Patent Publication Number: US-10764708-B2

Title: Spatial audio to enable safe headphone use during exercise and commuting

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of U.S. patent application Ser. No. 15/908,206, filed Feb. 28, 2018, the disclosure of which is incorporated herein by reference. 
    
    
     BACKGROUND 
     Headphone use when cycling, running, or other forms of commuting or exercise can be dangerous. For example, use of said headphones may interfere with the user&#39;s ability to hear the environment around them. As such, users may be unaware of objects surrounding or approaching them, which can result in collisions or other unexpected events. Audio pass-through headphones record noise from the environment through a microphone and then replay it digitally through the headphones with very little delay, allowing users to “tune in” and “tune out” from the environment around them. However, such systems do not offer much flexibility, and require the user to remember to “tune in.” 
     BRIEF SUMMARY 
     The present disclosure provides for an audio spatialization technique which correlates the spatialization with a recognized activity. For example, it may be detected when a user is performing an activity such as exercising, occupying a high traffic area, etc. Upon detection of such activity, the user&#39;s headphones may transition to an audio safety spatialization mode, in which sound is produced through the headphones based on a position of the headphones relative to a position of the sound source. For example, whereas a user may hear traffic behind him equally in both ears when facing directly forward, when the user turns his head to the left he may hear the traffic more distinctly in his left ear and more subtly in his right ear. 
     One aspect of the disclosure provides a method for producing sound through headphones having a right ear portion and a left ear portion. The method may include establishing a virtual audio source at a first position, the first position being a first point in space relative to a neutral position of the headphones when worn by a user. Sound is generated through the right ear portion and the left ear portion of the headphones, such that the sound is produced with an effect of emanating from the virtual source. Angular movement of the headphones with respect to the first position is detected, such that an angle of the headphones with respect to the first position may be determined. A sound level in at least one of the right ear portion or the left ear portion is reduced based on the determined angle. When one or more conditions are met, the virtual audio source is moved to a second position, the second position being a second point in space different from the first point in space but a same position relative to the neutral position of the headphones. 
     Another aspect of the disclosure provides a system. The system may include headphones comprising a left-ear audio output and a right-ear audio output, a memory storing instructions for generating audio through the left-ear audio output and the right-ear audio output, and one or more processors in communication with the memory. The one or more processors are configured to establish a virtual audio source at a first position, the first position being a first point in space relative to a neutral position of the headphones when worn by a user, and generate sound through the right-ear audio output and the left-ear audio output, such that the sound is produced with an effect of emanating from the virtual source. The one or more processors are further configured to detect angular movement of the headphones with respect to the first position, determine an angle of the headphones with respect to the first position as a result of the detected angular movement, and reduce a sound level in at least one of the right-ear audio output or the left-ear audio output based on the determined angle. Further, the one or more processors may move the virtual audio source to a second position when one or more conditions are met, the second position being a second point in space different from the first point in space but a same position relative to the neutral position of the headphones. 
     Yet another aspect of the disclosure provides a non-transitory computer-readable medium storing instructions executable by one or more processors in a pair of headphones including a left ear portion and a right ear portion for performing a method of audio safety spatialization. Such method may include establishing a virtual audio source at a first position, the first position being a first point in space relative to a neutral position of the headphones when worn by a user, generating sound through the right ear portion and the left ear portion of the headphones, such that the sound is produced with an effect of emanating from the virtual source, detecting angular movement of the headphones with respect to the first position, determining an angle of the headphones with respect to the first position as a result of the detected angular movement, reducing a sound level in at least one of the right ear portion or the left ear portion based on the determined angle, and moving the virtual audio source to a second position when one or more conditions are met, the second position being a second point in space different from the first point in space but a same position relative to the neutral position of the headphones. 
     Another aspect of the disclosure provides a method, including detecting a direction of movement of headphones having a right ear portion and a left ear portion, and establishing a virtual audio source for the headphones based on the direction of movement. Sound is generated through the right ear portion and the left ear portion of the headphones, such that the sound is produced with an effect of emanating from the virtual audio source. The method further includes detecting angular movement of the headphones with respect to the virtual audio source, and adjusting the sound generated through at least one of the right ear portion or the left ear portion based on the angular movement with respect to the virtual audio source. In some examples, detecting the direction of movement of the headphones includes detecting forward linear movement when the headphones are in a neutral orientation, and establishing the virtual audio source includes establishing the virtual audio source at a position in front of the headphones. The method may further include detecting a change in the direction of movement of the headphones, and moving the virtual audio source based on the detected change in the direction of movement. 
     Another aspect of the disclosure provides a system, including headphones comprising a left-ear audio output and a right-ear audio output, one or more sensors, a memory storing instructions for generating audio through the left-ear audio output and the right-ear audio output, and one or more processors in communication with the memory and the one or more sensors. The one or more processors are configured to receive input from the one or more sensors, detect a direction of movement of the headphones based on the received input, establish a virtual audio source for the headphones based on the direction of movement, generate sound through the right ear portion and the left ear portion of the headphones, such that the sound is produced with an effect of emanating from the virtual audio source, detect angular movement of the headphones with respect to the virtual audio source and adjust the sound generated through at least one of the right ear portion or the left ear portion based on the angular movement with respect to the virtual audio source. In some examples, the one or more sensors include at least one of an accelerometer, gyroscope, or magnetometer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a pictorial diagram of an example system according to aspects of the disclosure. 
         FIG. 2  is a block diagram of an example system according to aspects of the disclosure. 
         FIGS. 3A-3D  illustrate example audio spatialization techniques according to aspects of the disclosure. 
         FIGS. 4A-4C  illustrate example audio spatialization techniques according to aspects of the disclosure. 
         FIG. 5  is a flow diagram illustrating an example method according to aspects of the disclosure. 
         FIG. 6  is a flow diagram illustrating another example method according to aspects of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Overview 
     The present technology is directed to producing sound through earbuds or headphones in a manner that improves user experience and increases safety. In particular, in some circumstances, sound is spatialized such that when the user turns his head, the sound appears to be generated from a same position in space as before the user turned his head. If the user&#39;s head remains in the turned position, the spatialized sound will return to an initialized position with respect to the user&#39;s head. For example, if the sound appeared to be initially generated from a position in front of the user, when the user turned to the left the sound would remain in the same virtual location, appearing to be coming from the user&#39;s right side. If the user remains turned to the left, the virtual location of the sound would slowly return to a position in front of the user, such that after a period of time the sound would again appear to be generated from a position in front of the user. The circumstances in which sound is spatialized may be, for example, when the user is moving, such as during exercise, commuting, etc. 
     The technology includes three subsystems, acting in concert: 1) an activity detection unit; 2) an audio safety spatialization algorithm; and 3) a head-worn inertial measurement unit (IMU). The subsystems may be implemented as an integral part of the headphones and/or in combination with a communicatively coupled smart device, such as a tablet, watch, phone, etc. 
     The activity detection unit determines if the user is participating in an activity that qualifies for activation of a safety spatialization mode. Examples of such activities may include bicycling, running, skateboarding, or any other activity where a user is moving in a given direction within a threshold range of speed. For example, the threshold range of speed may encompass speeds associated with walking, skating, cycling, but may be slower than speeds associated with traveling in a motor vehicle. In some examples, activities which activate the audio spatialization mode may be ones in which a user is moving on or near a path traveled by motor vehicles, other people, animals, etc. The activity can be detected by the headphones themselves, by a paired device (e.g., phone, watch, etc.), or by any combination thereof. When such activity is detected, the audio safety spatialization algorithm is activated. In some examples, the audio safety spatialization feature may be activated by user input, such as by a gesture of press of a button. For example, if the user is sitting at a desk working, but wants to be able to turn around to better hear a conversation behind her, the user may activate the audio spatialization feature. 
     The audio safety spatialization algorithm reproduces the audio as a “virtual source” floating in front of the user. When the user turns his head, the virtual source remains in its position relative to the user, which greatly increases the user&#39;s spatial awareness of the environment. As an example, if the user is bicycling or running down the street, the virtual source will remain “in front” of him (i.e., the direction he is moving). If the user turns his head to the left to look over his left shoulder (e.g., to check for an automobile), the volume of the source in his left ear will decrease significantly, which enables heightened awareness toward sounds emanating from the direction he is facing. With a traditional pair of headphones, in contrast, if a listener turns his head, the volume in both ears remains constant, and thus the user is equally unable to hear ambient sounds, no matter which direction he is facing. When the audio safety spatialization feature is not activated, the headphones may operate as a traditional pair of headphones. 
     The “virtual source” may remain in a position relative to the user&#39;s direction of travel. For example, where the user that is bicycling or jogging in the example above makes a turn, as opposed to merely turning his head, the virtual source may move to a new position in front of the user in the new direction of travel. Movement of the virtual source may be based on time, detected direction of travel, or some combination of these or other factors. 
     When the audio safety spatialization feature is activated, an angle θ corresponding to the current direction the user is facing is initialized to 0. The angle θ may be determined by the IMU, for example, using data from a gyroscope, magnetometer, accelerometer, etc. The headphones operate with the audio spatialization feature based on this initial value of θ. Data may be continually fetched from the IMU, such as every 20 ms, 200 ms, etc. Each time data is fetched from the IMU, the angle θ is updated according to the direction the user is currently facing. In some examples, a “return to zero” function may be applied to the angle θ, with time constant τ, such that the angle of the source relative to the user always returns to zero. The return to zero repositions the virtual source of the audio to a position in front the user over time, such as when the user makes a turn other than just a quick turn of the head in one direction or other. The audio spatialization feature is updated, and the headphones operate based on, the current value of θ. 
     Example Systems 
       FIGS. 1 and 2  illustrate an example system  100  for audio safety spatialization. The system  100  can include a pair of headphones  180  in communication with one or more computing devices  160 ,  170 . The computing devices  160 ,  170  may be, for example, a mobile phone, a smart watch, a gaming system, a tablet, or any other mobile computing device. In some examples, the example system  100  may be entirely contained within the headphones  180 , such that the headphones  180  perform all audio safety spatialization operations without communication from other devices. In other examples, as illustrated in  FIGS. 1-2 , the computing devices  160 ,  170  may perform some operations and provide information to the headphones  180  based on such operations. While  FIGS. 1-2  illustrate the headphones  180  as communicating with and utilizing information from one or two computing devices, it should be understood that the headphones  180  may receive information from any number of computing devices. 
     Headphones  180  may include any type of audio source having a left speaker portion  187  and a right speaker portion  188 , such as shown in  FIG. 2 . For example, headphones may be a pair of earbuds where a portion of the device is inserted into a concha of a user&#39;s ear, a pair of over-ear or around-ear speakers held in place over or around the user&#39;s ears, such as by a headband portion, an in-ear monitor inserted into a canal of the user&#39;s ear, or any other types of headphones providing sound to the user&#39;s ears. In some examples, the headphones  180  may include an input portion input portion  185  adjacent an outer surface, attached to a cable, or elsewhere on the headphones. For example, the input portion  185  may be pressed or otherwise activated to change an operating mode of the headphone  180  or to perform other functions. In some examples, the input portion  185  may be activated to switch the headphones  180  between an audio safety spatialization mode and a standard operating mode. 
     The headphones  180  may communicated with the computing devices  160 ,  170  via a wired or wireless connection. For example, the devices may be wirelessly coupled via a short range pairing connection, such as Bluetooth. Other types of wireless connections are also possible. The headphones  180  and computing devices  160 ,  170  can utilize standard communications protocols, such as Ethernet, WiFi, HTTP, protocols described in IEEE 802.11, cellular technology (such as GSM, CDMA, UMTS, EV-DO, WiMAX, LTE, etc.) protocols that are proprietary to one or more companies, and various combinations of the foregoing. The subject matter described herein is not limited to any particular manner of transmission of information. 
     As illustrated in  FIG. 2 , the headphones  180  may include one or more processors  281 , memory  282  and other components typically present in headphones or other computing devices. 
     Memory  282  of headphones  180  can store information accessible by the one or more processors  281 , including instructions  283  that can be executed by the one or more processors  281 . Memory  282  can also include data  284  that can be retrieved, manipulated or stored by the processor  281 . The memory  282  can be of any non-transitory type capable of storing information accessible by the processor, such as a hard-drive, memory card, ROM, RAM, etc. 
     The instructions  283  can be any set of instructions to be executed directly, such as machine code, or indirectly, such as scripts, by the one or more processors. In that regard, the terms “instructions,” “application,” “steps,” and “programs” can be used interchangeably herein. The instructions can be stored in object code format for direct processing by a processor, or in any other computing device language including scripts or collections of independent source code modules that are interpreted on demand or compiled in advance. Functions, methods, and routines of the instructions are explained in more detail below. 
     Data  284  may be retrieved, stored or modified by the one or more processors  281  in accordance with the instructions  283 . The subject matter described herein is not limited by any particular data structure. The data can also be formatted in any computing device-readable format such as, but not limited to, binary values, ASCII or Unicode. Moreover, the data can comprise any information sufficient to identify the relevant information, such as numbers, descriptive text, proprietary codes, pointers, references to data stored in other memories such as at other network locations, or information that is used by a function to calculate the relevant data. 
     The one or more processors  281  can be any conventional processors, such as a commercially available CPU. Alternatively, the processors can be dedicated components such as an application specific integrated circuit (“ASIC”) or other hardware-based processor. 
     The headphones  180  may further include a transmitter/receiver  284 , output  287 , and one or more sensors  288 . The transmitter/receiver  284  may be any conventional type which enables communication with other devices, such as the computing device  160 . The output  287  may include audio speakers, including a first speaker designated for a user&#39;s right ear and a second speaker designated for the user&#39;s left ear. In some examples, other types of output may also be provided, such as tactile feedback, image output on a display, etc. 
     The one or more sensors  288  may provide for determination of an activity or condition associated with the user. For example, the sensors  288  may include a gyroscope which detects an inertial position of the headphones  180 , an accelerometer which detects linear movement of the headphones, a magnetometer, a pedometer, a global positioning system (GPS), camera, microphone, or any of a number of other types of sensors. The one or more sensors  288  may operate independently or in concert. Based on input from the sensors  288 , the processor  281  may determine that the user is, for example, jogging, cycling, skateboarding, walking on a crowded sidewalk, occupying another busy space, riding on public transit, or performing any of a number of other activities for which the user might want or need increased awareness of his surroundings. The one or more processors  281  may receive information from the computing device  160 , for example through transmitter/receiver  286 , in addition or in the alternative to receiving information from the sensors  288 . 
     The instructions  283  may provide for transitioning into an audio safety spatialization mode based on the input from the sensor  288  and/or  167 . For example, in a regular or default mode of operation, the headphones  180  may generate sound equally and consistently through both right and left ear portions of output  287 . However, upon detection of a condition or activity, such as exercising, commuting, or occupying a busy space, the instructions may provide for transition to the audio safety spatialization mode. In this mode, sound is generated through the right and left ear portions of the output  287  with the effect of emanating from a virtual audio source at a first position. The first position may be a position relative to the headphones or the user wearing the headphones. For example, the first position may be in front of the user, as described below in the example of  FIG. 3A . As angular movement of the headphone is detected, an effect of the sound is adjusted based on the angular movement. For example, when the user turns his head to the left, the virtual audio source in front of the user will be output more subtly or quietly in the left ear speaker portion and more distinctly or loudly in the right ear speaker portion. In this regard, based on the adjusted output in the respective speaker portions, the user perceives the virtual audio source as remaining in the same fixed position in space, despite the user&#39;s adjusted head position. This is described further in connection with  FIG. 3B  below. 
     According to some examples, when one or more conditions are met, the virtual audio source may be moved to a second position. The second position may be the same as the first position relative to the user or headphones (e.g., in front of the user), but a different position in space, as described further in connection with  FIG. 3C . The conditions which may result in moving the virtual audio source may include, for example, the headphones or user&#39;s head remaining in the adjusted angular position for a predefined period of time. Such period of time may be, for example, a few hundred milliseconds, several seconds, or any other length of time suggesting that the user&#39;s head is likely to remain in the updated position. 
     Computing device  160  may include components similar to those of the headphones  180 , including one or more processors  161  in communication with a memory  162  including instructions  163  and data  164 . The computing device  160  may be a mobile computing device intended for use by a user and capable of wirelessly exchanging data with a server over a network such as the Internet. By way of example only, computing device  160  may be a mobile phone or a device such as a wireless-enabled PDA, a tablet PC, a netbook, a smart watch, a head-mounted computing system, or any other device that is capable of sharing information with the headphones  180 . The user may input information using a small keyboard, a keypad, microphone, using visual signals with a camera, or a touch screen, etc. 
     The computing devices  160 ,  170  may have all of the components normally used in connection with a mobile computing device such as a processor, memory (e.g., RAM and internal hard drives) storing data and instructions, a display such as display  165 , and user input device  166  (e.g., input buttons, touch-screen, microphone, etc.). The client computing device may also include one or more sensors  167  for detecting conditions surrounding the mobile device. For example, the sensors  167  may include an image capture device, such as a camera for recording video streams and/or capturing images, speakers, a network interface device, and all of the components used for connecting these elements to one another. The sensors  167  may also include a location determination system, such as a GPS. Other examples of location determination systems may determine location based on wireless access signal strength, images of geographic objects such as landmarks, semantic indicators such as light or noise level, etc. 
     The sensors  167  may further include, by way of example and not limitation, a gyroscope, accelerometer, magnetometer, GPS, camera, microphone, light sensor, motion sensor, etc. Such sensors may be used to detect a variety of different conditions, such as movement, weather conditions, sounds, nearby objects, electromagnetic fields, etc. The sensors  167  may in some examples recognize detailed information relating to the conditions. For example, the gyroscope and accelerometer may not only detect whether the device  160  is moving or not, but may determine whether the movement is linear or rotational, a direction of the movement, a speed of the movement, etc. Information from different types of the sensors  167  may also be used to determine conditions or activities. For example, a low reading from a light sensor in combination with a high pressure reading from a barometer may indicate rain. As another example, a particular speed and level of vibration may indicate that the device  160  is traveling on a bicycle, while received sounds or smells indicate that the device  160  is passing a restaurant. 
     Memory  162  can store information accessible by the one or more processors  161 , including instructions  163  that can be executed by the one or more processors  161 . Memory  162  can also include data  164  that can be retrieved, manipulated or stored by the processor  161 . The memory  162  can be of any non-transitory type capable of storing information accessible by the processor, such as a hard-drive, memory card, ROM, RAM, DVD, CD-ROM, write-capable, and read-only memories. 
     The instructions  163  can be any set of instructions to be executed directly, such as machine code, or indirectly, such as scripts, by the one or more processors. In that regard, the terms “instructions,” “application,” “steps,” and “programs” can be used interchangeably herein. The instructions can be stored in object code format for direct processing by a processor, or in any other computing device language including scripts or collections of independent source code modules that are interpreted on demand or compiled in advance. Functions, methods, and routines of the instructions are explained in more detail below. 
     Data  164  may be retrieved, stored or modified by the one or more processors  161  in accordance with the instructions  163 . For instance, although the subject matter described herein is not limited by any particular data structure, the data can be stored in computer registers, in a relational database as a table having many different fields and records, or XML documents. The data can also be formatted in any computing device-readable format such as, but not limited to, binary values, ASCII or Unicode. Moreover, the data can comprise any information sufficient to identify the relevant information, such as numbers, descriptive text, proprietary codes, pointers, references to data stored in other memories such as at other network locations, or information that is used by a function to calculate the relevant data. 
     The one or more processors  161  can be any conventional processors, such as a commercially available CPU. Alternatively, the processors can be dedicated components such as an application specific integrated circuit (“ASIC”) or other hardware-based processor. Although not necessary, computing device  160  may include specialized hardware components to perform specific computing processes, such as image recognition, object recognition, voice recognition, etc. 
     The instructions  163  are executable by the processor  162 , for example, to perform a method including receiving a policy for reporting information, detecting surrounding conditions or activities, determining whether the detected condition or activity triggers reporting of information in accordance with the policy, and report information when it is triggered. The reporting may including at least one of sampling data or uploading information, or both. According to some examples, a first condition or activity may trigger the sampling of data, while a second different condition or activity triggers uploading information. 
     The device  160  further includes an input/output (I/O) interface  169 . I/O interface  169  may provide for communication, using analog or digital modulation, between the computing device  160  and other devices or networks. The I/O interface  169  may facilitate circuit-switched and/or packet-switched communication. For instance, I/O interface  169  may include a chipset and antenna arranged for wireless communication with a radio access network or an access point. I/O interface  169  may include a wireline interface, such as an Ethernet, Universal Serial Bus (USB), or High-Definition Multimedia Interface (HDMI) port. I/O interface  169  may also include a wireless interface, such as a Wi-Fi, or wide-area wireless interface (e.g., WiMAX or 3GPP Long-Term Evolution (LTE)). Other forms of physical layer interfaces and other types of communication protocols may also be used. Furthermore, I/O interface  169  may comprise multiple physical communication interfaces (e.g., a Wifi interface, a short range wireless interface, and a wide-area wireless interface), and may enable multiple simultaneous connections of different types. 
     The I/O interface  169  may be used to establish connectivity with one or more other computing devices, such as the headphones  180 . The I/O interface  169  may be used to establish connections with access points, to detect beacons or radio frequency identification (RFID) tags, to determine connectivity information, etc. Such information may further be used to determine conditions or activities associated with the device  160 , the headphones  180 , or the user. For example, a number of other computing devices moving in close proximity with the device  160  may suggest that the device  160  is on a public train or a busy sidewalk. More precise determinations can be made when combined with other sensor information, such as noise level, vibrations, speed, etc. 
     While several examples of how various types of detected information can be used separately or in combination to determine conditions surrounding the device  160  or activities, it should be understood that any number of various activities or conditions can be determined using various inputs. Moreover, while examples of information or activities detected by one device, such as the computing device  160 , were described, it should be understood that such information or activities could similarly be detected by other devices, such as the headphones  180 . 
       FIGS. 3A-3C  illustrate an example of audio spatialization. In  FIG. 3A , user  315  is wearing headphones including left ear portion  387  and right ear portion  388 . Audio is reproduced through the left ear portion  387  and the right ear portion  388  as a virtual source  350  in front of the user. For example, the user  315  would perceive audio generated through the headphones, such as music, audio books, etc., as being generated from the virtual source  350  in front of the user. As explained in further detail below, when the user  315  is facing forward in a neutral position, sound is played equally through the left and right ear portions  387 ,  388 . However, when the user  315  turns his head, the virtual audio source  350  remains in the same position. As such, sound is played louder in the portion of the headphones closer to the virtual audio source  350  than in the portion of the headphones further from the virtual audio source  350 . 
     As shown in  FIG. 3A , a first plane  360  that includes both the left ear portion  387  and the right ear portion  388 , forms a first angle α with respect to a second plane  365  that includes the virtual audio source  350  and a center point  389  between the left ear portion  387  and the right ear portion  388 . In this example, the angle α is approximately 90 degrees, and a first distance  377  between the virtual audio source  350  and the left ear portion  387  is approximately equal to a second distance  378  between the virtual audio source  350  and the right ear portion  388 . Accordingly, sound may be produced at a same level through the left ear portion  387  and the right ear portion  388 . For example, both portions of headphones may produce sound at the same volume, frequency, saturation, bass, etc. 
     While in the present example the virtual audio source  350  is in front of the user, in other examples the virtual audio source may have a different position relative to the user. For example, the virtual audio source  350  may be behind the user, to a side of the user, or in a position corresponding to a source of environmental sounds. Moreover, it should be understood that the angle of the virtual audio source  350  with respect to the user or the headphones may be measured in any of a number of different ways. 
     In  FIG. 3B , a position of the headphones has changed relative to the virtual audio source  350 . In particular, the user has turned his head approximately 45 degrees to the right. As such, the first plane  360  including the headphones has changed, and thus the angle α between the first plane  360  and the second plane  365  has also changed. Further, the first distance  377  is now shorter than the second distance  378 . In this example, sound generated through the left ear portion  387  may be at a higher level with respect to sound generated through the right ear portion  388 . For example, to give the effect of the virtual audio source  350  remaining in a same point in space, sound corresponding to the virtual audio source  350  may be played more loudly through the closer left ear portion  387  than through the farther right ear portion  388 . Any of a number of audio spatialization techniques may be implemented, such as volume-based panning, head related transfer function (HRTF) spatialization, or the like. 
       FIG. 3C  provides another example of a change in position. In this example, the user turns his head approximately 90 degrees with respect to the initial position of  FIG. 3A . As such, the angle α in this example is even greater, being approximately 180 degrees. Moreover, the first distance  377  is even shorter relative to  FIG. 3B , and the second distance  378  is even longer. Accordingly, sound generated through the left ear portion  387  may be at a higher level relative to the level in  FIG. 3B , and the sound generated through the right ear portion  388  maybe at a lower level relative to that of  FIG. 3B . Accordingly, the user has heightened awareness of his surroundings in the direction he is facing. 
     In each of the examples above, the virtual audio source  350  remains in generally the same point in space, though the user&#39;s angular position changes. In examples where the user is traveling, the virtual audio source  350  may also travel at a same rate of speed, such that it remains at a same linear position relative to the user. In such examples, though the linear position may be continually updated based on the user&#39;s movement, changes in angular position as described above in connection with  FIGS. 3A-3C  may be detected and used to effect a change in the sound generated through the headphones. 
     Where the change in angular position is a result of a quick turn of the user&#39;s head, the user may shortly thereafter return to the initial position. As the user&#39;s head turns, the adjustment in sound emitted through the left ear portion  387  and the right ear portion  388  may be instantaneous. As the user returns to the initial position of  FIG. 3A , the generated sound would return to the same levels as described in connection with  FIG. 3A . In some examples, however, the change in angular position of the headphones or user&#39;s head may remain for a prolonged period of time. By way of example only, if the user is jogging and makes a right turn, as opposed to quickly turning his head to check surroundings over his right shoulder, the virtual audio source  350  may be moved to a different position in space, such that it realigns with the initial position relative to the user. 
       FIG. 3D  illustrates an example of moving the virtual audio source  350 , such as when the user&#39;s or headphones&#39; angular position changes for at least a predetermined period of time, when the user changes a direction of travel, or when other conditions are met. The predetermined period of time may be, for example, one second or several seconds or more. In other examples, sensors in the headphones and/or coupled computing devices may detect a direction of the user&#39;s movement, and compare such direction to an orientation of the headphones. In such examples, the virtual audio source  350  may be moved in response to detecting a change in the user&#39;s direction of travel. It should be understood that other conditions for moving the virtual audio source  350  are also possible. 
     As shown in  FIG. 3D , the virtual audio source  350  is moved to a position in front of the user, such position corresponding to the initial position relative to the user illustrated in  FIG. 3A . Accordingly, the first plane  360  through the left and right ear portions  387 ,  388  is again at an angle of approximately 90 degrees with respect to the second plane  365  through the virtual audio source  350  and a center point of the headphones or the user&#39;s head. In this regard, the sound generated from the left and right ear portions  387 ,  388  is again equalized, such that an effect from the user&#39;s perspective is that the virtual audio source  350  is in front of his face. 
     The audio safety spatialization features described above may be activated upon detection of particular conditions or activities. For example, the headphones and/or coupled computing devices may determine based on sensor input that the user is jogging, cycling, skateboarding, traveling on a path near traffic, traveling on public transportation, occupying a busy space such as a crowded sidewalk, or performing any of a number of other activities for which the user may desire a heightened awareness of his surroundings. Upon detection of such conditions or activities, the headphones may automatically switch to an audio safety spatialization mode. 
       FIGS. 4A-4C  illustrate another example of audio safety spatialization. In this example, the feature is activated in response to detection of the user performing a predetermined activity of cycling. 
     As shown in  FIG. 4A , headphones user  405  is cycling in bicycle path  420  alongside a roadway  410 . A vehicle  440  is also traveling on the roadway  410 , and approaching the user  405  from behind. Detailed view  450  shows a relative position of left ear portion  487  and right ear portion  488  of the user&#39;s headphones, in relation to sound source  445  which corresponds to the vehicle  440 . The user&#39;s head is facing forward, and the left ear portion  487  and right ear portion  488  are generally parallel along a plane that is perpendicular to the user&#39;s direction of travel. As the sound source  445  approaches from behind on the user&#39;s left side, and is slightly closer to the user&#39;s left ear than the right ear, sounds from the vehicle  440  may be heard slightly louder in the user&#39;s left ear portion than the user&#39;s right ear. The virtual audio source  350 , however, is in front of the user, and each of the left ear portion  487  and right ear portion  488  are approximately equidistant from the virtual audio source  350 . Accordingly, sound, such as music, played through the left ear portion  487  is a same level as the sound played through the right ear portion  488 . 
     In  FIG. 4B , the user  405  turns his head to the left, such as to see the approaching vehicle  440 . The virtual audio source  350 , however, remains in the same position. Accordingly, as seen in detailed view  451 , as a result of the user&#39;s head turn, the right ear portion  488  of the headphones is angled closer to the virtual audio source  350  than the left ear portion  487 . As such, sound played through the left ear portion  487  is reduced as compared to sound played through the right ear portion  488 . This allows the user to more clearly hear the sound source  445  of the vehicle  400 , which is closer to the user&#39;s left ear than the right ear. 
     In  FIG. 4C , the user  405  has changed directions, and is now traveling along path  421  near roadway  411 , which is approximately perpendicular to his previous direction of travel. Accordingly, as shown in detailed view  452 , an orientation of the user&#39;s headphones has also changed with respect to the previous orientations of  FIGS. 4A-B . However, the headphones may determine that the change is orientation is due to a change in the user direction. For example, such determination may be based on the headphones remaining in the updated orientation for at least a predetermined period, a detected change in the user&#39;s direction of travel, or other information. Accordingly, the virtual audio source  350  may be automatically adjusted in relation to the updated orientation. As shown in  FIG. 4C , the virtual audio source  350  returns to a neutral position with respect to the updated orientation of the headphones, such that the right ear portion  488  and left ear portion  487  are again approximately equidistant from the virtual audio source  350 , similar to the relative positions of  FIG. 4A . In this orientation, music or other sound played through the left and right ear portions of the headphones is played at approximately equal levels. 
     As discussed above, the audio safety spatialization feature may be activated upon detection of particular activities performed by the user or conditions surrounding the user. In other examples, however, the audio safety spatialization features may be manually activated by the user, such as by pressing an input button or speaking a verbal command. As such, the user may still benefit from the audio safety spatialization features when performing other tasks, such as working at a desk in an open office environment, hiking through woods, shopping, or performing any other activity that may not necessarily be one of the predetermined activities that will trigger automatic activation of the feature. 
     Example Methods 
     In addition to the operations described above and illustrated in the figures, various operations will now be described. It should be understood that the following operations do not have to be performed in the precise order described below. Rather, various steps can be handled in a different order or simultaneously, and steps may also be added or omitted. 
       FIG. 5  illustrates an example method  500  for automatically determining a playback mode of a pair of headphones. The method may be performed by, for example, the headphones. In some examples, the method may also utilize information from one or more computing devices, such as mobile phones, smart watches, etc., coupled to the headphones. 
     In block  510 , the headphones provide audio output in a normal playback mode. In this normal mode, for example, the headphones may provide output at equal levels in both a left ear portion and a right ear portion. 
     In block  520 , input is received from one or more sensors. Examples of such sensors include an accelerometer, a gyroscope, a magnetometer, a pedometer, GPS, microphone, or any of a number of other types of sensors. The input may provide information relating to movements of the user or conditions surrounding the user. By way of example only, the information may indicate whether the user is outdoors, a direction in which the user is moving, a number of people or other devices within a certain proximity of the user, etc. The input may be received continually, or periodically, such as every few milliseconds, tenths of a second, seconds, etc. 
     In block  530 , an activity performed by the user and/or conditions surrounding the user may be determined based on the received sensor input. For example, it may be determined whether the user is cycling, jogging, performing some other type of exercise, commuting, sightseeing, etc. 
     In block  540 , it is determined whether the determined activity/condition triggers an audio safety spatialization mode. For example, a set of activities of conditions that will trigger the audio safety spatialization mode may be predefined, either by a manufacturer or by a user. The activities/conditions may be defined with varying degrees of specificity. For example, a more specific activity may designate an action of the user and an environment, such as cycling on a roadway where more than 5 vehicles pass by per minute. A less specific activity may designate fewer parameters, such as simply jogging. In some examples, threshold parameters may be set to distinguish particular activities from others. For example, traveling at a threshold range of speed may distinguish cycling from driving in a car. 
     If the determined activity/condition does not trigger audio safety spatialization mode, the method  500  may return to block  510  where playback continues in normal mode. However, if the activity/condition qualifies as one of the predefined activities/conditions, the headphones may automatically switch to operation in audio safety spatialization mode (block  550 ). 
       FIG. 6  illustrates an example method  600  of operation of the headphones in the audio safety spatialization mode. 
     In block  610 , a virtual audio source is established at a first position, relative to a neutral position of the headphones For example, when the user is wearing the headphones, an initial angle θ, corresponding to a current direction the user is facing, is set to zero. The user&#39;s direction may be determined based on information from any of one or more sensors in the headphones and/or coupled computing devices. Examples of such sensors include accelerometer, gyroscope, magnetometer, etc. The first position may be in front of the user, though in other examples the first position may be behind the user or in any other relative position. 
     In block  620 , sound is generated through the left ear portion and the right ear portion of the headphones as though the sound is emanating from the virtual source at the first position. Accordingly, for example, the sound may be played at an equal volume in both the left and right ear portions of the headphones. 
     In block  630 , it is determined whether an angular position of the headphones has changed with respect to the first position. For example, it may be determined whether an orientation of the headphones shifted in a way that indicates the user turned his head left or right. If the angular position does not change, the method  600  may return to block  620  and continue to generate sound as indicated. If a change is angular position is detected, however, the method  600  proceeds to block  640 . 
     In block  640 , an angle of the headphones with respect to the first position is determined. For example, where the angle θ was initialized to zero, an updated value for the angle θ may be determined. 
     In block  650 , playback in the left and/or right ear portions of the headphones is adjusted based on the determined angle. For example, sound may be reduced in volume at least one of the left ear portion or the right ear portion. In other examples, sound may be increased in volume in one of the left or right ear portions. The amount of reduction or increase in volume may vary as a function of the determined angle. 
     In some examples, a return-to-zero function may be applied to the angle θ, such that the angle of the virtual audio source relative to the user always returns to zero. For example, in block  660  it is determined whether conditions for changing a position of the virtual audio source are met. The conditions may be based on an amount of time the headphones remain at the angle θ, an amount of distance traveled while the headphones are at the angle θ, etc. Such conditions may not be met if, for example, the user briefly turns his head to one side and then returns to the initial neutral position. In such case, the method  600  returns to block  620 . However, if the conditions are met, the method  600  proceeds to block  670  where the return-to-zero-function is applied. 
     In block  670 , the virtual audio source is moved to a second position in space, such that the angular position of the virtual audio source relative to the user is consistent with the initial neutral position. For example, the angle θ may be reinitialized based on the current value determined in block  640 . In this regard, the virtual audio source may remain in the same relative position to the user for the majority of the user&#39;s use of the headphones. 
     The foregoing system and methods are advantageous in that they provide for increased safety of users wearing headphones while participating in various activities. By automatically activating the audio safety spatialization features, the user may perform a variety of tasks without having to remember to activate the feature. Moreover, as the feature enables increased awareness of the user&#39;s surroundings, the user will be more prepared to react to the environment around them. 
     Unless otherwise stated, the foregoing alternative examples are not mutually exclusive, but may be implemented in various combinations to achieve unique advantages. As these and other variations and combinations of the features discussed above can be utilized without departing from the subject matter defined by the claims, the foregoing description of the embodiments should be taken by way of illustration rather than by way of limitation of the subject matter defined by the claims. In addition, the provision of the examples described herein, as well as clauses phrased as “such as,” “including” and the like, should not be interpreted as limiting the subject matter of the claims to the specific examples; rather, the examples are intended to illustrate only one of many possible embodiments. Further, the same reference numbers in different drawings can identify the same or similar elements.