Latent Audio Tracking

Abstract

A system and method for presenting mixed reality audio is disclosed. In an exemplary method, audio is presented to a user of a wearable head device. A first position of the user's head at a first time is determined based on one or more sensors of the wearable head device. A second position of the user's head at a second time, after the first time, is determined based on the one or more sensors. An audio signal is determined based on a difference between the first position and the second position. The audio signal is presented to the user via a speaker of the wearable head device. Determining the audio signal includes determining an origin of the audio signal within the virtual environment. Presenting the audio signal to the user includes presenting the audio signal as if it originates from the determined origin.

Description

[Technical field]

[0001] (CROSS REFERENCE TO RELATED APPLICATIONS) This application claims the benefit of U.S. Provisional Application No. 62 / 976,986, filed February 14, 2020, the contents of which are incorporated herein by reference in their entirety.

[0002] TECHNICAL FIELD This disclosure relates generally to systems and methods for presenting audio to a user, and more particularly to systems and methods for presenting audio to a user within a mixed reality environment. [Background technology]

[0003] Virtual environments are ubiquitous in computing environments, finding use in video games (where a virtual environment may represent a game world), maps (where a virtual environment may represent a terrain to be navigated), simulations (where a virtual environment may simulate a real environment), digital storytelling (where virtual characters may interact with one another within a virtual environment), and many other applications. Modern computer users are generally comfortable perceiving and interacting with virtual environments. However, a user's experience with a virtual environment may be limited by the technology for presenting the virtual environment. For example, conventional displays (e.g., 2D display screens) and audio systems (e.g., fixed speakers) may be incapable of realizing a virtual environment in a way that creates a compelling, realistic, and immersive experience.

[0004] Virtual reality ("VR"), augmented reality ("AR"), mixed reality ("MR"), and related technologies (collectively, "XR") share the ability to present to a user of an XR system sensory information corresponding to a virtual environment represented by data in a computer system. Such systems can provide a uniquely increased sense of immersion and realism by combining virtual visual and audio cues with real sights and sounds. It may therefore be desirable to present digital sounds to a user of an XR system so that the sounds seem to occur naturally and are consistent with the user's expectations of sounds in the user's real environment. Generally, users expect that virtual sounds will take on the acoustic properties of the real environment in which they hear them. For example, a user of an XR system in a large concert hall would expect the virtual sounds of the XR system to have a cavernous sonic quality, and conversely, a user in a small apartment would expect the sounds to be more attenuated, close, and immediate. In addition to matching the acoustic properties of the virtual sounds with the real and / or virtual environment, realism is further enhanced by spatializing the virtual sounds. For example, a virtual object may visually fly over the user from behind, and the user may expect corresponding virtual sounds to similarly reflect the spatial movement of the virtual object relative to the user.

[0005] Existing technologies often miss these expectations, such as by presenting virtual audio that does not take into account the user's surroundings and does not accommodate the spatial movement of virtual objects, leading to a sense of inauthenticity that can detract from the user experience. Observations of users of XR systems indicate that while users can be relatively tolerant of visual inconsistencies between virtual content and the real environment (e.g., inconsistencies in lighting), they can be more sensitive to auditory inconsistencies. Our unique auditory experiences, continually refined throughout our lives, can make us acutely aware of how our physical environment affects the sounds we hear, and we can be highly sensitive to sounds that do not match those expectations. In XR systems, such inconsistencies can be uncomfortable, turning an immersive and engaging experience into a gimmicky imitation. In extreme examples, auditory inconsistencies can cause motion sickness and other adverse effects due to the inability of the inner ear to reconcile an auditory stimulus with its corresponding visual cue.

[0006] Due to our sensitivity to audio perception, an immersive audio experience may be equally, if not more important than an immersive visual experience. Due to the different sensing and computing power available to XR systems, XR systems may be positioned to provide a much more immersive audio experience than traditional audio systems, which may spatialize sound by splitting it into one or more channels. For example, stereo headphones may present audio to the user using left and right channels, giving the appearance of sounds originating from different directions. Some stereo headphones may simulate additional channels (such as 5.1 channels), further enhancing audio spatialization. However, traditional systems may suffer from the fact that spatialized sound locations are static relative to the user. For example, a guitar sound that may be presented to the user as originating 5 feet from the user's left ear may not dynamically change relative to the user as the user rotates his or her head. Such static behavior may not reflect the audio behavior in a "real" environment. A person listening to a live orchestra may experience slight changes in their audio experience based on, for example, small head movements. These small acoustic behaviors can accumulate and add to an immersive audio experience. It is therefore desirable to develop audio systems and methods for XR systems to enhance the audio experience of the user.

[0007] By taking into account the characteristics of the user's physical environment, the systems and methods described herein can simulate what the user would hear as if the virtual sounds were real sounds naturally generated in that environment. By presenting virtual sounds in a manner faithful to the way sounds behave in the real world, the user may experience an increased sense of connection with the mixed reality environment. Similarly, by presenting location-aware virtual content that responds to the user's movements and environment, the content becomes more subjective, interactive, and realistic; for example, a user's experience at point A may be entirely different from his or her experience at point B. This enhanced realism and interaction can provide the foundation for new applications of mixed reality, such as those that use spatially aware audio to enable novel forms of gameplay, social features, or interactive behaviors. Summary of the Invention [Means for solving the problem]

[0008] An embodiment of the present disclosure describes a system and method for presenting mixed reality audio. According to an embodiment of the present disclosure, audio is presented to a user of a wearable head device. A first position of the user's head at a first time is determined based on one or more sensors of the wearable head device. A second position of the user's head at a second time, later than the first time, is determined based on the one or more sensors. An audio signal is determined based on a difference between the first position and the second position. The audio signal is presented to the user via a speaker of the wearable head device. Determining the audio signal includes determining an origin of the audio signal within the virtual environment. Presenting the audio signal to the user includes presenting the audio signal as if originating from the determined origin. Determining the origin of the audio signal includes applying an offset to the position of the user's head. The present invention provides, for example, the following: (Item 1) 1. A system comprising: a wearable head device having a speaker and one or more sensors; One or more processors, determining a first position of a user's head at a first time based on the one or more sensors; determining a second position of the user's head at a second time, after the first time, based on the one or more sensors; and determining an audio signal based on a difference between the first position and the second position; presenting the audio signal to the user via the speaker; one or more processors configured to perform a method including: Equipped with determining the audio signal includes determining an origin of the audio signal within a virtual environment; presenting the audio signal to the user includes presenting the audio signal as if originating from the determined origin; The system, wherein determining an origin of the audio signal includes applying an offset to a position of the user's head. (Item 2) 2. The system of claim 1, wherein determining the origin of the audio signal further comprises determining the origin of the audio signal based on a rate of change of a position of the user's head. (Item 3) Determining an origin of the audio signal further comprises: determining that the origin comprises a first origin in accordance with determining that the rate of change exceeds a threshold; determining, in response to the determination that the rate of change does not exceed the threshold, that the origin comprises a second origin different from the first origin; 3. The system according to item 2, comprising: (Item 4) Determining an origin of the audio signal further comprises: determining that the origin comprises a first origin in accordance with determining that the magnitude of the offset is below a threshold; and determining, in response to determining that the magnitude of the offset is not less than the threshold, that the origin comprises a second origin different from the first origin; 2. The system according to item 1, comprising: (Item 5) determining the audio signal further includes determining a velocity within the virtual environment; presenting the audio signal to the user further includes presenting the audio signal as if the origin were moving at the determined velocity. Item 1. The system according to item 1. (Item 6) 6. The system of claim 5, wherein determining the velocity includes determining the velocity based on a difference between a first position of the user's head and a second position of the user's head. (Item 7) 2. The system of claim 1, wherein the offset is determined based on a first position of the user's head. (Item 8) 1. A method for presenting audio to a user of a wearable head device, comprising: determining a first position of the user's head at a first time based on one or more sensors of the wearable head device; determining a second position of the user's head at a second time, after the first time, based on the one or more sensors; and determining an audio signal based on a difference between the first position and the second position; presenting the audio signal to the user via a speaker of the wearable head device; Including, determining the audio signal includes determining an origin of the audio signal within a virtual environment; presenting the audio signal to the user includes presenting the audio signal as if originating from the determined origin; A method, wherein determining an origin of the audio signal includes applying an offset to a position of the user's head. (Item 9) 9. The method of claim 8, wherein determining an origin of the audio signal further comprises determining an origin of the audio signal based on a rate of change of a position of the user's head. (Item 10) Determining an origin of the audio signal further comprises: determining that the origin comprises a first origin in accordance with determining that the rate of change exceeds a threshold; determining, in response to the determination that the rate of change does not exceed the threshold, that the origin comprises a second origin different from the first origin; Item 10. The method according to item 9, comprising: (Item 11) Determining an origin of the audio signal further comprises: determining that the origin comprises a first origin in accordance with determining that the magnitude of the offset is below a threshold; and determining, in response to determining that the magnitude of the offset is not less than the threshold, that the origin comprises a second origin different from the first origin; The method according to item 8, comprising: (Item 12) determining the audio signal further includes determining a velocity within the virtual environment; presenting the audio signal to the user further includes presenting the audio signal as if the origin were moving at the determined velocity. The method according to item 8. (Item 13) Item 13. The method of item 12, wherein determining the velocity includes determining the velocity based on a difference between a first position of the user's head and a second position of the user's head. (Item 14) 9. The method of claim 8, wherein the offset is determined based on a first position of the user's head. (Item 15) 1. A non-transitory computer readable medium having instructions stored thereon that, when executed by one or more processors, cause the one or more processors to perform a method of presenting audio to a user of a wearable head device, the method comprising: determining a first position of the user's head at a first time based on one or more sensors of the wearable head device; determining a second position of the user's head at a second time, after the first time, based on the one or more sensors; and determining an audio signal based on a difference between the first position and the second position; presenting the audio signal to the user via a speaker of the wearable head device; Including, determining the audio signal includes determining an origin of the audio signal within a virtual environment; presenting the audio signal to the user includes presenting the audio signal as if originating from the determined origin; determining an origin of the audio signal includes applying an offset to a position of the user's head. Non-transitory computer readable medium. (Item 16) Item 16. The non-transitory computer-readable medium of item 15, wherein determining an origin of the audio signal further comprises determining an origin of the audio signal based on a rate of change of a position of the user's head. (Item 17) Determining an origin of the audio signal further comprises: determining that the origin comprises a first origin in accordance with determining that the rate of change exceeds a threshold; determining, in response to the determination that the rate of change does not exceed the threshold, that the origin comprises a second origin different from the first origin; 17. The non-transitory computer-readable medium of item 16, comprising: (Item 18) Determining an origin of the audio signal further comprises: determining that the origin comprises a first origin in accordance with determining that the magnitude of the offset is below a threshold; and determining, in response to determining that the magnitude of the offset is not less than the threshold, that the origin comprises a second origin different from the first origin; Item 16. The non-transitory computer-readable medium of item 15, comprising: (Item 19) determining the audio signal further includes determining a velocity within the virtual environment; presenting the audio signal to the user further includes presenting the audio signal as if the origin were moving at the determined velocity. Item 16. The non-transitory computer-readable medium of item 15. (Item 20) 20. The non-transitory computer-readable medium of claim 19, wherein determining the velocity includes determining the velocity based on a difference between a first position of the user's head and a second position of the user's head. [Brief description of the drawings]

[0009] [Figure 1A] 1A-1C illustrate an example mixed reality environment, according to some embodiments. [Figure 1B] 1A-1C illustrate an example mixed reality environment, according to some embodiments. [Figure 1C] 1A-1C illustrate an example mixed reality environment, according to some embodiments.

[0010] [Figure 2A] 2A-2D illustrate components of an example mixed reality system that can be used to generate and interact with a mixed reality environment, according to some embodiments. [Figure 2B] 2A-2D illustrate components of an example mixed reality system that can be used to generate and interact with a mixed reality environment, according to some embodiments. [Figure 2C] 2A-2D illustrate components of an example mixed reality system that can be used to generate and interact with a mixed reality environment, according to some embodiments. [Figure 2D]2A-2D illustrate components of an example mixed reality system that can be used to generate and interact with a mixed reality environment, according to some embodiments.

[0011] [Figure 3A] FIG. 3A illustrates an example mixed reality handheld controller that can be used to provide input to a mixed reality environment, according to some embodiments.

[0012] [Figure 3B] FIG. 3B illustrates an example auxiliary unit that may be used with an example mixed reality system, according to some embodiments.

[0013] [Figure 4] FIG. 4 illustrates an example functional block diagram for an example mixed reality system, according to some embodiments.

[0014] [Diagram 5] FIG. 5 illustrates an example of mixed reality spatialized audio, according to some embodiments.

[0015] [Figure 6A] 6A-6C illustrate examples of mixed reality spatialized audio, according to some embodiments. [Figure 6B] 6A-6C illustrate examples of mixed reality spatialized audio, according to some embodiments. [Figure 6C] 6A-6C illustrate examples of mixed reality spatialized audio, according to some embodiments. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Detailed Description In the following description of the embodiments, reference is made to the accompanying drawings which form a part hereof, and in which is shown, by way of illustration, specific embodiments which may be practiced. It is to be understood that other embodiments may be used and structural changes may be made without departing from the scope of the disclosed embodiments.

[0017] Mixed Reality Environment

[0018] Like all people, users of a mixed reality system exist in a real environment, i.e., the three-dimensional portion of the "real world" and all of its content are perceivable by the user. For example, the user perceives the real environment using normal human senses, i.e., sight, hearing, touch, taste, and smell, and interacts with the real environment by moving his or her body within the real environment. Locations within the real environment can be described as coordinates in a coordinate space. For example, coordinates can include latitude, longitude, and altitude relative to sea level, distance in three orthogonal dimensions from a reference point, or other suitable values. Similarly, a vector can describe a quantity, having a direction and magnitude in a coordinate space.

[0019] A computing device may maintain a representation of a virtual environment, for example, in a memory associated with the device. As used herein, a virtual environment is a computed representation of a three-dimensional space. A virtual environment may include representations of any objects, actions, signals, parameters, coordinates, vectors, or other properties associated with that space. In some examples, a circuit (e.g., a processor) of a computing device may maintain and update a state of the virtual environment. That is, the processor may determine a state of the virtual environment at a second time t1 based on data associated with the virtual environment and / or input provided by a user at a first time t0. For example, if an object in the virtual environment is located at a first coordinate at time t0 and has certain programmed physical parameters (e.g., mass, coefficient of friction), and input received from a user indicates that a force should be applied to the object in a certain directional vector, the processor may apply the laws of kinematics and use basic mechanics to determine the location of the object at time t1. The processor may use any suitable information known about the virtual environment and / or any suitable input to determine the state of the virtual environment at time t1. In maintaining and updating the state of the virtual environment, the processor may execute any suitable software, including software related to creating and deleting virtual objects in the virtual environment, software (e.g., scripts) for defining behavior of virtual objects or characters in the virtual environment, software for defining behavior of signals (e.g., audio signals) in the virtual environment, software for creating and updating parameters associated with the virtual environment, software for generating audio signals in the virtual environment, software for handling inputs and outputs, software for implementing network operations, software for applying asset data (e.g., animation data for moving a virtual object over time), or many other possibilities.

[0020] An output device, such as a display or speaker, can present any or all aspects of the virtual environment to the user. For example, the virtual environment may include virtual objects (which may include representations of inanimate objects, people, animals, lights, etc.) that may be presented to the user. The processor can determine a view of the virtual environment (e.g., corresponding to a "camera," with its origin coordinates, viewing axis, and frustum) and render on the display a viewable scene of the virtual environment corresponding to that view. Any suitable rendering technique may be used for this purpose. In some examples, the viewable scene may include only some virtual objects in the virtual environment and exclude certain other virtual objects. Similarly, the virtual environment may include audio aspects that may be presented to the user as one or more audio signals. For example, a virtual object in the virtual environment may generate a sound originating from the object's location coordinates (e.g., a virtual character may speak or create a sound effect), or the virtual environment may be associated with a musical cue or ambient sound that may or may not be associated with a particular location. The processor can determine audio signals corresponding to "listener" coordinates, e.g., audio signals corresponding to the synthesis of sounds in the virtual environment and that are mixed and processed to simulate the audio signals that would be heard by a listener at the listener coordinates, and present the audio signals to the user via one or more speakers.

[0021] Because the virtual environment exists only as a computational structure, the user cannot directly perceive the virtual environment using normal senses. Instead, the user can only indirectly perceive the virtual environment, as presented to the user, for example, by a display, a speaker, a tactile output device, etc. Similarly, the user cannot directly touch, manipulate, or otherwise interact with the virtual environment, but can provide input data via input devices or sensors to a processor, which can use the device or sensor data to update the virtual environment. For example, a camera sensor can provide optical data indicating that the user is attempting to move an object in the virtual environment, and the processor can use that data to cause the object to respond appropriately within the virtual environment.

[0022] A mixed reality system can present a user with a mixed reality environment ("MRE") that combines aspects of real and virtual environments, for example, using a see-through display and / or one or more speakers (which may be incorporated, for example, into a wearable head device). In some embodiments, the one or more speakers may be external to the head-mounted wearable unit. As used herein, an MRE is a simultaneous representation of a real environment and a corresponding virtual environment. In some examples, the corresponding real and virtual environments share a single coordinate space. In some examples, the real coordinate space and the corresponding virtual coordinate space are related to each other by a transformation matrix (or other suitable representation). Thus, a single coordinate (in some examples, together with the transformation matrix) may define a first location in the real environment and also a second corresponding location in the virtual environment, and vice versa.

[0023] In an MRE, a virtual object (e.g., in a virtual environment associated with the MRE) may correspond to a real object (e.g., in a real environment associated with the MRE). For example, if the real environment of the MRE includes a real lamppost (a real object) at a location coordinate, the virtual environment of the MRE may include a virtual lamppost (a virtual object) at a corresponding location coordinate. As used herein, a real object combines with its corresponding virtual object to comprise a "mixed reality object." It is not necessary for a virtual object to perfectly match or match a corresponding real object. In some examples, a virtual object may be a simplified version of a corresponding real object. For example, if the real environment includes a real lamppost, the corresponding virtual object may include a cylinder of approximately the same height and radius as the real lamppost (reflecting that a lamppost may be approximately cylindrical in shape). Simplifying virtual objects in this manner may enable computational efficiencies and simplify calculations to be performed on such virtual objects. Furthermore, in some examples of an MRE, not all real objects in the real environment may be associated with a corresponding virtual object. Similarly, in some embodiments of the MRE, not all virtual objects in the virtual environment may be associated with corresponding real objects, i.e., some virtual objects may exist solely within the virtual environment of the MRE without any real-world counterpart.

[0024] In some embodiments, virtual objects may have characteristics that differ, sometimes significantly, from those of the corresponding real object. For example, a real environment in an MRE may contain a green, two-pronged cactus, a thorny inanimate object, while the corresponding virtual object in the MRE may have the characteristics of a green, two-armed virtual character with human facial features and a surly attitude. In this embodiment, the virtual object resembles its corresponding real object in some characteristics (color, number of arms) but differs from the real object in other characteristics (facial features, personality). In this way, virtual objects have the potential to represent real objects in creative, abstract, exaggerated, or fictitious ways, or to impart behaviors (e.g., human personality) to otherwise inanimate real objects. In some embodiments, virtual objects may be purely fictitious creations with no real-world counterpart (e.g., virtual monsters in a virtual environment, perhaps in a location that corresponds to a void in the real environment).

[0025] Compared to a VR system that presents a virtual environment to a user while obscuring the real environment, a mixed reality system that presents an MRE offers the advantage that the real environment remains perceptible while the virtual environment is presented. Thus, a user of a mixed reality system can experience and interact with a corresponding virtual environment using visual and audio cues associated with the real environment. As an example, a user of a VR system may struggle to perceive or interact with a virtual object displayed in the virtual environment because the user cannot directly perceive or interact with the virtual environment, as described above, whereas a user of an MR system may find it intuitive and natural to interact with a virtual object by seeing, hearing, and touching the corresponding real object in his or her own real environment. This level of interaction may enhance the user's sense of immersion, connection, and engagement with the virtual environment. Similarly, by presenting a real environment and a virtual environment simultaneously, a mixed reality system may reduce the negative psychological sensations (e.g., cognitive dissonance) and negative physical sensations (e.g., motion sickness) associated with a VR system. Mixed reality systems also offer many possibilities for applications that can augment or modify our experience of the real world.

[0026] 1A illustrates an exemplary real environment 100 in which a user 110 uses a mixed reality system 112. The mixed reality system 112 may include a display (e.g., a see-through display) and one or more speakers, and one or more sensors (e.g., cameras), for example, as described below. The illustrated real environment 100 includes a rectangular room 104A in which the user 110 is standing, and real objects 122A (lamp), 124A (table), 126A (sofa), and 128A (painting). The room 104A further includes a location coordinate 106, which may be considered as the origin of the real environment 100. As shown in FIG. 1A, an environment / world coordinate system 108 (with an x-axis 108X, a y-axis 108Y, and a z-axis 108Z), with its origin at point 106 (world coordinates), may define a coordinate space for the real environment 100. In some embodiments, the origin 106 of the environment / world coordinate system 108 may correspond to where the mixed reality system 112 was powered on. In some embodiments, the origin 106 of the environment / world coordinate system 108 may be reset during operation. In some examples, the user 110 may be considered a real object in the real environment 100. Similarly, the body parts (e.g., hands, feet) of the user 110 may be considered real objects in the real environment 100. In some examples, the user / listener / head coordinate system 114 (comprising an x-axis 114X, a y-axis 114Y, and a z-axis 114Z) with its origin at point 115 (e.g., user / listener / head coordinate) may define a coordinate space for the user / listener / head on which the mixed reality system 112 is located. The origin 115 of the user / listener / head coordinate system 114 may be defined relative to one or more components of the mixed reality system 112. For example, the origin 115 of the user / listener / head coordinate system 114 may be defined relative to the display of the mixed reality system 112, such as during an initial calibration of the mixed reality system 112. Matrices (which may include translation matrices and quaternion or other rotation matrices) or other suitable representations can characterize the transformation between the user / listener / head coordinate system 114 space and the environment / world coordinate system 108 space.In some embodiments, the left ear coordinates 116 and right ear coordinates 117 may be defined relative to the origin 115 of the user / listener / head coordinate system 114. Matrices (which may include translation matrices and quaternion matrices or other rotation matrices) or other suitable representations can characterize the transformation between the left ear coordinates 116 and right ear coordinates 117 and the user / listener / head coordinate system 114 space. The user / listener / head coordinate system 114 can simplify the representation of location relative to the user's head or head-mounted device, e.g., relative to the environment / world coordinate system 108. Using simultaneous localization and mapping (SLAM), visual odometry, or other techniques, the transformation between the user coordinate system 114 and the environment coordinate system 108 can be determined and updated in real time.

[0027] 1B illustrates an exemplary virtual environment 130 that corresponds to the real environment 100. The virtual environment 130 shown includes a virtual rectangular room 104B that corresponds to the real rectangular room 104A, a virtual object 122B that corresponds to the real object 122A, a virtual object 124B that corresponds to the real object 124A, and a virtual object 126B that corresponds to the real object 126A. Metadata associated with the virtual objects 122B, 124B, 126B may include information derived from the corresponding real objects 122A, 124A, 126A. The virtual environment 130 additionally includes a virtual monster 132, which does not correspond to any real object in the real environment 100. A real object 128A in the real environment 100 does not correspond to any virtual object in the virtual environment 130. A persistent coordinate system 133 (with x-axis 133X, y-axis 133Y, and z-axis 133Z) with its origin at point 134 (persistent coordinate) may define a coordinate space for the virtual content. The origin 134 of the persistent coordinate system 133 may be defined relative to / with respect to one or more real objects, such as real object 126A. A matrix (which may include a translation matrix and a quaternion matrix or other rotation matrix) or other suitable representation may characterize the transformation between the persistent coordinate system 133 space and the environment / world coordinate system 108 space. In some embodiments, virtual objects 122B, 124B, 126B, and 132 may each have its own persistent coordinate point relative to the origin 134 of the persistent coordinate system 133. In some embodiments, there may be multiple persistent coordinate systems, and virtual objects 122B, 124B, 126B, and 132 may each have its own persistent coordinate point relative to one or more persistent coordinate systems.

[0028] 1A and 1B, the environment / world coordinate system 108 defines a shared coordinate space for both the real environment 100 and the virtual environment 130. In the illustrated embodiment, the coordinate space has its origin at point 106. Furthermore, the coordinate space is defined by the same three orthogonal axes (108X, 108Y, 108Z). Thus, a first location in the real environment 100 and a second corresponding location in the virtual environment 130 can be described with respect to the same coordinate space. This simplifies identifying and displaying corresponding locations in the real and virtual environments because the same coordinates can be used to identify both locations. However, in some embodiments, the corresponding real and virtual environments need not use a shared coordinate space. For example, in some embodiments (not shown), matrices (which may include translation matrices and quaternion matrices or other rotation matrices) or other suitable representations can characterize the transformation between the real environment coordinate space and the virtual environment coordinate space.

[0029] 1C illustrates an exemplary MRE 150 that simultaneously presents aspects of real environment 100 and virtual environment 130 to user 110 via mixed reality system 112. In the example shown, MRE 150 simultaneously presents to user 110 real objects 122A, 124A, 126A, and 128A from real environment 100 (e.g., via a transparent portion of a display of mixed reality system 112) and virtual objects 122B, 124B, 126B, and 132 from virtual environment 130 (e.g., via an active display portion of a display of mixed reality system 112). As described above, origin 106 acts as the origin for a coordinate space corresponding to MRE 150, and coordinate system 108 defines the x-, y-, and z-axes for the coordinate space.

[0030] In the illustrated example, the mixed reality objects include corresponding pairs of real and virtual objects (i.e., 122A / 122B, 124A / 124B, 126A / 126B) that occupy corresponding locations in coordinate space 108. In some examples, both real and virtual objects may be visible to user 110 at the same time. This may be desirable in instances where, for example, a virtual object presents information designed to augment the view of the corresponding real object (such as in a museum application where a virtual object presents a missing portion of an ancient damaged statue). In some examples, the virtual objects (122B, 124B, and / or 126B) may be displayed so as to occlude the corresponding real objects (122A, 124A, and / or 126A) (e.g., via active pixelated occlusion using a pixelated occlusion shutter). This may be desirable, for example, in instances where a virtual object acts as a visual replacement for a corresponding real object (such as in interactive storytelling applications where inanimate real objects become "living" characters).

[0031] In some examples, real objects (e.g., 122A, 124A, 126A) may be associated with virtual content or helper data that does not necessarily constitute a virtual object. The virtual content or helper data may facilitate processing or handling of the virtual object within a mixed reality environment. For example, such virtual content may include a two-dimensional representation of the corresponding real object, a custom asset type associated with the corresponding real object, or statistical data associated with the corresponding real object. This information may enable or facilitate calculations involving the real object without incurring unnecessary computational overhead.

[0032] In some embodiments, the presentation described above may also incorporate audio aspects. For example, in MRE 150, virtual monster 132 may be associated with one or more audio signals, such as footstep effects, that are generated as the monster walks around MRE 150. As described further below, a processor in mixed reality system 112 may calculate an audio signal corresponding to a mixed and processed combination of all such sounds within MRE 150 and present the audio signal to user 110 via one or more speakers included within mixed reality system 112 and / or one or more external speakers.

[0033] Exemplary Mixed Reality System

[0034] An exemplary mixed reality system 112 may include a wearable head device (e.g., a wearable augmented reality or mixed reality head device) with a display (which may include left and right see-through displays, which may be eyepiece displays, and associated components for coupling light from the displays to the user's eyes), left and right speakers (e.g., positioned adjacent the user's left and right ears, respectively), an inertial measurement unit (IMU) (e.g., mounted on a temple arm of the head device), a quadrature coil electromagnetic receiver (e.g., mounted on the left temple part), left and right cameras (e.g., depth (time of flight) cameras) oriented away from the user, and left and right eye cameras (e.g., for detecting the user's eye movements) oriented toward the user. However, the mixed reality system 112 may incorporate any suitable display technology and any suitable sensors (e.g., optical, infrared, acoustic, LIDAR, EOG, GPS, magnetic). In addition, the mixed reality system 112 may incorporate networking features (e.g., Wi-Fi capabilities) to communicate with other devices and systems, including other mixed reality systems. The mixed reality system 112 may further include a battery (which may be mounted in an auxiliary unit, such as a belt pack designed to be worn around the waist of the user), a processor, and a memory. The wearable head device of the mixed reality system 112 may include a tracking component, such as an IMU or other suitable sensor, configured to output a set of coordinates of the wearable head device relative to the user's environment. In some examples, the tracking component may provide input to the processor to implement simultaneous localization and mapping (SLAM) and / or visual odometry algorithms. In some examples, the mixed reality system 112 may also include an auxiliary unit 320, which may be a handheld controller 300 and / or a wearable belt pack, as described further below.

[0035] 2A-2D illustrate components of an example mixed reality system 200 (which may correspond to the mixed reality system 112) that may be used to present an MRE (which may correspond to the MRE 150) or other virtual environment to a user. FIG. 2A illustrates a perspective view of a wearable head device 2102 included in the example mixed reality system 200. FIG. 2B illustrates a top view of the wearable head device 2102 mounted on a user's head 2202. FIG. 2C illustrates a front view of the wearable head device 2102. FIG. 2D illustrates an edge view of an example eyepiece 2110 of the wearable head device 2102. As shown in FIGS. 2A-2C, the example wearable head device 2102 includes an example left eyepiece (e.g., a left transparent waveguide set eyepiece) 2108 and an example right eyepiece (e.g., a right transparent waveguide set eyepiece) 2110. Each eyepiece 2108 and 2110 can include a transmissive element through which the real environment is visible, and a display element for presenting a display (e.g., via image-wise modulated light) that is superimposed on the real environment. In some embodiments, such a display element can include a surface diffractive optical element for controlling the flow of image-wise modulated light. For example, the left eyepiece 2108 can include a left internal coupling grating set 2112, a left orthogonal pupil expansion (OPE) grating set 2120, and a left exit (output) pupil expansion (EPE) grating set 2122. Similarly, the right eyepiece 2110 can include a right internal coupling grating set 2118, a right OPE grating set 2114, and a right EPE grating set 2116. The image-wise modulated light can be transferred to the user's eye via the internal coupling gratings 2112 and 2118, the OPE 2114 and 2120, and the EPE 2116 and 2122. Each internal coupling grating set 2112, 2118 can be configured to deflect light towards its corresponding OPE grating set 2120, 2114. Each OPE grating set 2120, 2114 can be designed to progressively deflect light downward towards its associated EPE 2122, 2116, thereby extending the exit pupil formed horizontally.Each EPE 2122, 2116 can be configured to progressively redirect at least a portion of the light received from its corresponding OPE grating set 2120, 2114 outwardly to a user eyebox location (not shown), defined behind the eyepieces 2108, 2110, to vertically extend an exit pupil formed in the eyebox. Alternatively, instead of the internal coupling grating sets 2112 and 2118, the OPE grating sets 2114 and 2120, and the EPE grating sets 2116 and 2122, the eyepieces 2108 and 2110 can include gratings and / or other arrangements of refractive and reflective features to control the coupling of the image-wise modulated light into the user's eye.

[0036] In some embodiments, the wearable head device 2102 can include a left temple arm 2130 and a right temple arm 2132, with the left temple arm 2130 including a left speaker 2134 and the right temple arm 2132 including a right speaker 2136. A quadrature coil electromagnetic receiver 2138 can be located in the left temple piece or another suitable location in the wearable head unit 2102. An inertial measurement unit (IMU) 2140 can be located in the right temple arm 2132 or another suitable location in the wearable head device 2102. The wearable head device 2102 can also include a left depth (e.g., time-of-flight) camera 2142 and a right depth camera 2144. The depth cameras 2142, 2144 can be preferably oriented in different directions so that both cover a wider field of view.

[0037] 2A-2D, a left source 2124 of image-wise modulated light can be optically coupled into the left eyepiece 2108 through a left internal coupling grating set 2112, and a right source 2126 of image-wise modulated light can be optically coupled into the right eyepiece 2110 through a right internal coupling grating set 2118. The sources 2124, 2126 of image-wise modulated light can include, for example, a fiber optic scanner, a projector including an electronic light modulator such as a digital light processing (DLP) chip or a liquid crystal on silicon (LCoS) modulator, or an emissive display such as a micro light emitting diode (μLED) or micro organic light emitting diode (μOLED) panel that is coupled into the internal coupling grating sets 2112, 2118 using one or more lenses per side. The input coupling grating sets 2112, 2118 can deflect light from image-wise modulated light sources 2124, 2126 to angles above the critical angle for total internal reflection (TIR) ​​for the eyepieces 2108, 2110. The OPE grating sets 2114, 2120 progressively deflect the propagating light downwards by TIR towards the EPE grating sets 2116, 2122. The EPE grating sets 2116, 2122 progressively couple the light towards the user's face, including the pupils of the user's eyes.

[0038] In some examples, as shown in FIG. 2D , the left eyepiece 2108 and the right eyepiece 2110 each include multiple waveguides 2402. For example, each eyepiece 2108, 2110 can include multiple individual waveguides, each dedicated to a separate color channel (e.g., red, blue, and green). In some examples, each eyepiece 2108, 2110 can include multiple sets of such waveguides, each set configured to impart a different wavefront curvature to the emitted light. The wavefront curvature may be convex with respect to the user's eye, for example, to present a virtual object located at a distance in front of the user (e.g., a distance corresponding to the inverse of the wavefront curvature). In some examples, the EPE grating sets 2116, 2122 can include curved grating grooves to provide a convex wavefront curvature by modifying the Poynting vector of the light exiting across each EPE.

[0039] In some examples, stereoscopically accommodated left and right eye images can be presented to the user through light modulators 2124, 2126 and eyepieces 2108, 2110 for each image to create the perception that the displayed content is three-dimensional. The perceived realism of the presentation of three-dimensional virtual objects can be enhanced by selecting the waveguides (and thus the corresponding wavefront curvatures) such that the virtual objects are displayed at distances that approximate the distances shown by the stereoscopic left and right images. The technique can also reduce motion sickness suffered by some users, which can be caused by differences between the depth perception cues provided by the stereoscopic left and right eye images and the automatic accommodation (e.g., object distance-dependent focus) of the human eye.

[0040] FIG. 2D illustrates an edge view from the top of the right eyepiece 2110 of the exemplary wearable head device 2102. As shown in FIG. 2D, the plurality of waveguides 2402 can include a first subset 2404 of three waveguides and a second subset 2406 of three waveguides. The two subsets 2404, 2406 of waveguides can be distinguished by different EPE gratings that feature different grating line curvatures to impart different wavefront curvatures to the exiting light. Within each of the subsets 2404, 2406 of waveguides, each waveguide can be used to couple a different spectral channel (e.g., one of the red, green, and blue spectral channels) to the user's right eye 2206. (Although not shown in FIG. 2D, the structure of the left eyepiece 2108 is similar to that of the right eyepiece 2110.)

[0041] 3A illustrates an example handheld controller component 300 of a mixed reality system 200. In some examples, the handheld controller 300 includes a grip portion 346 and one or more buttons 350 disposed along a top surface 348. In some examples, the buttons 350 may be configured for use as an optical tracking target to track six degrees of freedom (6DOF) movement of the handheld controller 300, for example, in conjunction with a camera or other optical sensor (which may be mounted in a head unit (e.g., wearable head device 2102) of the mixed reality system 200). In some examples, the handheld controller 300 includes a tracking component (e.g., an IMU or other suitable sensor) for detecting a position or orientation, such as a position or orientation relative to the wearable head device 2102. In some examples, such a tracking component may be positioned in a handle of the handheld controller 300 and / or may be mechanically coupled to the handheld controller. The handheld controller 300 can be configured to provide one or more output signals corresponding to one or more of a button press state, or a position, orientation, and / or movement (e.g., via an IMU) of the handheld controller 300. Such output signals may be used as inputs to a processor of the mixed reality system 200. Such inputs may correspond to the position, orientation, and / or movement of the handheld controller (or, for that matter, the position, orientation, and / or movement of a user's hand holding the controller). Such inputs may also correspond to a user pressing a button 350.

[0042] 3B illustrates an example auxiliary unit 320 of the mixed reality system 200. The auxiliary unit 320 can include a battery for providing energy and operating the system 200, and can include a processor for executing programs and operating the system 200. As shown, the example auxiliary unit 320 includes a clip 2128 for attaching the auxiliary unit 320 to a user's belt, etc. It will be apparent that other form factors are also suitable for the auxiliary unit 320, including form factors that do not involve mounting the unit on a user's belt. In some embodiments, the auxiliary unit 320 is coupled to the wearable head device 2102 through a multi-tube cable, which may include, for example, electrical wires and optical fibers. A wireless connection between the auxiliary unit 320 and the wearable head device 2102 can also be used.

[0043] In some examples, the mixed reality system 200 can include one or more microphones to detect sounds and provide corresponding signals to the mixed reality system. In some examples, the microphones may be attached to or integrated with the wearable head device 2102 and configured to detect the user's voice. In some examples, the microphones may be attached to or integrated with the handheld controller 300 and / or the auxiliary unit 320. Such microphones may be configured to detect environmental sounds, ambient noise, the user's or a third party's voice, or other sounds.

[0044] FIG. 4 illustrates an example functional block diagram that may correspond to an example mixed reality system, such as the mixed reality system 200 described above (which may correspond to the mixed reality system 112 with respect to FIG. 1). As shown in FIG. 4, the example handheld controller 400B (which may correspond to the handheld controller 300 ("totem")) includes a totem / wearable head device six degree of freedom (6DOF) totem subsystem 404A, and the example wearable head device 400A (which may correspond to the wearable head device 2102) includes a totem / wearable head device 6DOF subsystem 404B. In an example, the 6DOF totem subsystem 404A and the 6DOF subsystem 404B cooperate to determine six coordinates (e.g., offsets in three translational directions and rotations along three axes) of the handheld controller 400B relative to the wearable head device 400A. The six degrees of freedom may be expressed relative to the coordinate system of the wearable head device 400A. The three translational offsets may be represented as X, Y, and Z offsets in such a coordinate system, a translation matrix, or some other representation. The rotational degrees of freedom may be represented as a sequence of yaw, pitch, and roll rotations, as a rotation matrix, as a quaternion, or some other representation. In some examples, the wearable head device 400A, one or more depth cameras 444 (and / or one or more non-depth cameras) included within the wearable head device 400A, and / or one or more optical targets (e.g., buttons 350 of handheld controller 400B as described above or dedicated optical targets included within handheld controller 400B) may be used for 6DOF tracking. In some examples, the handheld controller 400B may include a camera as described above, and the wearable head device 400A may include an optical target for optical tracking in conjunction with the camera. In some embodiments, the wearable head device 400A and the handheld controller 400B each include a set of three orthogonally oriented solenoids that are used to wirelessly transmit and receive three distinguishable signals.By measuring the relative magnitudes of the three distinguishable signals received in each of the coils used to receive, the 6DOF of the wearable head device 400A relative to the handheld controller 400B can be determined. Additionally, the 6DOF totem subsystem 404A can include an inertial measurement unit (IMU), which is useful for providing improved accuracy and / or more timely information regarding high speed movements of the handheld controller 400B.

[0045] In some examples, it may be necessary to transform coordinates from a local coordinate space (e.g., a coordinate space fixed relative to the wearable head device 400A) to an inertial coordinate space (e.g., a coordinate space fixed relative to the real environment), e.g., to compensate for movement of the wearable head device 400A relative to the coordinate system 108. For example, such a transformation may be necessary so that the display of the wearable head device 400A presents virtual objects in an expected position and orientation relative to the real environment (e.g., a virtual person sitting in a real chair facing forward, regardless of the position and orientation of the wearable head device), rather than in a fixed position and orientation on the display (e.g., the same position in the bottom right corner of the display), preserving the illusion that the virtual objects exist in the real environment (and do not appear unnaturally positioned in the real environment, e.g., as the wearable head device 400A shifts and rotates). In some examples, a compensation transformation between coordinate spaces can be determined by processing images from the depth camera 444 using SLAM and / or visual odometry procedures to determine a transformation of the wearable head device 400A relative to the coordinate system 108. In the example shown in FIG. 4, the depth camera 444 can be coupled to the SLAM / visual odometry block 406 and provide images to the block 406. The SLAM / visual odometry block 406 implementation can include a processor configured to process the images and then determine a position and orientation of the user's head, which can be used to identify a transformation between the head coordinate space and another coordinate space (e.g., an inertial coordinate space). Similarly, in some examples, an additional source of information regarding the user's head pose and location is obtained from the IMU 409. Information from the IMU 409 can be integrated with information from the SLAM / visual odometry block 406 to provide improved accuracy and / or more timely information regarding fast adjustments of the user's head pose and position.

[0046] In some examples, the depth camera 444 can provide 3D images to a hand gesture tracker 411, which can be implemented within a processor of the wearable head device 400A. The hand gesture tracker 411 can identify the user's hand gestures, for example, by matching the 3D images received from the depth camera 444 to stored patterns representing hand gestures. Other suitable techniques for identifying the user's hand gestures will also be apparent.

[0047] In some embodiments, one or more processors 416 may be configured to receive data from the 6DOF headgear subsystem 404B, the IMU 409, the SLAM / visual odometry block 406, the depth camera 444, and / or the hand gesture tracker 411 of the wearable head device. The processor 416 may also send and receive control signals to and from the 6DOF totem system 404A. The processor 416 may be wirelessly coupled to the 6DOF totem system 404A, such as in embodiments where the handheld controller 400B is not tethered. The processor 416 may further communicate with additional components, such as an audio / visual content memory 418, a graphical processing unit (GPU) 420, and / or a digital signal processor (DSP) audio spatializer 422. The DSP audio spatializer 422 may be coupled to a head-related transfer function (HRTF) memory 425. The GPU 420 may include a left channel output coupled to a left source of imagewise modulated light 424 and a right channel output coupled to a right source of imagewise modulated light 426. The GPU 420 may output stereoscopic image data to the imagewise modulated light sources 424, 426, for example, as described above with respect to FIGS. 2A-2D. The DSP audio spatializer 422 may output audio to the left speaker 412 and / or the right speaker 414. The DSP audio spatializer 422 may receive an input from the processor 419 indicating a direction vector from the user to a virtual sound source (e.g., which may be moved by the user via the handheld controller 320). Based on the direction vector, the DSP audio spatializer 422 may determine a corresponding HRTF (e.g., by accessing an HRTF or by interpolating multiple HRTFs). The DSP audio spatializer 422 may then apply the determined HRTF to an audio signal, such as an audio signal corresponding to a virtual sound generated by a virtual object.This can improve the believability and realism of virtual sounds by incorporating the user's relative position and orientation to the virtual sounds in the mixed reality environment, i.e., by presenting virtual sounds that match the user's expectations of what they would hear if the virtual sounds were real sounds in a real environment.

[0048] 4, one or more of the processor 416, GPU 420, DSP audio spatializer 422, HRTF memory 425, and audio / visual content memory 418 may be included in an auxiliary unit 400C (which may correspond to auxiliary unit 320 described above). The auxiliary unit 400C may include a battery 427 to power its components and / or provide power to the wearable head device 400A or handheld controller 400B. Including such components in an auxiliary unit, which may be mounted on the user's waist, can limit the size and weight of the wearable head device 400A, which in turn can reduce fatigue in the user's head and neck.

[0049] 4 presents elements corresponding to various components of an exemplary mixed reality system, various other suitable arrangements of these components will be apparent to those skilled in the art. For example, elements presented in FIG. 4 as being associated with the auxiliary unit 400C may instead be associated with the wearable head device 400A or the handheld controller 400B. Furthermore, some mixed reality systems may dispense with the handheld controller 400B or the auxiliary unit 400C entirely. Such variations and modifications should be understood as falling within the scope of the disclosed embodiments.

[0050] Latent Audio Tracking

[0051] The MR system may be well positioned to utilize sensing and / or computation to provide an immersive audio experience. In particular, the MR system may provide a unique way to spatialize sound and immerse the user in the MRE. The MR system may include speakers for presenting audio signals to the user, as described above with respect to speakers 412 and 414. The MR system may determine and play audio signals based on the virtual environment (e.g., the MRE). For example, the audio signal may adopt certain characteristics depending on the location in the virtual environment (e.g., the origin of the sound in the virtual environment) and the location of the user in the virtual environment. Similarly, the audio signal may adopt audio characteristics that simulate the effect of a sound traveling at a certain speed or with a certain orientation in the virtual environment. These characteristics may include placement in a stereo sound field. Some audio systems (e.g., headphones) split the soundtrack into one or more channels and present the audio as originating from different locations. For example, the headphones may utilize two channels, one channel for each ear of the user. If a soundtrack accompanies a virtual object moving across the screen (e.g., an airplane flying across the screen in a movie), an accompanying sound (e.g., engine noise) may be presented moving from the user's left to the user's right. Spatialized audio adds to the immersion of the virtual experience because the audio simulates how a person perceives real objects moving through the real world.

[0052] Some audio systems may suffer from limitations in their ability to provide immersive spatialized audio. For example, some headphone systems may present sounds in a stereo sound field by presenting left and right audio channels separately to the left and right ears of a user. However, without knowledge of the location (e.g., position and / or orientation) of the user's head, sounds may sound statically fixed in relation to the user's head. For example, a sound presented to the user's left ear through the left channel may continue to be presented to the user's left ear regardless of whether the user turns his or her head, moving forward, backward, sideways, etc. This static behavior may not be desirable for MR systems because it may not match the user's expectations of how sounds behave dynamically in a real environment. For example, in a real environment with a fixed location of a sound source, a listener would expect the sound emitted by the source and heard by the listener's left and right ears to be louder or quieter or to exhibit other dynamic audio characteristics (e.g., the Doppler effect) according to how the user moves and rotates relative to the location of the sound source. For example, if a static sound source is initially located on the user's left side, the sound emitted by that sound source may be predominant in the user's left ear compared to the user's right ear. However, if the user rotates 180 degrees so that the sound source is now located on the user's right side, the user would expect the sound to be predominant in the user's right ear. Similarly, while the user moves, the sound source may continually appear to change location relative to the user (e.g., slight position changes may result in slight, but perceptible changes in the volume detected at each ear). In a virtual or mixed reality environment, a user's sense of placement and immersion can be improved when sounds behave according to the user's expectations based on real-world audio experiences. In addition, users can utilize realistic audio cues to identify and place sound sources in the environment.

[0053] An MR system (e.g., MR system 112, 200) may improve the immersion of spatialized audio by adapting it to real-world audio behavior. For example, the MR system may utilize one or more cameras and / or one or more inertial measurement unit sensors of the MR system to perform SLAM calculations. Using SLAM techniques, the MR system may build a three-dimensional map of its surroundings and / or identify the location of the MR system within the surroundings. In some embodiments, the MR system may utilize SLAM to estimate head pose, which may include information about the position (e.g., location and / or orientation) of the user's head in three-dimensional space. In some embodiments, the MR system may utilize one or more coordinate frames to identify the location of objects and / or the MR system in an "absolute" sense (e.g., the location of a virtual object may be tied to a real location in the real environment instead of simply being anchored to the MR system or screen).

[0054] FIG. 5 illustrates an example of mixed reality spatialized audio, according to some embodiments. In some embodiments, the MR system may use SLAM techniques to place one or more virtual objects 504a and 504b in the MRE such that the virtual objects are fixed relative to the environment instead of being fixed relative to the user. In some embodiments, the virtual objects 504a and 504b may be configured to be sources of sound. The virtual objects 504a and / or 504b may be visible to the user 502 (e.g., as a virtual guitar) or the virtual objects 504a and / or 504b may not be visible to the user (e.g., as an invisible object from which sound emanates). Using SLAM techniques, the MR system may place multiple virtual sound sources (e.g., virtual objects 504a and / or 504b) around the user 502 and present spatialized audio. As the user 502 rotates his / her head, the user 502 may be able to perceive the location of the virtual objects 504a and 504b (e.g., by observing that the virtual object 504a is larger when the user 502 is in a first orientation and smaller when the user 502 is in a second orientation). This approach may have the advantage of allowing the user 502 to perceive dynamic changes in spatialization based on the movement of the user 502. This may create a more immersive audio experience than fixed sounds that do not fit the location of the user 502.

[0055] However, in some embodiments, the exemplary approach shown in FIG. 5 may suffer from some disadvantages. In some applications, such as composed musical scores, sound designers may want to limit the degree to which sounds exhibit spatialized behavior. Furthermore, in some situations, spatialized audio may lead to harsh or unpleasant results. For example, fixing the virtual object 504b relative to its position in the MRE may mean that the sound emanating from the virtual object 504b may be louder than intended when the user 502 approaches the virtual object 504b. If the virtual object 504b corresponds to a cello sound and is part of a virtual orchestra, the orchestra sound may sound distorted to the user 502 if the user 502 stands too close to the virtual object 504b. It may not be desirable to allow a user (e.g., user 502) to walk too close to a sound source (e.g., virtual object 504b) as this may deviate from the designed experience. For example, an overly strong sound from a virtual cello may dampen the sound from a virtual violin.

[0056] In addition to possible deviations from the designed experience, allowing the user to approach a virtual sound source may confuse or disorient the user, especially in extreme cases, such as when the user's location nearly overlaps with the location of the sound source, or when the user's head moves or rotates rapidly relative to the sound source. In some embodiments, the virtual object 504b may be a non-viewpoint from which the sound emanates. When the user 502 approaches the virtual object 504b, the user 502 may perceive the sound as clearly emanating from a non-viewpoint. This may be undesirable, for example, if the sound attracts unwanted attention to the virtual object 504b (e.g., if the virtual object 504b is configured to be invisible to avoid attracting the user's attention). In some embodiments, the intended central focus for the user may be a video and / or a narrated story, and spatialized audio may be used to enhance the user's immersion in the video and / or the narrated story. For example, the MR system may present the user with a three-dimensional "movie" in which the user can walk around and observe characters and / or objects from different perspectives. In such applications, it may be disconcerting for a user to perceive an invisible viewpoint located within a mixed reality scene from which a sound is emitted. For example, in a battle scene, it may not be desirable to allow a user to approach a point where an invisible guitar track is playing. Sound designers and story writers may want to obtain additional control of the spatialized audio experience to preserve the intended narration. Thus, it may be desirable to develop additional methods of providing immersive spatialized audio. For example, it may be desirable to allow audio designers to create custom audio behaviors that can be associated with sounds on an individual basis (e.g., controlled by scripts executed by a scripting engine). In some cases, default audio behaviors can be applied unless overridden by the custom audio behavior. In some cases, the custom audio behaviors can include manipulating the origin of the sound to produce a desired audio experience.

[0057] 6A-6C illustrate an example of mixed reality spatialized audio, according to some embodiments. Spatialized audio can create a believable three-dimensional MRE (e.g., MRE 150) experience, similar to persistent visual content. As a user walks around a real environment (e.g., real environment 100), the user may expect to see persistent virtual content that behaves like a real object (e.g., the persistent virtual content appears larger as the user approaches it and becomes smaller as the user moves away). Similarly, the user may expect sound sources to behave as if they are present in the real environment while the user moves around (e.g., the sound source may sound larger as the user approaches it and smaller as the user moves away). In some embodiments, immersive spatialized audio can be controlled by manipulating sound sources relative to the user's head, for example, through a "delayed follow" effect. For example, one or more sound sources can be spaced around the user's head and / or tied to it at a first location. At the first position, one or more sound sources may be located at a specified position, which may be a position where the sound source is intended (e.g., by a developer or audio designer) to produce a particular audio experience. The position of the sound source may correspond to the origin of the sound source, e.g., coordinates in the MRE from which the sound appears to originate. The sound source origin may be represented as an offset (e.g., vector offset) from the user's head (or other listener position). That is, presenting the sound to the user may include determining an offset from the user's head and applying the offset to the user's head to arrive at the sound source origin. The first position of the user's head at the first time may be determined, for example, by one or more sensors of a wearable head device as described above (e.g., with respect to the wearable head device 401A). The second position of the user's head at a second later time may then be determined. The difference between the first and second positions of the head may be used to manipulate the audio signal.For example, in some cases, when a user moves their head to a second position, one or more sound sources can be instructed to "follow" the movement of the head such that the position of the sound source may deviate from its designated position that may be spaced around and / or tied to the user's head (e.g., the designated position that may be spaced around and / or tied to the user's head may move / change relative to the user's head and the sound source may no longer be located at its designated position that may be spaced around and / or tied to the user's head). This manipulation of the sound source can be implemented, for example, by moving the sound source origin from the first position by an amount that is less than the difference between the first and second positions of the head. In some embodiments, the designated position may remain fixed relative to the user's head position, but the corresponding virtual sound source may be "elastically" tied to the user's head position and may follow behind the corresponding designated position. In some embodiments, the sound source may return to its designated location (e.g., the same location intended to produce a particular audio experience) spaced around and / or tied to the user's head at some point after the user's head reaches the second position. Other manipulations of the sound source origin, such as determining the origin based on the difference between the first and second head positions, are also contemplated and are within the scope of this disclosure. More generally, custom audio dynamics can be created by manipulating the sound source origin relative to the user's head or some other object (including a moving object) within the MRE. For example, the sound source origin can be defined as a function of the user's head position and orientation, or as a function of the change or accumulation of head position or orientation over time (e.g., a function of the integral or derivative of head position or orientation). Such functions can be used for creative effects to simulate sounds traveling at a particular speed or in a particular direction.For example, the speed of the user's head movement can be determined (e.g., as the derivative of the head movement, determined by one or more sensors in a wearable head device as described above), and sound can be presented as if the sound origin were traveling at that same speed (or a different speed based on the head speed). As another example, a change in the orientation of the user's head can be determined, such as via one or more sensors in a wearable head device as described above, and sound can be presented as if the sound origin were moving with an orientation based on the change in the user's head orientation. Representing the sound origin as a function of the user's head position or orientation can also be adapted to smoothly handle situations that would otherwise cause undesirable audio results. For example, by defining a function that limits the extent to which sound sources move relative to the user's head, extreme or undesirable audio effects from those sound sources can be limited or avoided. This can be implemented, for example, by establishing a threshold rate of change of the user's head position. That is, if the rate of change exceeds a threshold, the change in the location of the sound source origin can be appropriately limited (e.g., by setting the origin to a first coordinate if the threshold is exceeded and setting the origin to a different coordinate if the threshold is not exceeded). As another example of avoiding undesirable audio effects, the sound source origin can be configured to remain at least a minimum distance from the user at all times. For example, if the magnitude of the offset between the sound source origin and the user's head falls below a minimum threshold, the origin can be relocated to an alternative location that is at least a minimum distance from the user's head.

[0058] As shown in FIG. 6A, in some embodiments, virtual objects 604a and / or 604b may be spaced around and / or tied to center 602. Virtual objects 604a and / or 604b may be visible (e.g., displayed to a user) or invisible (e.g., not displayed to a user). In some embodiments, virtual objects 604a and / or 604b may not interact with other virtual objects. For example, virtual objects 604a and / or 604b may not collide with other virtual objects. Virtual objects 604a and / or 604b may not reflect / absorb / transmit light from other virtual objects, and / or virtual objects 604a and / or 604b may not reflect / absorb / transmit sound from other virtual objects. In some embodiments, virtual objects 604a and / or 604b may interact with other virtual objects.

[0059] In some embodiments, virtual objects 604a and / or 604b may be associated with one or more sound sources. In some cases, each virtual object may correspond to one sound source. For example, virtual objects 604a and / or 604b may be configured to virtually emit sound from its location in the MRE. Configuring the sound source so that it can be perceived as emanating from a location can be done using any suitable method. For example, a head-related transfer function ("HRTF") can be used to simulate a sound originating from a specific location. In some embodiments, a generic HRTF can be used. In some embodiments, for example, one or more microphones around the user's ears (e.g., one or more microphones in an MR system) can be used to determine one or more user-specific HRTFs. In some embodiments, the distance between the user and the virtual sound source may be simulated using suitable methods (e.g., sound pressure attenuation, high frequency attenuation, a mix of direct and reverberant sound, motion parallax, etc.). In some embodiments, virtual objects 604a and / or 604b may be configured to emit sound as a point source. In some embodiments, virtual objects 604a and / or 604b may include a physical three-dimensional model of a sound source, and sound may be generated by modeling interactions with the sound source. For example, virtual object 604a may include a virtual guitar, including a wooden body, strings, tuning pegs, etc. Sound may be generated by plucking one or more strings and modeling how the action interacts with other components of the virtual guitar.

[0060] In some embodiments, the virtual objects 604a and / or 604b may emit sound omnidirectionally. In some embodiments, the virtual objects 604a and / or 604b may emit sound directional. In some embodiments, the virtual objects 604a and / or 604b may be configured to include sound sources, each of which may include a musical stem. In some embodiments, a musical stem may be an arbitrary subset of the entire sound of the music. For example, a violin or orchestral soundtrack may include a violin stem, a cello stem, a bass stem, a trumpet stem, a timpanist stem, etc. In some embodiments, the channels of a multi-channel soundtrack may be represented as stems. For example, a two-channel soundtrack may include a left stem and a right stem. In some embodiments, a single track of a mix may be represented as a stem. In some embodiments, a musical soundtrack may be split into stems according to frequency bands. A stem may represent any arbitrary subset of the entire sound.

[0061] In some embodiments, virtual object 604a and / or 604b may be tied to one or more objects (e.g., center 602 and / or vector 606). For example, virtual object 604a may be assigned to a specified location 608a. In some embodiments, specified location 608a can be a fixed point relative to vector 606 and / or center 602. In some embodiments, virtual object 604b may be assigned to a specified location 608b. In some embodiments, specified location 608b can be a fixed point relative to vector 606 and / or center 602. Center 602 can be a point and / or a three-dimensional object. In some embodiments, virtual object 604a and / or 604b may be tied to a point of the three-dimensional object (e.g., a center point of the three-dimensional object or a point on its surface). In some embodiments, center 602 may correspond to any suitable point (e.g., the center of the user's head). The center of the user's head may be estimated using the center of the head-mounted MR system (which may have known dimensions) and the average head dimensions, or using other suitable methods. In some embodiments, the virtual objects 604a and / or 604b may be tied to a directional indicator (e.g., vector 606). In some embodiments, the virtual objects 604a and / or 604b may be placed at a specified location, which may include and / or be defined by its position relative to the center 602 and / or vector 606 (e.g., using a spherical coordinate system). In some embodiments, the virtual objects 604a and / or 604b may deviate from their specified location if the center 602 and / or vector 606 change position (e.g., location and / or orientation).In some embodiments, virtual object 604a and / or 604b may return to its specified position after center 602 and / or vector 606 stop changing position, e.g., after center 602 and / or vector 606 have a fixed position / value for a predetermined period of time (e.g., 5 seconds).

[0062] As shown in FIG. 6B, vector 606 may change direction. In some embodiments, designated locations 608a and / or 608b may move correspondingly. For example, designated locations 608a and / or 608b may be at the same positions relative to center 602 and / or vector 606 in FIG. 6B as in FIG. 6A. In some embodiments, virtual objects 604a and / or 604b may track the movement of designated locations 608a and / or 608b. For example, as vector 606 moves from a first position in FIG. 6A to a second position in FIG. 6B (e.g., to reflect the rotation of the user's head), virtual objects 604a and / or 604b may remain in the same position in both FIG. 6A and FIG. 6B (even as designated locations 608a and / or 608b move). In some embodiments, the virtual objects 604a and / or 604b may start moving after the vector 606 and / or the center 602 start moving and / or moving. In some embodiments, the virtual objects 604a and / or 604b may start moving after the vector 606 and / or the center 602 stop moving, for example, for a predetermined period of time. In FIG. 6C, the virtual objects 604a and / or 604b may return to their designated position relative to the vector 606 and / or the center 602. For example, the virtual objects 604a and / or 604b may occupy the same position relative to the vector 606 and / or the center 602 in FIG. 6C as in FIG. 6A.

[0063] The virtual objects 604a and / or 604b may deviate from their designated positions 608a and / or 608b over a period of time. In some embodiments, as the vector 606 and / or the center 602 change direction, the virtual objects 604a and / or 604b may "trace" the path of movement of the designated positions 608a and / or 608b, respectively. In some embodiments, the virtual objects 604a and / or 604b may follow an interpolated path from their current positions to the designated positions 608a and / or 608b, respectively. In some embodiments, the virtual objects 604a and / or 604b may return to their designated positions once the center 602 and / or the vector 606 have completely stopped accelerating and / or moving (e.g., linear and / or angular acceleration). For example, the center 602 may remain a stationary point and the vector 606 may rotate around the center 602 at a constant speed (e.g., because the user rotates their head). After a period of time, the virtual objects 604a and / or 604b may return to their designated positions despite the fact that the vector 606 remains moving at a constant speed. Similarly, in some embodiments, the center 602 may move at a constant speed (and the vector 606 may remain stationary or may also move at a constant speed) and the virtual objects 604a and / or 604b may return to their designated positions after the initial acceleration ceases. In some embodiments, the virtual objects 604a and / or 604b may return to their designated positions once the center 602 and / or vector 606 stop moving. For example, if the user's head is rotating at a constant speed, the virtual objects 604a and / or 604b may continue to "lag" from their designated positions until the user stops spinning their head. In some embodiments, the virtual object 604a and / or 604b may return to its specified position once the center 602 and / or the vector 606 stop accelerating.For example, if a user's head begins to rotate and then continues to rotate at a constant velocity, virtual objects 604a and / or 604b may initially lag from their designated position and then reach their designated position after the user's head reaches a constant velocity (e.g., over a threshold time period).

[0064] In some embodiments, the one or more sound sources may move as if they were "elastically" tied to the user's head. For example, as the user rotates his / her head from a first position to a second position, the one or more sound sources may not rotate at the same angular velocity as the user's head. In some embodiments, the one or more sound sources may start rotating at a slower angular velocity than the user's head, accelerate, and decelerate as they approach their initial position relative to the user's head. The rate of change of angular velocity may be capped, for example, at a level preset by the sound designer. This can strike a balance between allowing the sound sources to move very quickly (which may result in undesirable audio effects as described above) and preventing the sound sources from moving at all (which may not convey the benefits of spatialized audio).

[0065] In some embodiments, having one or more spatialized sound sources implement delayed following can have several advantages. For example, allowing the user to deviate in relative position from the spatialized sound source can allow the user to perceive a difference in sound. The user may notice that the spatialized sound becomes slightly quieter as the user turns away from the spatialized sound, enhancing the user's sense of immersion within the MRE. In some embodiments, delayed following can also maintain a desired audio experience. For example, the user may be prevented from unintentionally distorting the audio experience by approaching and remaining very close to the sound source. If the sound source is statically placed relative to the environment, the user may approach the sound source and the spatializer may undesirably present the sound source in a way that overly suppresses other sound sources as a result of the user's proximity (especially as the distance between the user and the sound source approaches zero). In some embodiments, delay tracking may move sound sources to a set position relative to the user after a delay (e.g., so that each sound source may generally be maintained at a desired distance from each other and / or the user) so that the user may experience enhanced spatialization without compromising the overall audio effect.

[0066] In some embodiments, virtual objects 604a and / or 604b can have a dynamically specified position. For example, the specified position 608a can be configured to move (e.g., follow the trajectory of the user's head or move closer to and / or farther away from the user's head) even when the center 602 and vector 606 remain stationary. In some embodiments, the dynamically specified position can be determined relative to a center and / or vector (e.g., a moving center and / or vector), and the virtual object can move in a delayed-following manner toward the specified position (e.g., by tracing the movement of the specified position and / or interpolating a path).

[0067] In some embodiments, the virtual objects 604a and / or 604b can be placed at their designated positions using asset design tools for the game engine (e.g., Unity). In some embodiments, the virtual objects 604a and / or 604b may comprise game engine objects, which may be placed in a three-dimensional environment (e.g., MRE, supported by the game engine). In some embodiments, the virtual objects 604a and / or 604b may be components of a parent object. In some embodiments, the parent object may include parameters, such as corresponding centers and / or vectors, for placing the virtual object at its designated position. In some embodiments, the parent object may include delay-following parameters, such as parameters for the speed at which the virtual object should return to its designated position and / or the circumstances under which the virtual object should return to its designated position (e.g., constant speed or no movement). In some embodiments, the parent object may include parameters for the speed at which the virtual object tracks its designated position (e.g., whether the virtual object should move at a constant speed, accelerate, and / or decelerate). In some embodiments, a parent object may include parameters for determining a path that a virtual object may take from its current position to its specified position (e.g., using linear and / or exponential interpolation). In some embodiments, a virtual object (e.g., virtual objects 604a and 604b) may include its own such parameters.

[0068] In some embodiments, the game engine may maintain some or all properties of the virtual objects 604a and 604b (e.g., the current and / or designated locations of the virtual objects 604a and 604b). In some embodiments, the current locations of the virtual objects 604a and 604b (e.g., the locations and / or properties of the virtual objects 604a and 604b, either through the locations and / or properties of a parent object or directly) may be passed to a spatialization and / or rendering engine. For example, the spatialization and / or rendering engine may receive sounds emanating from the virtual object 604a and the current location of the virtual object 604a. The spatialization and / or rendering engine may process the input and produce output, which may include spatialized sounds, which may be configured to be perceived as originating from the location of the virtual object 604a. The spatialization and / or rendering engine may render the spatialized sounds using any suitable techniques, including, but not limited to, head-related transfer functions and / or distance attenuation techniques.

[0069] In some embodiments, a spatialization and / or rendering engine may receive the data structure and render the delayed-following spatialized sound. For example, the delayed-following data structure may include a data format along with parameters and / or metadata and / or delayed-following parameters related to position relative to head pose. In some embodiments, an application running on the MR system may send one or more delayed-following data structures to a spatialization and / or rendering engine to render the delayed-following spatialized sound.

[0070] In some embodiments, the soundtrack may be processed into a delay-following data structure. For example, a 5.1 channel soundtrack may be split into six stems, and each stem may be assigned to one or more virtual objects (e.g., virtual objects 604a and 604b). Each stem / virtual object may be placed in a pre-configured orientation for 5.1 channel surround sound (e.g., the center speaker stem may be placed directly in front of the user's face, about 20 feet in front of the user). In some embodiments, the delay-following data structure may then be used by a spatialization and / or rendering engine to render delay-following spatialized sound.

[0071] In some embodiments, delayed-following spatialized sound may be rendered for more than one user. For example, a set of virtual objects configured to surround a first user may be perceptible to a second user. The second user may observe the virtual objects / sound sources following the first user in a delayed manner. In some embodiments, a set of virtual objects / sound sources may be configured to surround more than one user. For example, a center point may be calculated as a center point between the head of the first user and the head of the second user. A vector may be calculated as an average vector between vectors representing the direction facing each user. One or more virtual objects / sound sources may be placed relative to the dynamically calculated center point and / or vector.

[0072] Although two virtual objects are shown in Figures 6A-6C, it is contemplated that any number of virtual objects and / or sound sources may be used. In some embodiments, each virtual object and / or sound source may have its own separate parameters. A center point / object and vector are used to position the position virtual object, although any suitable coordinate system (e.g., Cartesian, spherical, etc.) may also be used.

[0073] A system, method, and computer readable medium are disclosed. According to some embodiments, the system comprises a wearable head device having a speaker and one or more sensors, and one or more processors configured to perform a method including: determining a first position of a user's head at a first time based on the one or more sensors; determining a second position of the user's head at a second time after the first time based on the one or more sensors; determining an audio signal based on a difference between the first position and the second position; and presenting the audio signal to the user via the speaker, where determining the audio signal includes determining an origin of the audio signal within the virtual environment, presenting the audio signal to the user includes presenting the audio signal as if originating from the determined origin, and determining the origin of the audio signal includes applying an offset to the position of the user's head. In some embodiments, determining the origin of the audio signal further includes determining the origin of the audio signal based on a rate of change of the position of the user's head. In some examples, determining an origin of the audio signal further includes determining that the origin comprises a first origin in accordance with a determination that the rate of change exceeds a threshold, and determining that the origin comprises a second origin different from the first origin in accordance with a determination that the rate of change does not exceed a threshold. In some examples, determining an origin of the audio signal further includes determining that the origin comprises a first origin in accordance with a determination that the magnitude of the offset is below a threshold, and determining that the origin comprises a second origin different from the first origin in accordance with a determination that the magnitude of the offset is not below a threshold. In some examples, determining the audio signal further includes determining a velocity within the virtual environment, and presenting the audio signal to the user further includes presenting the audio signal as if the origin were moving at the determined velocity. In some examples, determining the velocity includes determining the velocity based on a difference between a first position of the user's head and a second position of the user's head.In some embodiments, the offset is determined based on a first position of the user's head.

[0074] According to some embodiments, a method of presenting audio to a user of a wearable head device includes determining a first position of the user's head at a first time based on one or more sensors of the wearable head device, determining a second position of the user's head at a second time after the first time based on the one or more sensors, determining an audio signal based on a difference between the first position and the second position, and presenting the audio signal to the user via a speaker of the wearable head device, where determining the audio signal includes determining an origin of the audio signal within a virtual environment, where presenting the audio signal to the user includes presenting the audio signal as if originating from the determined origin, and where determining the origin of the audio signal includes applying an offset to the position of the user's head. In some embodiments, determining the origin of the audio signal further includes determining the origin of the audio signal based on a rate of change of the position of the user's head. In some examples, determining an origin of the audio signal further includes determining that the origin comprises a first origin in accordance with a determination that the rate of change exceeds a threshold, and determining that the origin comprises a second origin different from the first origin in accordance with a determination that the rate of change does not exceed a threshold. In some examples, determining an origin of the audio signal further includes determining that the origin comprises a first origin in accordance with a determination that the magnitude of the offset is below a threshold, and determining that the origin comprises a second origin different from the first origin in accordance with a determination that the magnitude of the offset is not below a threshold. In some examples, determining the audio signal further includes determining a velocity within the virtual environment, and presenting the audio signal to the user further includes presenting the audio signal as if the origin moves at the determined velocity. In some examples, determining the velocity includes determining the velocity based on a difference between a first position of the user's head and a second position of the user's head. In some examples, the offset is determined based on the first position of the user's head.

[0075] According to some embodiments, a non-transitory computer-readable medium stores instructions that, when executed by one or more processors, cause the one or more processors to perform a method of presenting audio to a user of a wearable head device, the method including: determining a first position of a user's head at a first time based on one or more sensors of the wearable head device; determining a second position of the user's head at a second time, later than the first time, based on the one or more sensors; determining an audio signal based on a difference between the first position and the second position; and presenting the audio signal to the user via a speaker of the wearable head device, where determining the audio signal includes determining an origin of the audio signal within the virtual environment, where presenting the audio signal to the user includes presenting the audio signal as if originating from the determined origin, and where determining the origin of the audio signal includes applying an offset to the position of the user's head. In some embodiments, determining the origin of the audio signal further includes determining the origin of the audio signal based on a rate of change of the position of the user's head. In some examples, determining an origin of the audio signal further includes determining that the origin comprises a first origin in accordance with determining that the rate of change exceeds a threshold and determining that the origin comprises a second origin different from the first origin in accordance with determining that the rate of change does not exceed a threshold. In some examples, determining an origin of the audio signal further includes determining that the origin comprises the first origin in accordance with determining that the magnitude of the offset is below a threshold and determining that the origin comprises a second origin different from the first origin in accordance with determining that the magnitude of the offset is not below a threshold. In some examples, determining the audio signal further includes determining a velocity within the virtual environment and presenting the audio signal to the user further includes presenting the audio signal as if the origin were moving at the determined velocity.In some examples, determining the velocity includes determining the velocity based on a difference between a first position of the user's head and a second position of the user's head. In some examples, the offset is determined based on the first position of the user's head.

[0076] Although the disclosed embodiments have been fully described with reference to the accompanying drawings, it should be noted that various changes and modifications will be apparent to those skilled in the art. For example, elements of one or more implementations may be combined, deleted, modified, or supplemented to form further implementations. Such changes and modifications should be understood as being included within the scope of the disclosed embodiments as defined by the appended claims.

Claims

1. 1. A system comprising: a wearable head device having a speaker and one or more sensors; One or more processors, determining a first position of a user's head at a first time based on the one or more sensors; determining a second position of the user's head at a second time, after the first time, based on the one or more sensors; and determining an audio signal based on a difference between the first position and the second position; presenting the audio signal to the user via the speaker; one or more processors configured to perform a method including: Equipped with determining the audio signal includes determining an origin of the audio signal within a virtual environment; presenting the audio signal to the user includes presenting the audio signal as if originating from the determined origin; Determining the origin of the audio signal includes applying an offset to a position of the user's head; determining the audio signal further comprises determining a velocity within the virtual environment; presenting the audio signal to the user further includes presenting the audio signal as if the origin were moving at the determined velocity with a delay; determining the velocity includes determining the velocity based on a difference between the first position of the user's head and the second position of the user's head; The system, wherein the origin of the audio signal moves based on the determined velocity after the delay, and while the origin is moving, a location of the movement of the origin within the virtual environment differs from a location of one or more objects associated with the audio signal in the virtual environment.

2. The system of claim 1 , wherein determining the origin of the audio signal further comprises determining the origin of the audio signal based on a rate of change of a position of the user's head.

3. Determining the origin of the audio signal comprises: determining that the origin comprises a first origin in accordance with determining that the rate of change exceeds a threshold; determining, in response to the determination that the rate of change does not exceed the threshold, that the origin comprises a second origin different from the first origin; The system of claim 2 further comprising:

4. Determining the origin of the audio signal comprises: determining that the origin comprises a first origin in accordance with determining that the magnitude of the offset is below a threshold; and determining, in response to determining that the magnitude of the offset is not less than the threshold, that the origin comprises a second origin different from the first origin; The system of claim 1 further comprising:

5. The system of claim 1 , wherein the determined velocity comprises an angular velocity.

6. The system of claim 1 , wherein the offset is determined based on the first position of the user's head.

7. 1. A method for presenting audio to a user of a wearable head device, the method comprising: determining a first position of the user's head at a first time based on one or more sensors of the wearable head device; determining a second position of the user's head at a second time, after the first time, based on the one or more sensors; and determining an audio signal based on a difference between the first position and the second position; presenting the audio signal to the user via a speaker of the wearable head device; Including, determining the audio signal includes determining an origin of the audio signal within a virtual environment; presenting the audio signal to the user includes presenting the audio signal as if originating from the determined origin; Determining the origin of the audio signal includes applying an offset to a position of the user's head; determining the audio signal further comprises determining a velocity within the virtual environment; presenting the audio signal to the user further includes presenting the audio signal as if the origin were moving at the determined velocity with a delay; determining the velocity includes determining the velocity based on a difference between the first position of the user's head and the second position of the user's head; The method of claim 1, wherein the origin of the audio signal moves based on the determined velocity after the delay, and while the origin is moving, a location of the movement of the origin within the virtual environment differs from a location of one or more objects associated with the audio signal in the virtual environment.

8. The method of claim 7 , wherein determining the origin of the audio signal further comprises determining the origin of the audio signal based on a rate of change of a position of the user's head.

9. Determining the origin of the audio signal comprises: determining that the origin comprises a first origin in accordance with determining that the rate of change exceeds a threshold; determining, in response to the determination that the rate of change does not exceed the threshold, that the origin comprises a second origin different from the first origin; The method of claim 8 further comprising:

10. Determining the origin of the audio signal comprises: determining that the origin comprises a first origin in accordance with determining that the magnitude of the offset is below a threshold; and determining, in response to determining that the magnitude of the offset is not less than the threshold, that the origin comprises a second origin different from the first origin; The method of claim 7 further comprising:

11. The method of claim 7 , wherein the determined velocity comprises an angular velocity.

12. The method of claim 7 , wherein the offset is determined based on the first position of the user's head.

13. 1. A non-transitory computer readable medium having instructions stored thereon that, when executed by one or more processors, cause the one or more processors to perform a method of presenting audio to a user of a wearable head device, the method comprising: determining a first position of the user's head at a first time based on one or more sensors of the wearable head device; determining a second position of the user's head at a second time, after the first time, based on the one or more sensors; and determining an audio signal based on a difference between the first position and the second position; presenting the audio signal to the user via a speaker of the wearable head device; Including, determining the audio signal includes determining an origin of the audio signal within a virtual environment; presenting the audio signal to the user includes presenting the audio signal as if originating from the determined origin; Determining the origin of the audio signal includes applying an offset to a position of the user's head; determining the audio signal further comprises determining a velocity within the virtual environment; presenting the audio signal to the user further includes presenting the audio signal as if the origin were moving at the determined velocity with a delay; determining the velocity includes determining the velocity based on a difference between the first position of the user's head and the second position of the user's head; A non-transitory computer-readable medium, wherein the origin of the audio signal moves based on the determined velocity after the delay, and while the origin is moving, a location of the movement of the origin within the virtual environment differs from a location of one or more objects associated with the audio signal in the virtual environment.

14. 14. The non-transitory computer-readable medium of claim 13, wherein determining the origin of the audio signal further comprises determining the origin of the audio signal based on a rate of change of a position of the user's head.

15. Determining the origin of the audio signal comprises: determining that the origin comprises a first origin in accordance with determining that the rate of change exceeds a threshold; determining, in response to the determination that the rate of change does not exceed the threshold, that the origin comprises a second origin different from the first origin; 15. The non-transitory computer readable medium of claim 14, further comprising:

16. Determining the origin of the audio signal comprises: determining that the origin comprises a first origin in accordance with determining that the magnitude of the offset is below a threshold; and determining, in response to determining that the magnitude of the offset is not less than the threshold, that the origin comprises a second origin different from the first origin; 14. The non-transitory computer readable medium of claim 13, further comprising:

17. The non-transitory computer-readable medium of claim 13 , wherein the determined velocity comprises an angular velocity.

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