PATENT DOCUMENT

Publication Number: US-10028071-B2
Application Number: US-201715465544-A
Country: US
Kind Code: B2

Title: Binaural sound reproduction system having dynamically adjusted audio output

Abstract:
A binaural sound reproduction system, and methods of using the binaural sound reproduction system to dynamically re-center a frame of reference for a virtual sound source, are described. The binaural sound reproduction system may include a head-mounted device, e.g., headphones, having a device sensor to provide device orientation data corresponding to a direction of the head-mounted device. The system may use the orientation data to determine whether the head-mounted device has moved over an angle within a range of movement, and may adjust an audio output to render the virtual sound source in an adjusted source direction based on the range of movement. Other embodiments are also described and claimed.

Claims:
What is claimed is: 
     
       1. A method, comprising:
 receiving, from a head-mounted device, device orientation data corresponding to a device direction of the head-mounted device; 
 outputting, by the head-mounted device, an audio output to render a virtual sound source in a source direction at an offset angle from an initial device direction of the head-mounted device; 
 determining that the device direction of the head-mounted device moves from the initial device direction to a current device direction over an angle; 
 determining, in response to the angle being greater than a predetermined angular change threshold, a rate of device angular change of the device direction; and 
 adjusting, in response to the rate of device angular change being less than a predetermined rate threshold, the audio output to render the virtual sound source in an adjusted source direction offset from the source direction by the angle, wherein the predetermined rate threshold is a predetermined rate of device angular change. 
 
     
     
       2. The method of  claim 1 , wherein the angle is within a range of movement, and wherein the range of movement is one of a plurality of ranges of movement offset from the initial device direction by at least the predetermined angular change threshold. 
     
     
       3. The method of  claim 2  further comprising:
 determining, in response to determining that the device direction of the head-mounted device moves within the range of movement, the rate of device angular change of the device direction when the device direction moves within the range of movement; 
 wherein adjusting the audio output is based on the rate of device angular change. 
 
     
     
       4. The method of  claim 3 , wherein the rate of device angular change is an amount of device angular change over a bin duration. 
     
     
       5. The method of  claim 4 , wherein the bin duration is a first duration when the range of movement is a first range of movement of the plurality of ranges of movement, and wherein the bin duration is a second duration when the range of movement is a second range of movement of the plurality of ranges of movement. 
     
     
       6. The method of  claim 5 , wherein the first range of movement is less than the second range of movement, and wherein the first duration is more than the second duration. 
     
     
       7. A binaural sound reproduction system, comprising:
 a head-mounted device including
 a device sensor to output device orientation data corresponding to a device direction of the head-mounted device, and 
 an audio processor configured to
 output an audio output to render a virtual sound source in a source direction at an offset angle from an initial device direction of the head-mounted device, 
 determine that the device direction of the head-mounted device moves from the initial device direction to a current device direction over an angle, 
 determine, in response to the angle being greater than a predetermined angular change threshold, a rate of device angular change of the device direction, and 
 adjust, in response to the rate of device angular change being less than a predetermined rate threshold, the audio output to render the virtual sound source in an adjusted source direction offset from the source direction by the angle, wherein the predetermined rate threshold is a predetermined rate of device angular change. 
 
 
 
     
     
       8. The binaural sound reproduction system of  claim 7 , wherein the angle is within a range of movement, and wherein the range of movement is one of a plurality of ranges of movement offset from the initial device direction by at least the predetermined angular change threshold. 
     
     
       9. The binaural sound reproduction system of  claim 8  further comprising:
 determining, in response to determining that the device direction of the head-mounted device moves within the range of movement, the rate of device angular change of the device direction when the device direction moves within the range of movement; 
 wherein adjusting the audio output is based on the rate of device angular change. 
 
     
     
       10. The binaural sound reproduction system of  claim 9 , wherein the rate of device angular change is an amount of device angular change over a bin duration. 
     
     
       11. The binaural sound reproduction system of  claim 10 , wherein the bin duration is a first duration when the range of movement is a first range of movement of the plurality of ranges of movement, and wherein the bin duration is a second duration when the range of movement is a second range of movement of the plurality of ranges of movement. 
     
     
       12. The binaural sound reproduction system of  claim 11 , wherein the first range of movement is less than the second range of movement, and wherein the first duration is more than the second duration. 
     
     
       13. A method, comprising:
 rendering, by a head-mounted device, a virtual sound source at a first location relative to the head mounted device when the head-mounted device is pointed in a first device direction; 
 rendering, by the head-mounted device, the virtual sound source at a second location relative to the head mounted device when the head-mounted device turns to point in a second device direction offset from the first device direction; and 
 rendering, by the head-mounted device, the virtual sound source at the first location relative to the head mounted device in response to determining that the head-mounted device is pointed in the second device direction and a rate of device angular change of the head-mounted device is less than a predetermined rate threshold, wherein the predetermined rate threshold is a predetermined rate of device angular change. 
 
     
     
       14. The method of  claim 13 , wherein the virtual sound source is rendered at the first location relative to the head mounted device when the head-mounted device is pointed in the second device direction and the second device direction is within a range of movement, wherein the range of movement is one of a plurality of ranges of movement offset from the first device direction by at least a predetermined angular change threshold. 
     
     
       15. The method of  claim 14  further comprising:
 determining whether the head-mounted device moves within the range of movement; and 
 determining the rate of device angular change of the head-mounted device in response to determining that the head-mounted device moves within the range of movement. 
 
     
     
       16. The method of  claim 15 , wherein the rate of device angular change is an amount of device angular change over a bin duration. 
     
     
       17. The method of  claim 16 , wherein the bin duration is a first duration when the range of movement is a first range of movement of the plurality of ranges of movement, wherein the bin duration is a second duration when the range of movement is a second range of movement of the plurality of ranges of movement, wherein the first range of movement is less than the second range of movement, and wherein the first duration is more than the second duration.

Description:
This application claims the benefit of priority of U.S. Provisional Patent Application No. 62/399,250, filed Sep. 23, 2016, and incorporates herein by reference that provisional patent application. 
    
    
     BACKGROUND 
     Field 
     Embodiments related to binaural sound reproduction systems are disclosed. More particularly, embodiments related to binaural sound reproduction systems having head-mounted devices in communication with electronic devices, are disclosed. 
     Background Information 
     Binaural headphones simulate virtual sound sources. To achieve realistic virtual sound sources, head-tracking may be used to anchor the virtual sound source to a reference frame, e.g., a room. Head-tracking systems may incorporate orientation sensors to allow an audio engine to predict an orientation of the binaural headphones relative to the reference frame, and thus, to simulate the virtual sound source in an appropriate direction as a listener&#39;s head turns. 
     SUMMARY 
     Existing binaural headphones having head-tracking can achieve realistic virtual sound sources when the reference frame is not moving. That is, current binaural headphones assume that the virtual sound source is spatially anchored to a stationary reference frame, and thus, movements of the head-tracker are attributed to the listener&#39;s head turning. Such an assumption may not be appropriate, however, when the reference frame is a moving frame of reference or when the listener&#39;s entire body is moving relative to the forward-facing direction. For example, the assumption may be incorrect when the listener is jogging along winding city streets or when the listener is traveling in a cabin of a car or an airplane. When the reference frame and the head of the user experience similar motion, e.g., when an airplane yaws rightward from an old heading to a new heading and causes a passenger&#39;s head to also turn rightward, a realistic virtual sound source should be positioned in a same direction relative to the new heading rather than remain fixed relative to the old heading. It will be appreciated that this does not occur in existing binaural headphones because the movement imparted to the head-tracker from the turning plane will result in a shift of the virtual sound source in a leftward direction, as perceived by the listener, even when there is no orientation change between the listener&#39;s head and the moving cabin. 
     In an embodiment, a binaural sound reproduction system performs a method to dynamically re-center a frame of reference for a virtual sound source. The binaural sound reproduction system includes a head-mounted device having an audio processor configured to output an audio output to render a virtual sound source in a source direction at an offset angle from a forward-facing device direction. Accordingly, a user of the head-mounted device may perceive the virtual sound source as coming from the source direction. The virtual sound source may be dynamically shifted according to movement of the head-mounted device. More particularly, the audio output may be adjusted based on a range of movement of the head-mounted device. 
     In an embodiment, when head-mounted device is in a dynamic use case, a frame of reference of head-mounted device is automatically re-centered according to a dynamic time constant. To implement the automatic re-centering, audio processor may determine an amount of a device angular change of a device direction of the head-mounted device, e.g., a degree to which a user&#39;s head rotates. When the amount of the device angular change is greater than a predetermined angular change threshold, the audio processor may determine a rate of movement of the head-mounted device. The rate may be determined over a predetermined duration. For example, the predetermined duration may be inversely proportional to the amount of the device angular change. That is, the predetermined duration may be greater when the amount of device angular change is smaller. Thus, when the device angular change from an initial direction to a current direction is within a first range of movement, e.g., 30-60 degrees, the predetermined duration may be a first time constant, e.g., 100 ms. When the device angular change from the initial direction to the current direction is within a second range of movement, e.g., 60-90 degrees, the predetermined duration may be a second time constant, e.g., 25 ms. Accordingly, the predetermined duration for determining a rate of movement of the head-mounted device may be inversely correlated with the degree to which the head-mounted device has rotated from an initial direction. In one embodiment, when the determined rate is less than a predetermined rate threshold (indicating that the user is now facing a new forward-facing direction) the audio processor may adjust the audio output to render the virtual sound source in an adjusted source direction. The adjusted source direction may be offset from the original source direction by the angle that the device moved from the initial direction to the current direction within the range of movement. Accordingly, automatic re-centering of the frame of reference of the head-mounted device based on movement of the head-mounted device may maintain the user&#39;s perception of the virtual sound source as coming from a same direction. 
     The above summary does not include an exhaustive list of all aspects of the present invention. It is contemplated that the invention includes all systems and methods that can be practiced from all suitable combinations of the various aspects summarized above, as well as those disclosed in the Detailed Description below and particularly pointed out in the claims filed with the application. Such combinations have particular advantages not specifically recited in the above summary. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a pictorial view of a user consuming audio or video content in a static use case, in accordance with an embodiment. 
         FIG. 2  is a pictorial view of a user consuming audio or video content in a dynamic use case, in accordance with an embodiment. 
         FIG. 3  is a pictorial view of a binaural sound reproduction system, in accordance with an embodiment. 
         FIG. 4  is a block diagram of a binaural sound reproduction system, in accordance with an embodiment. 
         FIG. 5  is a graphical representation of orientation data for a binaural sound reproduction system during a static use case and a dynamic use case, in accordance with an embodiment. 
         FIG. 6  is a flowchart of a method of using a binaural sound reproduction system to dynamically re-center a frame of reference for a virtual sound source, in accordance with an embodiment. 
         FIG. 7  is a pictorial representation of a binaural sound reproduction system being used in a static or dynamic use case, in accordance with an embodiment. 
         FIG. 8  is a flowchart of a method of using a binaural sound reproduction system to dynamically re-center a frame of reference for a virtual sound source in a static use case, in accordance with an embodiment. 
         FIGS. 9A-9C  are pictorial views of a binaural sound reproduction system in a static use case, in accordance with an embodiment. 
         FIG. 10  is a flowchart of a method of using a binaural sound reproduction system to dynamically re-center a frame of reference for a virtual sound source in a dynamic use case, in accordance with an embodiment. 
         FIG. 11  is a pictorial view of a binaural sound reproduction system in a dynamic use case, in accordance with an embodiment. 
         FIG. 12  is a graphical view of an angular change of a head-mounted device of a binaural sound reproduction system in a dynamic use case, in accordance with an embodiment. 
         FIGS. 13A-13C  are pictorial views of a binaural sound reproduction system in a dynamic use case, in accordance with an embodiment. 
         FIG. 14  is a flowchart of a method of using a binaural sound reproduction system to dynamically re-center a frame of reference for a virtual sound source in a dynamic use case, in accordance with an embodiment. 
         FIGS. 15A-15C  are pictorial views of a binaural sound reproduction system in a dynamic use case, in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments describe a binaural sound reproduction system, and methods of using the binaural sound reproduction system to dynamically re-center a frame of reference for a virtual sound source. The binaural sound reproduction system may include a reference device, such as a laptop computer, a tablet computer, a mobile device, or a wearable computer, and a head-mounted device, such as a headset or headphones. The binaural sound reproduction system may, however, incorporate other devices and apparatuses. For example, the head-mounted device may be a non-head-mounted device, e.g., the device may be a speaker system of a motor vehicle synced to a computer worn by a user. Likewise, the reference device may be an on-board computer of a motor vehicle. 
     In various embodiments, description is made with reference to the figures. However, certain embodiments may be practiced without one or more of these specific details, or in combination with other known methods and configurations. In the following description, numerous specific details are set forth, such as specific configurations, dimensions, and processes, in order to provide a thorough understanding of the embodiments. In other instances, well-known processes and manufacturing techniques have not been described in particular detail in order to not unnecessarily obscure the description. Reference throughout this specification to “one embodiment,” “an embodiment,” or the like, means that a particular feature, structure, configuration, or characteristic described is included in at least one embodiment. Thus, the appearance of the phrase “one embodiment,” “an embodiment,” or the like, in various places throughout this specification are not necessarily referring to the same embodiment. Furthermore, the particular features, structures, configurations, or characteristics may be combined in any suitable manner in one or more embodiments. 
     The use of relative terms throughout the description may denote a relative position or direction. For example, “clockwise” may indicate a first rotational direction about a reference point. Similarly, “counterclockwise” may indicate a second rotational direction opposite to the first rotation direction. Such terms are provided to establish relative frames of reference, however, and are not intended to limit the use or orientation of a binaural sound reproduction system to a specific configuration described in the various embodiments below. 
     In an aspect, a binaural sound reproduction system includes a head-mounted device to output audio that renders a virtual sound source in a source direction, and a secondary reference device that remains fixed relative to a frame of reference of the virtual sound source. For example, the secondary device may be on a torso of a jogging listener, or a mobile device or laptop computer resting on a console or tray of a moving automobile or airplane. Thus, the secondary device may have a reference direction that is a current orientation direction relative to some reference. For example, the reference direction may be a forward-facing direction, e.g., a direction that the listener is running or a direction that the automobile or airplane is travelling. Orientation data from the secondary device may be used to determine whether the head-mounted device is being used in a static or dynamic use case. Accordingly, movements of the head-mounted device may be differentiated against movements of the secondary device based on the particular use case to adjust the audio output in a manner that realistically locates the virtual sound source as expected by the listener. That is, the virtual sound source may be positioned relative to the frame of reference that the listener is listening within, as determined by the reference device, and local head movements can give auditory cues to achieve externalization and localization of the virtual sound source in the audio rendering. 
     Referring to  FIG. 1 , a pictorial view of a user consuming audio or video content in a static use case is shown in accordance with an embodiment. A static use case  100  may be a case in which a local frame of reference  102  associated with a user is stationary with respect to a global frame of reference  104 . Global frame of reference  104  may, for example, be the surface of the earth beneath the user. In such case, a reference device  106 , such as a mobile device, tablet computer, or a laptop computer resting on a desk in front of the user, may remain fixed relative to local frame of reference  102  and global frame of reference  104 . Similarly, a torso of the user may remain fixed relative to local frame of reference  102  and global frame of reference  104 . Accordingly, movement of a head-mounted device  108  being worn by the user may be attributed to the user turning his head rather than being attributed to local frame of reference  102  turning relative to global frame of reference  104 . 
     Referring to  FIG. 2 , a pictorial view of a user consuming audio or video content in a dynamic use case is shown in accordance with an embodiment. A dynamic use case  200  may be a case in which local frame of reference  102  associated with a user moves with respect to global frame of reference  104 . The user may be sitting in a seat of a moving vehicle  202 . In such case, reference device  106  may be resting on a console of vehicle  202 , and thus, reference device  106  may remain fixed relative to local frame of reference  102 . Similarly, the torso of the user may remain fixed relative to local frame of reference  102 . Local frame of reference  102 , however, may move relative to global frame of reference  104  when vehicle  202  changes directions. For example, when vehicle  202  is steered right, local frame of reference  102  turns right relative to global frame of reference  104 . As such, reference device  106  or the torso of the user, which may be fixed to the moving local frame of reference  102 , may also turn relative to global frame of reference  104 . 
     Whether the user is listening to a virtual sound source rendered by head-mounted device  108  in static use case  100  or dynamic use case  200 , it is desirable for the virtual sound source to be stable against the user&#39;s head motion. That is, head-mounted device  108  should adjust an audio output to render the virtual sound source in an appropriate direction relative to local frame of reference  102 . More particularly, it may be desirable to relocate the virtual sound source when the user turns his head, but not when the head turn results from turning the user&#39;s torso. An appropriate method of relocating the virtual sound source may, however, depend on the use case. For example, in a static use case  100 , when reference device  106  is fixed relative to global frame of reference  104 , the user may want to manually re-center a head-tracker when the user wishes to pivot in his chair to change a forward-facing direction from an old direction, e.g., facing reference device  106  on a desk, to a new direction, e.g., looking out a window. By contrast, in a dynamic use case  200 , when reference device  106  is moving relative to global frame of reference  104 , the user may want to automatically update the forward-facing direction to obviate the need to continually provide manual re-centering inputs each time he jogs or drives around a corner. 
     Referring to  FIG. 3 , a pictorial view of a binaural sound reproduction system is shown in accordance with an embodiment. A binaural sound reproduction system  300  may include reference device  106  and head-mounted device  108 . Head-mounted device  108  may output audio to render a virtual sound source in a source direction as perceived by a user listening to the audio output  302 . As described below, reference device  106  may be a secondary device used to provide orientation data corresponding to a direction or movement of local frame of reference  102 . A communication link  304  may be established between reference device  106  and head-mounted device  108  by a wired or wireless connection to communicate audio or orientation data between the devices. 
     Reference device  106  may be an electronic device such as a smartphone device, a tablet computer, a laptop computer, an on-board computer of an automobile, etc. That is, reference device  106  may be any portable device or apparatus that is movable relative to global frame of reference  104 . Reference device  106  may include various capabilities to allow the user to access features involving, for example, calls, voicemail, music, e-mail, internet browsing, scheduling, or photos. Reference device  106  may also include hardware to facilitate such capabilities. For example, a casing  306  may contain an audio speaker, e.g., a microspeaker, to deliver a far-end voice to a near-end user during a call, and a microphone to pick up the voice of the user during the call. A display  308  may present video content associated with audio output  302  to the user. Other conventional features are not shown but may of course be included in reference device  106 . 
     Head-mounted device  108  of binaural sound reproduction system  300  may be adapted to present audio content to the user. For example, head-mounted device  108  may be headphones or a headset having a left speaker  310  and a right speaker  312  to emit audio output  302  as stereo sound to the user. Audio output  302  may be associated with music files played by a music player application running on reference device  106  or a far-end voice of a call being serviced by reference device  106 . Head-mounted device  108  may include a microphone  314  to pick up the voice of the user during the call. Microphone  314  may also detect user inputs, such as voice activated commands. Similarly, head-mounted device  108  may include manual input features, such as a re-centering input switch  316  to receive a re-centering input from the user, as described below. 
     Referring to  FIG. 4 , a block diagram of a binaural sound reproduction system is shown in accordance with an embodiment. Reference device  106  may be any of several types of portable devices or apparatuses with circuitry suited to specific functionality. Accordingly, the diagrammed circuitry is provided by way of example and not limitation. Reference device  106  may include one or more processors  402  to execute instructions to carry out the different functions and capabilities described below. Instructions executed by processor(s)  402  of reference device  106  may be retrieved from a local memory  404 , which may include a non-transitory machine-readable medium. The instructions may be in the form of an operating system program having device drivers and/or an audio rendering engine for rendering a virtual sound source according to the methods described below. Processor(s)  402  may also retrieve audio data  406  from memory  404 , including audio data associated with phone and/or music play back functions controlled by the telephony or music application programs that run on top of the operating system. To perform such functions, processor(s)  402  may directly or indirectly implement control loops and receive input signals from and/or provide output signals to other electronic components. For example, reference device  106  may receive input signals from orientation devices of binaural sound reproduction system  300  and output audio signals to an audio speaker and/or to head-mounted device  108  via wired or wireless communication link  304 . Communication link  304  may include an audio jack connection in an embodiment, however, an audio jack is only one type of possible connector and other wired connectors may be used. Furthermore, in an embodiment, reference device  106  and/or head-mounted device  108  do not include an audio jack and/or a wired connection, and communication link  304  is established only by a wireless connection. Head-mounted device  108  may process the audio signals to render a virtual sound source, as described below. 
     In an embodiment, the electronic circuitry of reference device  106  includes a reference sensor  408  to output reference orientation data corresponding to a reference direction  702  of reference device  106 . The reference orientation data may be served to processor(s)  402  or memory  404 , and processor(s)  402  may retrieve the reference orientation data from memory  404 . Reference sensor  408  may be one or more of any known orientation sensor, such as accelerometers, magnetometers, gyroscopes, etc. For example, reference sensor  408  may be an inertial measurement unit (IMU) integrated within casing  306  of reference device  106 . Such inertial-based examples are not restrictive, however, and reference sensor  408  may include non-inertial sensors, such as optical sensors. More particularly, reference sensor  408  may be an optical sensor of a camera integrated in a robotic mapping system, e.g., simultaneous localization and mapping system. The robotic mapping system may be used to develop and provide reference orientation data corresponding to a reference direction of reference device  106 . 
     Reference sensor  408  may detect additional information relevant to a use case of binaural sound reproduction system  300 . For example, reference sensor  408  may include a global positioning system (GPS) sensor to determine whether reference device  106  is in transit, e.g., on a street or a rail line. Similarly, reference sensor  408  may include a microphone to receive ambient sounds that may be comparable to signature sound profiles, e.g., ambient noise from an aircraft engine, to gather further information about a context of the use case. 
     In an embodiment, head-mounted device  108  includes a device sensor  410  to output device orientation data corresponding to a device direction of head-mounted device  108 . Device sensor  410  may be similar to reference sensor  408 . For example, device sensor  410  may be an inertial or non-inertial sensor used to detect an orientation of head-mounted device  108 . Furthermore, device sensor  410  may detect a context of head-mounted device  108 , i.e., information related to a use case of head-mounted device  108 . 
     Head-mounted device  108  may store device orientation data from device sensor  410  in a respective memory (not shown), or the device orientation data may be served directly to an audio processor  412  of head-mounted device  108 . Audio processor  412  may be configured to present audio output  302  to the user via left speaker  310  and right speaker  312 . More particularly, audio processor  412  may provide audio electrical signals to the speakers such that stereo sound from the speakers renders a virtual sound source in a source direction. Audio data  406  corresponding to audio output  302  may be received by audio processor  412  via wired or wireless communication link  304  from reference device  106 . For example, the audio data  406  may correspond to a video playing on display  308  of reference device  106 . 
     Processor(s)  402  of reference device  106  and/or audio processor  412  of head-mounted device  108  may execute an audio rendering algorithm to determine the appropriate audio electrical signals for left speaker  310  and right speaker  312  to render the virtual sound source in the appropriate direction. More particularly, processor(s)  402  or audio processor  412  may determine a use case of binaural sound reproduction system  300  and dynamically re-center a frame of reference of binaural sound reproduction system  300  based on information gathered by reference sensor  408  and/or device sensor  410 . Re-centering may be performed manually or automatically by audio processor  412 . 
     Referring to  FIG. 5 , a graphical representation of orientation data for a binaural sound reproduction system during a static use case and a dynamic use case is shown in accordance with an embodiment. As described above, reference sensor  408  of reference device  106  may output reference orientation data  502 . Reference orientation data  502  may correspond to a rotation of local frame of reference  102 . During static use case  100 , reference orientation data  502  indicates that reference device  106  is stationary. More particularly, a reference direction of reference device  106 , which by convention is initially directed in a zero degree direction relative to global frame of reference  104 , remains directed in the zero degree direction. That is, reference device  106  experiences no discernible angular change or rotation in static use case  100 . By contrast, during dynamic use case  200 , reference orientation data  502  indicates that reference device  106  is not stationary. More particularly, the reference direction of reference device  106  departs from the zero degree direction, and moves relative to global frame of reference  104 . That is, reference device  106  experiences an angular change or rotation in dynamic use case  200 . Reference orientation data  502  during static use case  100  may be typical of the user sitting in a bus while the bus is parked at a bus stop, and reference orientation data  502  during dynamic use case  200  may be typical of the user sitting in the bus as the bus moves along city streets. 
     Device sensor  410  of head-mounted device  108  may output device orientation data  504 . Device orientation data  504  may correspond to a head azimuth of the user. During static use case  100 , device orientation data  504  indicates that head-mounted device  108  moves relative to reference device  106 . More particularly, a device direction of head-mounted device  108  changes as the user looks from left to right. More particularly, the device direction of head-mounted device  108  moves relative to both local frame of reference  102  and global frame of reference  104  in static use case  100 . Similarly, during dynamic use case  200 , device orientation data  504  indicates that head-mounted device  108  moves as the user looks from left to right. Device orientation data  504  during static use case  100  may be typical of the user looking around at other passengers in a bus while the bus is parked at a bus stop, and device orientation data  504  during dynamic use case  200  may be typical of the user looking out of the bus windows as the bus moves along city streets. Accordingly, device orientation data  504  indicates a degree to which the user&#39;s head is moving relative to global frame of reference  104 , but does not indicate a degree to which the head movement is attributable to movement of the local frame of reference  102  within which the user is situated. 
     A virtual sound source is rendered to the user such that the user perceives the sound source as being fixed in space. Maintaining the virtual sound source in a position that is expected by a listener, however, may require binaural sound reproduction system  300  to differentiate between movements of the listeners head caused by a rotation of the user&#39;s neck, and movements caused by a rotation of the local frame of reference  102  within which the user is situated. Accordingly, to anchor the virtual sound source to local frame of reference  102 , binaural sound reproduction system  300  may function to assess a use case and re-center a frame of reference for the virtual sound source based on the determined use case. 
     Referring to  FIG. 6 , a flowchart of a method of using a binaural sound reproduction system to dynamically re-center a frame of reference for a virtual sound source is shown in accordance with an embodiment.  FIG. 7  is a pictorial representation of a binaural sound reproduction system being used during the method of  FIG. 6 . Accordingly,  FIGS. 6 and 7  are described together below. 
     At operation  602 , processors of binaural sound reproduction system  300  may receive reference orientation data  502 . Reference orientation data  502  may be output by reference sensor  408  of reference device  106 . For example, referring to  FIG. 7 , reference orientation data  502  may correspond to a reference direction  702  of reference device  106 . Reference direction  702  may be established by convention. For example, reference direction  702  may be an output of an IMU or navigation system corresponding to a datum, such as a vector facing forward from a top surface of casing  306 . Reference direction  702  need not actually be frontward of user  706 , however. That is, the secondary device  106  does not have to be oriented or even know which way an actual forward direction is. Rather, the determinations described throughout this description may be based on relative changes in orientation, and do not necessarily account for an actual forward direction. As such, the term “forward-facing” as used throughout the description is to be interpreted as a relative term, and not necessarily an absolute term accounting for the spatial orientation of user  706 . 
     At operation  604 , processors of binaural sound reproduction system  300  may receive device orientation data  504 . Device orientation data  504  may be output by device sensor  410  of head-mounted device  108 . For example, referring to  FIG. 7 , device orientation data  504  may correspond to a device direction  704  of head-mounted device  108 . Head-mounted device  108 , of course, may be worn by a user  706  and thus device direction  704  may correspond to a forward-facing direction of user  706 . Accordingly, device direction  704  may change relative to global frame of reference  104  when user  706  turns his head or when local frame of reference  102  within which user  706  is situated moves relative to global frame of reference  104 . 
     At operation  606 , head-mounted device  108  provides audio output  302 . More particularly, audio processor  412  may generate an electrical audio signal for left speaker  310  and right speaker  312  to render a virtual sound source  708  in a source direction  710 . Virtual sound source  708  may be associated with content being played on reference device  106 . For example, virtual sound source  708  may be a voice of a participant sitting toward the periphery of user  706  during a video conference call. Accordingly, to accurately represent virtual sound source  708  to user  706 , audio output  302  may render virtual sound source  708  at an offset angle  712  from device direction  704  such that the voice is perceived by user  706  as coming from the periphery of his vision. 
     Local frame of reference  102  may be movable relative to global frame of reference  104 . As local frame of reference  102  shifts, reference device  106 , which may be fixed relative to local frame of reference  102 , may also shift. As reference device  106  rotates, reference direction  702  may experience a reference angular change relative to a datum of global frame of reference  104 , e.g., relative to a true north direction. When local frame of reference  102  moves, device direction  704  corresponding to the forward facing direction of user  706  may also move. To accurately represent virtual sound source  708 , however, any movement in device direction  704  attributable to movement of the local frame of reference  102  should be compensated for by also shifting source direction  710 . That is, when local frame of reference  102  moves relative to global frame of reference  104 , the frame of reference of head-mounted device  108  may be re-centered such that virtual sound source  708  continues to come from a direction that user  706  perceives as the periphery of his vision. Such re-centering may occur in response to determining an appropriate re-centering method, i.e., a method based on the use case of head-mounted device  108 . 
     At operation  608 , processor(s)  402  and/or audio processor  412  of binaural sound reproduction system  300  may determine whether head-mounted device  108  is in static use case  100  or dynamic use case  200 . Such determination may be made based on reference orientation data  502 . More particularly, the reference angular change of reference direction  702  may be compared to a predetermined range of motion  714  to assess whether head-mounted device  108  is being used in static use case  100  or dynamic use case  200 . 
     Range of motion  714  may be an angular range, e.g., −20 to 20 degrees, relative to a baseline reference direction of reference device  106 . That is, when reference orientation data  502  indicates that reference direction  702  experiences a static reference angular change  716  within range of motion  714 , e.g., less than 20 degrees in either direction, audio processor  412  may determine that head-mounted device  108  is in static use case  100 . Angular deviations within range of motion  714  may be attributed to natural shifts within a given static environment, e.g., trunk rotation while running on a treadmill, and may be insufficient to change the re-centering method from a manual method to an automatic method as described below. 
     When reference orientation data  502  indicates that reference direction  702  experiences a dynamic reference angular change  718  outside of the predetermined range of motion  714 , e.g., more than 20 degrees in either direction, audio processor  412  may determine that head-mounted device  108  is in dynamic use case  200 . Angular deviations outside of range of motion  714  may be attributed to preconceived dynamic environments, e.g., jogging or driving around a corner, and may be sufficient to change the re-centering method from a manual method to an automatic method as described below. 
     At operation  610 , binaural sound reproduction system  300  may adjust audio output  302  based on the determined use case. More particularly, audio processor  412  of head-mounted device  108  may alter electrical audio signals provided to left speaker  310  and right speaker  312  to render virtual sound source  708  in an adjusted source direction. Relocating virtual sound source  708  in the adjusted source direction may be achieved using different methodologies. For example, as described below, virtual sound source  708  may be relocated based on either a manual or an automatic re-centering of local frame of reference  102  associated with head-mounted device  108 . 
     Referring to  FIG. 8 , a flowchart of a method of using a binaural sound reproduction system to dynamically re-center a frame of reference for a virtual sound source in a static use case is shown in accordance with an embodiment.  FIGS. 9A-9C  are pictorial views of the binaural sound reproduction system during the method of  FIG. 8 . Accordingly,  FIGS. 8 and 9A-9C  are described together below. 
     At operation  802 , one or more processors of binaural sound reproduction system  300  may determine head-mounted device  108  is in static use case  100 . Such determination may be based on a reference angular change of reference direction  702  being within range of motion  714 , as described above. 
     When head-mounted device  108  is in static use case  100 , the frame of reference of head-mounted device  108  may be re-centered manually. By way of example, local frame of reference  102  as indicated by reference orientation data  502  may remain stationary relative to global frame of reference  104 . Nonetheless, user  706  may want to re-center device direction  704  in a new forward facing direction when, for example, user  706  wants to turn in his chair to look out a window while listening to a music reproduction. 
     Referring to  FIG. 9A , user  706  may initially face a first direction such that device direction  704  is forward facing in static use case  100 . As described above, virtual sound source  708  may be rendered to be perceived by user  706  as coming from a peripheral direction at offset angle  712  from reference direction  702 . 
     Referring to  FIG. 9B , user  706  may swivel his office chair such that a torso and face of user  706  are directed in a second direction offset from the first direction. User  706  may wish for the second direction to be a new forward facing direction. More particularly, the second direction may be a current device direction  902  offset from device direction  704  by an adjustment angle  904 . In  FIG. 9B , virtual sound source  708  may continue to be rendered in source direction  710  because head-mounted device  108  does not automatically re-center the frame of reference of virtual sound source  708  to adjust for movements of a user&#39;s torso in static use case  100 . Thus, even though user  706  has shifted his personal frame of reference by rotating his chair, and may expect virtual sound source  708  to shift to match the personal frame of reference, virtual sound source  708  may instead be perceived as coming from nearly the same direction as the user&#39;s new gaze. 
     At operation  804 , user  706  may manually override binaural sound reproduction system  300  to re-center the frame of reference of head-mounted device  108  such that virtual sound source  708  shifts to the expected location. Referring to  FIG. 9B , a re-centering input  906  may be received by audio processor  412  when head-mounted device  108  has current device direction  902 . Re-centering input  906  may be a manual input from user  706 . For example, user  706  may actuate re-centering input switch  316  to provide re-centering input  906  to head-mounted device  108 . Re-centering input switch  316  may be a voice activated switch actuated by a verbal command issued by user  706 . Similarly, re-centering input switch  316  may be a physical button on head-mounted device  108 , and user  706  may manually press the physical button to provide re-centering input  906 . 
     At operation  806 , audio output  302  may be adjusted in response to determining head-mounted devices  108  is in static use case  100 , and in response to receiving re-centering input  906 . For example, audio processor  412  may receive re-centering input  906  from re-centering input switch  316  after determining head-mounted device  108  is in static use case  100 , and audio processor  412  may adjust audio output  302  to render virtual sound source  708  in an adjusted source direction. Referring to  FIG. 9C , an adjusted source direction  908  may be at offset angle  712  from current device direction  902 . Accordingly, user  706  may manually calibrate a zero degree direction of head-mounted device  108  to align with the user&#39;s gaze by activating re-centering input switch  316 . Thus, virtual sound source  708  will continue to be perceived as coming from the peripheral vision of user  706  after user  706  has swiveled in his chair and manually re-centered the frame of reference of head-mounted device  108 . 
     Referring to  FIG. 10 , a flowchart of a method of using a binaural sound reproduction system to dynamically re-center a frame of reference for a virtual sound source in a dynamic use case is shown in accordance with an embodiment. An understanding of method illustrated in  FIG. 10  is facilitated with reference to  FIGS. 11, 12, and 13A-13C , and accordingly, those figures are described in combination below. 
     At operation  1002 , one or more processors of binaural sound reproduction system  300  may determine head-mounted device  108  is in dynamic use case  200 . Such determination may be based on a reference angular change of reference direction  702  being outside of range of motion  714 , as described above. 
     When head-mounted device  108  is in dynamic use case  200 , the frame of reference of head-mounted device  108  may be re-centered automatically. By way of example, when local frame of reference  102  as indicated by reference orientation data  502  moves relative to global frame of reference  104 , binaural sound reproduction system  300  may re-center device direction  704  in a new forward facing direction. Accordingly, virtual sound source  708  may be shifted to remain fixed within the moving local frame of reference  102  as perceived by the moving user  706 . In an embodiment, a manner of automatically shifting virtual sound source  708  may depend on an amount and/or a rate of the device angular change. 
     Referring to  FIG. 11 , a pictorial view of a binaural sound reproduction system in a dynamic use case is shown in accordance with an embodiment. At operation  1004 , an amount and a rate of an angular change of device direction  704  is determined. A device angular change  1102  may be measured as an angular distance between an initial device direction  704  and a current device direction  902  after user&#39;s head has moved in dynamic use case  200 . For example, device angular change  1102  may be 90 degrees when user  706  jogs around a corner and shifts the forward facing direction from device direction  704  pointing along one street to current device direction  902  pointing along an orthogonal street. 
     In an embodiment, the amount of device angular change  1102  may be within different ranges of movement. For example, the device direction of the head-mounted device  108  may move from an initial device direction  704  to a current device direction over an angle within a range of movement, and the range of movement may be one of several ranges of movement offset from the initial device direction by at least a predetermined angular change threshold, e.g., first angular change threshold  1104 . The amount of device angular change  1102  may be more than first angular change threshold  1104 . Small head motions made by user  706  while head-mounted devices  108  is in dynamic use case  200  may not require the virtual sound source  708  to be shifted. First angular change threshold  1104  may correspond to the predetermined range encompassing small head motions and glances that should not cause virtual sound source  708  to jump. By contrast, it may be desirable to shift virtual sound source  708  more when head-mounted device  108  experiences larger device angular changes  1102 . Thus, device angular changes  1102  may be further compartmentalized into ranges of movement. A first range of movement may encompass the range of movement between first angular change threshold  1104  and a second angular change threshold  1106 . A second range of movement may encompass the range of movement between second angular change threshold  1106  and a third angular change threshold  1108 . A third range of movement may encompass the range of movement beyond third angular change threshold  1108 . 
     Audio processor  412  may determine whether the amount of device angular change  1102  is less than a second predetermined angular change threshold  1106 , more than second angular change threshold  1106  and less than a third angular change threshold  1108 , or more than third angular change threshold  1108 . Audio processor  412  may determine that the device direction of the head-mounted device has moved from the initial device direction  704  to a current device direction within the first range of movement when the device direction is between first angular change threshold  1104  and second angular change threshold  1106 . Audio processor  412  may determine that the device direction of the head-mounted device has moved from the initial device direction  704  to a current device direction within the second range of movement when the device direction is between second angular change threshold  1106  and third angular change threshold  1108 , and so on. Re-centering may occur based on the angular change that current device direction  902  falls within. That is, audio processor  412  may adjust audio output based on the range of movement of the device direction to render the virtual sound source in an adjusted source direction offset from the source direction by the angle  1102  traversed by the head-mounted device. 
     Referring to  FIG. 12 , a graphical view of an angular change of a head-mounted device of a binaural sound reproduction system in a dynamic use case is shown in accordance with an embodiment. In an embodiment, audio processor  412  may determine a rate of the device angular change in response to the amount of the device angular change  1102  being greater than first predetermined angular change threshold  1104 . For example, audio processor  412  may determine a rate of device angular change when the device direction moves within the first range of movement between thresholds  1104 ,  1106 , or the second range of movement between thresholds  1106 ,  1108 . When movements of head-mounted device  108  are in a small range, virtual sound source  708  may remain fixed relative to an existing frame of reference of head-mounted device  108 , however, when movements of head-mounted device  108  exceed first angular change threshold  1104 , audio processor  412  may begin to assess when and where to shift virtual sound source  708 . Such an assessment may be made based on a rate  1202  of device angular change within the range of movement. 
     The rate of device angular change may be analyzed in terms of angle versus time. In an embodiment, a rate  1202  of device angular change corresponds to the amount of device angular change per unit of time. The rate of device angular change may be an amount of device angular change over a bin duration. For example, the analyzed time range may be divided into individual bins, and each bin may have a bin duration  1204 . Accordingly, audio processor  412  may determine rate  1202  of device angular change  1102  over predetermined bin duration  1204 . Rate  1202  may be a median rate of change of the device direction when the device direction is within the given range of movement. For example, when bin duration  1204  is set at 100 ms, a median rate of change of the device direction may be measured over each 100 ms time window. 
     In an embodiment, bin duration  1204  is based on the amount of device angular change  1102 . For example, bin duration  1204  may correspond to the range of movement within which the head-mounted device is currently directed and/or moving. Bin duration  1204  may be a first duration, e.g., 100 ms, when the amount of device angular change  1102  is greater than first angular change threshold  1104  and less than second angular change threshold  1106 . Bin duration  1204  may be a second duration different than the first duration when the amount of device angular change  1102  is more than second angular change threshold  1106 . For example, when the amount of device angular change  1102  is between second angular change threshold  1106  and third angular change threshold  1108 , bin duration  1204  may be a different value, e.g., 25 ms. When the amount of device angular change  1102  is greater than third angular change threshold  1108 , bin duration  1204  may be another value, e.g., 5 ms. Thus, a length of bin duration  1204  may be inversely correlated to an amount of device angular change  1102 . That is, the second bin duration associated with angular changes greater than second angular change threshold  1106  (within the second range of movement) may be less than the first bin duration associated with angular changes less than second angular change threshold  1106  (within the first range of movement). 
     At operation  1006 , audio processor  412  may adjust audio output  302  in response to rate  1202  of device angular change being less than a predetermined rate threshold  1206 . Referring again to  FIG. 12 , variance between individual bins may be compared to rate threshold  1206 . For example, the median rates of change of device direction  704  may be analyzed to determine whether rate  1202  has decreased to a point at which it is safe to assume that user  706  is now looking in a direction that is a new forward facing direction. It will be appreciated that rates  1202  of change occurring during extreme movements, e.g., jogging or driving around a corner, may be higher than rates of change occurring while user  706  is gazing in a forward direction. Accordingly, by altering bin duration  1204  inversely with the amount of device angular change  1102  appropriate smaller time windows may be analyzed to determine whether user  706  has turned to face a new forward facing direction. That is, big turns may receive nearly immediate shifts of virtual sound source  708 , while smaller turns may shift virtual sound source  708  more gradually. As a result, adjustments to source direction  710  of virtual sound source  708  may match movements of user  706  more naturally. 
       FIGS. 13A-13C  are pictorial views of the binaural sound reproduction system during the method of  FIG. 10 . Referring to  FIG. 13A , head-mounted device  108  may be facing reference direction  702  in dynamic use case  200  while audio output  302  renders virtual sound source  708  in source direction  710 . As described above, source direction  710  may be at an offset angle  712  from device direction  704 . Referring to  FIG. 13B , user  706  may shift device direction  704  to current device direction  902  by walking around a corner. More particularly, device direction  704  may experience device angular change  1102 . The amount of device angular change  1102  may be greater than first angular change threshold  1104 , indicating to head-mounted device  108  that audio output  302  should be adjusted to relocate virtual sound source  708 . Referring to  FIG. 13C , in response to head-mounted device  108  being in dynamic use case  200 , and in response to rate  1202  of device angular change  1102  being less than predetermined rate threshold  1206  as described above, audio processor  412  may adjust audio output  302  to render virtual sound source  708  in an adjusted source direction  908 . The angular shift may be equal to device angular change  1102 . That is, after determining that the device angular change  1102  is a result of user  706  changing to a desired forward facing direction, virtual sound source  708  may be shifted by the amount of device angular change  1102  to maintain the perception of virtual sound source  708  being at a same offset angle  712  from current device direction  902 . 
     The methods described throughout this description do not necessarily require the determination of static use case  100  or dynamic use case  200  by reference device  106  to be useful for head-tracking during binaural sound reproduction. For example, one or more of the methods may be performed without making an initial determination as to whether binaural sound reproduction system is being used in a dynamic case. That is, binaural sound reproduction system  300  may be presumed to be in dynamic use case  200  (or static use case  100 ), and audio output  302  may be adjusted accordingly. 
     In an embodiment, head-tracking for binaural sound reproduction includes a method similar to the method of  FIG. 10 . Operation  1002  may, however, be omitted. More particularly, audio output may be continuously updated according to operations  1004  and  1006  without making a determination as to whether the head-mounted device  108  is in dynamic use case  200 . As such, adjustments to audio output may be based on the operations illustrated in  FIGS. 11-12  to effect the audio adjustments shown in  FIGS. 13A-13C  without making an initial determination according to operation  1002 . Accordingly, time-based head-tracking may be performed for binaural sound reproduction using a dynamic time factor that continuously determines an appropriate source direction  710  (or  908 ). This is pointed out to clarify that any of the described methods may be practiced with fewer operations than are described, and in fact, operations from different methods of binaural sound reproduction may be combined within the scope of this description. Accordingly, the described methods are illustrative, and not restrictive. 
     Referring to  FIG. 14 , a flowchart of a method of using a binaural sound reproduction system to dynamically re-center a frame of reference for a virtual sound source in a dynamic use case is shown in accordance with an embodiment.  FIGS. 15A-15C  are pictorial views of the binaural sound reproduction system during the method of  FIG. 14 . Accordingly,  FIGS. 14 and 15A-15C  are described together below. 
     Referring to  FIG. 15A , head-mounted device  108  may be facing reference direction  702  in dynamic use case  200  while audio output  302  renders virtual sound source  708  in source direction  710 . As described above, source direction  710  may be at an offset angle  712  from device direction  704 . 
     At operation  1402 , one or more processors of binaural sound reproduction system  300  may determine head-mounted device  108  is in dynamic use case  200 . Such determination may be based on a reference angular change of reference direction  702  being outside of range of motion  714 , as described above. 
     When head-mounted device  108  is in dynamic use case  200 , the frame of reference of head-mounted device  108  may be re-centered automatically. By way of example, when local frame of reference  102  as indicated by reference orientation data  502  moves relative to global frame of reference  104 , binaural sound reproduction system  300  may re-center device direction  704  in a new forward facing direction. Accordingly, virtual sound source  708  may be automatically shifted to remain fixed within the moving local frame of reference  102  as perceived by the moving user  706 . In an embodiment, a manner of automatically shifting virtual sound source  708  may include coordination between reference orientation data  502  from reference device  106  and device orientation data  504  from head-mounted device  108 . 
     Referring to  FIG. 15B , reference device  106  may experience a reference angular change causing reference direction  702  to shift from the initial reference direction  702  to a new reference direction  1502 . The new reference direction  1502  may be offset from reference direction  702  by an adjustment angle  904 . In an embodiment, the change in reference direction  702  may also occur in device direction  704 . For example, when reference device  106  and user  706  are both situated in a moving vehicle, both reference device  106  and head-mounted device  108  will experience the same angular change when the vehicle turns around the corner. Accordingly, device direction  704  may rotate by adjustment angle  904  to current device direction  902 . 
     At operation  1404 , audio processor  412  may determine the amount of reference angular change of reference direction  702 . More particularly, when reference direction  702  rotates by adjustment angle  904 , audio processor  412  may determine that the amount of reference angular change is equal to adjustment angle  904 . 
     At operation  1406 , audio processor  412  may adjust audio output  302  based on the amount of reference angular change. More particularly, audio output  302  may be adjusted in response to determining head-mounted device  108  is in dynamic use case  200  to render virtual sound source  708  in an adjusted source direction  908  offset from the original source direction  710 . The amount of adjustment may be the same as the reference angular change. Accordingly, virtual sound source  708  may shift in coordination with angular shifts of reference device  106 . That is, when reference device  106  rotates by an amount, virtual sound source  708  may be shifted by the same amount. As a result, virtual sound source  708  may be automatically shifted to remain fixed within the moving local frame of reference  102  as perceived by the moving user  706 . 
     Referring to  FIG. 15C , the automatic re-centering of the frame of reference of head-mounted device  108  relative to local frame of reference  102  associated with reference device  106  may allow the frame of reference of virtual sound source  708  to shift based on movements of reference device  106  and not movements of head-mounted device  108 . More particularly, after virtual sound source  708  is shifted to adjusted source direction  908 , user  706  may rotate his head without affecting a location of virtual sound source  708  relative to local frame of reference  102 . Virtual sound source  708  may be rendered differently, however, when user  706  turns his head. For example, when user  706  turns his head to change device direction  704  from current device direction  902  back to initial device direction  704 , virtual sound source  708  may continue to be perceived as coming from adjusted source direction  908 , which may now be at a larger angle from device direction  704  than before. 
     It will be appreciated that the re-centering operations described above may be combined into hybrid embodiments. For example, a tuning method to control how often a component of binaural sound reproduction system  300  updates a direction may be applied to reference device  106 . Such a tuning method may be similar to the methods described above with respect to  FIG. 10 . For example, referring again to  FIG. 15B , the amount of reference angular change may be compared to angular change thresholds similar to those described with respect to  FIG. 11 . In an embodiment, a rate of reference angular change may be determined in response to the amount of reference angular change being greater than a predetermined angular change threshold, e.g., greater than a first angular change threshold as applied to movement of reference device  106 . The rate of reference angular change may be determined over a predetermined duration. That is, the rate of reference angular change may be determined in a manner similar to the determination of rate  1202  as described with respect to  FIG. 12 . Accordingly, referring again to operation  1406  of  FIG. 14 , the adjustment of audio output  302  may be made further in response to the rate of reference angular change being less than a respective predetermined rate threshold. Such a methodology is similar to the method used to dynamically re-center head-mounted device  108  based on a look direction of the user  706 . It will be appreciated that the application of such a smoothing method to the dynamic re-centering method of  FIG. 14  may provide another benefit. Namely, applying the smoothing algorithm to reference device  106  allows binaural sound reproduction system  300  to accurately and smoothly locate new reference direction  1502  to allow virtual sound source  708  to then be shifted by an appropriate adjustment angle  904 . 
     As described above, sensor inputs to binaural sound reproduction system  300  may be classified into different use cases. If binaural sound reproduction system  300  determines a dynamic use case  200 , re-centering will be used according to one of the methods described above. To illustrate an application of binaural sound reproduction system  300 , one may consider the case of user  706  watching a movie on an airplane. User  706  may watch the movie using binaural sound reproduction system  300 . For example, reference device  106  may be a tablet computer and display  308  may present video content to user  706 . Head-mounted device  108  may be a pair of headphones having sound calibrated so that dialogue from the video content is perceived as coming from the forward facing direction, i.e., display  308 , while surround content is perceived as coming from behind user  706 . As user  706  moves his head, e.g., to gaze out a window of the airplane, the dialogue will continue to be perceived as coming from the forward facing direction of the tablet computer. One will appreciate that, if the airplane yaws, without the aid of a dynamic re-centering function, a head tracker would detect the rotation of the airplane as a turn of the user&#39;s head, and thus, the dialogue and the surround content would be rotated incorrectly. Using the dynamic re-centering operations described above, however, binaural sound reproduction system  300  may differentiate between the user&#39;s head motion and the frame of reference (airplane) movement, and may compensate to ensure that the dialogue and the surround content is correctly rendered. 
     In the foregoing specification, the invention has been described with reference to specific exemplary embodiments thereof. It will be evident that various modifications may be made thereto without departing from the broader spirit and scope of the invention as set forth in the following claims. The specification and drawings are, accordingly, to be regarded in an illustrative sense rather than a restrictive sense.

Metadata:
Filing Date: 20170321
Publication Date: 20180717
Grant Date: 20180717
Priority Date: 20160923
Inventors: SATONGAR, Darius A.
FAMILY, AFROOZ
CHOISEL, Sylvain J.
MERIMAA, JUHA O.
Assignee: APPLE INC
CPC Classifications: [{"code": "H04S2420/01", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R5/04", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04S2420/01", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R2460/07", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04S2400/01", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04S2400/11", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04S2400/01", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04S2400/11", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R2460/07", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R5/04", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04S7/304", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04R5/033", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R2420/07", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/012", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R2460/07", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R2420/07", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R5/033", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04S2400/01", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04S7/304", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F3/012", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R2420/07", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/012", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04S2420/01", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04S7/304", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04S7/304", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04S2400/01", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04S2400/11", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04S2420/01", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04S2400/01", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04S7/304", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04R2460/07", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R2420/07", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R5/033", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/012", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 61686910