Audio playback device and audio playback method

1. An audio playback device which plays back an audio object including an audio signal and playback position information indicating a position in a three-dimensional space at which a sound image of the audio signal is localized, the audio playback device comprising:

at least one speaker array which includes speaker elements and converts an acoustic signal to acoustic vibration;

a converting unit configured to convert the playback position information to corrected playback position information which is information indicating a position of the sound image on a two-dimensional coordinate system based on a position of the at least one speaker array; and

a signal processing unit configured to localize the sound image of the audio signal included in the audio object according to the corrected playback position information, and output the localized sound image to the at least one speaker array, wherein:

when (i) a direction in which the speaker elements are arranged in each of the at least one speaker array is an X axis, (ii) a direction which is orthogonal to the X axis and parallel to a setting surface on which the at least one speaker array is arranged is a Y axis, and (iii) a direction which is orthogonal to the X axis and perpendicular to the setting surface is a Z axis,

the corrected playback position information indicates the position at coordinates (x, y) on the two-dimensional coordinate system expressed by the X axis and the Y axis, and

when the position identified by the playback position information is expressed by coordinates (x, y, z), the corrected playback position information indicates values corresponding to x and y,

on the two-dimensional coordinate system, a y coordinate located behind the at least one speaker array is a negative coordinate and a y coordinate located in front of the at least one speaker array is a positive coordinate,

the signal processing unit is configured to perform wavefront synthesis by signal processing using a Huygens' principle when a y-coordinate value of the corrected playback position information is a negative value, and

the signal processing unit is a beam forming unit configured to form a sound image at the position on the two-dimensional coordinate system when the y-coordinate value of the corrected playback position information is a positive value.

2. The audio playback device according to claim 1 ,

wherein when, on the two-dimensional coordinate system, (i) a y coordinate located behind the at least one speaker array is a negative coordinate and a y coordinate located in front of the at least one speaker array is a positive coordinate, and (ii) an x coordinate located to a left of a center of the at least one speaker array is a negative coordinate and an x coordinate located to a right of the center of the at least one speaker array is a positive coordinate, a value of the corrected playback position information is a value obtained by multiplying at least one of the x-coordinate value and the y-coordinate value by a predetermined value.

3. The audio playback device according to claim 1 ,

wherein an x-coordinate value of the corrected playback position information is limited to a width of the at least one speaker array.

4. The audio playback device according to claim 1 ,

wherein the corrected playback position information indicates the position on the two-dimensional coordinate system, the position on the two-dimensional coordinate system being indicated by (i) a direction angle to the position indicated by the corrected playback position information when seen from a position of a listener listening to an acoustic sound output from the at least one speaker array and (ii) a distance from the position of the listener to the position indicated by the corrected playback position information.

5. The audio playback device according to claim 4 ,

wherein the signal processing unit is configured to localize the sound image using a head related transfer function (HRTF), and

the HRTF is set so that a sound is audible from a direction of the position indicated by the corrected playback position information.

6. The audio playback device according to claim 5 ,

wherein the signal processing unit is configured to adjust a sound volume according to the distance from the position of the listener to the position indicated by the corrected playback position information.

7. The audio playback device according to claim 1 ,

wherein the signal processing unit is configured to change a signal processing method according to the position indicated by the corrected playback position information.

8. The audio playback device according to claim 1 , wherein:

the audio playback device includes a processor and a memory storing a program, and

the program, when executed by the processor, causes the processor to function as the converting unit and the signal processing unit.

9. The audio playback device according to claim 1 , further comprising

at least two speaker arrays,

wherein each of the at least two speaker arrays forms a corresponding one of at least two two-dimensional coordinate systems, and

when the position identified by the playback position information is expressed by coordinates (x, y, z) where (i) a direction in which speaker elements are arranged in one of the at least two speaker arrays is an X axis, (ii) a direction which is orthogonal to the X axis and parallel to a setting surface on which the one of the at least two speaker arrays is arranged is a Y axis, and (iii) a direction which is orthogonal to the X axis and perpendicular to the setting surface is a Z axis,

the signal processing unit is configured to control the at least two speaker arrays according to a z-coordinate value.

10. The audio playback device according to claim 8 ,

wherein, when the two two-dimensional coordinate systems are parallel to each other, the signal processing unit is configured to:

increase a sound volume of the one of the at least two speaker arrays which is on an upper two-dimensional coordinate system with respect to the setting surface when the z-coordinate value is larger than a predetermined value; and

increase a sound volume of the one of the at least two speaker arrays which is on a lower two-dimensional coordinate system with respect to the setting surface when the z-coordinate value is smaller than the predetermined value.

11. The audio playback device according to claim 9 ,

wherein when the two two-dimensional coordinate systems are orthogonal to each other, the signal processing unit is configured to:

increase a sound volume of one or more speaker elements in the one of the at least two speaker arrays when the z-coordinate value is larger than a predetermined value, the one or more speaker elements being arranged at positions above a predetermined position on a two-dimensional coordinate system perpendicular to the setting surface among the at least two two-dimensional coordinate systems; and

increase a sound volume of one or more speaker elements in the one of the at least two speaker arrays when z-coordinate value is smaller than the predetermined value, the one or more speaker elements being arranged at positions below the predetermined position on the two-dimensional coordinate system perpendicular to the setting surface among the at least two two-dimensional coordinate systems.

12. An audio playback device which plays back an audio object including an audio signal and playback position information indicating a position in a three-dimensional space at which a sound image of the audio signal is localized, the audio playback device comprising:

at least one speaker array which includes speaker elements and converts an acoustic signal to acoustic vibration;

a converting unit configured to convert the playback position information to corrected playback position information which is information indicating a position of the sound image on a two-dimensional coordinate system based on a position of the at least one speaker array; and

a signal processing unit configured to localize the sound image of the audio signal included in the audio object according to the corrected playback position information, and output the localized sound image to the at least one speaker array,

wherein when (i) a direction in which the speaker elements are arranged in each of the at least one speaker array is an X axis, (ii) a direction which is orthogonal to the X axis and parallel to a setting surface on which the at least one speaker array is arranged is a Y axis, and (iii) a direction which is orthogonal to the X axis and perpendicular to the setting surface is a Z axis,

when, on the two-dimensional coordinate system, a y coordinate located behind the at least one speaker array is a negative coordinate and a y coordinate located in front of the at least one speaker array is a positive coordinate, and

the signal processing unit is configured to:

when a y-coordinate value of the corrected playback position information is a negative value, perform wavefront synthesis by signal processing using a Huygens' principle;

when a y-coordinate value of the corrected playback position information is a positive value indicating a position in front of a listener, generate a sound image by signal processing using beam forming; and

when a y-coordinate value of the corrected playback position information is a positive value indicating a position behind the listener, localize a sound image by signal processing using a head related transfer function (HRTF).

13. An audio playback method for playing back, using a speaker array including speaker elements, an audio object including an audio signal and playback position information indicating a position in a three-dimensional space at which a sound image of the audio signal is localized, the audio playback method comprising:

converting the playback position information to corrected playback position information which is information indicating a position of the sound image on a two-dimensional coordinate system based on a position of the at least one speaker array; and

localizing the sound image of the audio signal included in the audio object according to the corrected playback position information, and outputting the localized sound image to the at least one speaker array,

wherein when (i) a direction in which the speaker elements are arranged in each of the at least one speaker array is an X axis, (ii) a direction which is orthogonal to the X axis and parallel to a setting surface on which the at least one speaker array is arranged is a Y axis, and (iii) a direction which is orthogonal to the X axis and perpendicular to the setting surface is a Z axis,

the corrected playback position information indicates the position at coordinates (x, y) on the two-dimensional coordinate system expressed by the X axis and the Y axis, and

when the position identified by the playback position information is expressed by coordinates (x, y, z), the corrected playback position information indicates values corresponding to x and y,

on the two-dimensional coordinate system, a y coordinate located behind the at least one speaker array is a negative coordinate and a y coordinate located in front of the at least one speaker array is a positive coordinate,

in the localizing, wavefront synthesis is performed by signal processing using a Huygens' principle when a y-coordinate value of the corrected playback position information is a negative value, and

in the localizing, a sound image at the position on the two-dimensional coordinate system is localized by signal processing using beam forming when the y-coordinate value of the corrected playback position information is a positive value.

14. An audio playback method for playing back, using at least one speaker array including speaker elements, an audio object including an audio signal and playback position information indicating a position in a three-dimensional space at which a sound image of the audio signal is localized, the audio playback method comprising:

converting the playback position information to corrected playback position information which is information indicating a position of the sound image on a two-dimensional coordinate system based on a position of the at least one speaker array; and

localizing the sound image of the audio signal included in the audio object according to the corrected playback position information, and outputting the localized sound image to the at least one speaker array,

wherein when (i) a direction in the speaker elements are arranged in each of the at least one speaker array is an X axis, (ii) a direction which is orthogonal to the X axis and parallel to a setting surface on which the at least one speaker array is arranged is a Y axis, and (iii) a direction which is orthogonal to the X axis and perpendicular to the setting surface is a Z axis,

when, on the two-dimensional coordinate system, a y coordinate located behind the at least one speaker array is a negative coordinate and a y coordinate located in front of the at least one speaker array is a positive coordinate, and

in the localizing:

when a y-coordinate value of the corrected playback position information is a negative value, wavefront synthesis is performed by signal processing using a Huygens' principle;

when a y-coordinate value of the corrected playback position information is a positive value indicating a position in front of a listener, a sound image is generated by signal processing using beam forming; and

when a y-coordinate value of the corrected playback position information is a positive value indicating a position behind the listener, a sound image is localized by signal processing using a head related transfer function (HRTF).