Method and apparatus to create a sound field

• US 20040151325A1
• Filed: 03/22/2004
• Published: 08/05/2004
• Est. Priority Date: 03/27/2001
• Status: Active Grant

• Current Assignee: Yamaha Corporation
• Original Assignee: Cambridge Mechatronics Limited
• Inventors: Hooley, Anthony, Davies, James, Easton, Mark George, Troughton, Paul Thomas, Goudie, Angus Gavin, Windle, Paul Raymond, Ryan, Damon Thomas, Bienek, Irving Alexander
• Granted Patent: US 7,515,719 B2
• Time in Patent Office: Days
• US Class Current: 381/18
• CPC Class Codes: F41H 13/0081 the high-energy beam being acoustic, e.g. sonic, infrasonic or ultrasonic
• CPC Class Codes: G10K 15/04 Sound-producing devices G10K15/02 takes precedence
• CPC Class Codes: H04R 1/26 Spatial arrangements of separate transducers responsive to two or more frequency ranges
• CPC Class Codes: H04R 1/403 loud-speakers
• CPC Class Codes: H04R 2201/401 2D or 3D arrays of transducers
• CPC Class Codes: H04R 2203/12 Beamforming aspects for stereophonic sound reproduction with loudspeaker arrays
• CPC Class Codes: H04R 2205/022 Plurality of transducers corresponding to a plurality of sound channels in each earpiece of headphones or in a single enclosure
• CPC Class Codes: H04R 3/12 for distributing signals to two or more loudspeakers specially adapted for hearing aids H04R25/407
• CPC Class Codes: H04S 1/002 Non-adaptive circuits, e.g. manually adjustable or static, for enhancing the sound image or the spatial distribution control circuits for electronic adaptation of the sound field H04S7/30
• CPC Class Codes: H04S 3/00 Systems employing more than two channels, e.g. quadraphonic H04S5/00, H04S7/00 take precedence
• CPC Class Codes: H04S 3/002 Non-adaptive circuits, e.g. manually adjustable or static, for enhancing the sound image or the spatial distribution control circuits for electronic adaptation of the sound field H04S7/30

Abstract

The invention generally relates to a method and apparatus for taking an input signal, replicating it a number of times and modifying each of the replicas before routing them to respective output transducers such that a desired sound field is created. This sound field may comprise a directed beam, focussed beam or a simulated origin. In a first aspect, delays are added to sound channels to remove the effects of different travelling distances. In a second aspect, a delay is added to a video signal to account for the delays added to the sound channels. In a third aspect, different window functions are applied to each channel to give improved flexibility of use. In a fourth aspect, a smaller extent of transducers is used top output high frequencies than are used to output low frequencies. An array having a larger density of transducers near the centre is also provided. In a fifth aspect, a line of elongate transducers is provided to give good directivity in a plane. In a sixth aspect, sound beams are focussed in front or behind surfaces to give different beam widths and simulated origins. In a seventh aspect, a camera is used to indicate where sound is directed.

Claims

1. A method of creating a sound field comprising a plurality of channels of sound using an array of output transducers, said method comprising:

for each channel, selecting a first delay value in respect of each output transducer, said first delay value being chosen in accordance with the position in the array of the respective transducer;

selecting a second delay value for each channel, said second delay value being chosen in accordance with the expected travelling distance of sound waves of that channel from said array to a listener;

obtaining, in respect of each output transducer, a delayed replica of a signal representing each channel, each delayed replica being delayed by a value having a first component comprising said first delay value and a second component comprising said second delay value.

2. A method according to claim 1 or 2, wherein said second delay is applied to each signal representing said channel before said signal is replicated;

each replica then being delayed by the respective first delay value.

3. A method according to claim 1 or 2, wherein said first delay value is also chosen in accordance with a given direction so that each channel of sound is directed in respective direction.

4. A method according to claim 3, wherein each channel is directed in a different respective direction.

5. A method according to any one of the preceding claims, wherein said second delay value is chosen such that corresponding parts of all sound channels reach the listener at substantially the same time.

6. Apparatus for creating a sound field comprising:

a plurality of inputs for a plurality of respective signals representing different sound channels;

an array of output transducers;

replication means arranged to obtain, in respect of each output transducer, a replica of each respective input signal;

first delay means arranged to delay each replica of each signal by a respective first delay value chosen in accordance with the position in the array of the respective output transducer;

second delay means arranged to delay each replica of each signal by a second delay value chosen for each channel in accordance with the expected travelling distance of sound waves of that channel from the array to a listener.

7. Apparatus according to claim 6, wherein said second delay means is arranged to delay said input signals before they are replicated by said replication means.

8. Apparatus according to claim 6 or 7, wherein said first delay value is also chosen in accordance with a given direction so that each channel of sound is directed in said respective direction.

9. Apparatus according to claim 8, wherein each channel is directed in a different direction.

10. Apparatus according to any one of claims 6 to 9, wherein said second delay means is arranged to choose said second delay for each channel such that all sound channels reach a listener at substantially the same time.

11. A method of creating a sound field comprising a centre channel and at least one surround sound channel using an array of output transducers to direct the at least one surround sound channel in a predetermined direction, said method comprising:

for the at least one surround sound channel, selecting a first delay value in respect of each output transducer, said first delay values being chosen in accordance with the position in the array of the respective transducer so as to direct the channel in said predetermined direction;

selecting a second delay value for the centre channel, said second delay value being chosen in accordance with the expected travelling distance of sound waves of the channels from the array to the listener;

obtaining, in respect of each output transducer, a delayed replica of a signal representing the at least one surround sound channel, each delayed replica being delayed by the first delay value calculated for that output transducer and that channel;

obtaining, in respect of each output transducer, a delayed replica of a signal representing the centre channel, each delayed replica being delayed by said second delay value;

outputting said delayed replicas using said array of output transducers.

12. A method according to claim 11, further comprising:

for the centre channel, selecting a first delay value in respect of each output transducer, said first delay values being chosen in accordance with the position in the array of the respective transducer so as to direct the centre channel in a predetermined direction;

and wherein said step of obtaining, in respect of each output transducer, a delayed replica of a signal representing the centre channel further comprises;

delaying each replica of the signal representing said centre channel by the first delay value calculated for the respective output transducer and the centre channel.

13. A method according to claim 11, wherein replicas of the signal representing said centre channel are not delayed by values other than said second delay value, said second delay values being the same for each replica of the signal.

14. A method according to any one claims 11 to 13, further comprising:

for the at least one surround sound channel, selecting a second delay value in respect of each output transducer, said second delay value being chosen in accordance with the expected travelling distance of sound waves of the channels from the array to the listener;

and wherein said step of obtaining, in respect of each output transducer, a delayed replica of a signal representing the at least one surround sound channel further comprises;

delaying each replica of the signal representing said at least one surround sound channel by the second delay value calculated for the respective output transducer and the at least one surround sound channel.

15. A method according to any one of claims 11 to 14, wherein said second delay is applied to each signal representing said centre channel before said signal is replicated.

16. A method according to any one of claims 11 to 15, wherein said sound field comprises two surround sound channels, each surround sound channel being directed in a different direction.

17. A method according to any one of claims 11 to 16, wherein said second delay value is chosen such that corresponding parts of all sound channels reach the listener at substantially the same time.

18. A method according to any one of claims 11 to 17, wherein said delayed replicas of the signal representing the at least one surround sound channel are added to respective delayed replicas of the signal representing the centre channel before being output by the respective output transducers.

19. A method according to any one of claims 11 to 18, wherein the sound waves of said at least one surround sound channel are bounced off a surface such as a wall before reaching the listener.

27. A method according to any one of claims 11 to 19 or an apparatus according to any one of claims 20 to 26, wherein said output transducers are directly driven by class-BD PWM amplifiers.

20. Apparatus for creating a sound field comprising:

means for receiving a plurality of input signals representing at least one surround sound channel and a centre channel;

an array of output transducers;

replication means arranged to obtain, in respect of each output transducer, a replica of said signal representing said at least one surround sound channel and a replica of said signal representing a centre channel;

first delay means arranged to delay each replica of said signal representing said at least one surround sound channel by a respective first delay value chosen in accordance with the position in the array of the respective transducer so as to direct the channel in a predetermined direction;

second delay means arranged to delay each replica of said signal representing said centre channel by a second delay value chosen in accordance with the expected travelling distance of sound waves of the channels from the array to a listener.

21. Apparatus according to claim 20, wherein said first delay means is also arranged to delay each replica of said signal representing said centre channel by a respective first delay value chosen in accordance with the position in the array of the respective transducer so as to direct the centre channel in a predetermined direction.

22. Apparatus according to claim 20 or 21, wherein said second delay means is also arranged to delay each replica of said signal representing said at least one surround sound channel by a respective second delay value chosen in accordance with the expected travelling distance of sound waves of the channels from the array to the listener.

23. Apparatus according to any one of claims 20 to 22, wherein said second delay means is arranged to delay said input signals before they are replicated by said replication means.

24. Apparatus according to any one of claims 20 to 23, wherein said sound field comprises two surround sound channels, and said first delay means is arranged to cause each surround sound channel to be directed in a different direction.

25. Apparatus according to any one of claims 20 to 24, wherein said second delay means is arranged to choose said second delay for the channels such that all sound channels reach a listener at substantially the same time.

26. Apparatus according to any one of claims 20 to 25, wherein said first delay means and said second delay means are the same physical means.

28. A method of providing temporal correspondence between pictures and sound in an audio-visual presentation using an array of output transducers to reproduce the sound content comprising a plurality of channels, said method comprising:

delaying, in respect of each output transducer, a replica of each signal representing a sound channel by a respective audio delay value;

delaying a video signal by a video delay value calculated so corresponding video pictures are displayed at substantially the time the temporally corresponding sound channels reach the listener.

29. A method according to claim 28, wherein each audio delay value is calculated in accordance with the position in the array of the respective transducer.

30. A method according to claim 29, wherein each audio delay value is also calculated in accordance with the expected travelling distance of sound waves of that channel from said array to a listener.

31. A method according to claim 30, wherein each audio delay value is calculated such that temporally corresponding parts of each sound channel reach the listener at substantially the same time.

32. A method according to any one of claims 28 to 31, wherein said video delay value is calculated so as to have a component equal to the time taken for the sound channel having the greatest distance to travel between said array and said listener to travel between said array and said listener.

33. Apparatus to provide temporal correspondence between pictures and a plurality of sound channels in an audio-visual presentation comprising:

an array of output transducers;

replication and delay means arranged to obtain, in respect of each output transducer, a delayed replica of each signal representing a sound channel;

video delay means arranged to delay a corresponding video signal by a video delay value calculated so corresponding video pictures are displayed at substantially the time the temporally corresponding sound channels reach the listener.

34. Apparatus according to claim 33, wherein said replication and delay means is arranged so that each audio delay value is calculated in accordance with the position in the array of the respective transducer.

35. Apparatus according to claim 34, wherein said replication and delay means is arranged so that each audio delay value is also calculated in accordance with the expected travelling distance of sound waves of that channel from said array to a listener.

36. Apparatus according to claim 35, wherein said replication and delay means is arranged so that each audio delay value is calculated such that temporally corresponding parts of each sound channel reach the listener at substantially the same time.

37. Apparatus according to claims 33 to 36, wherein said video delay means is arranged so that said video delay value is calculated so as to be equal to the time taken for the sound channel having the greatest distance to travel between said array and said listener to travel between said array and said listener.

38. A method of creating a sound field comprising a plurality of channels of sound using an array of output transducers, said method comprising:

for each channel, obtaining, in respect of each output transducer, a replica of a signal representing said channel so as to obtain a set of replica signals for each channel;

applying a first window function to a first set of replica signals originating from a first sound channel signal;

applying a second, different, window function to a second set of replica signals originating from a second sound channel signal.

39. A method according to claim 38, wherein applying a window function comprises:

attenuating or amplifying each replica signal such that replica signals destined for output transducers near the centre of the array are attenuated less or amplified more than replica signals destined for output transducers near the edges of the array, the amount of attenuation or amplification being determined by said window function.

40. A method according to claim 38 or 39, wherein the window function used is selected in accordance with how the respective sound channel is output by the array.

41. A method according to any one of claims 38 to 40, wherein the window function used is selected in accordance with a required beam type for that channel.

42. A method according to any one of claims 38 to 41, wherein the window function used has a shape alterable as a function of a volume control.

43. Apparatus to create a sound field comprising a plurality of channels of sound, comprising:

an array of output transducers;

replication means for providing, in respect of each output transducer, a replica of a signal representing each of said plurality of channels;

windowing means for applying a first window function to a first set of replica signals originating from a first sound channel signal and for applying a second, different, window function to a second set of replica signals originating from a second channel signal.

44. Apparatus according to claim 43, wherein said windowing means is arranged to attenuate or amplify each replica signal such that replica signals destined for output transducers near the centre of the array are attenuated less or amplified more than replica signals destined for output transducers near the edges of the array, the amount of attenuation or amplification being determined by said window function.

45. Apparatus according to claim 43 or 44, wherein said windowing means is provided directly after said replication means.

46. Apparatus according to any one of claims 43 to 45, wherein said windowing means is arranged to select a window function in accordance with a required beam type for that channel.

47. Apparatus according to any one of claims 43 to 46, wherein the window function applied to a set of replicas originating from a signal representing a channel is altered in shape in accordance with the volume selected for said channel.

48. A method of creating a sound field using an array of output transducers, said method comprising:

dividing an input signal into at least a low frequency component and a high frequency component;

using output transducers spanning a first portion of the array to output said low frequency component; and

using output transducers spanning a second portion of said array smaller than said first portion to output said high frequency component.

49. A method according to claim 48, wherein said second portion comprises a subset of said output transducers located near the centre of the array.

50. A method according to claim 48 or 49, wherein there are 3 or more divided signal frequency components and the portion of the array used for a signal component is determined such that the ratio of the shortest wavelength in said signal component to the portion of array used to output said signal component is substantially constant for all signal components.

51. A method according to any one of claims 48 to 50, wherein said second portion of the array used for said high frequency component is not used for said low frequency component.

52. A method according to any one of claims 48 to 51, wherein said second portion of the array used for said high frequency component comprises a greater density of output transducers than the array as a whole on average.

53. An apparatus arranged to perform the method according to any one of claims 48 to 52.

54. Apparatus for creating a sound field comprising:

an array of output transducers wherein in a first area of the array the output transducers are more densely packed than in the remainder of said array.

55. Apparatus according to claim 54, wherein said first area is located substantially at the centre of the array.

56. Apparatus according to claim 54 or 55, wherein the output transducers in said first area are less powerful than the output transducers in the remainder of the array.

57. Apparatus according to any one of claims 54 to 56, wherein the output transducers in said first area are smaller than the output transducers in the remainder of the array.

58. Apparatus according to any one of claims 54 to 57, further comprising means for routing a high frequency component of a signal to said first area of the array, but not to the remainder of the array.

59. Apparatus according to any one of claims 54 to 58, further comprising means to route a low frequency components of a signal to the remainder of the array.

60. An array of output transducers positioned next to each other in a line:

wherein each of said output transducers has a dimension in the direction perpendicular to said line larger than the dimension parallel to said line.

61. An array according to claim 60, wherein each output transducer has an aspect ratio defined as the ratio of the dimension perpendicular to the line to the dimension parallel to the line and said aspect ratio is at least 2:

1.

62. An array according to claim 61, wherein said aspect ratio is at least 3:

1.

63. An array according to any one of claims 60 to 62, wherein said arrangement is such that sound is concentrated substantially in a plane containing said line and extending perpendicularly away from the sound emitting side of said transducers.

64. A method of causing plural input signals representing respective channels to appear to emanate from respective different positions in space, said method comprising:

providing a sound reflective or resonant surface at each of said positions in space;

providing an array of output transducers distal from said positions in space; and

directing, using said array of output transducers, sound waves of each channel towards the respective position in space to cause said sound waves to be retransmitted by said reflective or resonant surface, said sound waves being focussed at a position in space in front of, or behind, said reflective or resonant surface;

said step of directing comprising;

obtaining, in respect of each transducer, a delayed replica of each input signal delayed by a respective delay selected in accordance with the position in the array of the respective output transducer and said respective focus position such that the sound waves of the channel are directed towards the focus position in respect of that channel;

summing, in respect of each transducer, the respective delayed replicas of each input signal to produce an output signal; and

routing the output signals to the respective transducers.

65. A method according to claim 64, wherein said step of obtaining, in respect of each output transducer, a delayed replica of the input signal comprises:

replicating said input signal said predetermined number times to obtain a replica signal in respect of each output-transducer;

delaying each replica of said input signal by said respective delay selected in accordance with the position in the array of the respective output transducer and the desired position of focus.

66. A method according to claim 64 or claim 65, further comprising:

calculating, before said delaying step, the respective delays in respect of each input signal replica by;

determining the distance between each output transducer and the focus position in respect of that input signal;

deriving respective delay values such that the sound waves from each transducer for a single channel arrive at said focus position in space simultaneously.

67. A method according to any one of claims 64 to 66, wherein at least one of said surfaces is provided by a wall of a room or other permanent structure.

68. An apparatus for causing plural input signals representing respective channels to appear to emanate from respective different positions in space, said apparatus comprising:

a sound reflective or resonant surface at each of said positions in space;

an array of output transducers distal from said positions in space; and

a controller for directing, using said array of output transducers, sound waves of each channel towards that channel'"'"'s respective position in space such that said sound waves are re-transmitted by said reflective or resonant surface, said sound waves being focussed at a position in space in front of, or behind, said reflective or resonant surface;

said controller comprising;

replication and delay means arranged to obtain, in respect of each transducer, a delayed replica of the input signal delayed by a respective delay selected in accordance with the position in the array of the respective output transducer and the respective focus position such that the sound waves of the channel are directed towards the focus position in respect of that input signal;

adder means arranged to sum, in respect of each transducer, the respective delayed replicas of each input signal to produce an output signal; and

means to route the output signals to the respective transducers such that the channel sound waves are directed towards the focus position in respect of that input signal.

69. An apparatus according to claim 68, wherein said controller further comprises:

calculation means for calculating the respective delays in respect of each input signal replica by;

determining the distance between each output transducer and the focus position in respect of that input signal;

deriving respective delay values such that the sound waves from each transducer for a single channel arrive at said focus position simultaneously.

70. An apparatus according to claims 68 or 69, wherein said surfaces are reflective and have a roughness on the scale of the wavelength of sound frequency it is desired to diffusely reflect.

71. An apparatus according to any one of claims 68 to 70, wherein said surfaces are optically-transparent.

72. An apparatus according to any one of claims 68 to 71, wherein at least one of said surfaces is a wall of a room or other permanent structure.

73. A method of selecting a direction in which to focus sound, said method comprising;

pointing a video camera in the desired direction, using the viewfinder or other screen means to determine if the direction is that desired;

calculating a plurality of signal delays to be applied to a set of replicas of an input signal so as to direct sound in the selected direction.

75. A method according to claim 73 or 74, wherein said sound is focussed and said camera is arranged to be focussed at the same position as said sound.

76. A method according to claim 73 or 74, wherein said sound is focussed using reference points in the room.

74. A method of determining where sound is directed, said method comprising:

automatically adjusting the direction in which a video camera points in accordance with the direction in which sound is directed;

discerning from the viewfinder or other screen means which direction the camera is pointing in.

77. An apparatus for setting up or monitoring a sound field comprising:

an array of output transducers;

a directable video camera;

means controlling said array of output transducers and said video camera such that said video camera points in the same direction as a sound beam from said array is directed.

78. An apparatus according to claim 77, wherein said camera is attached to said array.

79. An apparatus according to claim 77 or 78, wherein said sound beam is arranged to be focussed and said camera is arranged to be focussed at substantially the same point.

80. An apparatus according to claim 77 or 79, wherein said sound beam is arranged to be focussed at a reference point within the camera'"'"'s field of view.