Patent Document 2). Has also been proposed. In addition, as a means for perceiving a sound image at an appropriate position regardless of the listening position, a method of collecting sound with N (N> 2) channels and expanding the number of speakers according to the number of sound collecting channels can be considered. . In this case, the collected sound is transmitted on the N channel.
Japanese Patent Publication No. 6-32560 JA Rodenas et al. "Derivation of an optimal directivity pattern for sweet spot widening in stereo sound reproduction," J. Acoust. Soc. Am., Vol. 113 (1), pp.267-278, 2003 Fujino, Nishikawa, “Stereo reproduction of wide listening area sound localization using multi-beam directional array speakers,” IEICE Transactions Vol. J87-A No.4, pp. 439-447. April 2004

  However, as described above, when normal stereo reproduction is performed, the position of the sound image is perceived differently depending on the listening position. Furthermore, in this case, when listening at the center of the left and right speakers, the voices of multiple speakers perceived as being spatially separated may be heard as the same position depending on the listening position. May also have a negative impact. On the other hand, in the method using three speakers on one side, it is necessary to operate a delay of several ms in accordance with the difference in distance from the left and right speakers to the listening position. It will greatly affect On the other hand, the method of making the sound pressure level from the left and right speakers constant by controlling the directivity of the speakers does not compensate for the difference in arrival time due to the difference in listening position, so it is the main clue for sound image localization. The contradiction occurs between the information on the intensity difference between both ears and the information on the time difference between both ears, and as a result, the sound image is blurred. Furthermore, in the method using the narrow directivity speaker array, a system for obtaining good localization characteristics becomes large-scale, and inconvenience occurs when considering application to an audio conference apparatus. Furthermore, in the method of collecting sound with the N (N> 2) channel and expanding the sound with the number of speakers corresponding to the number of sound collecting channels, due to the operating conditions of the echo canceller, which is essential for two-way calls such as communication conferences, etc. There is a problem that it is impossible at present to make N larger than 2.

  The present invention has been made in view of the above points, and on the premise of application to a two-way call, a technique for providing a stable and clear localization characteristic regardless of the listening position while keeping the reproduction system small. The purpose is to provide.

  In the present invention, in order to solve the above problems, a sum signal obtained by adding the left and right channel signals of the stereo input signal is output from a center speaker having a directivity characteristic with low sound pressure in the front direction and high sound pressure on both sides. The left and right channel signals are delayed to such an extent that a preceding sound effect is generated in the sum signal, and output from two side speakers arranged on both sides of the center speaker.

  Here, a stable and clear localization characteristic can be obtained regardless of the listening position by the arrangement of the center speaker having the directional characteristics as described above and the preceding sound effect of the sum signal by delaying the left and right channel signals. (Details will be described later). In addition, since the delay amount of the left and right channel signals only needs to be within a range that causes the preceding sound effect in the sum signal, a slight deviation of the listening position of the listener may greatly affect the localization accuracy. Absent. In addition, since this configuration can be configured by adding a center speaker or the like to the configuration of a normal stereo playback device, the system can be small. Further, since this configuration uses a two-channel signal, the echo canceller can be operated and can be applied to a two-way call.

In the present invention, preferably, the sum signal output from the center speaker is a signal limited to a frequency band in which a preceding sound effect can occur. Thereby, the preceding sound effect can be obtained more remarkably, and the object of the present invention can be realized more effectively.
Preferably, in the present invention, the adder generates and outputs a sum signal by adding the left and right channel signals, and the low-pass filter outputs the high-frequency component of the sum signal output from the adder. By blocking, the sum signal is limited to the frequency band where the preceding sound effect can occur, and the center speaker outputs the sum signal output from the low-pass filter, and the delay unit outputs the left and right channel signals. Are delayed so as to cause a preceding sound effect to the sum signal, and the two side speakers respectively output the left and right channel signals output from the delay unit.

In the present invention, it is preferable that the center speaker includes a first speaker and a second speaker arranged at a distance satisfying a spatial sampling theorem corresponding to the frequency band of the sum signal, and the sum signal is transmitted to the first speaker. Is input, and the polarity inversion signal of the sum signal is input to the second speaker, so that the directional characteristic of the center speaker is set to be bi-directional. Preferably, the first speaker and the second speaker are respectively input with a sum signal and a polarity inversion signal limited to a frequency band in which the bidirectional characteristics can be realized.
This makes it possible to easily obtain the directivity characteristics of the center speaker necessary for the configuration of the present invention.

  As described above, in the present invention, it is possible to obtain a stable localization characteristic regardless of the listening position while keeping the reproduction system small on the premise of application to a two-way call.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[Configuration / Operation]
FIG. 1A is a block diagram illustrating the configuration of the stereo playback device 10 of the present embodiment.
As illustrated in FIG. 1A, the stereo reproduction device 10 of the present embodiment adds the left and right channel signals to the input terminals 11a and 11b to which the left and right channel signals of the stereo input signal are input, respectively. An adder 12 that generates a sum signal, and a low-pass filter 13 that blocks the high-frequency component of the sum signal output from the adder 12 to limit the sum signal to a frequency band in which a preceding sound effect can occur. Delayers 16a and 16b, three amplifiers 14, 17a and 17b, two side speakers 18a and 18b, and one center speaker for delaying the left and right channel signals to the extent that a leading sound effect is generated in the sum signal. 15. The center speaker 15 is disposed between the two side speakers 18a and 18b (in this example, the center).

The left and right channel signals of the stereo input signal are input from the input terminals 11 a and 11 b, respectively, and part of them are input to the adder 12. The adder 12 generates a sum signal of the input left and right channel signals and outputs it.
On the other hand, the left and right channel signals input from the input terminals 11a and 11b are also input to the delay units 16a and 16b, respectively, and the delay units 16a and 16b output these delay signals. The output delay signals are input to the amplifiers 17a and 17b, respectively, and the amplifiers 17a and 17b amplify them. The amplified signals are input to and output from the left and right side speakers 18a and 18b, respectively.

The sum signal of the left and right channels output from the adder 12 is input to the low-pass filter 13, and the low-pass filter 13 blocks the Takagi component of the sum signal. The reason for blocking the Takashiro component will be described later. The sum signal whose frequency component is limited is input to the amplifier 14, and the amplifier 14 amplifies and outputs the sum signal. The sum signal output from the amplifier 14 is input to the center speaker 15, and the center speaker 15 outputs this.
Here, the output characteristics of the center speaker 15 of this embodiment have nulls in the front direction A as illustrated in C1 and C2 in FIG. 1A, and the front positions B1 and B2 of the left and right side speakers 18a and 18b. It has a directional characteristic showing a high sound pressure distribution. Although it is difficult to realize this characteristic with a single speaker, a similar directional characteristic can be obtained by the method described below. FIG. 1B is a diagram illustrating a method for obtaining this directivity characteristic.

  In the example of FIG. 1B, the center speaker 15 is constituted by a polarity inverter 15a and two speakers 15b and 15c installed adjacent to each other. Part of the sum signal output from the amplifier 14 is directly input to and output from the speaker 15c (corresponding to “first speaker”). At the same time, a part of the sum signal output from the amplifier 14 is input to the polarity inverter 15a. The polarity inverter 15a inverts the polarity of the input sum signal, outputs this polarity inversion signal, and reverses the polarity. The polarity inversion signal output from the device 15a is input to and output from the speaker 15b (corresponding to “second speaker”). As a result, the sum signal and the polarity inversion signal interfere with each other between the speaker 15b and the speaker 15c, and a bidirectional characteristic as illustrated in FIG. 1B is obtained. The distance D between the speakers 15b and 15c is a distance that satisfies the spatial sampling theorem corresponding to a desired frequency band to be reproduced (frequency band of the sum signal). The spatial sampling theorem is a theorem that indicates that the distance between speakers must be at least twice the wavelength of the highest frequency to be controlled. In this embodiment, the distance D is set to 12 cm. In FIG. 1B, a pair of speakers 15b and 15c is used, but the center speaker 15 may be constituted by a plurality of sets of speakers (first speaker and second speaker). In this case, the directivity characteristics of the center speaker 15 can be set relatively freely depending on the combination of the position and orientation of the speaker, the output power, and the like. As a result, as shown in FIG. 1 (a), a configuration is possible in which the null range in the front direction A of the center speaker 15 is wide and the sound pressure suddenly increases at the front positions B1 and B2 of the side speakers 18a and 18b. . Such directivity is ideal in the configuration of the present invention. This is because the effects of the present invention described below appear remarkably. In this case, the number of speakers that output the polarity inversion signal and the number of speakers that output the sum signal may be the same or different.

[Hearing when stereo sound is played]
Next, hearing when stereo sound is reproduced by the above-described stereo reproduction device 10 will be described.
FIG. 2 is a conceptual diagram for explaining hearing when stereo sound is reproduced by the stereo reproduction device 10. This figure shows an example in which the listener listens to the sound output from the left and right side speakers 18a and 18b and the center speaker 15 at the listening positions 21, 22, and 23. Reference numerals 31, 32, and 33 denote positions of sound images to be reproduced. Further, it is assumed that the center speaker 15 of this example is configured as shown in FIG.

  First, a case where the listener listens to the sound at the listening position 21 located at the center will be described. The listener at the listening position 21 listens to the sound emitted from the center speaker 15 prior to the sounds of the left and right side speakers 18a and 18b. Here, the center speaker 15 of this example is configured by adjoining two speakers 15b and 15c as described with reference to FIG. 1B, and the polarity of the speaker 15b on one side is reversed. Therefore, the sound radiated from the center speaker 15 has an 8-shaped bi-directionality with a null facing the front direction of the center speaker 15 and is small in the listening position 21 direction which is the front direction viewed from the center speaker 15. Pressure level. Therefore, the sound radiated from the center speaker 15 is shielded (masked) by the sounds from the left and right side speakers 18a and 18b that are subsequently heard. As a result, the listener perceives only the sound from the left and right side speakers 18a, 18b, which is the same state as normal stereo reproduction. Since the listening position 21 is a place where the distances from the left and right side speakers 18a and 18b are substantially equal, the listener at the listening position 21 can perceive a sound image with good localization characteristics.

  Next, a case where the listener listens at the listening position 22 which is substantially the front position of the side speaker 18a will be described. First, when the virtual sound image is in the center, that is, at the sound image position 31, the listener at the listening position 22 listens to the sound of the center speaker 15 at a sound pressure level larger than that at the listening position 21 for the following three reasons. Will do. First, the input signal to the center speaker 15 is based on the output of the adder 12 in FIG. At this time, in the signal corresponding to the sound image position 31, the signals of the left and right channels are substantially the same level and have high correlation. Therefore, the output of the adder 12 is larger than that input to the left and right speakers. In addition, since the sound radiated from the center speaker 15 is bi-directional as described above, the sound pressure level at the listening position 22 is higher than that at the listening position 21. Further, the left and right channel signals output from the side speakers 18 a and 18 b are delayed from the sum signal output from the center speaker 15 by the action of the delay units 16 a and 16 b. That is, the sound from the center speaker 15 reaches the ears of the listener ahead of the sound radiated from the left and right side speakers 18a and 18b. In this case, a preceding sound effect known as human auditory characteristics is produced. Here, the preceding sound effect refers to a phenomenon in which when two highly correlated sounds reach the ear with a time difference, the direction of the sound that has reached first is perceived as the position of the sound source. By this effect, it is perceived that the sound image is at the position of the sound image position 31. On the other hand, when the sound image position is in the front direction of the listening position 22, that is, in the sound image position 32, the sound pressure level output from the side speaker 18 a and heard at the listening position 22 is output from the center speaker 15. The sound pressure level that is heard at the listening position 22 is exceeded. That is, the stereo signal at the sound image position 32 has a large left channel signal and a small right channel signal. Therefore, the input signal to the center speaker 15 based on the output of the adder 12 in FIG. 1 (a) is substantially equivalent to the signal to the side speaker 18a. Then, because of the difference between the distance from the side speaker 18a to the listening position 22 and the distance from the center speaker 15 to the listening position 22, the sound output from the center speaker 15 is blocked by the sound output from the side speaker 18a. Is done. As a result, the sound image is correctly localized in front of the listening position 22, that is, the sound image position 32. Further, when the sound image position is at a position opposite to the listening position 22, that is, the sound image position 33, the sound output from the center speaker 15 precedes the sound output from the side speaker 18b, and the side speaker 18b. The listening position 22 is reached at a sound pressure level greater than the sound output from. For this reason, it is perceived by being localized near the sound image position 31, but even if the conventional stereo reproduction system is used, the position of the sound image on the opposite side is ambiguous, so this is not a problem in practice. .

[Specific example of configuration]
<Low-pass filter 13>
FIG. 3 is an example of frequency characteristics of the low-pass filter 13 of FIG. In this example, the cutoff frequency is set to 600 Hz. It is known that the preceding sound effect described above can be confirmed more significantly in a frequency band of approximately 1 kHz or less. In addition, the center speaker 15 in FIG. 1B has a bi-directional characteristic having an 8-shaped characteristic by installing speakers 15b and 15c having opposite phase relations adjacent to each other, and the speaker 15b. , 15c, but it is difficult to form effective bidirectionality at 1 kHz or higher. Eventually, the cut-off frequency of the low-pass filter 13 may be any band that can produce a preceding sound effect and can realize an 8-shaped bi-directional characteristic. That is, the low-pass filter 13 is preferably a filter that cuts off a frequency band of about 1 kHz or more, and more preferably a filter that cuts off a frequency band of about 800 Hz or more. In addition, a sound having only a low frequency band of about 100 Hz to 200 Hz does not cause a sense of direction. Therefore, instead of the low-pass filter 13, a band-pass filter may be installed to cut off not only the high-frequency but also the low-frequency. As this band pass filter, it is desirable to pass only signals in the frequency band of about 200 Hz to 1000 Hz, and it is more desirable to pass only signals in the frequency band of about 300 Hz to 800 Hz. Further, the low-pass filter 13 and the band-pass filter may not be provided, and the sum signal output from the adder 12 may be amplified as it is and output from the center speaker 15. Even in this case, if there are originally few signal components of 1 kHz or more, a leading sound effect can be produced and an 8-shaped bi-directional characteristic can be realized.

<Amplifier 14>
The setting of the amplifier 14 connected to the center speaker 15 is such that the sound output from the center speaker 15 at the listening position 21 is smaller than the sound from the left and right side speakers 18a and 18b with respect to the sound at the sound image position 31 in FIG. At the same time, the sound output from the center speaker 15 must be observed larger than the sounds from the left and right side speakers 18a and 18b at the listening position 22 or 23.

<Delayers 16a and 16b>
Setting of the delay amounts of the delay units 16a and 16b in FIG. 1A allows the signal output from the center speaker 15 to produce a preceding sound effect on the signals output from the side speakers 18a and 18b. You should just make it. Specifically, the delay amount of the delay units 16a and 16b is optimally about 10 to 20 ms, for example. If there is a delay of 20 ms or more, this is not a sound emitted from one sound source but a perception that there are two sound sources, which causes a problem. On the other hand, since the influence of the preceding sound effect is generally reduced as the delay amount is reduced, the effect of the present invention using the preceding sound effect cannot be exhibited with a delay of about 10 ms or less.

〔Experimental result〕
4 and 5 are diagrams showing examples of the subjective evaluation experiment results when the conventional method is used (FIG. 4) and when the method of the present embodiment is used (FIG. 5). Here, (a) in each figure shows the evaluation experiment results when the listener observes at the center position, that is, the place corresponding to the listening position 21 in FIG. 2, and-(b) shows the lateral position, that is, FIG. The evaluation experiment results when the listener observes at the location corresponding to the listening position 22 in FIG. In each figure, the horizontal axis and the vertical axis indicate the place where the sound image is presented and the place where it is perceived (answered), respectively. In both the horizontal and vertical axes, the direction of the listening position 23 in FIG. 2 is positive, and the direction of the listening position 22 is negative. The size of the circle represents the frequency.

4 (a) and 5 (a), in either method, a good sound image localization is achieved when the listener is at the center position of the left and right side speakers.
On the other hand, as clearly shown in FIG. 4B, good sound image localization is not achieved at the listening position in the lateral direction, and the sound image is perceived almost biased to the speaker in front of the listener. . On the other hand, as shown in FIG. 4A, when the method of the present embodiment is used, a good sound image localization is achieved regardless of the listening position.

[Features of this embodiment]
As described above, according to this embodiment, it is possible to perceive a stereo sound signal transmitted through two channels with a good localization at a wide listening position. At this time, since the fine operation of the ms order is not performed as the delay amount of the left and right speakers, the influence on the localization characteristic due to the difference in the position of the listener is reduced. Therefore, it is possible to present sound with a high sense of presence to a large number of participants in the communication conference. In addition, the sound image position can be perceived as being appropriately spread in the space, thereby improving the clarity of the sound. Further, the time difference and intensity difference between both ears related to the perceived sound image are not contradictory and the sound image is not blurred. Furthermore, since this embodiment is basically realized by installing three speakers, the system configuration is much smaller than that using a speaker array, and is suitable for application to a teleconferencing device. is there.

Needless to say, the present invention is not limited to the above-described embodiment, and can be appropriately changed without departing from the spirit of the present invention. For example, in this embodiment, the center speaker 15 has a null in the front direction, and has a directivity characteristic showing a high sound pressure distribution at the front position of the left and right side speakers 18a and 18b. However, if the sound pressure in the front direction is low and the sound pressures on both sides thereof have high directivity characteristics, the sound pressure in the front direction of the center speaker 15 does not necessarily have to be null.
The configuration other than the side speakers 17a and 17b and the center speaker 15 described above can be executed by a computer. In this case, the processing contents of the functions that each device should have are described by a program. The processing functions are realized on the computer by executing the program on the computer.

  The program describing the processing contents can be recorded on a computer-readable recording medium. The computer-readable recording medium may be any medium such as a magnetic recording device, an optical disk, a magneto-optical recording medium, or a semiconductor memory. Specifically, for example, the magnetic recording device may be a hard disk device or a flexible Discs, magnetic tapes, etc. as optical discs, DVD (Digital Versatile Disc), DVD-RAM (Random Access Memory), CD-ROM (Compact Disc Read Only Memory), CD-R (Recordable) / RW (ReWritable), etc. As the magneto-optical recording medium, MO (Magneto-Optical disc) or the like can be used, and as the semiconductor memory, EEP-ROM (Electronically Erasable and Programmable-Read Only Memory) or the like can be used.

The program is distributed by selling, transferring, or lending a portable recording medium such as a DVD or CD-ROM in which the program is recorded. Furthermore, the program may be distributed by storing the program in a storage device of the server computer and transferring the program from the server computer to another computer via a network.
A computer that executes such a program first stores, for example, a program recorded on a portable recording medium or a program transferred from a server computer in its storage device. When executing the process, the computer reads the program stored in its own recording medium and executes the process according to the read program. As another execution form of the program, the computer may directly read the program from a portable recording medium and execute processing according to the program, and the program is transferred from the server computer to the computer. Each time, the processing according to the received program may be executed sequentially.

  Further, at least a part of the processing content may be realized by hardware.

  As an industrial application field of the present invention, a communication conference system, an audio reproduction system, and the like can be exemplified.

FIG. 1A is a block diagram illustrating the configuration of the stereo playback apparatus of this embodiment. FIG. 1B is a diagram illustrating a method for obtaining directivity characteristics of the center speaker of the present embodiment. It is a conceptual diagram for demonstrating the hearing at the time of reproducing | regenerating stereo sound with a stereo reproduction | regeneration apparatus. FIG. 3 is an example of frequency characteristics of the low-pass filter of FIG. FIG. 4 is a diagram showing an example of a subjective evaluation experiment result when a conventional method is used. FIG. 5 is a diagram showing an example of a subjective evaluation experiment result when the method of the present embodiment is used. FIG. 6 is a conceptual diagram for explaining hearing during conventional stereo reproduction.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Stereo reproduction apparatus 12 Adder 13 Low-pass filter 15 Center speaker 15b, 15c Speaker 16a, 16b Delay device 18a, 18b Side speaker

Claims (10)

From the center speaker with low directivity and high directivity of sound pressure on both sides, output a sum signal that adds the left and right channel signals of the stereo input signal,
The left and right channel signals are delayed to such an extent that a preceding sound effect is generated in the sum signal, and output from two side speakers arranged on both sides of the center speaker, respectively.
Stereo reproduction method characterized by the above. The stereo reproduction method according to claim 1,
The sum signal output from the center speaker is
It is a signal limited to a frequency band where the precedence effect can occur.
Stereo reproduction method characterized by the above. The stereo reproduction method according to claim 2,
An adder adds the left and right channel signals to generate and output the sum signal,
The low-pass filter blocks the high-frequency component of the sum signal output from the adder, thereby limiting the sum signal to a frequency band where the preceding sound effect can occur, and outputting the sum signal.
The center speaker outputs the sum signal output from the low-pass filter,
A delay device delays and outputs the left and right channel signals to the extent that a leading sound effect is generated in the sum signal,
The two side speakers output the left and right channel signals output from the delay unit, respectively.
Stereo reproduction method characterized by the above. The stereo reproduction method according to claim 1,
The center speaker is constituted by a first speaker and a second speaker arranged at a distance satisfying a spatial sampling theorem corresponding to the frequency band of the sum signal,
When the sum signal is input to the first speaker and the polarity inversion signal of the sum signal is input to the second speaker, the directional characteristic of the center speaker is set to be bi-directional.
Stereo reproduction method characterized by the above. The stereo reproduction method according to claim 4,
The sum signal and the polarity inversion signal, which are limited to a frequency band that can realize the bi-directional characteristics, are input to the first speaker and the second speaker, respectively.
Stereo reproduction method characterized by the above. Two side speakers that output the left and right channel signals of the stereo input signal,
It is placed between the two side speakers, has a directivity characteristic that the sound pressure in its front direction is low, the sound pressure in the front part of the two side speakers is high, and outputs the sum signal of the left and right channel signals A center speaker,
Comprising
By delaying the left and right channel signals output from the two side speakers from the sum signal output from the center speaker, the two side speakers are added to the sum signal output from the center speaker. To produce a preceding sound effect on the left and right channel signals respectively output from
A stereo reproduction apparatus characterized by the above. The stereo playback device according to claim 6,
The sum signal output from the center speaker is
It is a signal limited to a frequency band where the precedence effect can occur.
A stereo reproduction apparatus characterized by the above. The stereo playback device according to claim 7,
An adder that generates the sum signal by adding the left and right channel signals;
A low-pass filter that limits the high-frequency component of the sum signal output from the adder to limit the sum signal to a frequency band in which a preceding sound effect can occur;
A delay device that delays the left and right channel signals to an extent that causes a preceding sound effect in the sum signal;
Comprising
The center speaker is
Output the sum signal output from the low-pass filter,
The two side speakers are
Output the left and right channel signals output from the delay unit,
A stereo reproduction apparatus characterized by the above. The stereo playback device according to claim 6,
The center speaker is constituted by a first speaker and a second speaker arranged at a distance satisfying a spatial sampling theorem corresponding to the frequency band of the sum signal,
When the sum signal is input to the first speaker and the polarity inversion signal of the sum signal is input to the second speaker, the directional characteristic of the center speaker is set to a bi-directional characteristic.
A stereo reproduction apparatus characterized by the above. The stereo playback device according to claim 9,
The sum signal and the polarity inversion signal, which are limited to a frequency band that can realize the bi-directional characteristics, are input to the first speaker and the second speaker, respectively.
A stereo reproduction apparatus characterized by the above.

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