Rendering audio objects with complex shapes

Abstract

A method (900) for representing an audio object in an extended reality scene includes obtaining (s902) first metadata describing a first three-dimensional (3D) shape associated with the audio object. The method also includes transforming (s904) the obtained first metadata to produce transformed metadata describing a two-dimensional (2D) plane or a one-dimensional (1D) line, the 2D plane or the 1D line representing at least a portion of the audio object.

Description

[Technical field]

[0001] SUMMARY OF THE DISCLOSURE Embodiments are disclosed that relate to rendering audio objects with complex shapes. [Background technology]

[0002] Spatial audio rendering is a process used to present audio in an extended reality (XR) scene (e.g., a virtual reality (VR), augmented reality (AR), or mixed reality (MR) scene) to give the listener the impression that the sound is coming from a physical source in the scene at a certain location and having a certain size and shape (i.e., extent). Presentation can be through headphone speakers or other speakers. When presentation is through headphone speakers, the process used is called binaural rendering and uses spatial cues of human spatial hearing that make it possible to determine from which direction a sound is coming. The cues involve inter-aural time delay (ITD), inter-aural level difference (ILD), and / or spectral differences.

[0003] The most common form of spatial audio rendering is based on the point source concept, where each sound source is defined to emanate sound from one specific point. Because each sound source is defined to emanate sound from one specific point, the sound sources do not have a size or shape. Different methods have been developed to render sound sources that have a range (size and shape).

[0004] One such known method is to create multiple copies of a mono audio object at positions around the audio object. This configuration results in the perception of a spatially uniform object with a certain size. This concept is used, for example, in the "object spread" and "object divergence" features of the MPEG-H 3D Audio standard (see references [1] and [2]) and in the "object divergence" feature of the EBU Audio Definition Model (ADM) standard (see reference [4]). This idea of ​​using mono audio sources is further developed as described in reference [7], where the area-volume geometry of the sound object is projected onto a sphere around the listener and the sound is rendered to the listener using a pair of head-related (HR) filters that are evaluated as the integral of all HR filters that cover the geometric projection of the object on the sphere. For a spherical volume source, this integral has an analytical solution. However, for an arbitrary area-volume source geometry, the integral is evaluated by sampling the projected source surface on the sphere using so-called Monte Carlo ray sampling.

[0005] Another rendering method renders a spatially diffuse component in addition to the mono audio signal, which results in the perception of somewhat diffuse objects that, in contrast to the original mono audio objects, do not have a distinct pinpoint location. This concept is used, for example, in the "object diffuseness" feature of the MPEG-H 3D audio standard (see Reference [3]) and the "object diffuseness" feature of the EBU ADM (see Reference [5]).

[0006] Combinations of the two above methods are also known: for example, the "object extent" feature of EBU ADM combines the creation of multiple copies of a mono audio object with the addition of a diffuse component (see reference [6]).

[0007] In many cases, the actual shape of an audio object can be described well enough using primitive shapes (e.g., a sphere or a box). However, sometimes the actual shape is more complex and needs to be described in a more detailed form (e.g., a mesh structure or a parametric description format). In such cases, rendering of the audio object requires a real-time evaluation of how the audio object will be rendered based on the listener's current relative position with respect to the audio object. This real-time evaluation can be processing intensive. Summary of the Invention

[0008] Existing methods for rendering volumetric audio objects generally use a single point source to represent the audio object and set the position of the point source as the center of the audio object (see, for example, FIG. 1). This means that the height and width of the audio object are not represented. More sophisticated methods of rendering volumetric audio objects exist. Such methods attempt to represent the shape of the audio object, but they are limited to mono sources. This results in the audio object being rendered as either spatially uniform or spatially diffuse. In both cases, the rendering is based on a mono recording without spatial information.

[0009] Another option for rendering volumetric audio objects is to represent the audio object using a large number of point sources that together compose the sound emanating from the audio object. However, this method is highly inefficient due to the number of point sources required for an accurate representation of the object's shape from different angles. Also, the number of point sources needs to be increased proportionally to the size of the object.

[0010] Thus, the present disclosure supports the use of audio objects with defined sizes and shapes represented by multi-channel audio signals in which different channels represent spatial information of the audio object in different dimensions. An example is a stereo recording that represents spatial information along the horizontal dimension of the audio object. More specifically, the present disclosure provides a method for simplifying the three-dimensional (3D) shape of an audio object into a one-dimensional (1D) or two-dimensional (2D) representation that describes the width and / or height of the audio object as seen from the listener's position. The multi-channel audio signal is then rendered such that the perceived spatial extent matches that of the simplified extent.

[0011] Thus, in one aspect, a method is provided for representing an audio object in an extended reality scene. The method includes obtaining first metadata describing a first three-dimensional (3D) shape associated with the audio object. The method also includes transforming the obtained first metadata to produce transformed metadata describing a two-dimensional (2D) plane or a one-dimensional (1D) line. The 2D plane or 1D line represents at least a portion of the audio object.

[0012] In another aspect, a computer program is provided comprising instructions which, when executed by a processing circuit, cause the processing circuit to perform the method described above. In one embodiment, a carrier is provided containing the computer program, the carrier being one of an electronic signal, an optical signal, a radio signal, and a computer readable storage medium.

[0013] In another aspect, an apparatus is provided for representing an audio object in an extended reality scene. The apparatus is adapted to obtain first metadata describing a first three-dimensional (3D) shape associated with the audio object. The apparatus is further adapted to transform the obtained first metadata to produce transformed metadata describing a two-dimensional (2D) plane or a one-dimensional (1D) line. The 2D plane or 1D line represents at least a portion of the audio object. In one embodiment, the apparatus comprises a processing circuit and a storage unit that stores instructions for configuring the apparatus to perform any of the processes disclosed herein.

[0014] Compared to existing methods of rendering audio objects, the embodiments described herein provide a more efficient way to dynamically represent both the width and height of audio objects as a listener moves around in a six degrees of freedom (6DoF) XR scene.

[0015] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate various embodiments. [Brief description of the drawings]

[0016] [Figure 1] FIG. 2 illustrates an exemplary representation of an audio object. [Diagram 2] FIG. 1 illustrates an example of a simplified range. [Diagram 3] 1A and 1B show an exemplary process for finding description points. [Figure 4] FIG. 1 illustrates an exemplary process for defining a 2D plane. [Diagram 5] 13A-13C illustrate scenarios where very small movements of the listener trigger a jump in the position of the anchor point. [Figure 6] 1A to 1C are diagrams showing examples of rendering settings. [Figure 7] FIG. 1 illustrates a system, according to some embodiments. [Figure 8] 1A and 1B are diagrams illustrating a system according to some embodiments. [Figure 9] FIG. 2 illustrates a process according to some embodiments. [Figure 10] FIG. 1 illustrates an apparatus, according to some embodiments. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] To render audio objects with complex extents (i.e., complex shapes) in a 6DoF virtual environment, the object's shape needs to be evaluated in real-time as the listener's listening position changes. The object's shape with respect to the listener's listening position should affect the audio object's apparent position, width, and height to match the behavior of real sound sources.

[0018] The level of range detail that needs to be taken into account when rendering the audio of an audio object without affecting the perceived spatial quality will vary, for example, depending on the distance from the listener's position to the audio object. When the listener is moving further away from the audio object, shape detail will have less importance. This can be exploited by an efficient implementation by gradually simplifying the range shape description.

[0019] Typically, the extent of a volumetric audio object is either described by a primitive shape (e.g., a sphere or a box) or by a more elaborate description, e.g., based on a combination of primitive shapes, mesh structures, or other forms of shape description. In order to efficiently render these audio objects with complex shape descriptions in real time, it is desirable to simplify the description of the object's shape in a manner that preserves the important cues perceived by the auditory system, but does not require too much complexity. In many cases, such simplification is possible because extremely fine shape details are generally not perceptually important to audio rendering, and therefore it would be a waste of computational resources to take these fine shape details into account in the rendering process.

[0020] This disclosure describes methods for simplifying complex descriptions of audio objects so that a plausible impression of the audio objects can be rendered to a listener at low computational cost.

[0021] In one embodiment, the method is divided into three basic steps.

[0022] (1) An optional pre-processing step that simplifies a complex description of the extent (i.e., shape) of an audio object into a simpler description. For example, the simpler description could be a mesh structure with fewer vertices, a primitive shape (e.g., a box, sphere, ellipsoid, or cylinder), or a combination of several primitive shapes. This simplified shape description can be used instead of the original description either always, or, for example, only when the distance to the listener's listening position is sufficiently long. This step is described in Section 1.

[0023] (2) A real-time simplification step in which the range is represented using a two-dimensional plane or a one-dimensional line, where the instantaneous listening position of the listener is taken into account. This step is explained in section 2.

[0024] (3) Rendering of the audio objects given the simplified geometric extent of the audio objects as determined in step 2. During the rendering stage, processing may be added to add perceptual effects, such as distance gain. This step is described in section 3.

[0025] 1. Simplified pre-rendering

[0026] The pre-rendering simplification step is performed before rendering begins, or alternatively, while rendering is running, but as a parallel process whose results are not used until the step is completed. The purpose of this step is to find one or more simplified descriptions of the range that can be used depending on the amount of detail needed at a particular moment. Several alternative range descriptions can be stored in a list so that the real-time rendering step can select the most appropriate range description at any time. Since the pre-rendering simplification step is not performed in real time, it may involve complex calculations and optimizations as necessary. This step may even be performed as part of the content creation step, where several alternative representations are pre-computed. Alternatively, the encoding node or the pre-rendering node may perform this step in order to offload the listener's device.

[0027] The amount of detail in the range description needed to provide high quality rendering for a listener in an extended reality scene depends on many things that can vary in real time, such as i) the distance of the audio object to the listener's listening position in the extended reality scene, ii) the size of the audio object, iii) how many other audio objects are currently active, iv) the current audio energy level of the audio object, and v) the current CPU load of the renderer that will be used to render the audio object.

[0028] Any audio object can be represented sufficiently well with a simple point source if the distance is large enough, but the closer the listener is to the audio object, the more detail is needed to provide a subjectively accurate audio rendering of the audio object.

[0029] By predetermining one or more simplified descriptions of the extent, the description that provides the most efficient tradeoff of detail versus complexity can be chosen at any given time. As an example, a complex mesh structure describing the extent of an audio object can be simplified into two alternative simplified shapes, one that is still a mesh structure but has a reduced number of vertices, and the second that is just a box shape with dimensions set to match the original shape. An example of such simplification is shown in Figure 2, which shows a complex mesh structure 202, a first less complex version 204 of the complex mesh structure 202, and a second less complex version 206 of the complex mesh structure 202.

[0030] As shown in Fig. 2, the mesh structure 202 has a relatively large number of vertices. In the illustrated example, the mesh structure 202 represents a forest viewed from above. In this example, a first less complex version 204 of the complex mesh structure 202 is itself a mesh structure, but the mesh structure 204 has fewer vertices than the mesh structure 202, and a second less complex version 206 of the complex mesh structure 202 is a simple box shape used to represent the shape of the forest. That is, in the example of Fig. 2, two simplified shapes are created, one created by reducing the number of vertices of the original mesh structure 202 and one created based on a basic box shape 206. The two alternative shape descriptions 204 and 206 represent different levels of simplification, and depending on the required amount of detail, either of these representations may be selected as the basis for the real-time simplification step. For the box shape 206, the box shape is rotated so that one dimension represents the largest dimension of the forest (i.e., mesh structure 202), and the width and height of the box are adjusted so that the box matches as closely as possible to the mesh structure 202. Even simple shapes such as spheres or boxes can be simplified to point sources when the distance to the listener is far enough.

[0031] Many methods are known for reducing the number of vertices in a mesh (see, for example, Reference [8]). The problem of decomposing an arbitrary shape into one or a few primitive shapes, such as boxes, is also a well-known problem that can be solved, for example, by using minimum volume bounding box decomposition (see Reference [9]). As described herein, several alternative representations are precomputed, along with a parameterized way of choosing which representation to use at any time during real-time rendering.

[0032] The parameterized selection of which of these representations to use as the basis for the real-time simplification, step 2, may be based on the distance of the audio object from the listener's listening position. An example of this is illustrated in Table 1. TIFF0007654683000001.tif81170

[0033] Here, D1 and D2 are threshold distance parameters that can be either constant or variable, for example controlled by the number of currently active audio objects or the current CPU load. The design parameters may depend on the size of the audio object. For example, the listening position of the listener may need to be further away from the large audio object for a single point representation of the large audio object to be adequate. In the example shown in Table 1, there are three different representations for the audio object, and two parameters (i.e., D1 and D2) are used to indicate to the renderer when to switch between the three different representations. Any additional representations, such as the simplified mesh structure 204 representation in FIG. 2, would require additional parameters that specify when such representations should be used.

[0034] The following is an example of how D1 and D2 can be selected: D1=2S max And D2=20S max where S max is the size of the range in its largest dimension (e.g., length, width, height, or depth).

[0035] In some cases (e.g., when the computational resources available for rendering fall below some lower limit), D1 may be extremely small or even 0 (i.e., the original mesh is always simplified to at least the first level of simplification, i.e., a box shape in the case of Table 1).

[0036] 2. Real-time simplification step

[0037] The real-time simplification step may be performed as part of the rendering process when the current listening position of the listener is known. This step may generally be performed at a uniform rate related to the frame size used by the rest of the renderer (e.g., this step may be performed each time a new audio frame is received or processed). Alternatively, this step may be triggered only when there is a change in position or rotation of either the audio object or the listener.

[0038] Since that step is performed in real time, one of the different representations determined in step 1 may be selected according to the parameterized selection rules and the current listening position of the listener. Other parameters that may be taken into account in the selection of one of the representations are the number of active audio objects, the CPU load of the renderer, the current audio energy level of the rendered audio objects, etc.

[0039] After one of the representations (i.e., the original description or one of the simplified descriptions) is selected, the selected representation may be further simplified to a two-dimensional (2D) plane or a one-dimensional (1D) line. In this further simplification, the depth of an audio object is not taken into account, since the depth of an audio object placed in front of a listener of the audio object is not subjectively perceived in the same way as the width and height of the audio object.

[0040] When an audio object is placed directly in front of a listener, the perceived horizontal width perceived by the listener is determined primarily by time and level difference cues, however the perceived vertical height of the object is determined primarily by less precise spectral cues.

[0041] Thus, a listener can generally estimate the horizontal width of an audio object more accurately than the vertical height of that audio object. Perceptual estimation of the depth of an audio object is less accurate and is usually simply not possible. Thus, the depth dimension of an audio object generally does not need to be included in the rendering of the audio object.

[0042] Thus, a 2D plane representing both the width and height of an audio object captures most of the important spatial cues, and in many cases a 1D line representation of only the position and horizontal width of an audio object turns out to be an efficient representation that captures the most important spatial cues of the original audio object.

[0043] This simplification step simplifies the geometry of the region, which does not necessarily correspond directly to the perceived width and height experienced by the listener. These perceptual effects should be handled by the rendering step, where the perceived width and height are calculated from the geometric size and shape of the region.

[0044] 2.1 Finding the writing point

[0045] The process of finding a two-dimensional plane to represent an audio object begins with finding anchor points on, within, or near the area as seen from the listener's listening position, as well as the outer edge of the area. Thus, the following steps may be performed:

[0046] (1) Find an anchor point on, within, or close to the range. The 2D plane that will be defined in the following steps will be fitted so that it passes through the anchor point. The line between the listener's listening position and this point will act as a reference direction from which the angles of subsequent points will be calculated.

[0047] (2) Find the range point that represents the right edge of the range from the listener's listening position. This corresponds to the point that has the highest azimuth angle with respect to the reference direction.

[0048] (3) Find the range point that represents the left edge of the range from the listener's listening position. This corresponds to the point that has the lowest azimuth angle with respect to the reference direction.

[0049] (4) Find the point in the range that represents the upper edge of the range from the listener's listening position. This corresponds to the point with the highest elevation angle relative to the reference direction.

[0050] (5) Find the range point that represents the lower edge of the range from the listener's listening position. This corresponds to the point that has the lowest elevation angle relative to the reference direction.

[0051] The five points found during this process will be shown as description points of the representation of the range. Figure 3A shows an example of the process of finding description points. That is, Figure 3A shows how description points are found for a mesh-based range 302. For simplicity, Figure 3A is shown in a bird's-eye view, which means that the elevation axis is not shown. A line 310 between the listener's listening position and an anchor point (A) on the range 302 is used as the basis for angle measurement, where the azimuth angle is 0 in the direction of the anchor point, increases to the right, and decreases below zero to the left. The right edge (B) and left edge (C) are then found as the points on the range with the maximum respective minimum azimuth angle. The top edge and bottom edge are the points with the maximum respective minimum elevation angle.

[0052] 2.1.1 Finding an anchor point

[0053] An anchor point is a point that will serve as a base point for the resulting two-dimensional plane or one-dimensional line. The plane or line will be defined such that they intersect this point, and thus the anchor point will, to a large extent, define the distance and angle to the listener. Different methods for finding the anchor point are described below.

[0054] 2.1.1.1 Use the closest point as the anchor point

[0055] A simple way to find the anchor point is to use the point on the range that is closest to the listener's listening position. The exact method for finding the closest point on the range will vary depending on the type of representation used, for example, a basic cylindrical shape has no vertices, so the closest point on its surface needs to be found using a parametric model based on its radius, length, position and rotation. A box shape has vertices, but the closest point may be somewhere on one of its surfaces and not exactly on one of those vertices. For some shapes, the closest point is easy to calculate, such as for a sphere, but for other shapes, approximations may be necessary, making identifying the exact closest point a too complicated process.

[0056] For complex mesh geometries, a limited number of points, representing both vertices and points on the surface, may be evaluated. Each of these points is then evaluated to determine its Euclidean distance D to the listening position, i.e., D=|P k -P L Identify which point is closest by calculating |, where P k is the 3D position of point k on the range, and P L is the listener's listening position.

[0057] 2.1.1.2 Alternatives for Determining Anchor Points

[0058] As an alternative to using the closest point as the anchor point, a spatial average of the points on the range (or, in some embodiments, within the range) may be used to select the anchor point.

[0059] In one particular embodiment, the anchor point is found by determining the geometric "center of gravity" of the portion of the area that is "visible" from the listener's listening position.

[0060] The "visible" part of the range may be defined by the largest contour on the object's extent surface that has a direct line of sight from the listener's current listening position. For example, for a spherical extent, the contour would be a circle with the same radius as the sphere, and the "visible" part of the range would be the frontal hemisphere of the spherical extent relative to the listener's listening position.

[0061] For a cubic extent of length L, with one of the cube's vertical edges facing the listener, the contour is TIFF0007654683000002.tif10170, and the visible part of the region will be half the cube surface facing the listener. For more arbitrarily shaped regions, the contour may have any shape, and the visible part of the region surface will generally not be just half the total region surface.

[0062] Once the "visible" portion has been determined, the anchor point can be found by finding the geometric center of gravity of the visible portion (e.g., by spatially averaging the position vectors of all points on the visible portion of the range). In the example of a spherical range, the anchor point will therefore be located at a point within the range on a line between the listener's listening position and the center of the range, somewhere between the surface and the center of the spherical range. Thus, in this example, the anchor point is located on the same line from the listener as the closest point used in the first embodiment, but at a slightly larger distance from the listener. For arbitrarily shaped ranges, this will typically not be the case, i.e., for arbitrarily shaped ranges, the anchor point derived as described above and the closest point will generally not be located on the same line from the listener's listening position.

[0063] 3B illustrates the difference between using the closest point on the region (A) as the anchor point versus using the geometric centroid of the visible portion of the region (B) for the example of an elliptical region 304. Note that the visible portion of the region is indicated in the figure by a bold line segment.

[0064] If the range is defined in an individual manner (e.g., through a set of mesh vertices) and the distribution of points (as seen from the listener's listening position) is not uniform, this non-uniformity in the spatial sampling of the range surface can be taken into account by appropriate weighting of the position vectors in the spatial averaging procedure used to determine the anchor points.

[0065] In other alternative embodiments, the anchor point may be determined as the geometric center of gravity of the entire spatial range, as opposed to only the "visible" portion of the range. This would result in the anchor point being located at the spatial center of gravity of the volume enclosed by the range. In the simple example of a spherical range, the anchor point would be located at the center of the sphere. FIG. 3B also illustrates this alternative anchor point (C) for an exemplary elliptical range. This alternative embodiment may be suitable for smaller volumetric sound sources, while the embodiment using the "visible" portion of the range may be more suitable for large volumetric sound sources.

[0066] In yet another alternative embodiment, the anchor point is determined as the geometric centroid of a bounded area around the closest point determined according to the method described in Section 2.1.1.1.

[0067] An advantage of the alternative embodiments described in this section is that the position of the anchor point varies more smoothly with changes in the listener's listening position and / or the object position / orientation than when the nearest point is used as the anchor point, especially in areas of irregular shape. As a result, the position and orientation of the adapted 2D plane also varies more smoothly with changes in the listener position and / or the object position / orientation. In particular, these alternative embodiments do not exhibit the problem of the adapted 2D plane changing abruptly with discontinuous jumps in the anchor point, as described in more detail below. This advantage comes at the expense of a somewhat more complex calculation of the position of the anchor point, while the embodiment may not require the smoothing process described below in section 2.3.

[0068] 2.1.2 Finding a description point based on an anchor point

[0069] Given an anchor point, a number of methodologies can be used to determine the other description points, one of which is described below, for example, using a mesh shape as an example.

[0070] The right and left edges of the range are determined by the azimuth angle φ of the vector between the listening position and the point being evaluated relative to the vector between the listening position and the range anchor point, i.e., the azimuth angle This can be found by evaluating TIFF0007654683000003.tif15170, where v k is the vector between the listening position and point k on the range, and v c is the vector between the listener's listening position and the range's anchor point, and both vectors have an elevation component set to 0. In this example, as shown in Figure 3A, the azimuth angle is defined to be 0 in the direction of the anchor point, increasing towards the right and decreasing towards the left.

[0071] Similarly, the top and bottom edges are found by evaluating the elevation angle of a vector from the listening position and the point being evaluated relative to the horizontal plane of the scene. k Elevation angle θ of the upper point k is the elevation angle TIFF0007654683000004.tif13164, where the coordinate system is defined such that the z component represents the up direction in the scene.

[0072] 2.2 Specifying a 2D plane or 1D line representation

[0073] After determining the description points, the next step may include defining a two-dimensional plane. Figure 4 shows an example of the process. For simplicity, Figure 4 is shown from a bird's-eye view, which means that the elevation axis is not shown. As shown in Figure 4, a plane 402 is defined such that the plane 402 intersects the anchor point at a horizontal angle α that corresponds to the angle between a line from the listener's listening position to the anchor point (A) of the range 302 and a line from the right edge (B) to the left edge (C) of the range. The outer edges of the plane should be aligned with the lowest and highest azimuth angles of each outer edge of the range. The same approach is used when calculating the height and vertical tilt of the plane using the upper and lower description points as a basis.

[0074] In another embodiment, a simplified one-dimensional representation is used, where the elevation side of the plane is ignored, and the representation is a line passing through the anchor point at a horizontal angle α that matches the angle between a line from the listener's listening position to the anchor point (A) and a line from the right edge (B) to the left edge (C) of the range. The ends of the line should align with the lowest and highest azimuth angles of each outer edge of the range. For this simplified representation, the upper and lower edge description points are not required.

[0075] If the range representation selected from the simplified representation derived in the pre-rendering simplification step is a point source, the calculation of the 2D plane or 1D line representation may be bypassed.

[0076] Alternatively, a two-dimensional plane may be fitted that passes through the anchor point and is oriented perpendicular to a line from the listener's listening position to the anchor point. In this case, the edge points described above are still used to determine the "opening angle" of the range (as seen from the listener's listening position) and its two-dimensional plane representation, but the orientation of the 2D plane is always perpendicular to the line from the listener to the anchor point. This representation may be preferable for some range shapes.

[0077] 2.3 Movement-Synchronized Smoothing of Range Descriptions

[0078] One potentially important aspect of real-time simplification is that changes in position and range may need to be smooth, so that the listener does not experience unexpected abrupt changes in the spatial representation of an audio object.

[0079] When the listener or audio objects move around or rotate, the description points of the range representation sometimes jump from one point to another. This can also happen when switching between different representations defined in the pre-rendering simplification step. Such abrupt jumps need to be smoothed out in order not to produce unnatural audio artifacts. However, normal time smoothing is not preferred here, since the smoothing can make audio objects appear to move even when they do not.

[0080] A better approach is to use smoothing that is synchronized with the relative movement of the listener and the audio object. This means that changes in the range description are only updated if either the listener moves or the audio object moves or rotates. This will avoid situations where the range of the audio object changes while the listener remains stationary, or where very small listener movements cause large changes in the position or shape of the audio object, which can occur with time smoothing.

[0081] Figure 5 shows an example of when a very small movement of the listener will trigger a jump in the position of the anchor point. By measuring the change in the relative distance between the listener and the center position of the audio object, the change in the description points can be synchronized with this change. This is done by applying a constraint on the change in the description points so that they never move more than the relative distance change. In the example of Figure 5, the closest point is used as the anchor point. If the listener moves t n-1 From the position at t n When moving to a position in , the closest point of the range makes an abrupt jump from one edge to another (i.e., from the "previous anchor point" to the "target anchor point"). In this case, a very small change in listening position will create a large difference in the position of the range, which will be experienced as unnatural. Using time smoothing techniques will not solve this problem. If smoothing is combined with a change in the relative distance dD between the listener and the audio object, R A more natural behavior can be achieved by basing the smoothing on the relative distance dD. In this example, only the listener is moving, so the change in relative position is the same as the change in the listener's position. Smoothing moves the anchor point in a direction toward the target position, but not in a relative distance change dD. R This means that the object can only travel a limited distance.

[0082] Rotation of the listener will not affect the range description, but rotation of the audio object may affect the range description, therefore rotation of the audio object should also be taken into account when defining the changes in the range description.

[0083] Next, a specific example of smoothing proportional to the change in relative position is described. R Let denote the relative distance between the audio object and the listener's listening position, and dD R Let dD be the delta change in relative distance. R , dD R =|(p AEn -p Ln )|-|(p AEn-1 -p Ln-1 )|, where p AEn and p Ln is the 3D position of the audio object and the listener at time n, and p AEn-1 and p Ln-1 is the corresponding position from the last time point.

[0084] The five different description points of the range expression are all such that the maximum change in the position of each point is dD R This is done by first calculating the delta change at each point, dD vSmooth =min(dD v ,αdD R ) where dD v denotes the distance between the old position of the description point and the new target point, and dD vSmooth denotes the smoothed distance at which the description points are updated, α denotes the update speed and dD R is a design constant that controls the relationship between. In most cases, a value between 1.0 and 2.0 is preferred.

[0085] Next, the description points are It is updated as TIFF0007654683000005.tif14170, where p pnis the target description point, and p pn-1 is the previous description point. Thus, the change of the description point is made in the direction of the new target description point, but the distance is limited to be at most as large as the change in the relative position between the listener and the audio object. See, for example, Figure 5.

[0086] To include the rotation of the audio object as part of the smoothing, dD R An additional term can be added to the calculation of dD, where the rotation is calculated as a circular movement around the midpoint of the range at the radius of the anchor point. Then, dD R But, dD R =|(p AE1 -p L1 )|-|(p AE1 -p L1 )|+|dθr|, where dθ is the change in rotation since the last iteration of the method, and r is the distance from the center point of the range to the anchor point to the listener's listening position. To capture rotation in all directions, dθ may be calculated as the sum of the rotations about all axes.

[0087] 3. Rendering

[0088] The two previously described steps were performed to simplify the three-dimensional geometry of the audio object into a two-dimensional plane or one-dimensional line. The rendering step uses this simplified description of the geometry and renders the audio object to a listener using spatial rendering techniques. That is, the rendering step uses the simplified description together with spatial rendering techniques to render an audio signal (e.g., a multi-channel audio signal) representing the audio object. Different spatial rendering techniques may be used depending on what speaker setup is used, for example, binaural rendering is commonly used for headphones and speaker panning techniques are commonly used for other speaker setups. In some cases, the rendering is done in an intermediate format, such as ambisonic or some specific multi-channel audio format.

[0089] To convey spatial information from a multi-channel audio object, the different channels should be rendered such that they represent the intended dimensions of the object. For a stereo audio object, the two channels generally represent spatial information in the horizontal plane and should therefore be rendered as the left and right sides of the object. This can be done by using two sources that represent the right and left sides of a simplified scope, respectively. In the simplest embodiment, these can be point sources, but in more advanced implementations, these sources can use head-related transfer functions (HRTFs) that better describe the scope of the two-dimensional plane. For a multi-channel source that includes a channel that also describes spatial information in the elevation dimension, more sources are needed to also represent the elevation dimension.

[0090] Examples of the rendering setup described above are shown in Fig. 6A, Fig. 6B and Fig. 6C. In these figures, three different ways of rendering an audio object represented by a two-dimensional plane using multiple virtual sound sources are shown. In the example of Fig. 6A, two point sources are used to render an audio object with a stereo audio signal. In the example of Fig. 6B, two virtual sound sources with associated HRTFs representing sub-areas of the two-dimensional plane are used to render an audio object with a stereo audio signal. In particular, Fig. 6B shows how a two-dimensional plane can be divided into segments that together cover the entire two-dimensional plane, and each segment can then be rendered through a virtual sound source with associated HRTFs that represent that entire segment. In the example of Fig. 6C, four virtual point sources are used to render an audio object with a four-channel audio signal, where different channels represent spatial information in both the horizontal and vertical planes.

[0091] Additional processing of the signals of the virtual sound sources before binaural rendering may also be required to achieve a perceptually correct spatial distribution across the plane, for example using Mid / Side mixing techniques. If the shape is relatively long in one dimension, it may be rendered as a line source, where the special behavior of line sources may be taken into account.

[0092] 4. Exemplary Implementations

[0093] 7 illustrates an example system 700 (aka a renderer) for creating sound for an XR scene. The system 700 includes a controller 701, a signal modifier 702 for modifying an audio signal 751 (e.g., a multi-channel audio signal), a left speaker 704, and a right speaker 705. Although one audio signal and two speakers are illustrated in FIG. 7, this is merely for illustrative purposes and does not limit the embodiments of the present disclosure in any way.

[0094] The controller 701 may be configured to receive one or more parameters and trigger the modifier 702 to implement a modification to the audio signal 751 (e.g., increase or decrease the volume level) based on the received parameters. The received parameters include (1) information 753 about the position of the listener (e.g., direction and distance to the audio source), and (2) metadata 754 about the audio object, such as, for example, transformed metadata describing a 2D plane or 1D line as described herein (in some embodiments, the controller 701 itself generates the metadata 754).

[0095] In some embodiments of the present disclosure, the information 753 may be provided from one or more sensors included in the XR system 800 shown in FIG. 8A. As shown in FIG. 8A, the XR system 800 is configured to be worn by a listener. As shown in FIG. 8B, the XR system 800 may include an orientation sensing unit 801, a position sensing unit 802, and a processing unit 803 coupled to a controller 851 of the system 800. The orientation sensing unit 801 is configured to detect a change in the orientation of the listener and provide information regarding the detected change to the processing unit 803. In some embodiments, the processing unit 803 determines an absolute orientation (with respect to some coordinate system) given the detected change in orientation detected by the orientation sensing unit 801. There may also be different systems for determining the orientation and position, for example, a system using a lighthouse tracker (lidar). In one embodiment, the orientation sensing unit 801 may determine an absolute orientation (with respect to some coordinate system) given the detected change in orientation. In this case, the processing unit 803 may simply multiplex the absolute orientation data from the orientation sensing unit 801 and the absolute position data from the position sensing unit 802. In some embodiments, the orientation sensing unit 801 may comprise one or more accelerometers and / or one or more gyroscopes.

[0096] 9 is a flow diagram illustrating a process 900 for representing audio objects in an extended reality scene. The process 900 may begin at step s902.

[0097] Step s902 includes obtaining first metadata describing a first three-dimensional (3D) shape associated with the audio object.

[0098] Step s904 includes transforming the obtained first metadata to produce transformed metadata describing a two-dimensional (2D) plane or a one-dimensional (1D) line, the 2D plane or the 1D line representing at least a portion of the audio object.

[0099] In some embodiments, obtaining the first metadata includes selecting the first metadata from a set of metadata comprising the first metadata and second metadata describing a second 3D shape associated with the audio object, wherein the second 3D shape described by the second metadata is in the form of one of a mesh structure, a box shape, a sphere shape, an ellipsoid shape, a cylinder shape having fewer vertices than the first 3D shape described by the first metadata.

[0100] In some embodiments, the set of metadata further comprises third metadata describing a single point in the extended reality scene.

[0101] In some embodiments, the selection is based on one or more of the distance between the audio object in the extended reality scene and the listener's listening position and at least one threshold distance parameter (e.g., D1 or D2), the size of the audio object, the number of currently active audio objects in the extended reality scene, the current load of the renderer that will be used to render the audio object, or the current audio energy level of the audio object.

[0102] In some embodiments, transforming the obtained first metadata to produce the transformed metadata includes determining a set of description points, the set of description points comprising an anchor point, and determining a 2D plane or 1D line using the description points, the 2D plane or 1D line passing through the anchor point. For many 3D shapes, the anchor point is in or on the 3D shape, but for some other 3D shapes (e.g., concave shapes), the anchor point is not on or in the 3D shape, but is usually close to the 3D shape.

[0103] In some embodiments, the anchor point is the point on the surface of the 3D shape that is closest to the listener's listening position in the extended reality scene.

[0104] In some embodiments, the anchor points are spatial averages of points on or within the 3D shape.

[0105] In some embodiments, a portion of the shape is visible to the listener in the extended reality scene, and the anchor point is the centroid of the portion of the shape that is visible to the listener.

[0106] In some embodiments, the set of description points further comprises a first point on the first 3D shape representing a first edge of the first 3D shape relative to a listening position of the listener, and a second point on the first 3D shape representing a second edge of the first 3D shape relative to the listening position.

[0107] In some embodiments, the method also includes determining a dimension (eg, width, height, length) of the 2D plane or 1D line based on the first point and the second point.

[0108] In some embodiments, the method further includes determining a horizontal angle of the 2D plane or the 1D line based on the first point and the second point.

[0109] In some embodiments, the set of description points further comprises a third point on the first 3D shape representing a third edge of the first 3D shape relative to the listening position, and a fourth point on the first 3D shape representing a fourth edge of the first 3D shape relative to the listening position.

[0110] In some embodiments, the method also includes determining a dimension (eg, width, height, length) of the 2D plane or 1D line based on the third point and the fourth point.

[0111] In some embodiments, the method further includes determining an vertical angle of the 2D plane or 1D line based on the third point and the fourth point.

[0112] In some embodiments, the audio object is represented by a multi-channel audio signal, and the method further comprises rendering the multi-channel audio signal using the transformed metadata.

[0113] 10 is a block diagram of an apparatus 1000 according to some embodiments for performing methods disclosed herein (e.g., the renderer 700 may be implemented using the apparatus 1000). As shown in FIG. 10, the apparatus 1000 includes a processing circuit (PC) 1002 that may include one or more processors (P) 1055 (e.g., a general-purpose microprocessor and / or one or more other processors, such as an application specific integrated circuit (ASIC), field programmable gate array (FPGA), etc.), which may be co-sited in a single housing or in a single data center or may be geographically distributed (i.e., the apparatus 1000 may be a distributed computing device), and at least one network interface 1048, which may be connected to the network interface 1048. The PC 1002 may comprise at least one network interface 1048, and a storage unit (a.k.a. "data storage system") 1008, which may include one or more non-volatile storage devices and / or one or more volatile storage devices. In an embodiment in which the PC 1002 includes a programmable processor, a computer program product (CPP) 1041 may be provided. The CPP 1041 includes a computer readable medium (CRM) 1042, which stores a computer program (CP) 1043, which includes computer readable instructions (CRI) 1044. The CRM 1042 may be a non-transitory computer-readable medium, such as a magnetic medium (eg, a hard disk), an optical medium, a memory device (eg, a random access memory, a flash memory), or the like.In some embodiments, the CRI 1044 of the computer program 1043, when executed by the PC 1002, is configured such that the CRI causes the device 1000 to perform the steps described herein (e.g., steps described herein with reference to flow charts). In other embodiments, the device 1000 may be configured to perform the steps described herein without the need for code; that is, for example, the PC 1002 may simply consist of one or more ASICs. Thus, features of the embodiments described herein may be implemented in hardware and / or software.

[0114] 5. Overview of Various Embodiments

[0115] A1. A method (900) for representing an audio object relative to a listening position of a listener in an extended reality scene, the method including obtaining (s902) first metadata describing a first three-dimensional (3D) shape associated with the audio object, and transforming (s904) the obtained first metadata to produce transformed metadata describing a two-dimensional (2D) plane or a one-dimensional (1D) line, the 2D plane or 1D line representing at least a portion of the audio object.

[0116] A2a. The method of embodiment A1, wherein obtaining the first metadata includes selecting the first metadata from a set of metadata comprising the first metadata and second metadata describing a second 3D shape associated with the audio object (in one embodiment, the second 3D shape described by the second metadata has fewer vertices than the first 3D shape described by the first metadata).

[0117] A2b. The method of embodiment A2a, wherein the second 3D shape is in the form of one of a mesh structure, a box shape, a sphere shape, an ellipsoid shape, and a cylinder shape having fewer vertices than the first 3D shape described by the first metadata.

[0118] A3. The method of embodiment A2a or A2b, wherein the set of metadata further comprises third metadata describing a single point in the extended reality scene.

[0119] A4. The method of embodiment A2a, A2b, or A3, wherein the selection is based on one or more of the distance between the audio object in the extended reality scene and the listening position of the listener and at least one threshold distance parameter, the size of the audio object, the number of currently active audio objects in the extended reality scene, the current load of the renderer that will be used to render the audio object, or the current audio energy level of the audio object.

[0120] A5. A method according to any one of embodiments A1 to A4, wherein transforming the acquired first metadata to produce transformed metadata includes determining a set of description points, the set of description points comprising an anchor point, and determining a 2D plane or a 1D line using the description points, the 2D plane or the 1D line passing through the anchor point.

[0121] A6. The method of embodiment A5, wherein the anchor point is a point on the surface of the 3D shape that is closest to the listener's listening position in the extended reality scene.

[0122] A7. The method of embodiment A5, wherein the anchor points are spatial averages of points on or within the 3D shape.

[0123] A8. The method of embodiment A5, in which a portion of the shape is visible to the listener in the extended reality scene and the anchor point is the center of gravity of the portion of the shape that is visible to the listener.

[0124] A9. A method according to any one of embodiments A5 to A8, wherein the set of description points further comprises a first point on the first 3D shape representing a first edge of the first 3D shape relative to a listening position of the listener, and a second point on the first 3D shape representing a second edge of the first 3D shape relative to the listening position.

[0125] A10. The method of embodiment A9, further comprising determining a dimension (e.g., width, height, length) of the 2D plane or 1D line based on the first point and the second point.

[0126] A11. The method of embodiment A9 or A10, further comprising determining a horizontal angle of the 2D plane or 1D line based on the first point and the second point.

[0127] A12. A method according to any one of embodiments A5 to A11, wherein the set of description points further comprises a third point on the first 3D shape representing a third edge of the first 3D shape relative to the listening position, and a fourth point on the first 3D shape representing a fourth edge of the first 3D shape relative to the listening position.

[0128] A13. The method of embodiment A12, further comprising determining a dimension (e.g., width, height, length) of the 2D plane or 1D line based on the third point and the fourth point.

[0129] A14. The method of embodiment A12 or A13, further comprising determining an apex angle of the 2D plane based on the third point and the fourth point.

[0130] A15. A method according to any one of embodiments A5 to A14, wherein the position of at least one description point is smoothed using a technique in which the magnitude of the change in position between two time instances is limited to be at most proportional to the magnitude of the change in the relative distance between the audio object and the listener between the same two time instances.

[0131] A16. The method of embodiment A16, in which rotational changes in the extent of the audio object are taken into account by calculating the expected position change of the anchor point, and the position change of the description point is limited to be at most proportional to the sum of the magnitude of this position change and the magnitude of the change in the relative position between the audio object and the listener.

[0132] A17. A method according to any one of embodiments A1 to A16, wherein the audio object is represented by a multi-channel audio signal, the method further comprising rendering the multi-channel audio signal using the transformed metadata.

[0133] A18. The method of embodiment A17, in which the multi-channel audio signal is rendered using virtual sound sources representing 2D shapes or 1D line edges.

[0134] A19. The method of embodiment A17 or A18, in which the multi-channel audio signal is rendered using a virtual sound source having an associated head-related transfer function (HRTF) representing a sub-area of ​​a 2D shape or a 1D line.

[0135] B1. An apparatus (1000) for representing an audio object in an extended reality scene, the apparatus being configured to: obtain (s902) first metadata describing a first three-dimensional (3D) shape associated with the audio object; and transform (s904) the obtained first metadata to produce transformed metadata describing a two-dimensional (2D) plane or a one-dimensional (1D) line, the 2D plane or 1D line representing at least a portion of the audio object.

[0136] B2. The apparatus of embodiment B1, wherein the apparatus is further configured to perform a method according to any one of embodiments A2 to A19.

[0137] B3. An apparatus (1000) for representing an audio object in an extended reality scene, the apparatus comprising: a storage unit (1008) and a processing circuit (1002) coupled to the storage unit, the apparatus being configured to: obtain (s902) first metadata describing a first three-dimensional (3D) shape associated with the audio object; and transform (s904) the obtained first metadata to produce transformed metadata describing a two-dimensional (2D) plane or a one-dimensional (1D) line, the 2D plane or 1D line representing at least a portion of the audio object.

[0138] B4. The apparatus of embodiment B3, wherein the storage unit (1008) comprises a memory (1042) storing instructions for configuring the apparatus to perform the method of any one of embodiments A1 to A19.

[0139] C1. A computer program (1043) comprising instructions that, when executed by a processing circuit (1002), cause the processing circuit to perform a method according to any one of embodiments A1 to A19.

[0140] C2. A carrier containing the computer program of embodiment C1, the carrier being one of an electronic signal, an optical signal, a radio signal, or a computer-readable storage medium (1042).

[0141] Although various embodiments have been described herein, it should be understood that the embodiments are presented by way of example only, not limitation. Thus, the breadth and scope of the present disclosure should not be limited by any of the exemplary embodiments described above. Moreover, unless otherwise indicated herein or clearly contradicted by context, any combination of the above-described objects in all possible variations thereof is encompassed by the present disclosure.

[0142] Additionally, while the processes described above and illustrated in the Figures have been shown as a sequence of steps, this has been done for purposes of illustration only, and it is therefore contemplated that some steps may be added, some steps may be omitted, the order of the steps may be rearranged, and some steps may be performed in parallel.

[0143] References

[0144] [1]MPEG-H 3D Audio,Clause 8.4.4.7:“Spreading”

[0145] [2]MPEG-H 3D Audio,Clause 18.1:“Element Metadata Preprocessing”

[0146] [3]MPEG-H 3D Audio,Clause 18.11:“Diffuseness Rendering”

[0147] [4]EBU ADM Renderer Tech 3388,Clause 7.3.6:“Divergence”

[0148] [5]EBU ADM Renderer Tech 3388,Clause 7.4:“Decorrelation Filters”

[0149] [6]EBU ADM Renderer Tech 3388,Clause 7.3.7:“Extent Panner”

[0150] [7]Efficient HRTF-based Spatial Audio for Area and Volumetric Sources“, IEEE Transactions on Visualization and Computer Graphics 22(4):1-1 January 2016

[0151] [8] "Surface Simplification Using Quadric Error Metrics", ACM SIGGRAPH Computer Graphics, July 1997

[0152] [9] "Minimum volume bounding box decomposition for shape approximation in robot grasping", 2008 IEEE International Conference on Robotics and Automation.

Claims

1. 1. A method (900) for representing an audio object relative to a listening position of a listener in an extended reality scene, the method comprising: Obtaining (s902) first metadata describing a first three-dimensional (3D) shape associated with the audio object; and transforming (s904) the obtained first metadata to produce transformed metadata describing a two-dimensional (2D) plane or a one-dimensional (1D) line; the 2D plane or the 1D line represents at least a portion of the audio object; Method (900).

2. obtaining the first metadata includes selecting the first metadata from a set of metadata comprising the first metadata and second metadata describing a second 3D shape associated with the audio object. The method of claim 1.

3. The second 3D shape is: a mesh structure having fewer vertices than the first 3D shape described by the first metadata; Box shape, spherical shape, Ellipsoidal shape, Cylindrical The method of claim 2, wherein the method is in one of the following forms:

4. The method of claim 2 or 3, wherein the set of metadata further comprises third metadata describing a single point in the extended reality scene.

5. The selection, a distance between the audio object in the extended reality scene and the listening position of the listener and at least one threshold distance parameter; the size of the audio object; the number of currently active audio objects in the extended reality scene; the current load of the renderer that will be used to render said audio object, or The current audio energy level of the audio object The method according to any one of claims 2 to 4, based on one or more of:

6. Transforming the obtained first metadata to produce the transformed metadata includes: determining a set of description points, said set of description points comprising an anchor point; determining the 2D plane or the 1D line using the description points, the 2D plane or the 1D line passing through the anchor points; The method of any one of claims 1 to 5, comprising:

7. The method of claim 6 , wherein the anchor point is a point on a surface of the first 3D shape that is closest to the listening position of the listener in the extended reality scene.

8. The method of claim 6 , wherein the anchor points are a spatial average of points on or within the first 3D shape.

9. a portion of the shape is visible to the listener in the extended reality scene; the anchor point is the center of gravity of the portion of the shape that is visible to the listener; The method according to claim 6.

10. Said set of description points: a first point on the first 3D shape representing a first edge of the first 3D shape relative to the listening position of the listener; a second point on the first 3D shape representing a second edge of the first 3D shape relative to the listening position of the listener; and The method of any one of claims 6 to 9, further comprising:

11. determining the first point on the first 3D shape such that the first point has the largest azimuth angle with respect to a reference direction; determining a second point on the first 3D shape such that the second point has a smallest azimuth angle with respect to the reference orientation; Further comprising: The method of claim 10 , wherein the reference direction is a line connecting the listening position of the listener and the anchor point.

12. The method of claim 10 or 11, further comprising determining a first dimension of the 2D plane or the 1D line based on the first point and the second point.

13. The method of claim 10 , further comprising determining a horizontal angle of the 2D plane or the 1D line based on the first point and the second point.

14. Said set of description points: a third point on the first 3D shape representing a third edge of the first 3D shape relative to the listening position of the listener; and a fourth point on the first 3D shape representing a fourth edge of the first 3D shape relative to the listening position; and 14. The method of claim 6, further comprising:

15. determining a third point on the first 3D shape such that the third point has the largest elevation angle relative to a reference orientation; determining a fourth point on the first 3D shape such that the fourth point has a smallest elevation angle with respect to the reference orientation; Further comprising: The method of claim 14 , wherein the reference direction is a line connecting the listening position of the listener and the anchor point.

16. The method of claim 14 or 15, further comprising determining a second dimension of the 2D plane or the 1D line based on the third point and the fourth point.

17. 17. The method of claim 14, further comprising determining an angle of the 2D plane or the 1D line based on the third point and the fourth point.

18. 18. A method according to any one of claims 6 to 17, wherein the position of at least one description point is smoothed using a technique in which the magnitude of the position change between two time instances is limited to be at most proportional to the magnitude of the change in the relative distance between the audio object and the listener between the same two time instances.

19. 20. The method of claim 18, wherein rotational changes in extent of the audio object are taken into account by calculating an expected position change of the anchor point, and the position change of a description point is limited to be at most proportional to the sum of the magnitude of the expected position change of the anchor point and the magnitude of the change in relative position between the audio object and the listener.

20. the audio object is represented by a multi-channel audio signal; the method further comprising: rendering the multi-channel audio signal using the converted metadata.

20. The method according to any one of claims 1 to 19.

21. The method of claim 20, wherein the multi-channel audio signal is rendered using a virtual source representing the 2D plane or the edges of the 1D lines.

22. 22. The method of claim 20 or 21, wherein the multi-channel audio signal is rendered using a virtual sound source having an associated head-related transfer function (HRTF) that represents a sub-area of ​​the 2D plane or the 1D line.

23. An apparatus (1000) for representing an audio object in an extended reality scene, the apparatus comprising: Obtaining (s902) first metadata describing a first three-dimensional (3D) shape associated with the audio object; Transforming (s904) the obtained first metadata to produce transformed metadata describing a two-dimensional (2D) plane or a one-dimensional (1D) line; It is set to do the 2D plane or the 1D line represents at least a portion of the audio object; Equipment (1000).

24. 24. Apparatus according to claim 23, wherein the apparatus is further configured to carry out a method according to any one of claims 2 to 22.

25. An apparatus (1000) for representing an audio object in an extended reality scene, the apparatus comprising: A storage unit (1008); A processing circuit (1002) coupled to the storage unit; The apparatus comprises: Obtaining (s902) first metadata describing a first three-dimensional (3D) shape associated with the audio object; Transforming (s904) the obtained first metadata to produce transformed metadata describing a two-dimensional (2D) plane or a one-dimensional (1D) line; It is set to do the 2D plane or the 1D line represents at least a portion of the audio object; Equipment (1000).

26. 26. The apparatus of claim 25, wherein the storage unit (1008) comprises a memory (1042) for storing instructions for configuring the apparatus to perform the method of any one of claims 2 to 22.

27. A computer program (1043) comprising instructions which, when executed by a processing circuit (1002), cause said processing circuit to perform a method according to any one of claims 1 to 22.

28. 28. A computer readable storage medium (1042) containing the computer program of claim 27.

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