Patent Publication Number: US-2023139901-A1

Title: Efficient rendering of virtual soundfields

Description:
REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 17/412,084, filed Aug. 25, 2021 and is a continuation of U.S. patent application Ser. No. 16/861,111, filed Apr. 28, 2020, now U.S. Pat. No. 11,134,357, issued Sep. 28, 2021 and is a continuation of U.S. patent application Ser. No. 16/438,358, filed on Jun. 11, 2019, now U.S. Pat. No. 10,667,072, issued May 26, 2020, which claims benefit of U.S. Provisional Patent Application No. 62/684,093, filed on Jun. 12, 2018, which are hereby incorporated by reference in their entirety. 
    
    
     FIELD 
     This disclosure relates in general to spatial audio rendering and associated systems. More specification, this disclosure relates to systems and methods for increasing the efficiency of virtual speaker-based spatial audio systems. 
     BACKGROUND 
     Virtual environments are ubiquitous in computing environments, finding use in video games (in which a virtual environment may represent a game world); maps (in which a virtual environment may represent terrain to be navigated); simulations (in which a virtual environment may simulate a real environment); digital storytelling (in which virtual characters may interact with each other in a virtual environment); and many other applications. Modern computer users are generally comfortable perceiving, and interacting with, virtual environments. However, users&#39; experiences with virtual environments can be limited by the technology for presenting virtual environments. For example, conventional displays (e.g., 2D display screens) and audio systems (e.g., fixed speakers) may be unable to realize a virtual environment in ways that create a compelling, realistic, and immersive experience. 
     Virtual reality (“VR”), augmented reality (“AR”), mixed reality (“MR”), and related technologies (collectively, “XR”) share an ability to present, to a user of an XR system, sensory information corresponding to a virtual environment represented by data in a computer system. Such systems can offer a uniquely heightened sense of immersion and realism by combining virtual visual and audio cues with real sights and sounds. Accordingly, it can be desirable to present digital sounds to a user of an XR system in such a way that the sounds seem to be occurring—naturally, and consistently with the user&#39;s expectations of the sound—in the user&#39;s real environment. Generally speaking, users expect that virtual sounds will take on the acoustic properties of the real environment in which they are heard. For instance, a user of an XR system in a large concert hall will expect the virtual sounds of the XR system to have large, cavernous sonic qualities; conversely, a user in a small apartment will expect the sounds to be more dampened, close, and immediate. Additionally, users expect that virtual sounds will be presented without delays. 
     Ambisonics and non-ambisonics, among other techniques, may be used to generate spatial audio. For a large number of sound source objects, ambisonics or non-ambisonics may be an efficient way of rendering spatial audio because of its design and architecture. This may especially be the case when reflections are modelled. Ambisonics and non-ambisonics multi-channel based spatial audio systems may render the audio signals through several steps. Example steps can include a per-source encode step, a fixed overhead soundfield decode step, and/or a fixed speaker virtualization step. One or more hardware components may perform the steps. 
     In a first method for rendering the audio signals, each sound source can have its own pair of finite impulse response (FIR) filters. In such systems, a perceived position of a sound is changed by changing filter coefficients of FIR filters. In some embodiments, each sound may use a plurality (e.g., two pairs) of FIR filters. Each pair may use two filters (i.e., four FIR filters). As sounds move around the virtual environment, the FIR filters can be crossfaded. In some embodiments, four FIR filters may be used for each sound. 
     In a second method for rendering the audio signals, virtual speaker panning may be implemented using a fixed number of virtual speakers. Each sound source may be panned across the fixed virtual speakers. In some embodiments, a plurality (e.g., two) FIR filters may be used for each virtual speaker. The virtual speaker panning may be efficient for certain applications and may use a negligible amount of computation resources. 
     In some embodiments, a certain method may have increased efficiency compared to the other method depending on the number of sounds playing concurrently. For example, 30 sounds may be playing concurrently. If four FIR filters are used for each sound source, then 120 FIR filters (30 sound sources×4 FIR filters per sound source=120 FIR filters) may be required for the first method. If 2 FIR filters are used for each virtual speaker, then only 32 FIR filters may be required for the second method (16 virtual speakers×2 FIR filters per virtual speaker=32 FIR filters). 
     As another example, only one sound may be playing. The first method may require only four FIR filters (1 sound source×4 FIR filters per sound source=4 FIR filters), while the second method may require 32 FIR filters (16 virtual speakers×2 FIR filters per virtual speaker=32 FIR filters). 
     As illustrated through the above examples, the first method may be beneficial for a small number of sounds, and the second method may be beneficial for a large number of sounds. Accordingly, an audio system and method that increased the efficiency based on the number of sound sources at a given time may be desired. 
     BRIEF SUMMARY 
     An audio system and method of rendering audio signals that uses modified virtual speaker panning is disclosed. The audio system may include a fixed number F of virtual speakers, and the modified virtual speaker panning may dynamically select and use a subset P of the fixed virtual speakers. Each sound source may be panned across the subset P of virtual speakers. In some embodiments, a plurality (e.g., two) of FIR filters may be used for each virtual speaker of the subset P. The subset P of virtual speakers may be selected based one or more factors, such as proximity to a sound source. The subset P of virtual speakers may be referred to as active speakers. 
     The modified virtual speaker panning method can be compared to the above disclosed first and second methods by way of example. If three sounds are playing concurrently and the audio system has 16 fixed virtual speakers, the first method may require 12 FIR filters (3 sound sources×4 FIR filters per sound source=12 FIR filters), and the second method may require 32 FIR filters (16 virtual speakers×2 FIR filters per virtual speaker=32 FIR filters). The modified virtual speaker panning method, on the other hand, may dynamically select three virtual speakers to be active virtual speakers as part of the subset P. The modified virtual speaker panning method may require six FIR filters, two FIR filters for each active virtual speaker (3 virtual speakers×2 FIR filters=6 FIR filters). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    illustrates an example wearable system, according to some embodiments. 
         FIG.  2    illustrates an example handheld controller that can be used in conjunction with an example wearable system, according to some embodiments. 
         FIG.  3    illustrates an example auxiliary unit that can be used in conjunction with an example wearable system, according to some embodiments. 
         FIG.  4    illustrates an example functional block diagram for an example wearable system, according to some embodiments. 
         FIG.  5 A  illustrates a block diagram of an example spatial audio system, according to some embodiments. 
         FIG.  5 B  illustrates a flow of an example method for operating the system of  FIG.  5 A , according to some embodiments. 
         FIG.  5 C  illustrates a flow of an example method for operating an example decoder/virtualizer, according to some embodiments. 
         FIG.  6    illustrates an example configuration of a sound source and speakers, according to some embodiments. 
         FIG.  7 A  illustrates a block diagram of an example decoder/virtualizer including a plurality of detectors, according to some embodiments. 
         FIG.  7 B  illustrates a flow of an example method for operating the decoder/virtualizer of  FIG.  7 A , according to some embodiments. 
         FIG.  8 A  illustrates a block diagram of an example decoder/virtualizer, according to some embodiments. 
         FIG.  8 B  illustrates a flow of an example method for operating the decoder/virtualizer of  FIG.  8 A , according to some embodiments. 
         FIG.  9    illustrates an example configuration of a sound source and speakers, according to some embodiments. 
         FIG.  10 A  illustrates a block diagram of an example decoder/virtualizer used in a system including active speakers, according to some embodiments. 
         FIG.  10 B  illustrates a flow of an example method for operating the decoder/virtualizer of  FIG.  10 A , according to some embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description of examples, reference is made to the accompanying drawings which form a part hereof, and in which it is shown by way of illustration specific examples that can be practiced. It is to be understood that other examples can be used and structural changes can be made without departing from the scope of the disclosed examples. 
     Example Wearable System 
       FIG.  1    illustrates an example wearable head device  100  configured to be worn on the head of a user. Wearable head device  100  may be part of a broader wearable system that comprises one or more components, such as a head device (e.g., wearable head device  100 ), a handheld controller (e.g., handheld controller  200  described below), and/or an auxiliary unit (e.g., auxiliary unit  300  described below). In some examples, wearable head device  100  can be used for virtual reality, augmented reality, or mixed reality systems or applications. Wearable head device  100  can comprise one or more displays, such as displays  110 A and  110 B (which may comprise left and right transmissive displays, and associated components for coupling light from the displays to the user&#39;s eyes, such as orthogonal pupil expansion (OPE) grating sets  112 A/ 112 B and exit pupil expansion (EPE) grating sets  114 A/ 114 B); left and right acoustic structures, such as speakers  120 A and  120 B (which may be mounted on temple arms  122 A and  122 B, and positioned adjacent to the user&#39;s left and right ears, respectively); one or more sensors such as infrared sensors, accelerometers, GPS units, inertial measurement units (IMU)(e.g. IMU  126 ), acoustic sensors (e.g., microphone  150 ); orthogonal coil electromagnetic receivers (e.g., receiver  127  shown mounted to the left temple arm  122 A); left and right cameras (e.g., depth (time-of-flight) cameras  130 A and  130 B) oriented away from the user; and left and right eye cameras oriented toward the user (e.g., for detecting the user&#39;s eye movements)(e.g., eye cameras  128  and  128 B). However, wearable head device  100  can incorporate any suitable display technology, and any suitable number, type, or combination of sensors or other components without departing from the scope of the invention. In some examples, wearable head device  100  may incorporate one or more microphones  150  configured to detect audio signals generated by the user&#39;s voice; such microphones may be positioned in a wearable head device adjacent to the user&#39;s mouth. In some examples, wearable head device  100  may incorporate networking features (e.g., Wi-Fi capability) to communicate with other devices and systems, including other wearable systems. Wearable head device  100  may further include components such as a battery, a processor, a memory, a storage unit, or various input devices (e.g., buttons, touchpads); or may be coupled to a handheld controller (e.g., handheld controller  200 ) or an auxiliary unit (e.g., auxiliary unit  300 ) that comprises one or more such components. In some examples, sensors may be configured to output a set of coordinates of the head-mounted unit relative to the user&#39;s environment, and may provide input to a processor performing a Simultaneous Localization and Mapping (SLAM) procedure and/or a visual odometry algorithm. In some examples, wearable head device  100  may be coupled to a handheld controller  200 , and/or an auxiliary unit  300 , as described further below. 
       FIG.  2    illustrates an example mobile handheld controller component  200  of an example wearable system. In some examples, handheld controller  200  may be in wired or wireless communication with wearable head device  100  and/or auxiliary unit  300  described below. In some examples, handheld controller  200  includes a handle portion  220  to be held by a user, and one or more buttons  240  disposed along a top surface  210 . In some examples, handheld controller  200  may be configured for use as an optical tracking target; for example, a sensor (e.g., a camera or other optical sensor) of wearable head device  100  can be configured to detect a position and/or orientation of handheld controller  200 —which may, by extension, indicate a position and/or orientation of the hand of a user holding handheld controller  200 . In some examples, handheld controller  200  may include a processor, a memory, a storage unit, a display, or one or more input devices, such as described above. In some examples, handheld controller  200  includes one or more sensors (e.g., any of the sensors or tracking components described above with respect to wearable head device  100 ). In some examples, sensors can detect a position or orientation of handheld controller  200  relative to wearable head device  100  or to another component of a wearable system. In some examples, sensors may be positioned in handle portion  220  of handheld controller  200 , and/or may be mechanically coupled to the handheld controller. Handheld controller  200  can be configured to provide one or more output signals, corresponding, for example, to a pressed state of the buttons  240 ; or a position, orientation, and/or motion of the handheld controller  200  (e.g., via an IMU). Such output signals may be used as input to a processor of wearable head device  100 , to auxiliary unit  300 , or to another component of a wearable system. In some examples, handheld controller  200  can include one or more microphones to detect sounds (e.g., a user&#39;s speech, environmental sounds), and in some cases provide a signal corresponding to the detected sound to a processor (e.g., a processor of wearable head device  100 ). 
       FIG.  3    illustrates an example auxiliary unit  300  of an example wearable system. In some examples, auxiliary unit  300  may be in wired or wireless communication with wearable head device  100  and/or handheld controller  200 . The auxiliary unit  300  can include a battery to provide energy to operate one or more components of a wearable system, such as wearable head device  100  and/or handheld controller  200  (including displays, sensors, acoustic structures, processors, microphones, and/or other components of wearable head device  100  or handheld controller  200 ). In some examples, auxiliary unit  300  may include a processor, a memory, a storage unit, a display, one or more input devices, and/or one or more sensors, such as described above. In some examples, auxiliary unit  300  includes a clip  310  for attaching the auxiliary unit to a user (e.g., a belt worn by the user). An advantage of using auxiliary unit  300  to house one or more components of a wearable system is that doing so may allow large or heavy components to be carried on a user&#39;s waist, chest, or back—which are relatively well-suited to support large and heavy objects—rather than mounted to the user&#39;s head (e.g., if housed in wearable head device  100 ) or carried by the user&#39;s hand (e.g., if housed in handheld controller  200 ). This may be particularly advantageous for relatively heavy or bulky components, such as batteries. 
       FIG.  4    shows an example functional block diagram that may correspond to an example wearable system  400 , such as may include example wearable head device  100 , handheld controller  200 , and auxiliary unit  300  described above. In some examples, the wearable system  400  could be used for virtual reality, augmented reality, or mixed reality applications. As shown in  FIG.  4   , wearable system  400  can include an example handheld controller  400 B, referred to here as a “totem” (and which may correspond to handheld controller  200  described above); the handheld controller  400 B can include a totem-to-headgear six degree of freedom (6DOF) totem subsystem  404 A. Wearable system  400  can also include example wearable head device  400 A (which may correspond to wearable headgear device  100  described above); the wearable head device  400 A includes a totem-to-headgear 6DOF headgear subsystem  404 B. In the example, the 6DOF totem subsystem  404 A and the 6DOF headgear subsystem  404 B cooperate to determine six coordinates (e.g., offsets in three translation directions and rotation along three axes) of the handheld controller  400 B relative to the wearable head device  400 A. The six degrees of freedom may be expressed relative to a coordinate system of the wearable head device  400 A. The three translation offsets may be expressed as X, Y, and Z offsets in such a coordinate system, as a translation matrix, or as some other representation. The rotation degrees of freedom may be expressed as sequence of yaw, pitch, and roll rotations; as vectors; as a rotation matrix; as a quaternion; or as some other representation. In some examples, one or more depth cameras  444  (and/or one or more non-depth cameras) included in the wearable head device  400 A; and/or one or more optical targets (e.g., buttons  240  of handheld controller  200  as described above, or dedicated optical targets included in the handheld controller) can be used for 6DOF tracking. In some examples, the handheld controller  400 B can include a camera, as described above; and the headgear  400 A can include an optical target for optical tracking in conjunction with the camera. In some examples, the wearable head device  400 A and the handheld controller  400 B each include a set of three orthogonally oriented solenoids which are used to wirelessly send and receive three distinguishable signals. By measuring the relative magnitude of the three distinguishable signals received in each of the coils used for receiving, the 6DOF of the handheld controller  400 B relative to the wearable head device  400 A may be determined. In some examples, 6DOF totem subsystem  404 A can include an Inertial Measurement Unit (IMU) that is useful to provide improved accuracy and/or more timely information on rapid movements of the handheld controller  400 B. 
     In some examples involving augmented reality or mixed reality applications, it may be desirable to transform coordinates from a local coordinate space (e.g., a coordinate space fixed relative to wearable head device  400 A) to an inertial coordinate space, or to an environmental coordinate space. For instance, such transformations may be necessary for a display of wearable head device  400 A to present a virtual object at an expected position and orientation relative to the real environment (e.g., a virtual person sitting in a real chair, facing forward, regardless of the position and orientation of wearable head device  400 A), rather than at a fixed position and orientation on the display (e.g., at the same position in the display of wearable head device  400 A). This can maintain an illusion that the virtual object exists in the real environment (and does not, for example, appear positioned unnaturally in the real environment as the wearable head device  400 A shifts and rotates). In some examples, a compensatory transformation between coordinate spaces can be determined by processing imagery from the depth cameras  444  (e.g., using a Simultaneous Localization and Mapping (SLAM) and/or visual odometry procedure) in order to determine the transformation of the wearable head device  400 A relative to an inertial or environmental coordinate system. In the example shown in  FIG.  4   , the depth cameras  444  can be coupled to a SLAM/visual odometry block  406  and can provide imagery to block  406 . The SLAM/visual odometry block  406  implementation can include a processor configured to process this imagery and determine a position and orientation of the user&#39;s head, which can then be used to identify a transformation between a head coordinate space and a real coordinate space. Similarly, in some examples, an additional source of information on the user&#39;s head pose and location is obtained from an IMU  409  of wearable head device  400 A. Information from the IMU  409  can be integrated with information from the SLAM/visual odometry block  406  to provide improved accuracy and/or more timely information on rapid adjustments of the user&#39;s head pose and position. 
     In some examples, the depth cameras  444  can supply 3D imagery to a hand gesture tracker  411 , which may be implemented in a processor of wearable head device  400 A. The hand gesture tracker  411  can identify a user&#39;s hand gestures, for example, by matching 3D imagery received from the depth cameras  444  to stored patterns representing hand gestures. Other suitable techniques of identifying a user&#39;s hand gestures will be apparent. 
     In some examples, one or more processors  416  may be configured to receive data from headgear subsystem  404 B, the IMU  409 , the SLAM/visual odometry block  406 , depth cameras  444 , a microphone (not shown); and/or the hand gesture tracker  411 . The processor  416  can also send and receive control signals from the 6DOF totem system  404 A. The processor  416  may be coupled to the 6DOF totem system  404 A wirelessly, such as in examples where the handheld controller  400 B is untethered. Processor  416  may further communicate with additional components, such as an audio-visual content memory  418 , a Graphical Processing Unit (GPU)  420 , and/or a Digital Signal Processor (DSP) audio spatializer  422 . The DSP audio spatializer  422  may be coupled to a Head Related Transfer Function (HRTF) memory  425 . The GPU  420  can include a left channel output coupled to the left source of imagewise modulated light  424  and a right channel output coupled to the right source of imagewise modulated light  426 . GPU  420  can output stereoscopic image data to the sources of imagewise modulated light  424 ,  426 . The DSP audio spatializer  422  can output audio to a left speaker  412  and/or a right speaker  414 . The DSP audio spatializer  422  can receive input from processor  416  indicating a direction vector from a user to a virtual sound source (which may be moved by the user, e.g., via the handheld controller  400 B). Based on the direction vector, the DSP audio spatializer  422  can determine a corresponding HRTF (e.g., by accessing a HRTF, or by interpolating multiple HRTFs). The DSP audio spatializer  422  can then apply the determined HRTF to an audio signal, such as an audio signal corresponding to a virtual sound generated by a virtual object. This can enhance the believability and realism of the virtual sound, by incorporating the relative position and orientation of the user relative to the virtual sound in the mixed reality environment—that is, by presenting a virtual sound that matches a user&#39;s expectations of what that virtual sound would sound like if it were a real sound in a real environment. 
     In some examples, such as shown in  FIG.  4   , one or more of processor  416 , GPU  420 , DSP audio spatializer  422 , HRTF memory  425 , and audio/visual content memory  418  may be included in an auxiliary unit  400 C (which may correspond to auxiliary unit  300  described above). The auxiliary unit  400 C may include a battery  427  to power its components and/or to supply power to wearable head device  400 A and/or handheld controller  400 B. Including such components in an auxiliary unit, which can be mounted to a user&#39;s waist, can limit the size and weight of wearable head device  400 A, which can in turn reduce fatigue of a user&#39;s head and neck. 
     While  FIG.  4    presents elements corresponding to various components of an example wearable system  400 , various other suitable arrangements of these components will become apparent to those skilled in the art. For example, elements presented in  FIG.  4    as being associated with auxiliary unit  400 C could instead be associated with wearable head device  400 A or handheld controller  400 B. Furthermore, some wearable systems may forgo entirely a handheld controller  400 B or auxiliary unit  400 C. Such changes and modifications are to be understood as being included within the scope of the disclosed examples. 
     Mixed Reality Environment 
     Like all people, a user of a mixed reality system exists in a real environment—that is, a three-dimensional portion of the “real world,” and all of its contents, that are perceptible by the user. For example, a user perceives a real environment using one&#39;s ordinary human senses sight, sound, touch, taste, smell—and interacts with the real environment by moving one&#39;s own body in the real environment. Locations in a real environment can be described as coordinates in a coordinate space; for example, a coordinate can comprise latitude, longitude, and elevation with respect to sea level; distances in three orthogonal dimensions from a reference point; or other suitable values. Likewise, a vector can describe a quantity having a direction and a magnitude in the coordinate space. 
     A computing device can maintain, for example, in a memory associated with the device, a representation of a virtual environment. As used herein, a virtual environment is a computational representation of a three-dimensional space. A virtual environment can include representations of any object, action, signal, parameter, coordinate, vector, or other characteristic associated with that space. In some examples, circuitry (e.g., a processor) of a computing device can maintain and update a state of a virtual environment; that is, a processor can determine at a first time, based on data associated with the virtual environment and/or input provided by a user, a state of the virtual environment at a second time. For instance, if an object in the virtual environment is located at a first coordinate at time, and has certain programmed physical parameters (e.g., mass, coefficient of friction); and an input received from user indicates that a force should be applied to the object in a direction vector; the processor can apply laws of kinematics to determine a location of the object at time using basic mechanics. The processor can use any suitable information known about the virtual environment, and/or any suitable input, to determine a state of the virtual environment at a time. In maintaining and updating a state of a virtual environment, the processor can execute any suitable software, including software relating to the creation and deletion of virtual objects in the virtual environment; software (e.g., scripts) for defining behavior of virtual objects or characters in the virtual environment; software for defining the behavior of signals (e.g., audio signals) in the virtual environment; software for creating and updating parameters associated with the virtual environment; software for generating audio signals in the virtual environment; software for handling input and output; software for implementing network operations; software for applying asset data (e.g., animation data to move a virtual object over time); or many other possibilities. 
     Output devices, such as a display or a speaker, can present any or all aspects of a virtual environment to a user. For example, a virtual environment may include virtual objects (which may include representations of inanimate objects; people; animals; lights; etc.) that may be presented to a user. A processor can determine a view of the virtual environment (for example, corresponding to a “camera” with an origin coordinate, a view axis, and a frustum); and render, to a display, a viewable scene of the virtual environment corresponding to that view. Any suitable rendering technology may be used for this purpose. In some examples, the viewable scene may include only some virtual objects in the virtual environment, and exclude certain other virtual objects. Similarly, a virtual environment may include audio aspects that may be presented to a user as one or more audio signals. For instance, a virtual object in the virtual environment may generate a sound originating from a location coordinate of the object (e.g., a virtual character may speak or cause a sound effect); or the virtual environment may be associated with musical cues or ambient sounds that may or may not be associated with a particular location. A processor can determine an audio signal corresponding to a “listener” coordinate—for instance, an audio signal corresponding to a composite of sounds in the virtual environment, and mixed and processed to simulate an audio signal that would be heard by a listener at the listener coordinate—and present the audio signal to a user via one or more speakers. 
     Because a virtual environment exists only as a computational structure, a user cannot directly perceive a virtual environment using one&#39;s ordinary senses. Instead, a user can perceive a virtual environment only indirectly, as presented to the user, for example by a display, speakers, haptic output devices, etc. Similarly, a user cannot directly touch, manipulate, or otherwise interact with a virtual environment; but can provide input data, via input devices or sensors, to a processor that can use the device or sensor data to update the virtual environment. For example, a camera sensor can provide optical data indicating that a user is trying to move an object in a virtual environment, and a processor can use that data to cause the object to respond accordingly in the virtual environment. 
     Digital Reverberation and Environmental Audio Processing 
     A XR system can present audio signals that appear, to a user, to originate at a sound source with an origin coordinate, and travel in a direction of an orientation vector in the system. The user may perceive these audio signals as if they were real audio signals originating from the origin coordinate of the sound source and traveling along the orientation vector. 
     In some cases, audio signals may be considered virtual in that they correspond to computational signals in a virtual environment, and do not necessarily correspond to real sounds in the real environment. However, virtual audio signals can be presented to a user as real audio signals detectable by the human ear, for example, as generated via speakers  120 A and  120 B of wearable head device  100  in  FIG.  1   . 
     Advantages to the below disclosed embodiments include reduced network bandwidth, reduced power consumption, reduced computational complexity, and reduced computational delays. These advantages may be particularly significant to mobile systems, including wearable systems, where processing resources, networking resources, battery capacity, and physical size and heft are often at a premium. 
     In an environment as dynamic as AR, the system may be continuously rendering audio signals. Rendering audio signals using all of the virtual speakers may especially lead high computational power, a large amount of processing, high network bandwidth, high power consumption, and the like. Thus, using modified virtual speaker panning to dynamically select and use a subset set of the fixed virtual speakers based one or more factors may be desired. 
     Example Spatial Audio System 
       FIG.  5 A  illustrates a block diagram of an example spatial audio system, according to some embodiments.  FIG.  5 B  illustrates a flow of an example method for operating the system of  FIG.  5 A . 
     The spatial audio system  500  may include a spatial modeler  510 , an internal spatial representation  530 , and a decoder/virtualizer  540 A. The spatial modeler  510  may include a direct path portion  512 , one or more reflections portions  520  (optional), and a spatial encoder  526 . The spatial modeler  510  may be configured to model a virtual environment. The direct path portion  512  may include a direct source  514 , and optionally, a Doppler  516 . The direct source  514  may be configured to provide an audio signal (step  552  of process  550 ). The Doppler  516  may receive a signal from the direct source  514  and may be configured to introduce a Doppler effect into its input signal (step  554 ). For example, the Doppler  516  may change the pitch of the sound source (e.g., pitch shifting) to change relative to the motion of the sound source, the user of the system, or both. 
     The reflections portions  520  may include a sound reflector  522 , an optional Doppler  516 , and a delay  524 . The sound reflector  522  may be configured to introduce reflections in its signal (step  556 ). The reflections introduced may be representative of one or more properties of the environment. The Doppler  516  in a reflections portion  520  may receive a signal from the sound reflector  522  and may be configured to introduce a Doppler effect into its input signal (step  558 ). The delay  524  may receive a signal from the Doppler  516  and may be configured to introduce a delay (step  560 ). 
     The spatial encoder  526  may receive signals from the direct path portion  512  and the reflections portion(s)  520 . In some embodiments, the signal from the direct path portion  512  to the spatial encoder  526  may be the output signal from the Doppler  516  of the direct path portion  512 . In some embodiments, the signal(s) from the reflections portion(s)  520  to the spatial encoder  526  may be the output signal(s) from the delay(s)  524  of the reflections portion(s)  520 . 
     The spatial encoder  526  may include one or more M-way Pans  528 . In some embodiments, each input received by the spatial encoder  526  may be associated with a unique M-way Pan  528 . “Panning” may refer to distributing a signal across multiple speakers, multiple locations, or both. The M-way pan  528  may be configured to distribute its input signal across multiple number of virtual speakers (step  562 ). For example, an M-way pan  528  can distribute its input signal across all M virtual speakers. For example, as shown in the  FIG.  5 A , M may be equal to four, and each M-way pan  528  may be configured to distribute its input signal across four virtual speakers. Although the figure illustrates a system having four virtual speakers, examples of the disclosure can include any number of virtual speakers. 
     As one example, a car system may include left and right speakers. The sound in such system may be panned between left and right speakers in a car by splitting the sound into two, one for each speaker. The scaling volume of each speaker may be set according to the configuration of two speakers, and the result may sent to the left and right speakers. 
     As another example, a surround sound system may include a plurality of speakers, such as six speakers. The sound in such system may be panned as stereo among the six speakers. The sound may be split into six (instead of two, as in the car system example), the scaling volume of each speaker may be set according to the configuration of six speakers, and the result may be sent to the six speakers. 
     For example, a first M-way pan  528  may receive the output of the Doppler  516  of the direct path  512 , and the other M-way pans  528  may receive the outputs of the reflections portions  520 . Each M-way pan  528  can split its input signal so that it may be distributed across multiple outputs. As such, each M-way pan  528  may have a greater number of outputs than inputs. 
     The spatial modeler  510  may output signals to the internal spatial representation  530  (step  564 ). In some embodiments, the output(s) from the spatial modeler  510  can include the output of each M-way pan  528 . The internal spatial representation  530  may be configured to represent the spatial configuration of the virtual environment (step  566 ). One example representation can include representing the relative location of the user, the sound source(s), and the virtual speaker(s). In some embodiments, the internal spatial representation  530  may output one or more signals representative of the headpose rotation, the headpose translation, soundfield decode, one or more head-related transfer functions (HRTFs), or a combination thereof, of the user of the system  500 . In some embodiments, the internal spatial representation  530  may be a representation of a non-ambisonics multi-channel based system, an ambisonics/wavefield based system, or the like. One example ambisonics/wavefield based system can be a high order ambisonics (HOA). 
     The internal spatial representation  530  may output its signals  552  to the decoder/virtualizer  540 A (step  568 ). The decoder/virtualizer  540  may decode its input signals and introduce virtualized sounds into the signals (step  570 ). Step  570  can include a plurality of substeps and is discussed in more detail below. The system then outputs the signals from the decoder/virtualizer  540  (step  580 ) as the left signal  502 L, which may be output to the left speaker, and the right signal  502 R, which may be output to the right speaker. 
     The system  500  may include any number of different types of a decoder/virtualizer  540 . One example decoder/virtualizer  540 A is shown in  FIG.  5 A . Other example decoder/virtualizers  540  are discussed below. 
     The decoder/virtualizer  540 A may include a rotated/translated representation  542 , a soundfield decoder  544 , one or more HRTFs  546 , and one or more combiners  548 .  FIG.  5 C  illustrates a flow of an example method for operating an example decoder/virtualizer, which may be referred to as step  570 - 1 . The rotated/translated representation  542  may receive signal(s) from the internal spatial representation  530  and may be configured to introduce representations of the movements associated with the audio signals. For example, the movements can be of the sound source(s), the user, or both (step  572 ). The rotated/translated representation  542  can output signal(s) to the soundfield decoder  544 . The soundfield decoder  544  may receive signal(s) from the rotated/translated representation  542  and may be configured to decode the signals (step  574 ). Each HRTF  546  may receive signal(s) from the soundfield decoder  544 . Each HRTF  546  may be configured to determine a HRTF corresponding to its input signal and apply it to the signal (step  576 ). The one or more HRTFs  546  may be referred to collectively as a speaker virtualizer. In some embodiments, the HRTF  546  may be configured for finite impulse response (FIR) filtering. Each combiner  548  may receive and combine signal(s) from the HRTF(s)  546  (step  578 ). 
     In some embodiments, the decoder/virtualizer  540 A may represent a “baseline” processing overhead. The baseline processing overhead may be complex, involving matrix calculations and long FIR filters to apply HRTF processing for each virtual speaker. 
     The outputs from the combiners  548  may be the output signals form the system  500 . In some embodiments, the output signals  502  from the system  500  may be audio signals for the left and right speakers (e.g., speakers  120 A and  120 B of  FIG.  1   ). 
     In some instances, when the number of sound sources for play back is large, the spatial audio system of  FIG.  5 A  may be beneficial. However, in some instances, when the number of sound sources for play back is small, the spatial audio system of  FIG.  5 A  may not be beneficial. It may be desirable to utilize efficiencies of non-ambisonics multi-channel based spatial audio systems or ambisonics-based spatial audio systems, such as system  500  of  FIG.  5 A , in a way that is efficient for situations when the number of sound sources for play back is small. 
     There may be ways to improve the efficiencies of spatializing using soundfield synthesis and decoding. A first way may be through low energy speaker detection and culling. In low energy speaker detection and culling, if the energy output of a virtual speaker channel of a non-ambisonics multi-channel based spatial audio system or ambisonics/soundfield channel of an ambisonics based spatial audio system is less than a predetermined threshold, processing of the signals from the virtual speaker channel is not performed. In some embodiments, the system may determine whether an output of a given virtual speaker is above a predetermined threshold, for example, before the sound field decoding is performed on the signals from that given virtual speaker. Low energy speaker detection and culling is discussed in more detail below. 
     A second way for improving the efficiency of spatializing using soundfield synthesis and decoding can be source geometry-based virtual speaker culling. In source geometry-based virtual-speaker culling, the decoder/virtualizer processing can be selectively disabled. The selective disablement (or selective enablement) can be based on the location(s) of the sound source(s) relative to the user/listener. Source geometry-based virtual speaker culling is discussed in more detail below. 
     A third way may be to combine the low energy speaker detection and culling technique with the source-virtual speaker coupling technique. 
     A spatial modeler  510  may have a compute complexity that may represent the number of operations needed to process the audio signals. The compute complexity may be proportional to M multiplied by N, where M may be equal to the number of sound sources (including direct sources and optional reflections) and N may be equal to the number of channels needed to represent an ambisonic soundfield. In some embodiments, N may equal to (O+1) 2 , where O is the order of ambisonics used. 
     A decoder/virtualizer  540  may have a compute complexity proportional to nVS, where nVS is a number of virtual speakers. The compute power of each speaker may be high and may generally consist of a pair of FIR filters typically implemented with fast Fourier transform (FFT) or inverse FFT (IFFT), both of which may be computationally expensive processes. 
     Example Low Energy Output Detection and Culling Method 
     In some embodiments, some virtual speakers may have little or not signal input energy; for example, when the spatial audio system has a small number of sound sources. Speaker virtualization processing may be computationally expensive (e.g., CPU intensive) process. For example, if there is a sound source located at zero degrees azimuth (e.g., directly in front of a user), there may be little or no energy in the signals from the virtual speakers located between 90 degrees and 270 degrees azimuth (e.g., behind the user). The low energy signals may not have a significant effect on the perceived location of a sound source, so it may be computationally inefficient to perform speaker virtualization processing on the low energy signals and/or to determine the characteristics of the corresponding virtual speaker. 
     To lessen computation resources required, the system employing low energy output detection and culling method can include detectors located between the soundfield decoder and a HRTF. Alternatively, the detectors may be located between the multi-channel output and a HRTF. The detectors may be configured to detect one or more energy levels associated with one or more audio signals from one or more virtual speakers. 
     If the energy level of a signal coming from a virtual speaker Vn is less than an energy threshold α, the signal may be considered a low energy signal. In accordance with the detected energy level associated with the audio signal being less than the energy threshold α, the HRTF block and its processing of the low energy signal may be bypassed. 
     The determination of the energy levels of a signal may use any number of techniques. For example, a RMS algorithm may be applied to a signal routed to a virtual speaker to measure its energy. “Attack” and “release” times similar to those used by times similar to those by traditional audio compressors may be used to keep a speaker&#39;s signal from abruptly “popping” in and out. 
       FIG.  6    illustrates an example configuration of a sound source and speakers, according to some embodiments. System  600  may include a sound source  620  and a plurality of speakers. The plurality of speakers  622  may include one or more active virtual speakers  622 A and one or more inactive virtual speakers  622 B. An active virtual speaker  622 A may be one whose signal is processed by a HRTF  546  at a given time. An inactive virtual speaker  622 B may be one whose signal not need to be processed by a HRTF  546  because, e.g., its signal was already processed at a previous time, or because the system determines that signal from the virtual speaker  622 B does not need processing. M can refer to the number of sound sources playing, and N can refer to the number of virtual speakers in the system. Although the figure illustrates a single sound source, examples of the disclosure can include any number of sound sources. Although the figure illustrates eight sound sources, examples of the disclosure can include any number of sources, such as 16 (N=16). 
     As one example, system  600  can include a single (M=1) sound source  620  and 8 virtual speakers  622 , as shown in the figure. At a given instance, most of energy may be output across only three virtual speakers. That is, the system  600  may have three active virtual speakers at a first time. For example, the virtual speakers  622 A- 1 ,  622 A- 2 , and  622 - 3  may be active virtual speakers. In some embodiments, the active virtual speakers  622 A may be those closest to the sound source  620 . Additionally, the system  600  may include five inactive virtual speakers  622 B. The system  600  may be determine that the energy level from each of the five inactive virtual speakers is less than an energy threshold, and in accordance with such determination, may bypass the HRTF processing of the signals from the five inactive virtual speakers  622 B. 
     The system  600  may also determine that the energy level from each of the active virtual speakers is not less than the energy threshold, and in accordance with such determination, may perform HRTF processing of the signals from the three active virtual speakers  622 A. 
     The system  600  may output two signals, one for the right speaker and one for the left speakers, such as right signal  502 R and left signal  502 L, as shown in  FIG.  5 A . The reduction in number of HRTF operations due to bypassing the HRTF processing may be equal to the number of inactive virtual speakers multiplied by the number of signals output from the system. In the example of  FIG.  6   , since the HRTF processing of the five signals are bypassed, 10 (five inactive virtual speakers×two output signals) HRTF operations may be saved. 
     As another example, if the system includes 16 virtual speakers, where 13 are inactive virtual speakers, the number of HRTF operations saved may be equal to 26 (16 virtual speakers×two output signals). 
       FIG.  7 A  illustrates a block diagram of an example decoder/virtualizer including a plurality of detectors, according to some embodiments.  FIG.  7 B  illustrates a flow of an example method for operating the decoder/virtualizer of  FIG.  7 A , according to some embodiments. In some embodiments, the decoder/virtualizer  540 B may be included in system  500 , instead of decoder/virtualizer  540 A (shown in  FIG.  5 A ), as discussed below. The step  570 - 2  may be included in the process  550 , instead of step  570 - 1  (shown in  FIG.  5 C ). 
     The decoder/virtualizer  540 B can include a rotated/translated representation  542 , soundfield decoder  544 , one or more detectors  710 , one or more switches  712 , one or more HRTFs  546 , and one or more combiners  548 . The decoder/virtualizer  540 B can receive signal(s)  552  from the internal spatial representation  530  (as shown in  FIG.  5 A ). The rotated/translated representation  542  may receive signals from the internal spatial representation  530  and may be configured to introduce representations of the movements of the sound source(s), the user, or both (step  772 ). The rotated/translated representation  542  can output signal(s) to the soundfield decoder  544 . The soundfield decoder  544  can receive signals from the rotated/translated representation  542  and may be configured to decode the signals (step  774 ). The soundfield decoder  544  can output signals to the detector(s)  710 . 
     The detector(s)  710  may receive a signal from the soundfield decoder  544  and may be configured to determine the energy level of its input signal (step  776 ). Each detector  710  may be coupled to a unique switch  712 . If the energy level of the input signal (from the soundfield decoder  544 ) is greater than or equal to the energy threshold (step  778 ), then the switch  712  can close the loop thereby routing its input signal (from the detector  710 ) to the HRTF  546  that the switch is coupled to (step  780 ). Each HRTF determines a corresponding HRTF and applies it to the signal (step  782 ). 
     If the energy level of the input signal is less than the energy threshold, then the switch  712  can open such that its input signal (from the detector  710 ) is not coupled to the corresponding HRTF  546 . Thus, the corresponding HRTF  546  may be bypassed (step  784 ). 
     The signals from the HRTF(s)  546  can be output to the combiners  548  (step  786 ). The combiners  548  can be configured to combine (e.g., add, aggregate, etc.) the signals from the HRTF(s)  546 . Those signals that bypassed a HRTF  546  may not be combined by the combiners  548 . The outputs from the combiners  548  may be the output signals form the system  500 . In some embodiments, the output signals  502  from the system  500  may be audio signals for the left and right speakers (e.g., speakers  120 A and  120 B of  FIG.  1   ). 
     In some embodiments, each detector  710  can be coupled to a unique signal corresponding to a virtual speaker. In this manner, the processing of each virtual speaker  622  can be independently performed (i.e., the processing of one speaker, such as  622 A- 1 , can occur without affecting the processing of another speaker, such as  622 B). 
     In some embodiments, the type of decoder/virtualizer  540  may depend on the number of sound sources. For example, if the number of sound sources is less than or equal to a predetermined sound source threshold, then the decoder/virtualizer  540 B of  FIG.  7 A  may be included in the system  500 . In such instance, the signals from the soundfield decoder  544  may be input to the detector(s)  710 . 
     If the number of sound sources is greater than the predetermined sound source threshold, then the decoder/virtualizer  540 A of  FIG.  5 A  may be included in the system. In such instance, the signals from the soundfield decoder  544  may be input to the HRTFs  546 . 
     In some embodiments, the system may include a decoder/virtualizer  540  that may select whether to execute or to bypass the detectors and its energy level detection.  FIG.  8 A  illustrates a block diagram of an example decoder/virtualizer, according to some embodiments.  FIG.  8 B  illustrates a flow of an example method for operating the decoder/virtualizer of  FIG.  8 A , according to some embodiments. In some embodiments, the decoder/virtualizer  540 C may be included in system  500 , instead of decoder/virtualizer  540 A (shown in  FIG.  5 A ) and decoder/virtualizer  540 B (shown in  FIG.  7 A ). The step  570 - 3  may be included in the process  550 , instead of step  570 - 1  (shown in  FIG.  5 C ). 
     The decoder/virtualizer  540 C can include a rotated/translated representation  542 , soundfield decoder  544 , one or more detectors  710 , one or more first switches  712 , one or more HRTFs  546 , and one or more combiners  548 , similar to the decoder/virtualizer  540 B, discussed above. Steps  872 ,  874 , and  882  may be correspondingly similar to steps  772 ,  774 , and  782 , discussed above. 
     The decoder/virtualizer  540 C may also include a second switch  814 . The second switch  814  can be configured to open or close a first loop from the soundfield decoder  544  to the detector(s)  710  and the first switch(es)  712 . Additionally or alternatively, the second switch  814  can be configured to open or close a second loop from the system  500  bypassing the detector(s)  710  and first switch(es)  712 . In some embodiments, the second switch  814  may be a two-way switch configured to select between passing the signals directly to the detectors  710  (the first loop) or directly to the HRTFs  546  (the second loop). 
     For example, the system can determine whether the number of sound sources is greater than or equal to a predetermined sound source threshold (step  876 ). If the number of sound sources is greater than or equal to a predetermined sound source threshold, then the second switch  814  can close the second loop and cause the signals from the soundfield decoder  544  to be pass directly to the HRTFs  546  (step  878 ). Each HRTF  546  then determines a corresponding HRTF and applies it to the signal (step  880 ). When the number of sound sources is greater in number, the likelihood of the signals having low energy levels may be reduced. 
     If, on the other hand, the number of sound sources is less than a predetermined sound source threshold, then the signals are more likely to have low energy levels, so the second switch  814  can close the first loop and cause the signals from the soundfield decoder  544  to pass directly to the detector(s)  710  (step  882 ). The detector(s)  710  may receive a signal from the soundfield decoder  544  and may be configured to determine the energy level of its input signal (step  884 ). If the energy level of the input signal (from the soundfield decoder  544 ) is greater than or equal to the energy threshold (step  886 ), then the switch  712  can close the loop thereby routing its input signal (from the detector  710 ) to the HRTF  546  that the switch is coupled to (step  888 ). If the energy level of the input signal is less than the energy threshold, then the switch  712  can open such that its input signal (from the detector  710 ) is not coupled to the corresponding HRTF  546 , causing the HRTF  546  to be bypassed (step  890 ). 
     The signals from the HRTF(s)  546  can be output to the combiners  548  (step  892 ). 
     In some embodiments, the one or more energy threshold detection may be active responsive to energy. In some embodiments, the one or more energy threshold detection may be active responsive to amplitude, may be subject to traditional attack, release times, and the like. 
     Example Source Geometry-Based Speaker Culling Method 
     Source geometry-based virtual speaker culling can be another method to reduce CPU consumption. In some embodiments, source geometry-based virtual speaker culling can include selectively disabling the decoder/virtualizer processing (e.g., decoder/virtualizer  540 A of  FIG.  5 A , decoder/virtualizer  540 B of  FIG.  7 A , decoder/virtualizer  540 C of  FIG.  8 A , etc.). In some embodiments, the selective disablement (or selective enablement) can be based on the location(s) of the sound source(s) relative to the user/listener. In some embodiments, the selective disablement of the decoder/virtualizer processing can include bypassing all of the processing blocks of the decoder/virtualizer. 
     With source geometry-based virtual speaker culling, the ambisonic output can be calculated. If the ambisonic output requires a significant amount of energy to be decoded, then it may be beneficial to use a simpler method (that requires less CPU consumption) such as a real-time energy detection method. Additionally, in some embodiments, the real-time energy detection method can perform a calculation less frequently. 
       FIG.  9    illustrates an example configuration of a sound source and speakers, according to some embodiments. System  900  may include a sound source  920  and a plurality of speakers. Compared to the system  600  of  FIG.  6   , the sound source  920  may be located at a second position, which may be different from first position of the sound source  620  of  FIG.  6   . The plurality of speakers  922  may include one or more active virtual speakers  922 A, one or more inactive virtual speakers  922 B, and one or more inactive virtual speakers  922 C. The active virtual speakers  922 A and the inactive virtual speakers  922 B may be correspondingly similar to the active virtual speakers  622 A and the inactive virtual speakers  622 B of  FIG.  6   , respectively. 
     The inactive virtual speakers  922 C may differ from the inactive virtual speakers  922 B in that virtual speakers  922 C may have been active at a first time, but its signal is being processed at a second time (e.g., the ring out period). In the example of  FIG.  9   , the sound source  920  may have moved from a first position (e.g., close to virtual speaker  922 C) to a second position (e.g., not close to virtual speaker  922 ). Due to the movement of the sound source, the two virtual speakers may no longer have sound sources mixing into them at the second time. Due to filter processing of the two virtual speakers, the two virtual speakers may need to be active for a following frame (e.g., the second time) to properly complete the filter processing. 
     In some embodiments, the system may include a decoder/virtualizer  540  in a system that uses active virtual speakers.  FIG.  10 A  illustrates a block diagram of an example decoder/virtualizer used in a system including active speakers, according to some embodiments.  FIG.  10 B  illustrates a flow of an example method for operating the decoder/virtualizer of  FIG.  10 A , according to some embodiments. In some embodiments, the decoder/virtualizer  540 D may be included in system  500 , instead of decoder/virtualizer  540 A (shown in  FIG.  5 A ), decoder/virtualizer  540 B (shown in  FIG.  7 A ), and decoder/virtualizer  540 C (shown in  FIG.  8 A ). The step  570 - 4  may be included in the process  550 , instead of step  570 - 1  (shown in  FIG.  5 C ), step  570 - 2  (shown in  FIG.  7 B ), and step  570 - 3  (shown in  FIG.  8 B ). 
     The decoder/virtualizer  540 C can include a soundfield decoder  544  one or more HRTFs  546 , and one or more combiners  548 , similar to the decoder/virtualizer  540 B and decoder/virtualizer  540 C, discussed above. Steps  1072 ,  1076 ,  1078 , and  1080  may be correspondingly similar to steps  872 ,  874 , and  782 , discussed above. 
     The decoder/virtualizer  540 D may also include a rotated/translated representation  1042  and a soundfield decode determination  1044 . The rotated/translated representation  1042  may receive signal(s) from the internal spatial representation  530  and may be configured to introduce representations of the movements of the sound source(s), the user, or both (step  1072 ). The representations of the movement may also take into consider the azimuth/elevation of the sound source  920 . The rotated/translated representation  542  can output signal(s) to the soundfield decoder determination  1044 . 
     The soundfield decoder determination  1044  may receive signal(s) from the rotated/translated representation  1042  and may be configured to determine which signals have “noticeable” output and pass those signals to the soundfield decoder  544  (step  1074 ). A noticeable output may be an output that would affect a perceived sound. For example, a noticeable output can be an audio signal that has an amplitude greater than or equal to a predetermined amplitude threshold. The soundfield decoder  544  may receive signal(s) from the soundfield decoder determination  1044  having noticeable output and may be configured to decode the signals (step  1076 ). In some embodiments, the soundfield decoder  1044  may receive signals from the soundfield decoder determination  1044  that have noticeable output. Each HRTF  546  may receive signal(s) from the soundfield decoder  544 . Each HRTF  546  may be configured to determine a HRTF corresponding to its input signal and apply it to the signal (step  1078 ). The one or more HRTFs  546  may be referred to collectively as a speaker virtualizer. Each combiner  548  may receive and combine signal(s) from the HRTF(s)  546  (step  1080 ). 
     In some embodiments, those audio signals that do not have a noticeable output (e.g., has an amplitude less than the predetermined amplitude threshold) may not be passed to the soundfield decoder  544 . Thus, the soundfield decoder  544  and the HRTFs  546  on the audio signals not having a noticeable output may be bypassed. 
     The example source geometry-based speaker culling method can designate virtual speakers as being active virtual speakers based on the position (e.g., X, Y, Z location) of the sound source. The location of the sound source may be representative of the location of a source object. The system may determine the location of each sound source and determine which virtual speaker(s) are located close to the respective sound source. In some embodiments, the determination of which virtual speakers are located close to the sound source may be performed at, e.g., the beginning of every video frame (on a video-frame rate based approach). The video-frame rate based approach may require less computation than other approaches such as the sample-rate based approach. 
     A sound source may contribute significantly to a particular virtual speaker based on, for example, the video-frame rate based approach calculation and an ambisonic decode formula. As discussed above, a virtual speaker that contributes little to no energy if decoded may have the corresponding ambisonic decode and HRTF processing of the decoded ambisonics channel bypassed. In some embodiments, the system may disable any processing block that is bypassed. 
     Example pseudo-code for executing the designation method can be:
         For each sound source, S and decode channel n   Enable[n] |=f(sourcePosition Vector3, sourceOrientation Vector3, ListenerPosition Vector3, ListenerOrientation Vector3, VirtualSpeakerPosition[n] Vector3).       

     Ambisonic/Soundfield Example 
     
       
         
           
               
               
             
               
                   
                   
               
             
            
               
                   
                 For each Ambisonic Decode Channel 
               
               
                   
                 If (Enable[n]) { 
               
               
                   
                  AmbisonicDecode(n) 
               
               
                   
                  Virtualize(n) 
               
               
                   
                 } 
               
               
                   
                   
               
            
           
         
       
     
     Multichannel Example 
     
       
         
           
               
               
             
               
                   
                   
               
             
            
               
                   
                 For each Channel 
               
               
                   
                 If (Enable[n]) { 
               
               
                   
                  Virtualize(n) 
               
               
                   
                 } 
               
               
                   
                   
               
            
           
         
       
     
     With respect to the above pseudo-code, the variable sourcePosition may refer to a position of a sound source, sourceOrientation may refer to an orientation of the sound source, ListenerPosition may refer to a position of a user/listener, ListenerOrientation may refer to an orientation of the user/listener, VirtualSpeakerPosition may refer to a position of a virtual speaker, AmbisonicDecode may refer to a function that performs ambisonic decoding, and Virtualize may refer to a function that does virtualization. 
     With respect to the above pseudo-code, for each sound source S and decode channel n, the decode channel n may be enabled based on one or more factors such as the position of the sound source S, the orientation of the sound source S, the position of the user/listener, the orientation of the user/listener, and the position of the virtual speaker. Still referring to the above pseudo-code, for each ambisonic decode channel, if the channel is enabled, then the system may execute the AmbisonicDecode function and the Virtualize function. 
     The pseudo-code may be enhanced by providing a “ring out” period for each virtual speaker. For example, if a source has moved in position during a video frame, it may be determined that a virtual speaker may no longer have any sound sources mixing into it. However, due to filter processing of the virtual speaker, that virtual speaker may need to be an active speaker for a following frame to properly complete the filter processing. 
     Examples of the disclosure can include using all active sound sources to determine which decoded soundfield outputs have a “noticeable” output (e.g., an output that would affect a perceived soundfield). Ambisonics or non-ambisonics multi-channel outputs that would affect the perceived soundfield may be decoded. Further, in some embodiments, only HRTFs  546  corresponding to those detected outputs are processed. There may be significant CPU savings for synthetically generated ambisonic soundfield or non-ambisonic multi-channel rendering where a number of the sound sources are small, or are numerous but near each other. 
     Example Method Combination of the Source Geometry-Based Virtual Speaker Culling Method and the Low Energy Output Detection and Culling Method 
     In some embodiments, source geometry-based virtual speaker culling and low energy output detection and culling may both be used sequentially to further reduce CPU consumption. As described above, source geometry-based virtual speaker culling may include, for example, selectively disabling virtual speaker processing based on, e.g., locations of sound sources relative to a user/listener. Low energy output detection and culling may include, for example, placing a signal energy/level detector between soundfield decoding or multi-channel output and HRTF processing. The output/result of the source geometry-based virtual speaker culling may be input to the low energy output detection and culling. 
     With respect to the systems and methods described above, elements of the systems and methods can be implemented by one or more computer processors (e.g., CPUs or DSPs) as appropriate. The disclosure is not limited to any particular configuration of computer hardware, including computer processors, used to implement these elements. In some cases, multiple computer systems can be employed to implement the systems and methods described above. For example, a first computer processor (e.g., a processor of a wearable device coupled to a microphone) can be utilized to receive input microphone signals, and perform initial processing of those signals (e.g., signal conditioning and/or segmentation, such as described above). A second (and perhaps more computationally powerful) processor can then be utilized to perform more computationally intensive processing, such as determining probability values associated with speech segments of those signals. Another computer device, such as a cloud server, can host a speech recognition engine, to which input signals are ultimately provided. Other suitable configurations will be apparent and are within the scope of the disclosure. 
     Although the disclosed examples have been fully described with reference to the accompanying drawings, it is to be noted that various changes and modifications will become apparent to those skilled in the art. For example, elements of one or more implementations may be combined, deleted, modified, or supplemented to form further implementations. Such changes and modifications are to be understood as being included within the scope of the disclosed examples as defined by the appended claims.