Abstract:
A system and method for sound generation is disclosed. In at least some embodiments, the system including a first surface serving to at least partially enclose a first region, a first speaker positioned on the first surface, and a second region within the first region. The system further includes a first fictitious source location within the first region, the location being outside of the second region, and a control device coupled at least indirectly within the first speaker. The control device generates control signals configured to cause the first speaker to generate first sounds that in turn produce actual sounds within the second region, and the actual sounds simulate fictitious sounds emanating from the first fictitious source location.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of U.S. provisional patent application no. 60/840,865 entitled “System and Method for Sound Generation” filed on Aug. 29, 2006, which is hereby incorporated by reference herein. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002]     --  
       Field of the Invention  
       [0003]     The present invention relates to sound generation systems such as, for example, speaker systems, and more particularly relates to sound generation systems that operate to generate sounds that simulate sounds that would be provided by things (animate or inanimate) positioned at locations other than those at which the sound generating equipment is positioned.  
       BACKGROUND OF THE INVENTION  
       [0004]     There continues to be a need for enhanced stereo and other sound generating systems for use in a variety of environments including, for example, movie theaters, homes and automobiles. In particular, audience members continue to desire an ever-more intense and realistic entertainment experience. Among the new technologies that have been developed in this regard are sound generating technologies that allow an audience member to hear sounds that appear to be coming from locations outside of the physical environment in which the audience member is situated, e.g., outside a theater. For example, in a movie environment in which an airplane is being displayed on the movie screen, apparently at a location far beyond the physical location of the screen itself, such new technologies can allow an audience member to hear sounds that appear to the audience member as if they had originated from the fictitious, distant airplane rather than from the audio speakers positioned around the theater.  
         [0005]     One such technology that has allowed for such simulated sounds to be achieved was developed by F. Richard Moore, and is described in “ A general model for spatial processing of sounds ”, Computer Music Journal, 7(6):6-15, 1983, which is hereby incorporated by reference herein. To achieve such simulated sounds, this technology models a given physical environment of an audience member as having two nested areas. The outer room is an imaginary acoustic space within which the inner room (or the real performance space, e.g., the theater room) is located. The inner room is denoted by the location of the speakers which simulate the sound heard in the inner room as if the speakers were “openings” connecting the inner and the outer room. The spatial impression is produced by diffusing simulated direct sound rays, early echos, and global reverberation of the sound sources as heard at each speaker location. Based on the location of the source and geometry of the inner and outer rooms, simple ray-tracing algorithms are used to calculate the direct and reflected rays to the speaker locations. Direct paths are simply straight lines to the speaker locations.  
         [0006]      FIG. 1  illustrates this Prior Art manner of modeling fictitious sounds coming from a fictitious source positioned outside a region, which allows for the generation of actual sounds by one or more sound sources (e.g., speakers) positioned along the border of the region such that at one or more locations within the region the actual sounds appear as if they were emanating from the fictitious source. More particularly,  FIG. 1  shows exemplary paths  8 ,  10  for first order reflections of sound waves (represented by rays) emanating from a fictitious source  2  located outside of an inner region  4  having a boundary  6 , within which could be located audience member(s) (or other listener(s) or listening device(s)), e.g., a room such as a theater chamber, etc.  
         [0007]     As shown, the paths  8 ,  10  are shown to travel from the fictitious source  2  toward an outer boundary  16  of a second, outer region  14  encompassing the inner region  4 , at which the paths then are reflected toward the inner region  4 . The particular paths shown are those which travel from the fictitious source  2  toward each of four exemplary speaker locations  12  located at corners of the region  4 , albeit it will be understood that other paths will also occur and could be shown. The exemplary paths  8 , shown as solid lines, are paths that need not traverse the boundary  6  of the inner region  4  in order to arrive at their respective speaker locations  12 , while the exemplary paths  10 , shown as dashed lines, are paths that need to traverse the boundary  6  and a portion of the inner region  4  in order to arrive at their respective speaker locations.  
         [0008]     Other than continuous control over the location of the fictitious source  2 , three other parameters are defined to characterize the diffusion pattern of the sound source. Thus, a radiation vector (RV) is defined as follows: 
 
RV=( x,y ,θ,amp,back),  (1) 
 
 where x and y denote the location of the source with (0,0) being at the center of the inner room, θ is the source radiation direction, amp is the amplitude of the vector, and back is the relative radiation factor in the opposite direction of θ (0&lt;back&lt;1). Back and θ are used to denote the supercardiod shape for radiation pattern of the sound source. Setting back to zero denotes a strongly directional source and setting back to one denotes an omnidirectional source. 
 
         [0009]     The following equation (2) is used to calculate the amplitude scale factor for a simulated sound ray:  
               r   ⁡     (   ∅   )       =       [     1   +         (     back   -   1     )     ⁢          θ   -   ∅            Π       ]     2             (   2   )             
 
 where r(ø) is the scale factor and ø is the direction of the ray being simulated. Subsequently, the final attenuation factor for each simulated sound ray is calculated based on the following equations: 
 
α i =ρ i K i B i D i   (3) 
 
               D   i     =     1     d   i   y               (   4   )             
 
 where α is the total attenuation factor, ρ is the amplitude scalar determined based on the radiation pattern of the sound source and the angle by which the sound ray leaves the source (see eqn. 2), K is the “cut factor” (zero if a sound ray “cut”s through a wall of the inner room, and one otherwise), B accounts for absorption at reflection points, D is the attenuation factor due to the length of the path calculated based on d, the distance that the ray has to travel, and y denotes the power law governing the relation between subjective loudness and distance. 
 
         [0010]     The delay values for each simulated sound ray is calculated by the relation  
               τ   i     =       R   ×     d   i       c             (   5   )             
 
 where τ is the delay value, R is the sampling rate in Hz, d i  is the distance between the source and a speaker, and c is the speed of sound. Moore made a partial, though fairly complete, practical and useful, implementation of the general model in the “space unit generator” of cmusic. This implementation used a fixed 50 millisecond fade time for turning sound rays on and off based on the result of the “cut” factor of each ray and the inner walls. 
 
         [0011]     The above-described scheme of Moore works well so long as a given fictitious source such as the source  2  can be assumed to be located outside of the boundary  6  on which the speakers are located, at a considerable distance from that boundary  6 . The scheme simulates spatial impressions by assuming that the sounds of an outer room are heard inside an inner room, such that the model&#39;s results are more convincing when the source is outside the inner room. In most applications it is not desired for the inner room to have a physical presence; meaning that when a sound source passes through a wall, it is usually not meant to be heard as such.  
         [0012]     However, the above-described scheme does not address the need for allowing simulated sounds of things (both animate and inanimate) located within the boundary  6  along which speakers are located (e.g., within the inner region  4 ). When the source is inside the inner region, the model can no longer be applied realistically, hence the undesirable effect of speakers in opposite sides turning on and off abruptly when a sound source passes through an inner wall. For example, if a source comes close to a wall of the inner region or if it passes through the boundary of that region, turning on and turning off speakers with a fixed 50 millisecond delay in opposite speakers to the wall would be perceived as noticeable distraction.  
         [0013]     For at least these reasons, therefore, it would be advantageous if an improved method and system could be developed that allowed for sounds to be generated within a region such as (but not limited to) a theater, where the generated sounds gave the appearance to audience member(s) (or other listener(s) or listening device(s)) within the region that the sounds were emanating from one or more thing(s) located within the region instead of outside of the region (or in addition to).  
       SUMMARY OF THE INVENTION  
       [0014]     In at least some embodiments, the present invention relates to a method of generating an actual sound that simulates a fictitious sound supposedly emanating from a first location within a first region, where the actual sound is to be sensed at a second location within the first region. The method includes determining the fictitious sound, and identifying a second region within the first region, where the first location is positioned outside the second region while still being positioned inside the first region. The method additionally includes calculating at least one adjustment value based at least in part upon the position of the second region, and generating a modified sound at a first speaker positioned proximate a first boundary of the first region, the modified sound being determined from the fictitious sound at least in part based upon the at least one adjustment value. The generating of the modified sound at the first speaker results in the generating of the actual sound at the second location.  
         [0015]     Further, in at least some embodiments, the present invention relates to a method of generating actual sounds that simulate fictitious sounds supposedly emanating from a fictitious source at a first location and moving within a first region, where the actual sounds are to be sensed at a recipient location within the first region. The method includes determining the fictitious sounds, and identifying a second region within the first region, where the recipient location is within the second region and where the first location is positioned outside the second region while still being positioned inside the first region. The method additionally includes determining whether fictitious ray paths connecting the fictitious source with a fictitious speaker as the source moves must cross a second boundary of the second region in order to reach the fictitious speaker, where the fictitious speaker is positioned proximate the second boundary, and where the fictitious ray paths proceed from the fictitious source to a third boundary of a third region extending around the first region, are reflected off of the third boundary and subsequently proceed to the fictitious speaker. The method further includes generating modified sounds at a first speaker positioned proximate a first boundary of the first region, the modified sounds being determined at least in part based upon the determining of whether the fictitious ray paths must cross the second boundary, where the generating of the modified sounds at the first speaker results in the generating of the actual sounds at the recipient location.  
         [0016]     Additionally, in at least some embodiments, the present invention relates to a system including a first surface serving to at least partially enclose a first region, a first speaker positioned on the first surface, and a second region within the first region. The system further includes a first fictitious source location within the first region, the location being outside of the second region, and a control device coupled at least indirectly within the first speaker. The control device generates control signals configured to cause the first speaker to generate first sounds that in turn produce actual sounds within the second region, and the actual sounds simulate fictitious sounds emanating from the first fictitious source location. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]      FIG. 1  illustrates a Prior Art manner of modeling fictitious sounds coming from a fictitious source positioned outside a region that allows for the generation of actual sounds by one or more sound sources (e.g., speakers) positioned along the border of the region such that at one or more locations within the region the actual sounds appear as if they were emanating from the fictitious source;  
         [0018]      FIG. 2  illustrates an improved manner of modeling fictitious sounds coming from a fictitious source in accordance with at least some embodiments of the present invention, where this manner of modeling the sounds allows for the generation of actual sounds by sound source(s) positioned along the border of a region even when the fictitious source is located within that region; and  
         [0019]      FIG. 3  shows in schematic form a system that can be used to generate the actual sounds in a region as represented by  FIG. 2 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0020]     Referring to  FIG. 2 , a schematic diagram  20  illustrates an improved manner of modeling fictitious sounds coming from a fictitious source  22  in accordance with at least some embodiments of the present invention. This manner of modeling the fictitious sounds allows for actual sounds to be generated within a first region  24  by one or more sound generating source(s) such as speakers located along a boundary  26  of that region, where the actual sounds give the appearance to one or more listener(s) (e.g., audience member(s) or other listener(s) or listening device(s)) of emanating from the fictitious source  22  even though the fictitious source is located within the first region  24  rather than outside that region as presumed in the Prior Art modeling methodology described above. Thus, while (as in the Prior Art embodiment described above)  FIG. 2  shows exemplary paths  28  and  30  extending from the fictitious source  22  toward an outer boundary  46  of a second, outer region  44 , which are then reflected back inward toward the first region  24 , the fictitious source  22  is located within the first region  24  rather than outside that region (in contrast to the Prior Art embodiment).  
         [0021]     In accordance with at least some embodiments of the present invention, the improved manner of modeling the fictitious sounds includes three aspects: 1) an improved ray inter-section algorithm, 2) definition of nested imaginary inner rooms; and 3) slightly altered delay time and attenuation factor calculations. These three aspects, as well as a system and method for generating actual sounds based upon the results of applying this model, are described in further detail below.  
         [0000]     Improved Ray Intersection Algorithm  
         [0022]     In accordance with at least some embodiments of the present invention, a simple frequency independent ray intersection algorithm for fading in/out sound rays in speakers smoothly as a sound source moves in the space can be employed. Instead of producing binary “cut” factors, in this algorithm fractional “cut” factors are calculated based on a distance between the edge of an inner wall and the inter-section point, a diffraction threshold, and a crossfade factor. If a ray intersects with multiple walls, the final “cut” factor is calculated as the product of the “cut” factors with each wall, according to the following relations:  
               k     i   ,   s       =     {           0             (       TH   -     δ     i   ,   s         TH     )           ⁢           ⁢   CF   ⁢           ⁢               When   ⁢           ⁢     δ     i   ,   s         &gt;   TH     ,                 When   ⁢           ⁢   TH     &gt;     δ     i   ,   s       &gt;   0                       (   6   )                 K   i     =       ∏     S   =   1     S     ⁢     k     i   ,   s                 (   7   )             
 
 where k i,s  is the diffraction attenuation factor for ray i intersecting with surface s, δ i,s  is the distance between intersection point and the corner of the wall, TH is the diffraction threshold variable (TH could be defined as a constant or as a fraction of the size of the wall), CF is the crossfade exponential factor, S is the number of surfaces of the inner room, and K i  is the final “cut” factor for ray i. 
 
 Imaginary Inner Rooms 
 
         [0023]     In accordance with at least some embodiments of the present invention, the first region  24 , is understood to correspond to a physical region such as a room, along the boundary  26  of which is to be positioned one or more sound generating sources (e.g., speakers). Additionally the first region  24  is understood to encompass one or more nested imaginary regions (or rooms), one of which is shown in  FIG. 3  as a third region  54  having an outer boundary  56 . The specific imaginary region  54  chosen for calculations typically is the largest possible inner region based on the location of the fictitious source  22 , such that the source is always outside of that inner region regardless of movement of the source as shown in  FIG. 2 . Where multiple nested imaginary regions are identified, the innermost imaginary inner region is a point at the center of the first region  24  and has dimensions of zero.  
         [0024]     As with the Prior Art model described with respect to  FIG. 1 , the present model presumes that one or more actual speakers (or other sound generating devices) are located at one or more speaker locations  32  along the boundary  26  of the first region  24 , e.g., at the four corners of that region as shown in  FIG. 2 . At the same time, the present model further defines imaginary speakers to be located at one or more speaker locations  52  along the boundary  56  of that third region  54 , e.g., at the four corners of that region. The imaginary speakers can be understood as being located at the intersections of the lines drawn from the center of the room to each real speaker location, and the walls of the imaginary room. Thus, as shown in  FIG. 3 , the exemplary paths  28 ,  30  shown in  FIG. 2  as extending from the fictitious source  22  extend from that source to the boundary  46  and, upon being reflected at that boundary, then proceed to the four speaker locations  52 .  
         [0025]     As described in Her detail below, attenuation factors and delay times for each path (ray) will be calculated in relation to the chosen imaginary room. Thus, the sound diffused by each speaker located at the boundary  26  of the first region  24  (which is typically the real, physical room within which a listener or listening device is located) is attenuated and delayed in proportion to the distance between the center of the room and the location of the imaginary speaker that the real speaker is shadowing.  
         [0026]     Also, the diffraction threshold factor TH and the crossfade factor CF will also be set for each imaginary region/room such as the region  54 . Various implementations can offer linear or exponential scaling of TH and CF for imaginary inner rooms (e.g., the closer one gets to the center of the room, the smaller the TH factor could get). Keeping TH constant for all the imaginary rooms will cause the walls of smaller imaginary rooms to be more translucent. Thus, when a source travels from outside of the main inner room towards the center of the room, the speakers located on the opposite wall gradually become louder as the source approaches the center of the room. In such a scenario, when the source gets closer to the center of the inner room, the closer the “cut” factors get to one.  
         [0000]     Delay and Attenuation Factor Calculations  
         [0027]     In the Prior Art model of Moore described above, delay values and their corresponding attenuation factors are calculated based on the distance between the fictitious source and speaker location. In contrast, in accordance with at least some embodiments of the present invention, delay values can be calculated based on the distance between the source and a specific speaker (which could be an imaginary one), plus the distance between that speaker and the center of the room. Accordingly the attenuation factor D i  used in equation 3 above would also be calculated based on the distance between the source and the center of the room, as follows:  
               τ   i     =       R   ×     (       d   i     +     λ   j       )       C             (   8   )                 D   i     =     1       (       d   i     +     λ   j     +   Λ     )     γ               (   9   )             
 
 where τ is the delay value, R is the sampling rate in Hz, d i  is the distance between the source and the speaker on the chosen inner room, j is the speaker number of chosen inner room, λ j  is the distance between that speaker and center of the room, c is the speed of sound, Λ is a constant distant factor added to further control the attenuation factors due to distance, and γ denotes the power law governing the relation between subjective loudness and distance. 
 
         [0028]     Also, in the Prior Art model of Moore, the sound diffused by a speaker would be louder if a source were located right on that speaker than the resulting diffused sound when a source is in the middle of the room. It is so, due to the fact that the delay and attenuation factors were calculated based on the distance between the source and the speaker. This matter further complicates the simulated spatial impression of a sound source inside of the inner room. By comparison, the calculation of delay times and attenuation factors in relation to the center of the room in accordance with embodiments of the present invention not only solves the above problem but also seamlessly accounts for the delay time simulation of imaginary speakers at the perimeter of an imaginary room by the physical speakers located at the perimeter of the primary inner room. Due to the fact that in this improved model attenuation factors are calculated in relation to the distance between the source and the center of the room, when a source is at the center of the room, all speakers are engaged with the least amount of attenuation. Thus, the resulting impression could perceptually become much stronger compared to when the source is at a considerable distance from the center. Even though γ in equation 9 could be used to control the relation between attenuation of sounds due to distance, the addition of Λ as a constant has been found to be useful to balance the sound levels between the simulated impressions when the source is in the center of the room or when it is her away.  
         [0000]     Practical Implementation  
         [0029]     Assuming that the improved model described above is utilized, it is possible for actual sounds to be generated by one or more speakers arranged around the boundary  26  of the first region  24  that, when heard by one or more listener(s) (e.g., audience member(s)) or listening device(s) (e.g., microphone(s)), appear to be emanating from the fictitious source  22  (or possibly from multiple such fictitious sources). More specifically, for the effect to be achieved, the listener(s) or listening device(s) must be positioned not only within the first region  24  but also more specifically within the assumed imaginary region(s) such as the third region  54 .  
         [0030]     Referring to  FIG. 3 , a schematic diagram shows exemplary component parts of a system  60  that can produce such actual sounds through the use of the above-described model. As shown, the system  60  includes a computer or other processor  64  (e.g., a microprocessor) that is preferably capable of significant numbers of calculations in real time. The computer  64  receives information, for example, by way of one or more input/output devices  62  (which could be, for example, a keyboard, a network connection, etc.) that inform the computer  64  about the fictitious sounds that are supposed to be generated by one or more fictitious sources. This sound information could be, for example, portions of a sound track to a movie. The information received by the computer  64  also includes location information of the fictitious position(s) of the fictitious source(s), including possibly directional or velocity movement of the source(s) if they are supposed to be moving. The information received by the computer  64  also can include specific information of the one or more location(s) of one or more listener(s) or listening device(s) located within the actual physical region within which actual sounds are to be provided (e.g., within the first region  24 ).  
         [0031]     Upon receiving this information, the computer  64  calculates signals that should be provided to one more speakers (in this example, shown to be first and second speakers  66  and  68 ) in order to generate actual sounds that, when heard by the listener(s) or listening device(s), will appear to emanate from the location(s) of the fictitious source(s). These calculations are achieved using the improved model described above. As described above, to use the improved model, one or more imaginary third regions such as the region  56  must be identified, within which are located the listeners) or listening device(s) but not the fictitious source(s). In at least some embodiments, the computer  64  itself is capable of determining the extent (and possibly number) of imaginary region(s) of interest automatically. Once the computer  64  determines the actual sounds that should be generated by the speakers  66 ,  68 , the computer  64  sends appropriate signals to those speakers to generate those sounds. The components  62 ,  64 ,  66  and  68  shown in  FIG. 3  can communicate with one another and with respect to outside components by way of any of a variety of communication formats and technologies including, for example, wired connections, wireless connections, internet connections, etc.  
         [0000]     Additional Considerations  
         [0032]     The spatial impression produced through the use of the improved model in accordance with embodiments of the present invention, for a source located inside of the first region  24 , is optimal for a listener located at the center of the region. It should be understood that, when using loudspeakers, it is impossible to create the same spatial impression of a fictitious source located within the first region  24  for all listening locations within that room (e.g., within the third region  54 ). At the same time, this shortcoming need not be a significant drawback in many practical circumstances. For example, to the extent that this improved model is intended for performance situations, the above-mentioned shortcoming can be dealt with compositionally so that the different perceived spatial impressions will carry general meaningful musical connotations.  
         [0033]     Also it should be noted that, if the physical speaker locations (e.g., the locations  32 ) are not located at an equal distance to the center of the first region  24 , calculation of the delays in relation to the center of the room will cause exaggeration of any inequalities in the distance of the speakers to the center of the room. While this effect could be used musically, if the simulated impressions are to follow the original model, to use this extension, speakers should be placed in equal distance to the center of the room. At the same time, it should be noted that, while a recipient located at the center of the third region  54  will likely experience the best simulated impressions, recipients located at other locations other than the very center of the third region (e.g., recipients located at other locations within the third region) will also likely experience sounds that are enhanced relative to what they would be using Prior Art techniques.  
         [0034]     Additionally, it should be noted that, while all of the regions  24 ,  44  and  54  shown in  FIG. 2  are shown to be rectangular (square), two-dimensional regions, the present system and method employing the improved modeling methodology described above is not only applicable to such regions but also is applicable to two-dimensional regions of arbitrary shape (e.g., circular regions) as well as to three-dimensional regions of arbitrary shape (e.g., cubic regions, spherical regions, etc.). Thus, the present invention is intended to be applicable not only within rectangularly-shaped theater rooms, but also within a variety of other environments including, for example, home environments and automobiles. The present invention is also intended to be applicable for use in connection with virtual reality systems, including virtual reality systems providing imaging capabilities such as holographic imaging capabilities.  
         [0035]     In at least some alternate embodiments, in order to achieve a more psychoacoustically salient spatialization (or localization) impression, direct or reflected simulated sound rays to the speakers along the boundary  26  of the first region  24  can be attenuated further based on the angle by which the direct ray or the last segment of a reflected ray arrives at a speaker. This attenuation factor can be between 0 (zero) and 1 (one). In particular, if a sound ray arrives at a speaker at an angle (angle “ray_angle”) that is the same angle as the angle of the sound diffusion of the speaker (angle “speaker_angle”), the attenuation factor will be 1 (one), and if the ray arrives at the speaker exactly in the opposite direction of the angle of the sound diffusion of the speaker, the attenuation factor will be 0 (zero). Thus, a linear calculation of the attenuation factor (“angle_attenuation) based on the arrival angle of the ray to the speaker can be: 
 
angle_attenuation=1−(|ray_angle−speaker_angle|/Π)  (10) 
 
 This technique can be particularly useful when the model is applied to three dimensions and when speakers are located on the corners of the box denoting the first region  24 , where for simulating sound in most locations most speakers will be active. 
 
         [0036]     It will further be understood that the present invention can also be used in combination with the Prior Art methodology described above. For example, if it is desired to generate actual sounds that appear to be emanating from a fictitious source that is moving from a location outside of the first region  24  of  FIG. 2  to a location inside of that region, then the computer  64  can switch between the Prior Art methodology and the improved methodology in determining the actual sounds at a time when the fictitious source is supposedly crossing the boundary  26  of the region  24 . Also, if the sounds of multiple fictitious sources both inside and outside the boundary  26  are to be simulated, the computer  64  can use both the Prior Art and improved techniques to simulate the sounds of the respective fictitious sources.  
         [0037]     It is specifically intended that the present invention not be limited to the embodiments and illustrations contained herein, but include modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments as come within the scope of the following claims.