SOUND IMAGE LOCALIZATION DEVICE, SOUND IMAGE LOCALIZATION METHOD, AND PROGRAM

Abstract

Provided is a sound image localizing device, a sound image localizing method, and a program that enable a virtual speaker to reproduce sound in a wide frequency band with high sound quality. A sound image localizing device 10 includes a directivity control filter design unit 11 that computes a directivity control filter from a desired directional characteristic, a filter coefficient correction unit 12 that corrects the directivity control filter computed by the directivity control filter design unit 11, and a convolution operation unit 13 that computes an output acoustic signal by performing convolution of an input acoustic signal and the directivity control filter corrected by the filter coefficient correction unit 12. Filters that respectively correspond to speakers constituting a speaker array are computed by the directivity control filter design unit 11 and the filter coefficient correction unit 12, an acoustic beam is generated using directivity control by the speaker array, and the acoustic beam is caused to be reflected from a wall surface or a ceiling to generate a virtual sound source.

Claims

1. A sound image localizing device comprising: a directivity control filter design unit, including one or more processors, configured to compute a directivity control filter from a desired directional characteristic; a filter coefficient correction unit, including one or more processors, configured to correct the directivity control filter computed by the directivity control filter design unit; and a convolution operation unit, including one or more processors, configured to compute an output acoustic signal by performing convolution of an input acoustic signal and the directivity control filter corrected by the filter coefficient correction unit, wherein filters that respectively correspond to speakers constituting a speaker array are computed by the directivity control filter design unit and the filter coefficient correction unit, an acoustic beam is generated using directivity control by the speaker array, and the acoustic beam is caused to be reflected from a wall surface or a ceiling to generate a virtual sound source.

2. The sound image localizing device according to claim 1, wherein the filter coefficient correction unit is configured to perform computation such that a filter gain becomes constant, the filter gain being an absolute value of a filter coefficient at each frequency.

3. A sound image localizing device comprising: an objective function setting unit, including one or more processors, configured to set an objective function from a desired directional characteristic; a constraint setting unit, including one or more processors, configured to set a linear or non-linear constraint; an optimization unit, including one or more processors, configured to compute an optimum filter coefficient from the objective function set by the objective function setting unit and the constraint set by the constraint setting unit; and a convolution operation unit, including one or more processors, configured to compute an output acoustic signal by performing convolution of an input acoustic signal and a directivity control filter that is computed by the optimization unit, wherein filters that respectively correspond to speakers constituting a speaker array are computed by the objective function setting unit, the constraint setting unit, and the optimization unit, an acoustic beam is generated using directivity control by the speaker array, and the acoustic beam is caused to be reflected from a wall surface or a ceiling to generate a virtual sound source.

4. The sound image localizing device according to claim 3, wherein the constraint setting unit is configured to set at least one of a constraint that makes a value of a filter gain constant at each frequency and a constraint relating to directional characteristics that is based on the desired directional characteristic.

5. A sound image localizing method comprising: a directivity control filter designing step of computing a directivity control filter from a desired directional characteristic; a filter coefficient correction step of correcting the directivity control filter computed in the directivity control filter designing step; and a convolution operation step of computing an output acoustic signal by performing convolution of an input acoustic signal and the directivity control filter corrected in the filter coefficient correction step, wherein filters that respectively correspond to speakers constituting a speaker array are computed in the directivity control filter designing step and the filter coefficient correction step, an acoustic beam is generated using directivity control by the speaker array, and the acoustic beam is caused to be reflected from a wall surface or a ceiling to generate a virtual sound source.

6. A sound image localizing method comprising: an objective function setting step of setting an objective function from a desired directional characteristic; a constraint setting step of setting a linear or non-linear constraint; an optimization step of computing an optimum filter coefficient from the objective function set in the objective function setting step and the constraint set in the constraint setting step; and a convolution operation step of computing an output acoustic signal by performing convolution of an input acoustic signal and a directivity control filter that is computed in the optimization step, wherein filters that respectively correspond to speakers constituting a speaker array are computed in the objective function setting step, the constraint setting step, and the optimization step, an acoustic beam is generated using directivity control by the speaker array, and the acoustic beam is caused to be reflected from a wall surface or a ceiling to generate a virtual sound source.

7. A non-transitory computer readable medium storing one or more instructions for causing a computer to serve as the sound image localizing device according to claim 1.

8. A non-transitory computer readable medium storing one or more instructions for causing a computer to serve as the sound image localizing device according to claim 3.

9. The sound image localizing method according to claim 5, wherein the filter coefficient correction step further comprises: performing computation such that a filter gain becomes constant, the filter gain being an absolute value of a filter coefficient at each frequency.

10. The sound image localizing method according to claim 6, wherein the constraint setting step further comprises: setting at least one of a constraint that makes a value of a filter gain constant at each frequency and a constraint relating to directional characteristics that is based on the desired directional characteristic.

11. The non-transitory computer readable medium according to claim 7, wherein the filter coefficient correction unit is configured to perform computation such that a filter gain becomes constant, the filter gain being an absolute value of a filter coefficient at each frequency.

12. The non-transitory computer readable medium according to claim 8, wherein the constraint setting unit is configured to set at least one of a constraint that makes a value of a filter gain constant at each frequency and a constraint relating to directional characteristics that is based on the desired directional characteristic.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0039] FIG. 1 is a diagram showing a configuration of a sound image localizing device according to a first embodiment.

[0040] FIG. 2 is a flowchart showing operations of the sound image localizing device according to the first embodiment.

[0041] FIG. 3 is a diagram showing a method for setting a directional characteristic in the sound image localizing device according to the first embodiment.

[0042] FIG. 4 is a diagram showing a method for setting a directional characteristic in the sound image localizing device according to the first embodiment.

[0043] FIG. 5 is a diagram showing a configuration of a sound image localizing device according to a second embodiment.

[0044] FIG. 6 is a flowchart showing operations of the sound image localizing device according to the second embodiment.

[0045] FIG. 7 is a diagram showing an observation system for finding a directivity control filter.

[0046] FIG. 8 is a conceptual diagram of sound image localization that is performed using reflection of the directivity of sound.

[0047] FIG. 9 is a diagram showing an observation system for designing a normalization matched filter.

DESCRIPTION OF EMBODIMENTS

[0048] The following describes embodiments that are most suited to implement the present invention, by using the drawings.

[0049] Overview

[0050] As described above, in terms of the frequency band and the sound quality, it is difficult to generate a virtual speaker by generating an acoustic beam using directivity control performed through a conventional method and causing the acoustic beam to be reflected from a wall surface. A virtually generated speaker needs to support a wide frequency band as a single speaker and give high sound quality.

[0051] In the embodiments of the present invention, a directivity control filter that can generate a desired directional characteristic is designed while restricting filter gains to be equal in all of the frequency band as in the case of NPL 2, rather than suppressing the filter gains using a penalty term as in the case of NPL 1, and a virtual speaker is generated using reflection from a wall surface as shown in FIG. 8.

First Embodiment

[0052] A first embodiment is an example in which directional reproduction that enables reproduction in a wide frequency band with high sound quality is realized by performing correction for restricting the filter gain with respect to a directivity control filter that is designed using a method such as the least squares method.

[0053] FIG. 1 is a diagram showing a configuration of a sound image localizing device 10 according to the first embodiment, and FIG. 2 is a flowchart showing operations of the sound image localizing device 10. The sound image localizing device 10 according to the first embodiment is a sound image localizing device that uses reflected sound, and includes a directivity control filter design unit 11, a filter coefficient correction unit 12, and a convolution operation unit 13. It goes without saying that the sound image localizing device 10 may also include another constituent element. For example, the sound image localizing device 10 may also include a directivity control filter shown in FIG. 8.

[0054] The directivity control filter design unit 11 computes a fundamental directivity control filter from a desired directional characteristic, which has been input (step S11-S12 in FIG. 2). Here, the desired directional characteristic corresponds to the vector d in Expression (1), and the fundamental directivity control filter corresponds to the vector w in Expression (1). At this time, the input desired directional characteristic does not particularly relate to a speaker, but corresponds to control points, and is set as desired on the outside of the sound image localizing device 10 (e.g., FIGS. 3 and 4, which will be described later, if there are 36 control points at intervals of 10 degrees on a circle surrounding the speaker, the desired characteristic d is a vector with 36 rows and 1 column). Although any method can be used to compute the fundamental directivity control filter so long as the method minimizes an error between the desired directional characteristic and a directional characteristic that is observed at an observation point when the fundamental directivity control filter is used, the least squares method can be used, for example.

[0055] The filter coefficient correction unit 12 computes a corrected directivity control filter from the fundamental directivity control filter, which has been input (step S13 in FIG. 2). The filter coefficient correction unit 12 computes the corrected directivity control filter by correcting the fundamental directivity control filter such that the filter gain becomes constant, the filter gain being the absolute value of a filter coefficient at each frequency. For example, focusing on a frequency of the fundamental directivity control filter, a filter coefficient corresponding to the frequency is divided by the absolute value of the filter coefficient and the result is multiplied by a constant determined in advance. As a result of this processing being carried out with respect to all frequencies of interest, the filter gain can be made constant at each frequency.

[0056] The convolution operation unit 13 computes an output acoustic signal from an input acoustic signal, which has been input, and the corrected directivity control filter (step S14 in FIG. 2). The convolution operation unit 13 computes the output acoustic signal by performing convolution of the input acoustic signal and the directivity control filter.

[0057] An acoustic signal that corresponds to the desired directional characteristic can be reproduced by reproducing the output acoustic signal from a speaker array.

[0058] Method for Setting Directional Characteristic FIG. 3 shows a case where the shape of directivity (directional characteristic) that is desired to be obtained is definitely determined. Here, an observation system that includes M control points will be considered. If there are 36 control points at intervals of 10 degrees on a circle surrounding a speaker, for example, the desired characteristic d is a vector with 36 rows and 1 column. In such a case, d(ω)=[d.sub.1, d.sub.2, d.sub.3, . . . , d.sub.M-2, d.sub.M-1, d.sub.M].sup.T is the desired directional characteristic as shown in FIG. 3.

[0059] FIG. 4 shows a case where the shape of directivity (directional characteristic) that is desired to be obtained is not definitely determined. Here, assume that there is a condition to be satisfied, for example, “sound is to be heard by a person who is at a control point 1 and the sound is not to be heard by a person who is at a control point 2”. In such a case, the desired directional characteristic also includes maximizing the difference between a sound pressure observed at the control point 1 and a sound pressure observed at the control point 2 (control point 1>control point 2). That is, the desired directional characteristic is obtained by modeling the above-described condition.

[0060] As described above, the sound image localizing device 10 according to the first embodiment includes the directivity control filter design unit 11 that computes a directivity control filter from a desired directional characteristic, the filter coefficient correction unit 12 that corrects the directivity control filter computed by the directivity control filter design unit 11, and the convolution operation unit 13 that computes an output acoustic signal by performing convolution of an input acoustic signal and the directivity control filter corrected by the filter coefficient correction unit 12. Filters that respectively correspond to speakers constituting a speaker array are computed by the directivity control filter design unit 11 and the filter coefficient correction unit 12, an acoustic beam is generated using directivity control by the speaker array, and the acoustic beam is caused to be reflected from a wall surface or a ceiling to generate a virtual sound source. Thus, it is possible to provide the sound image localizing device 10 that enables the virtual speaker to reproduce sound in a wide frequency band with high sound quality.

[0061] Also, it is desirable that the filter coefficient correction unit 12 performs computation such that a filter gain becomes constant, the filter gain being the absolute value of a filter coefficient at each frequency. Thus, desired directional reproduction can be realized.

[0062] Note that the meaning of “a wall surface or a ceiling” in the expression “the acoustic beam is caused to be reflected from a wall surface or a ceiling” should be widely interpreted. That is, “a wall surface or a ceiling” includes what reflects the acoustic beam similarly to a wall surface or a ceiling.

Second Embodiment

[0063] The following describes a second embodiment. Note that the following mainly describes differences from the first embodiment, and detailed descriptions of aspects similar to those in the first embodiment will be omitted.

[0064] The second embodiment is an example in which desired directional reproduction is realized by designing a filter by solving an optimization problem to which a function that forms a desired directional characteristic is given as an objective function and a non-linear equality constraint that restricts the filter gain to a constant value is given as a constraint.

[0065] FIG. 5 is a diagram showing a configuration of a sound image localizing device 20 according to the second embodiment, and FIG. 6 is a flowchart showing operations of the sound image localizing device 20. The sound image localizing device 20 according to the second embodiment includes an objective function setting unit 21, a constraint setting unit 22, an optimization unit 23, and a convolution operation unit 24.

[0066] The objective function setting unit 21 sets an objective function from a desired directional characteristic, which has been input (step S21-S22 in FIG. 6). It is possible to use, as a representative example, the least square error expressed by Expression (3), which is the sum of squares of errors between the desired directional characteristic d and a directional characteristic d.sup.O observed at each control point. Similarly to the first embodiment, the desired directional characteristic is set on the outside of the sound image localizing device 20.

[0067] The constraint setting unit 22 sets a constraint relating to the filter gain (step S23 in FIG. 6). It is also possible to additionally set a constraint relating to directional characteristics based on the desired directional characteristic that has been input (step S21-S23 in FIG. 6). As the constraint relating to the filter gain, a constraint is given that makes the value of the filter gain constant at each frequency similarly to the first embodiment. As an example of the constraint relating to directional characteristics, it is possible to use a constraint that suppresses sound radiation in directions other than a target direction or a constraint that makes frequency response in the target direction constant.

[0068] The optimization unit 23 computes a directivity control filter by solving an optimization problem based on the objective function and the constraint, which have been input (step S24 in FIG. 6). The following shows an optimization problem in which the filter gain and the frequency response in the target direction are restricted, taking the least squares method as an example.

[00006]$\begin{array}{cc}.Math.\begin{array}{cc}\mathrm{minimize}& {\left(d\left(\omega \right)-G\left(\omega \right)w\left(\omega \right)\right)}^H\left(d\left(\omega \right)-G\left(\omega \right)w\left(\omega \right)\right)\\ \mathrm{subject}\mathrm{to}& .Math.w_l\left(\omega \right).Math.=c\\ & G^{\mathrm{point}}\left(\omega \right)w\left(\omega \right)=1\end{array}& \left(10\right)\end{array}$

[0069] Here, G(ω) represents a transfer function matrix in which transfer functions from speakers to control points are stored, w(ω)=[w.sub.1(ω), w.sub.2(ω), . . . , w.sub.L(ω)] represents a filter coefficient vector in which filter coefficients w.sub.1(ω) corresponding to the respective speakers are stored, c represents a constant, and G.sup.point(ω) represents a transfer function vector in which transfer functions from the respective speakers to the target direction are stored. A directivity control filter of which the filter gain is suppressed can be computed by solving the optimization problem as that expressed by Expression (10).

[0070] The convolution operation unit 24 is similar to that in the first embodiment, and therefore a description thereof is omitted (step S25 in FIG. 6).

[0071] As described above, the sound image localizing device 20 according to the second embodiment includes the objective function setting unit 21 that sets an objective function from a desired directional characteristic, the constraint setting unit 22 that sets a linear or non-linear constraint, the optimization unit 23 that computes an optimum filter coefficient from the objective function set by the objective function setting unit 21 and the constraint set by the constraint setting unit 22, and the convolution operation unit 24 that computes an output acoustic signal by performing convolution of an input acoustic signal and the directivity control filter computed by the optimization unit 23. Filters that respectively correspond to speakers constituting a speaker array are computed by the objective function setting unit 21, the constraint setting unit 22, and the optimization unit 23, an acoustic beam is generated using directivity control by the speaker array, and the acoustic beam is caused to be reflected from a wall surface or a ceiling to generate a virtual sound source. Thus, it is possible to provide the sound image localizing device 20 that enables the virtual speaker to reproduce sound in a wide frequency band with high sound quality.

[0072] Also, it is desirable that the constraint setting unit 22 sets at least one of a constraint that makes the value of the filter gain constant at each frequency and a constraint relating to directional characteristics that is based on the desired directional characteristic. Thus, desired directional reproduction can be realized.

[0073] Note that the present invention can be realized not only as the sound image localizing devices 10 and 20 described above, but also as a sound image localizing method that includes, as steps, functional units that are characteristic to the sound image localizing devices 10 and 20, or a program that causes a computer to execute those steps. It goes without saying that such a program can be distributed via a recording medium such as a CD-ROM or a transmission medium such as the Internet.

REFERENCE SIGNS LIST

[0074] 10 Sound image localizing device [0075] 11 Directivity control filter design unit [0076] 12 Filter coefficient correction unit [0077] 13 Convolution operation unit [0078] 20 Sound image localizing device [0079] 21 Objective function setting unit [0080] 22 Constraint setting unit [0081] 23 Optimization unit [0082] 24 Convolution operation unit