Facebook Patent | Power reduction via smart microphone selection using environmental intelligence

Patent: Power reduction via smart microphone selection using environmental intelligence

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Publication Number: 20210029479

Publication Date: 20210128

Applicant: Facebook

Abstract

A system reduces power consumption by optimizing a selection of acoustic sensors of a sensor array based on environmental parameters of a local area. The system includes the sensor array including the acoustic sensors configured to detect sound in a local area, and processing circuitry. The processing circuitry is configured to: determine an environmental parameter of the local area; determine a performance metric for the sensor array; determine a selection of a subset of acoustic sensors from the acoustic sensors of the sensor array that satisfies the performance metric based on the environmental parameter of the local area; and process audio data from the subset of the acoustic sensors of the sensor array.

Claims

1. A method, comprising, by an audio system including a sensor array: determining an environmental parameter of a local area surrounding the sensor array, the sensor array including acoustic sensors configured to detect sounds in the local area; determining a performance metric for the sensor array; determining a selection of a subset of acoustic sensors from the acoustic sensors of the sensor array that satisfies the performance metrics based on the environmental parameter of the local area, the subset of acoustic sensors including a minimum number of acoustic sensors that satisfies the performance metric as determined from the environmental parameter; and processing audio data from the subset of the acoustic sensors of the sensor array, wherein audio content presented by the audio system is based in part on the processed audio data.

2. The method of claim 1, further comprising activating the subset of acoustic sensors.

3. The method of claim 2, further comprising deactivating acoustic sensors of the sensory array that are outside of the subset.

4. The method of claim 2, wherein a first acoustic sensor of the sensor array is outside of the subset and the first acoustic sensor is active, the method further comprising: removing audio data produced by the first acoustic sensor from audio data generated by the sensor array to form the audio data of the subset.

5. The method of claim 1, wherein: the environmental parameter includes a reverberation time; and the performance metric includes an array gain.

6. The method of claim 1, wherein the environmental parameter includes one of: a number of acoustic sound sources; a location of a sound source; a direction of arrival of a sound source; loudness of background noise; or a spatial property of background noise.

7. The method of claim 1, wherein processing the audio data includes performing at least one of: an application of an acoustic transfer function; a beamforming; a direction of arrival estimation; a signal enhancement; or a spatial filtering.

8. The method of claim 1, wherein the performance metric includes one of: a word error rate; an array gain; a distortion threshold level; a signal to noise ratio; white noise gain; signal to noise ratio of a beamformer; a distance for sound pick-up; speech quality; speech intelligibility; or listening effort.

9. The method of claim 1, wherein determining the selection of the subset of acoustic sensors from the acoustic sensors of the sensor array that satisfies the performance metric based on the environmental parameter further comprises: using a neural network defining relationships between inputs including environmental parameters and performance metrics and outputs including subsets of the acoustic sensors of the sensor array.

10. The method of claim 1, further comprising receiving the environmental parameter from a server based on a location associated with the sensor array.

11. The method of claim 1, further comprising receiving the performance metric from a headset including another sensor array.

12. The method of claim 1, further comprising updating the subset of acoustic sensors based on a change in the environmental parameter.

13. A system, comprising: a sensor array including acoustic sensors configured to detect sound in a local area; and processing circuitry configured to: determine an environmental parameter of the local area; determine a performance metric for the sensor array; determine a selection of a subset of acoustic sensors from the acoustic sensors of the sensor array that satisfies the performance metric based on the environmental parameter of the local area, the subset of acoustic sensors including a minimum number of acoustic sensors that satisfies the performance metric as determined from the environmental parameter; and process audio data from the subset of the acoustic sensors of the sensor array wherein audio content presented by the system is based in part on the processed audio data.

14. The system of claim 13, wherein the processing circuitry is further configured to activate the subset of acoustic sensors.

15. The system of claim 14, wherein the processing circuitry is further configured to deactivate acoustic sensors of the sensory array that are outside of the subset.

16. The system of claim 14, wherein a first acoustic sensor of the sensor array is outside of the subset and the first acoustic sensor is active, and the processing circuitry is further configured to: remove audio data produced by the first acoustic sensor from audio data generated by the sensor array to form the audio data of the subset

17. The system of claim 13, wherein: the environmental parameter includes a reverberation time; and the performance metric includes an array gain.

18. The system of claim 13, wherein: the environmental parameter includes one of: a number of acoustic sound sources; a location of a sound source; a direction of arrival of a sound source; loudness of background noise; or a spatial property of background noise; and the processing circuitry configured to process the audio data includes the audio controller being configured to perform at least one of: an application of an acoustic transfer function; a beamforming; a direction of arrival estimation; a signal enhancement; or a spatial filtering.

19. The system of claim 13, wherein the performance metric includes: a word error rate; an array gain; a distortion threshold level; a signal to noise ratio; white noise gain; signal to noise ratio of a beamformer; a distance for sound pick-up speech quality; speech intelligibility; or listening effort.

20. A non-transitory computer-readable medium storing instructions that, when executed by one or more processors, cause the one or more processors to: determine an environmental parameter of a local area surrounding a sensor array, the sensor array including acoustic sensors configured to detect sounds in the local area; determine a performance metric for the sensor array; determine a selection of a subset of acoustic sensors from the acoustic sensors of the sensor array that satisfies the performance metric based on the environmental parameter of the local area, the subset of acoustic sensors including a minimum number of acoustic sensors that satisfies the performance metric as determined from the environmental parameter; and process audio data from the subset of the acoustic sensors of the sensor array.

Description

BACKGROUND

[0001] The present disclosure generally relates to acoustic sensor arrays and specifically to optimization of sensor array usage using environmental intelligence.

[0002] Energy limitations and heat dissipation are challenges for wearable devices, and can make it difficult to implement certain types of functionality on the wearable devices. Microphone array processing, for example, uses a sensor array that consumes power to capture audio data and real-time process heavy algorithms to process the audio data. It is desirable to reduce power consumption and processing requirements while achieving a sufficient level of performance.

SUMMARY

[0003] Embodiments relate to using environmental parameters as a basis for selecting an optimal subset of acoustic sensors from a sensor array to reduce power consumption while maintaining high performance, such as in terms of satisfying performance metrics related to the sensor array or audio processing. Some embodiments include a method, performed by an audio system, that determines an environmental parameter of a local area surrounding a sensor array. The sensor array includes acoustic sensors configured to detect sounds in the local area. A performance metric is determined for the sensor array, and a selection of a subset of acoustic sensors are determined from the acoustic sensors of the sensor array that satisfies the performance metric based on the environmental parameter of the local area. Audio data is processed from the subset of the acoustic sensors of the sensor array. Audio content presented by the audio system is based in part on the processed audio data

[0004] Some embodiments include a system including a sensor array and an audio controller. The sensor array includes acoustic sensors configured to detect sound in a local area. The audio controller determines an environmental parameter of the local area and determines a performance metric for the sensor array. The audio controller determines a selection of a subset of acoustic sensors from the acoustic sensors of the sensor array that satisfies the performance metric based on the environmental parameter of the local area, and processes audio data from the subset of the acoustic sensors of the sensor array. Audio content presented by the system is based in part on the processed audio data.

[0005] Some embodiments include a non-transitory computer-readable medium storing instructions that, when executed by one or more processors, cause the one or more processors to determine an environmental parameter of a local area surrounding a sensor array including acoustic sensors configured to detect sounds in the local area and determine a performance metric for the sensor array. The instructions further cause the one or more processors to determine a selection of a subset of acoustic sensors from the acoustic sensors of the sensor array that satisfies the performance metric based on the environmental parameter of the local area, and process audio data from the subset of the acoustic sensors of the sensor array.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] FIG. 1A is a perspective view of a headset implemented as an eyewear device, in accordance with one or more embodiments.

[0007] FIG. 1B is a perspective view of a headset implemented as a head-mounted display, in accordance with one or more embodiments.

[0008] FIG. 2 is a block diagram of an audio system, in accordance with one or more embodiments.

[0009] FIG. 3 is a flowchart illustrating a process of optimizing acoustic sensors on a headset, in accordance with one or more embodiments.

[0010] FIG. 4 is a graph illustrating the relationship between array gain and number of acoustic sensors for different reverberation times, in accordance with one or more embodiments.

[0011] FIG. 5 is a system environment that includes a headset, in accordance with one or more embodiments.

[0012] The figures depict embodiments of the present disclosure for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles, or benefits touted, of the disclosure described herein.

DETAILED DESCRIPTION

[0013] Embodiments relate to reducing power consumption for sensor arrays employed in spatial sound applications using environmental intelligence. Environmental intelligence refers to information about the environment, as may be defined by environmental parameters captured by various types of sensors. For example, the environmental parameters of a local area surrounding a sensor array and target performance metrics are determined, and used as a basis for selecting an optimal subset of acoustic sensors from the sensor array. The environmental parameters may be determined based on data captured by the acoustic sensors or other types of sensors. The selection may include activating or deactivating acoustic sensors, or processing data from only the subset of acoustic sensors. As such, power consumption is reduced while maintaining a target (e.g., high) performance. In one example, an environmental parameter of the local area includes a reverberation time and a performance metric includes an array gain. A longer reverberation time corresponds with a larger number of activated acoustic sensors to achieve a target array gain. A selection of a subset of acoustic sensors of the sensor array that achieves the target array gain is determined based on the reverberation time of the local area.

[0014] Embodiments of the present disclosure may include or be implemented in conjunction with an artificial reality system. Artificial reality is a form of reality that has been adjusted in some manner before presentation to a user, which may include, e.g., a virtual reality (VR), an augmented reality (AR), a mixed reality (MR), a hybrid reality, or some combination and/or derivatives thereof. Artificial reality content may include completely generated content or generated content combined with captured (e.g., real-world) content. The artificial reality content may include video, audio, haptic feedback, or some combination thereof, and any of which may be presented in a single channel or in multiple channels (such as stereo video that produces a three-dimensional effect to the viewer). Additionally, in some embodiments, artificial reality may also be associated with applications, products, accessories, services, or some combination thereof, that are used to, e.g., create content in an artificial reality and/or are otherwise used in (e.g., perform activities in) an artificial reality. The artificial reality system that provides the artificial reality content may be implemented on various platforms, including a headset connected to a host computer system, a standalone headset, a mobile device or computing system, or any other hardware platform capable of providing artificial reality content to one or more viewers.

Eyewear Device Configuration

[0015] FIG. 1A is a perspective view of a headset 100 implemented as an eyewear device, in accordance with one or more embodiments. In some embodiments, the eyewear device is a near eye display (NED). In general, the headset 100 may be worn on the face of a user such that content (e.g., media content) is presented using a display assembly and/or an audio system. However, the headset 100 may also be used such that media content is presented to a user in a different manner. Examples of media content presented by the headset 100 include one or more images, video, audio, or some combination thereof. The headset 100 includes a frame, and may include, among other components, a display assembly including one or more display elements 120, a depth camera assembly (DCA), an audio system, and a position sensor 190. While FIG. 1A illustrates the components of the headset 100 in example locations on the headset 100, the components may be located elsewhere on the headset 100, on a peripheral device paired with the headset 100, or some combination thereof. Similarly, there may be more or fewer components on the headset 100 than what is shown in FIG. 1A.

[0016] The frame 110 holds the other components of the headset 100. The frame 110 includes a front part that holds the one or more display elements 120 and end pieces (e.g., temples) to attach to a head of the user. The front part of the frame 110 bridges the top of a nose of the user. The length of the end pieces may be adjustable (e.g., adjustable temple length) to fit different users. The end pieces may also include a portion that curls behind the ear of the user (e.g., temple tip, ear piece).

[0017] The one or more display elements 120 provide light to a user wearing the headset 100. As illustrated the headset includes a display element 120 for each eye of a user. In some embodiments, a display element 120 generates image light that is provided to an eyebox of the headset 100. The eyebox is a location in space that an eye of user occupies while wearing the headset 100. For example, a display element 120 may be a waveguide display. A waveguide display includes a light source (e.g., a two-dimensional source, one or more line sources, one or more point sources, etc.) and one or more waveguides. Light from the light source is in-coupled into the one or more waveguides which outputs the light in a manner such that there is pupil replication in an eyebox of the headset 100. In-coupling and/or outcoupling of light from the one or more waveguides may be done using one or more diffraction gratings. In some embodiments, the waveguide display includes a scanning element (e.g., waveguide, mirror, etc.) that scans light from the light source as it is in-coupled into the one or more waveguides. Note that in some embodiments, one or both of the display elements 120 are opaque and do not transmit light from a local area around the headset 100. The local area is the area surrounding the headset 100. For example, the local area may be a room that a user wearing the headset 100 is inside, or the user wearing the headset 100 may be outside and the local area is an outside area. In this context, the headset 100 generates VR content. Alternatively, in some embodiments, one or both of the display elements 120 are at least partially transparent, such that light from the local area may be combined with light from the one or more display elements to produce AR and/or MR content.

[0018] In some embodiments, a display element 120 does not generate image light, and instead is a lens that transmits light from the local area to the eyebox. For example, one or both of the display elements 120 may be a lens without correction (non-prescription) or a prescription lens (e.g., single vision, bifocal and trifocal, or progressive) to help correct for defects in a user’s eyesight. In some embodiments, the display element 120 may be polarized and/or tinted to protect the user’s eyes from the sun.

[0019] Note that in some embodiments, the display element 120 may include an additional optics block (not shown). The optics block may include one or more optical elements (e.g., lens, Fresnel lens, etc.) that direct light from the display element 120 to the eyebox. The optics block may, e.g., correct for aberrations in some or all of the image content, magnify some or all of the image, or some combination thereof.

[0020] The DCA determines depth information for a portion of a local area surrounding the headset 100. The DCA includes one or more imaging devices 130 and a DCA controller (not shown in FIG. 1A), and may also include an illuminator 140. In some embodiments, the illuminator 140 illuminates a portion of the local area with light. The light may be, e.g., structured light (e.g., dot pattern, bars, etc.) in the infrared (IR), IR flash for time-of-flight, etc. In some embodiments, the one or more imaging devices 130 capture images of the portion of the local area that include the light from the illuminator 140. As illustrated, FIG. 1A shows a single illuminator 140 and two imaging devices 130. In alternate embodiments, there is no illuminator 140 and at least two imaging devices 130.

[0021] The DCA controller computes depth information for the portion of the local area using the captured images and one or more depth determination techniques. The depth determination technique may be, e.g., direct time-of-flight (ToF) depth sensing, indirect ToF depth sensing, structured light, passive stereo analysis, active stereo analysis (uses texture added to the scene by light from the illuminator 140), some other technique to determine depth of a scene, or some combination thereof.

[0022] The audio system provides audio content. The audio system includes a transducer array, a sensor array, and an audio controller 150. However, in other embodiments, the audio system may include different and/or additional components. Similarly, in some cases, functionality described with reference to the components of the audio system can be distributed among the components in a different manner than is described here. For example, some or all of the functions of the controller may be performed by a remote server.

[0023] The transducer array presents sound to user. The transducer array includes a plurality of transducers. A transducer may be a speaker 160 (e.g., an acoustic transducer) or a tissue transducer 170 (e.g., a bone conduction transducer or a cartilage conduction transducer). Although the speakers 160 are shown exterior to the frame 110, the speakers 160 may be enclosed in the frame 110. In some embodiments, instead of individual speakers for each ear, the headset 100 includes a speaker array comprising multiple speakers integrated into the frame 110 to improve directionality of presented audio content. The tissue transducer 170 couples to the head of the user and directly vibrates tissue (e.g., bone or cartilage) of the user to generate sound. The number and/or locations of transducers may be different from what is shown in FIG. 1A.

[0024] The sensor array detects sounds within the local area of the headset 100. The sensor array includes a plurality of acoustic sensors 180a-h (each referred to as an acoustic sensor 180). An acoustic sensor 180 captures sounds emitted from one or more sound sources in the local area (e.g., a room). Each acoustic sensor is configured to detect sound and convert the detected sound into an electronic format (analog or digital). The acoustic sensors 180 may be acoustic wave sensors, microphones, sound transducers, or similar sensors that are suitable for detecting sounds. The sensor array may dynamically activate or deactivate each acoustic sensor 180 in accordance with instructions from the audio controller 150. Activating an acoustic sensor 180 results the acoustic sensor 180 in an active state and deactivating an acoustic sensor 180 results in the acoustic sensor 10 being in an inactive state. In some embodiments, an acoustic sensor 180 is powered on in the active state and powered off in the inactive state.

[0025] In some embodiments, one or more acoustic sensors 180 may be placed in an ear canal of each ear (e.g., acting as binaural microphones). An acoustic sensor 180 may be placed in the ear canal along with a transducer. In some embodiments, the acoustic sensors 180 may be placed on an exterior surface of the headset 100, placed on an interior surface of the headset 100, separate from the headset 100 (e.g., part of some other device), or some combination thereof. The number and/or locations of acoustic sensors 180 may be different from what is shown in FIG. 1A. For example, the number of acoustic detection locations may be increased to increase the amount of audio information collected and the sensitivity and/or accuracy of the information. The acoustic detection locations may be oriented such that the microphone is able to detect sounds in a wide range of directions surrounding the user wearing the headset 100.

[0026] The audio controller 150 processes information from the sensor array that describes sounds detected by the sensor array. The audio controller 150 may comprise a processor and a computer-readable storage medium. The audio controller 150 may be configured to generate direction of arrival (DOA) estimates, generate acoustic transfer functions (e.g., array transfer functions and/or head-related transfer functions), track the location of sound sources, form beams in the direction of sound sources, classify sound sources, generate sound filters for the speakers 160, or some combination thereof.

[0027] The audio controller 150 detects sound to generate one or more acoustic transfer functions for a user. An acoustic transfer function characterizes how a sound is received from a point in space. The acoustic transfer functions may be array transfer functions (ATFs), head-related transfer functions (HRTFs), other types of acoustic transfer functions, or some combination thereof. The one or more acoustic transfer functions may be associated with the headset 100, the user wearing the headset 100, or both. The audio controller 150 may then use the one or more acoustic transfer functions to generate audio content for the user.

[0028] The audio controller 150 generates instructions for activating and deactivating various acoustic sensors 180 of the sensor array. The instructions may be generated based on environmental parameters captured by the sensor array or other sensor (e.g., imaging device 130, position sensor 190, etc.) of the headset 100 and target performance metrics.

[0029] The configuration of the acoustic sensors 180 of the sensor array may vary. While the headset 100 is shown in FIG. 1A as having eight acoustic sensors 180, the number of acoustic sensors 180 may be increased or decreased. Increasing the number of acoustic sensors 180 may increase the amount of audio information collected and the sensitivity and/or accuracy of the audio information. Decreasing the number of acoustic sensors 180 may decrease the computing power required by the audio controller 150 to process the collected audio information, or decrease the power consumption of the headset 100. In addition, the position of each acoustic sensor 180 of the sensor array may vary. The position of an acoustic sensor 180 may include a defined position on the user, a defined coordinate on the frame 110, an orientation associated with each acoustic sensor, or some combination thereof. For example, the acoustic sensors 180a, 180b may be positioned on a different part of the user’s ear, such as behind the pinna or within the auricle or fossa, or there may be additional acoustic sensors on or surrounding the ear in addition to the acoustic sensors 180 inside the ear canal. Having an acoustic sensor (e.g., acoustic sensors 180a, 180b) positioned next to an ear canal of a user enables the sensor array to collect information on how sounds arrive at the ear canal. The acoustic sensors 180 on the frame 110 may be positioned along the length of the temples, across the bridge, above or below the display element 120, or some combination thereof. The acoustic sensors 180 may be oriented such that the sensor array is able to detect sounds in a wide range of directions surrounding the user wearing the headset 100.

[0030] The audio controller 150 processes information from the sensor array that describes sounds detected by the sensor array. The information associated with each detected sound may include a frequency, an amplitude, and/or a duration of the detected sound. For a detected sound, the audio controller 150 may perform a DoA estimation. The DoA estimation is an estimated direction from which the detected sound arrived at an acoustic sensor 180 of the sensor array. If a sound is detected by at least two acoustic sensors 180 of the sensor array, the audio controller 150 can use the known positional relationship of the acoustic sensors 180 and the DoA estimation from each acoustic sensor to estimate a source location or direction of the detected sound, for example, via triangulation. The accuracy of the source location estimation may increase as the number of acoustic sensors 180 that detected the sound increases and/or as the distance between the acoustic sensors 180 that detected the sound increases.

[0031] In some embodiments, the audio controller 150 populates an audio data set with information. The information may include a detected sound and parameters associated with each detected sound. Example parameters may include a frequency, an amplitude, a duration, a DoA estimation, a source location, or some combination thereof. Each audio data set may correspond to a different source location relative to the headset 110 and include one or more sounds having that source location. This audio data set may be associated with one or more acoustic transfer functions for that source location. The one or more acoustic transfer functions may be stored in the data set. In alternate embodiments, each audio data set may correspond to several source locations relative to the headset 110 and include one or more sounds for each source location. For example, source locations that are located relatively near to each other may be grouped together. The audio controller 150 may populate the audio data set with information as sounds are detected by the sensor array. The audio controller 150 may further populate the audio data set for each detected sound as a DoA estimation is performed or a source location is determined for each detected sound.

[0032] In some embodiments, the audio controller 150 selects the detected sounds for which it performs a DoA estimation. The audio controller 150 may select the detected sounds based on the parameters associated with each detected sound stored in the audio data set. The audio controller 150 may evaluate the stored parameters associated with each detected sound and determine if one or more stored parameters meet a corresponding parameter condition. For example, a parameter condition may be met if a parameter is above or below a threshold value or falls within a target range. If a parameter condition is met, the audio controller 150 performs a DoA estimation for the detected sound. For example, the audio controller 150 may perform a DoA estimation for detected sounds that have a frequency within a frequency range, an amplitude above a threshold amplitude, a duration below a threshold duration, other similar variations, or some combination thereof. Parameter conditions may be set by a user of the audio system, based on historical data, based on an analysis of the information in the audio data set (e.g., evaluating the collected information of the parameter and setting an average), or some combination thereof. The audio controller 150 may create an element in the audio set to store the DoA estimation and/or source location of the detected sound. In some embodiments, the audio controller 150 may update the elements in the audio set if data is already present.

[0033] In some embodiments, the audio controller 150 may receive position information of the headset 100 from a system external to the headset 100. The position information may include a location of the headset 100, an orientation of the headset 100 or the user’s head wearing the headset 100, or some combination thereof. The position information may be defined relative to a reference point. The orientation may correspond to a position of each ear relative to the reference point. Examples of systems include an imaging assembly, a console (e.g., as described in FIG. 7), a simultaneous localization and mapping (SLAM) system, a depth camera assembly, a structured light system, or other suitable systems. In some embodiments, the headset 100 may include sensors that may be used for SLAM calculations, which may be carried out in whole or in part by the audio controller 150. The audio controller 150 may receive position information from the system continuously or at random or specified intervals.

[0034] In one embodiment, based on parameters of the detected sounds, the audio controller 150 generates one or more acoustic transfer functions. The acoustic transfer functions may be array transfer functions (ATFs), head-related transfer functions (HRTFs), other types of acoustic transfer functions, or some combination thereof. An ATF characterizes how the sensor array receives a sound from a point in space. Specifically, the ATF defines the relationship between parameters of a sound at its source location and the parameters at which the sensor array detected the sound. Parameters associated with the sound may include frequency, amplitude, duration, a DoA estimation, etc. In some embodiments, at least some of the acoustic sensors of the sensor array are coupled to the headset 100 that is worn by a user. The ATF for a particular source location relative to the sensor array may differ from user to user due to a person’s anatomy (e.g., ear shape, shoulders, etc.) that affects the sound as it travels to the person’s ears. Accordingly, the ATFs of the sensor array are personalized for each user wearing the headset 100. Once the ATFs are generated, the ATFs may be stored in local or external memory.

[0035] The HRTF characterizes how an ear receives a sound from a point in space. The HRTF for a particular source location relative to a person is unique to each ear of the person (and is unique to the person) due to the person’s anatomy (e.g., ear shape, shoulders, etc.) that affects the sound as it travels to the person’s ears. For example, in FIG. 1, the audio controller 150 may generate two HRTFs for the user, one for each ear. An HRTF or a pair of HRTFs can be used to create audio content that includes sounds that seem to come from a specific point in space. Several HRTFs may be used to create surround sound audio content (e.g., for home entertainment systems, theater speaker systems, an immersive environment, etc.), where each HRTF or each pair of HRTFs corresponds to a different point in space such that audio content seems to come from several different points in space. In some embodiments, the audio controller 150 may update one or more pre-existing acoustic transfer functions based on the DoA estimation of each detected sound. The pre-existing acoustic transfer functions may be obtained from local or external memory or obtained from an external system. As the position of the headset 100 changes within the local area, the audio controller 150 may generate a new acoustic transfer function or update a pre-existing acoustic transfer function accordingly. Once the HRTFs are generated, the HRTFs may be stored in local or external memory.

[0036] The position sensor 190 generates one or more measurement signals in response to motion of the headset 100. The position sensor 190 may be located on a portion of the frame 110 of the headset 100. The position sensor 190 may include an inertial measurement unit (IMU). Examples of position sensor 190 include: one or more accelerometers, one or more gyroscopes, one or more magnetometers, another suitable type of sensor that detects motion, a type of sensor used for error correction of the IMU, or some combination thereof. The position sensor 190 may be located external to the IMU, internal to the IMU, or some combination thereof.

[0037] In some embodiments, the headset 100 may provide for simultaneous localization and mapping (SLAM) for a position of the headset 100 and updating of a model of the local area. For example, the headset 100 may include a passive camera assembly (PCA) that generates color image data. The PCA may include one or more RGB cameras that capture images of some or all of the local area. In some embodiments, some or all of the imaging devices 130 of the DCA may also function as the PCA. The images captured by the PCA and the depth information determined by the DCA may be used to determine parameters of the local area, generate a model of the local area, update a model of the local area, or some combination thereof. Furthermore, the position sensor 190 tracks the position (e.g., location and pose) of the headset 100 within the room. Additional details regarding the components of the headset 100 are discussed below in connection with FIG. 5.

[0038] FIG. 1B is a perspective view of a headset 105 implemented as a HMD, in accordance with one or more embodiments. In embodiments that describe an AR system and/or a MR system, portions of a front side of the HMD are at least partially transparent in the visible band (.about.380 nm to 750 nm), and portions of the HMD that are between the front side of the HMD and an eye of the user are at least partially transparent (e.g., a partially transparent electronic display). The HMD includes a front rigid body 115 and a band 175. The headset 105 includes many of the same components described above with reference to FIG. 1A, but modified to integrate with the HMD form factor. For example, the HMD includes a display assembly, a DCA, an audio system, and a position sensor 190. FIG. 1B shows the illuminator 140, a plurality of the speakers 160, a plurality of the imaging devices 130, a plurality of acoustic sensors 180, and the position sensor 190.

Audio System Overview

[0039] FIG. 2 is a block diagram of an audio system 200, in accordance with one or more embodiments. The audio system in FIG. 1A or FIG. 1B may be an embodiment of the audio system 200. The audio system 200 generates one or more acoustic transfer functions for a user. The audio system 200 may then use the one or more acoustic transfer functions to generate audio content for the user. In the embodiment of FIG. 2, the audio system 200 includes a transducer array 210, a sensor array 220, and an audio controller 230. Some embodiments of the audio system 200 have different components than those described here. Similarly, in some cases, functions can be distributed among the components in a different manner than is described here.

[0040] The transducer array 210 is configured to present audio content. The transducer array 210 includes a plurality of transducers. A transducer is a device that provides audio content. A transducer may be, e.g., a speaker (e.g., the speaker 160), a tissue transducer (e.g., the tissue transducer 170), some other device that provides audio content, or some combination thereof. A tissue transducer may be configured to function as a bone conduction transducer or a cartilage conduction transducer. The transducer array 210 may present audio content via air conduction (e.g., via one or more speakers), via bone conduction (via one or more bone conduction transducer), via cartilage conduction audio system (via one or more cartilage conduction transducers), or some combination thereof. In some embodiments, the transducer array 210 may include one or more transducers to cover different parts of a frequency range. For example, a piezoelectric transducer may be used to cover a first part of a frequency range and a moving coil transducer may be used to cover a second part of a frequency range.

[0041] The bone conduction transducers generate acoustic pressure waves by vibrating bone/tissue in the user’s head. A bone conduction transducer may be coupled to a portion of a headset, and may be configured to be behind the auricle coupled to a portion of the user’s skull. The bone conduction transducer receives vibration instructions from the audio controller 230, and vibrates a portion of the user’s skull based on the received instructions. The vibrations from the bone conduction transducer generate a tissue-borne acoustic pressure wave that propagates toward the user’s cochlea, bypassing the eardrum.

[0042] The cartilage conduction transducers generate acoustic pressure waves by vibrating one or more portions of the auricular cartilage of the ears of the user. A cartilage conduction transducer may be coupled to a portion of a headset, and may be configured to be coupled to one or more portions of the auricular cartilage of the ear. For example, the cartilage conduction transducer may couple to the back of an auricle of the ear of the user. The cartilage conduction transducer may be located anywhere along the auricular cartilage around the outer ear (e.g., the pinna, the tragus, some other portion of the auricular cartilage, or some combination thereof). Vibrating the one or more portions of auricular cartilage may generate: airborne acoustic pressure waves outside the ear canal; tissue born acoustic pressure waves that cause some portions of the ear canal to vibrate thereby generating an airborne acoustic pressure wave within the ear canal; or some combination thereof. The generated airborne acoustic pressure waves propagate down the ear canal toward the ear drum.

[0043] The transducer array 210 generates audio content in accordance with instructions from the audio controller 230. In some embodiments, the audio content is spatialized. Spatialized audio content is audio content that appears to originate from a particular direction and/or target region (e.g., an object in the local area and/or a virtual object). For example, spatialized audio content can make it appear that sound is originating from a virtual singer across a room from a user of the audio system 200. The transducer array 210 may be coupled to a wearable device (e.g., the headset 100 or the headset 105). In alternate embodiments, the transducer array 210 may be a plurality of speakers that are separate from the wearable device (e.g., coupled to an external console).

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