Patent Publication Number: US-2023136161-A1

Title: Apparatus and method for performing active occulsion cancellation with audio hear-through

Description:
RELATED PATENT DOCUMENTS 
     This application claims the benefit of U.S. Provisional Application No. 63/273,436, filed on Oct. 29, 2021, which is incorporated herein by reference in its entirety. 
    
    
     SUMMARY 
     This application relates generally to ear-level electronic systems and devices, including hearing aids, personal amplification devices, and hearables. In one embodiment, an apparatus and method facilitate active occlusion cancellation with audio hear-through. One embodiment involves performing occlusion cancellation in an ear-wearable device using an adaptive occlusion cancellation filter. An adaptive gain of the adaptive occlusion cancellation filter is used to determine a leakage path estimate between an external source and an eardrum of a user through the ear-wearable device. The leakage path estimate is used to update an adaptive hear-through filter of the ear-wearable device. The updated adaptive hear-through filter is used for hear-through processing in the ear-wearable device. 
     Another embodiment involves performing occlusion cancellation in an ear-wearable device using a first adaptive filter. Hear-though processing is performed in the ear-wearable device using a second adaptive filter. A leakage path is estimated between an external source and an eardrum of a user through the ear-wearable device based on an adaptive gain of the first adaptive filter. Adaptive filter parameters of the second adaptive filter are updated based on the estimate of the leakage path. 
     The above summary is not intended to describe each disclosed embodiment or every implementation of the present disclosure. The figures and the detailed description below more particularly exemplify illustrative embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The discussion below makes reference to the following figures. 
         FIG.  1    is an illustration of a hearing device according to an example embodiment; 
         FIGS.  2  and  3    are diagrams showing own-voice, acoustic paths for open and occluded cases according to an example embodiment; 
         FIG.  4    shows differences in hear-through acoustic paths with and without an ear-wearable device; 
         FIG.  5    is a frequency response diagram showing differences in hearing device response with active occlusion cancellation activated and deactivated; 
         FIG.  6    is a block diagram showing processing paths for hear-through and active occlusion cancellation in an ear wearable device according to an example embodiment; 
         FIG.  7    is a block diagram showing closed loop transfer function for a hearing device according to an example embodiment; 
         FIGS.  8 ,  9 , and  10    are graphs illustrating an own-voice detection scheme according to an example embodiment; 
         FIG.  11    is a formula illustrating obtaining frequency-domain coefficients based on time-domain filer coefficients according to an example embodiment; 
         FIG.  12    is a diagram of a method according to an example embodiment; and 
         FIGS.  13  and  14    are flowcharts of methods according to example embodiments. 
     
    
    
     The figures are not necessarily to scale. Like numbers used in the figures refer to like components. However, it will be understood that the use of a number to refer to a component in a given figure is not intended to limit the component in another figure labeled with the same number. 
     DETAILED DESCRIPTION 
     Embodiments disclosed herein are directed to an ear-worn or ear-level electronic hearing device. Such a device may include cochlear implants and bone conduction devices, without departing from the scope of this disclosure. The devices depicted in the figures are intended to demonstrate the subject matter, but not in a limited, exhaustive, or exclusive sense. Ear-worn electronic devices (also referred to herein as “hearing aids,” “hearing devices,” and “ear-wearable devices”), such as hearables (e.g., wearable earphones, ear monitors, and earbuds), hearing aids, hearing instruments, and hearing assistance devices, typically include an enclosure, such as a housing or shell, within which internal components are disposed. 
     In embodiments described below, a hearing device includes active occlusion cancellation (AOC). The occlusion effect describes the boost of own voice and boost/reduction of other sounds due to a partially- or fully occluded ear canal. The occlusion effect can be reduced in an ear-wearable device including vents up to diameters of 1.8 mm and some more than 1.8 mm. However, full occlusion is desirable for proper active noise cancellation (ANC) processing. Therefore, an ear-wearable device that is designed to occlude the ear canal can include AOC circuitry to reduce the effects of the occlusion. 
     The goal of AOC technology is to make the own voice for an occluded ear canal sound the same as that for nonoccluded listening when the user is talking. Embodiments described herein combine the active occlusion cancellation system with hear-through. Generally, hear-through processing involves receiving sound via an external microphone and reproducing the sound in the ear canal with a receiver/loudspeaker. Hear-through processing may also condition the sound to account for hearing loss, e.g., boosting overall volume, boosting high frequencies. In order to achieve the overall goal of making the perception of ambient sound and own-voice for an occluded ear canal sound equivalent as that for unaided listening, there are advantages in having both occlusion cancellation and hear-through processing jointly optimized, which features adaptations for both occlusion cancellation processing and hear-through filter design. 
     In  FIG.  1   , a diagram illustrates an example of an ear-wearable device  100  according to an example embodiment. The ear-wearable device  100  includes an in-ear portion  102  that fits into the ear canal  104  of a user/wearer. The ear-wearable device  100  may also include an external portion  106 , e.g., worn over the back of the outer ear  108 . The external portion  106  is electrically and/or acoustically coupled to the internal portion  102 . The in-ear portion  102  may include an acoustic transducer  103 , although in some embodiments the acoustic transducer may be in the external portion  106 , where it is acoustically coupled to the ear canal  104 , e.g., via a tube. The acoustic transducer  103  may be referred to herein as a “receiver,” “loudspeaker,” etc., however could include a bone conduction transducer. One or both portions  102 ,  106  may include an external microphone, as indicated by respective microphones  110 ,  112 . 
     The device  100  may also include an internal microphone  114  that detects sound inside the ear canal  104 . The internal microphone  114  may also be referred to as an inward-facing microphone or error microphone. For purposes of the following discussion, path  118  represents a secondary path, which is the physical propagation path from receiver  103  to the error microphone  114  within the ear canal  104 . Path  120  represents an acoustic coupling path between the receiver  103  and the eardrum  122  of the user. In embodiments below, other audio coupling paths will be described that are more specific to AOC and hear-through processing. 
     Other components of hearing device  100  not shown in the figure may include a processor (e.g., a digital signal processor or DSP), memory circuitry, power management and charging circuitry, one or more communication devices (e.g., one or more radios, a near-field magnetic induction (NFMI) device), one or more antennas, buttons and/or switches, for example. The hearing device  100  can incorporate a long-range communication device, such as a Bluetooth® transceiver or other type of radio frequency (RF) transceiver. 
     While  FIG.  1    show one example of a hearing device, often referred to as a hearing aid (HA), the term hearing device of the present disclosure may refer to a wide variety of ear-level electronic devices that can aid a person with impaired hearing. This includes devices that can produce processed sound for persons with normal hearing. Hearing devices include, but are not limited to, behind-the-ear (BTE), in-the-ear (ITE), in-the-canal (ITC), invisible-in-canal (IIC), receiver-in-canal (RIC), receiver-in-the-ear (RITE) or completely-in-the-canal (CIC) type hearing devices or some combination of the above. Throughout this disclosure, reference is made to a “hearing device” or “ear-wearable device,” which is understood to refer to a system comprising a single left ear device, a single right ear device, or a combination of a left ear device and a right ear device. 
     In  FIGS.  2  and  3   , diagrams illustrate the different acoustic path models in an open, non-occluded state ( FIG.  2   ) and an occluded state ( FIG.  3   ). As seen in the open state in  FIG.  2   , the user&#39;s own voice  200  travels through an outer path  202  to the inner microphone  114 , e.g., conducted through the air. The inner path  203  conducts sound through the user&#39;s body to the inner microphone  114 . Arrow  204  represents sound leaving the user&#39;s ear. As seen in the occluded state in  FIG.  3   , the user&#39;s own voice  200  travels through an outer path  302  to the outer microphone  110 , e.g., conducted through the air. The inner path  303  conducts sound through the user&#39;s body to the inner microphone  114 . Due to the occlusion, there is negligible sound leaving the ear in  FIG.  3   . 
     The occlusion effect describes the boost of own voice and other sounds due to a partially- or fully-occluded ear canal. Therefore, path  303  will be boosted relative to path  203 , and path  302  will be attenuated relative to path  202 . Further, the boost attenuation is not uniform over all frequencies. For own voice, the boost is generally in frequency range 125 Hz-1.5 kHz. Illustration of the occlusion effect can be found in May, A. E., and Dillon, H. (1992); “A comparison of physical measurements of the hearing aid occlusion effect with subjective reports,” The Australian Journal of Audiology, Supplement 5, May 12. Occlusion effect sound pressure levels may vary in amplitude between patients from as little as 5-9 dB to 25-32 dB, with peaks at different frequencies. 
     The task in active occlusion cancellation is to make the perception of own-voice and external sound source(s) for an occluded ear canal sound the same as that for non-occluded listening. The embodiments described herein consider the active occlusion cancellation system with hear-through. In order to achieve the overall goal of making the perception of ambient sound-plus-own-voice for an occluded ear canal sound equivalent as that for unaided listening, both occlusion cancellation and hear-through processing are jointly optimized/designed. Conventionally, the (individualized) hear-through filter and active occlusion cancellation are implemented separately. In doing this, an issue of inaccurate reproduction of audio transparency may arise as AOC systems actively cancels the residual ambient sound that leaks into ear-canal. 
     In  FIG.  4   , a diagram shows details of an individualized hear-through filter design according to an example embodiment. On the left side of  FIG.  4   , an unaided (open) audio path is shown, and on the right side, an aided path is shown with in-ear portion  102  in use. Note that the eardrum  400  is modeled as a microphone in this example, and the in-ear portion of the ear-wearable device  102  would include an error microphone  114  that would estimate the eardrum response. The equalization filter G EQ (W) can be computed based on a frequency-domain least-squares optimization problem. Acoustic hear-through means that the transfer function from external source(s) to the eardrum is equivalent in the open and the aided case such that D o (ω)=D aided (ω), such that D o (w)=D m (ω) D I (ω) G EQ (ω)+D c (ω). 
     Therefore, a least-squares optimization is found using the matrix form ∥(D m ′{circumflex over (D)} I G EQ +D r ′)−D o   ′ ∥ 2   2 +μ∥G EQ ∥ 2 , where D m  ‘are diagonal matrices containing the discrete Fourier transform (DFT) coefficients of Dm(ω), {circumflex over (D)} I  are diagonal matrices containing the DFT coefficients of MO)), and D c ’ and D o ′ are corresponding vectors containing the DFT coefficients of the occluded and open responses. However, it should be noted that feedback AOC actively suppress both residual own voice and the direct path D c (ω) that leaks into ear canal (especially at lower frequencies). Therefore, there is a mismatch between the feedback-loop suppressed direct path function and the ground-truth D c ′(ω). 
     Assume the active residual path from external source to eardrum is D c,active (ω), thus D o (ω)=D m (ω) D o (ω) G EQ ′(ω)+D c,active ′(ω). Therefore, updating the hearthrough filter G EQ (ω) will involve actively estimating the residual path from external source to ear canal D c,active ′(ω). In  FIG.  6   , a block diagram illustrates a proposed system for an ear-wearable device that features both adaptive occlusion cancellation processing and adaptation to hear-through filters. The diagram is divided into two sections, with section  600  illustrating the AOC processing components and section  602  illustrating the hear-through processing components. 
     An adaptive filter  606  performs adaptive occlusion cancellation in the ear-wearable device. An adaptive gain  607  of the adaptive filter  606  is used to determine a leakage path estimate  608  between the ear-wearable device and an ear of the user. Note that the term “gain” used in this context refers to parameters, coefficients, taps, etc., that affect a response of the adaptive filter. The leakage path estimate  608  is used to update an adaptive hear-through filter  609  of the ear-wearable device. The adaptive hear-through filter  609  is used for hear-through processing in the ear-wearable device. The output of the adaptive hear-through filter  609  is combined with the AOC processing output before the receiver  103 . If streaming is utilized, the streaming audio signal s audio (n) is combined with the output of the adaptive hear-through filter  609  before being reproduced by the receiver  103 . 
     Note that the updates to the adaptive filters  606 ,  609  may occur synchronously or asynchronously. For example, updates to one filter may occur more frequently than updates to another due to complexity of the filter algorithms, sensitivity of the processing to update frequency, relative resource utilization (e.g., processor or memory), etc. As noted elsewhere, the updates to adaptive hear-through filter  609  via the leakage path estimate  608  may be paused in some situations (e.g., streaming audio, presence of own-voice), although the hear-through processing may experience adjustments elsewhere in the processing path during those times. 
     Using the leakage path estimate  608  to update the hear-through filter  609  can optimize the hear-through processing. In addition to the adaptive filter  606 , the occlusion cancellation include spectrum shaping filter  610  and equalization filter  611  that provide inputs to a normalized least mean squares (NLMS) algorithm processor  612 . Another spectrum shaping filter  613  is also input to the NLMS processor  612 , and an output of the NLMS processor  612  causes the changes to the adaptive filter  606 . 
     Because adaptive feedback system is input signal-dependent, the transfer function from input signal x(n) ( 604 ) to output error signal e(n) ( 605 ) is time-variant. For a static feedback system (as shown below), the close-loop transfer function can be derived as shown in the block diagram of  FIG.  7    and expressed as in Equations (1)-(3) below. 
         C   closeloop =(1+ W   2 )/(1−[ W   1   −W   2 ])  (1)
 
         W   1   =G*EQ   m   *SP   r   (2)
 
         W   2   =G*EQ   m   *SP   m   (3)
 
     For adaptive feedback system for occlusion cancellation, the adaptive filter G′ is used, which is available from AOC adaptation based on a filtered-x (Fx) NLMS algorithm). The updated closed loop function then becomes as shown in Equations (4)-(6) below. 
         C =(1+ W   2 )/(1−[ W   1   ′−W   2 ′])  (4)
 
         W   1   ′=G′*EQ   m   *SP   r   (5)
 
         W   2   ′=G′*EQ   m   *SP   m   (6)
 
     Then, the active residual path from external source to eardrum D c,active (ω) can be estimated as D c,active (0))=D c (ω)*C(ω), where D c (ω) is the actual path (see  FIG.  4   ) and C(ω) is actively updated as shown in (4)-(6). In order to estimate D c,active (ω) accurately based on the active adaptive filter gain G′, it may be more appropriate to update the estimate of D c,active (ω) when the own voice is absent and only ambient sound leakage in the ear canal is presented. Therefore, in one embodiment the D c,active (ω) and corresponding G eq ′(ω) are updated based on an own voice detection (OVD) flag: D c,active (t)=a* D c,active (t-1)+(1-a)D c ′ *C, when OVD_flag=0, where ‘a’ is a forgetting factor within (0,1); e.g., a=0.8 in one example. 
     For OVD, an energy-level thresholding-based detection may be used, e.g., power level calculation of band-passed e(n) at corner frequencies of 350 Hz and 900 Hz with smoothing constant of 250 ms for smoothing. The threshold can be empirically set at a threshold vale, e.g., if the smoothed power level is larger than a threshold, then OVD flag=1. In  FIG.  8   , a spectrogram shows an example of an audio signal containing own-voice together with ambient noise. The darkest regions in  FIG.  8    represent relatively high power levels around the 350 Hz to 900 Hz range indicative of own-voice. It will be understood that other frequency range limits may be used for this purpose, e.g., tailored based on the average pitch of the user&#39;s own voice. In  FIG.  9   , a graph shows the band-passed power as a function of time for the signal shown in  FIG.  8   , with an own-voice detection threshold indicated by the horizontal dashed line. The threshold may be set around −48 dB to −50 dB in this example. In  FIG.  10   , a graph shows how the application of the threshold to the signal in  FIG.  8    can be used to set the OVD flag. 
     In other embodiments, inertial measurement data (e.g., from an accelerometer) can be used to detect bone-conducted vibration or physical movement due to own voice. These measurements can also be bandpass filtered to improve detection accuracy. In some embodiments, the output of multiple sensors (e.g., internal external/microphones, inertial measurement data) can be combined to jointly estimate periods when the user is and is not speaking and thereby set the OVD flag. 
     Given the active residual path from external source to eardrum D c,active (0)), the updates to hearthrough filter G EQ ′(ω) are based on ∥(D m ′{circumflex over (D)} I G EQ ′+D c,active ′)−D o ′∥ 2   2 +μ∥G EQ ′∥ 2 . Note that the hearthrough filters in these examples are designed in frequency domain while the AOC updates FIR filters in the time-domain. It is challenging to implement the combination of these two processing in digital signal processor (DSP) filter engine. In one embodiment, a DFT matrix is applied to make the time-domain filter coefficients g′ (e.g., vector N T  of length  64 ) decoupled from the spectral resolution, giving G′= F g′ where F is a N F ×N T  DFT matrix and N F  is the FFT length for firmware implementation, as shown in the equation of  FIG.  11   , where N F &gt;N T . In this equation, I is an N T -by-N T  identity matrix and O is an (N F −N T ) by N T  zero matrix. 
     Hear-through can be seen as a special case for hearing aids processing, e.g., hearthrough processing aims to achieve 0 dB insertion gain for all frequency bands. The proposed hearthrough design can be extend to match with hearing aid processing by adding a targeted insertion gain (derived from fitting software) into the following equation: {circumflex over (D)} ha (ω)=D m (ω)D I (ω)G EQ ′(ω)+D c,active ′(ω) and solve for the optimal G EQ ′ or g′, such that {circumflex over (D)} ha (ω)=D o  (ω)*E(ω), where E(ω) denotes the targeted insertion gain vector. 
     The proposed system can also work with the feature of auto-vent, which is a function that automatically and physically optimizes the venting in hearing aid, to optimize hearing benefit for music or speech under noise. The auto-vent operates by automatically selecting the appropriate vent size for different listening scenarios. As for the settings of auto-vent ON and OFF, D I (ω) and D c (ω) in  FIG.  4    are different for two conditions. Therefore, D I (ω) and D c (ω) are pre-measured separately for auto-vent ON and OFF the coefficients stored in the device memory. Additionally, two coefficients sets of H sp , H eq , H eqsp  in  FIG.  6    can also be measured separately in the active noise cancellation initialization stage and stored in the device memory. It is suggested to reset the whole processing in  FIG.  6    when switching between auto-vent ON and OFF to prevent chirping artifacts due to adaptation divergence. 
     Apart from the hearing device microphone signal that is filtered by hearthrough filter, streaming audio contents can also be added to the receiver end (as shown by S audio (n) in  FIG.  5   ). It may be more appropriate to update the estimate of D c,active (0)) when both the own voice and streamed audio is absent and only ambient sound leakage in the ear canal is presented. Therefore, the D c,active (ω) and corresponding G EQ ′ (ω) can be updated based on the own voice detection flag as well as the audio streaming flag: D c,active (t)=a*D c,active (t-1)+(1-a)D c ′ *C, when (OVD_flag∥Streaming_flag)=0. 
     In  FIG.  12   , a block diagram illustrates a system and ear-worn hearing device  1100  in accordance with any of the embodiments disclosed herein. The hearing device  1100  includes a housing  1102  configured to be worn in, on, or about an ear of a wearer. The hearing device  1100  shown in  FIG.  11    can represent a single hearing device configured for monaural or single-ear operation or one of a pair of hearing devices configured for binaural or dual-ear operation. The hearing device  1100  shown in  FIG.  11    includes a housing  1102  within or on which various components are situated or supported. The housing  1102  can be configured for deployment on a wearer&#39;s ear (e.g., a behind-the-ear device housing), within an ear canal of the wearer&#39;s ear (e.g., an in-the-ear, in-the-canal, invisible-in-canal, or completely-in-the-canal device housing) or both on and in a wearer&#39;s ear (e.g., a receiver-in-canal or receiver-in-the-ear device housing). 
     The hearing device  1100  includes a processor  1120  (also referred to as a system processor) operatively coupled to a main memory  1122  and a non-volatile memory  1123 . The processor  1120  can be implemented as one or more of a multi-core processor, a digital signal processor (DSP), a microprocessor, a programmable controller, a general-purpose computer, a special-purpose computer, a hardware controller, a software controller, a combined hardware and software device, such as a programmable logic controller, and a programmable logic device (e.g., FPGA, ASIC). The processor  1120  can include or be operatively coupled to main memory  1122 , such as RAM (e.g., DRAM, SRAM). The processor  1120  can include or be operatively coupled to non-volatile (persistent) memory  1123 , such as ROM, EPROM, EEPROM or flash memory. As will be described in detail hereinbelow, the non-volatile memory  1123  is configured to store instructions that facilitate using active occlusion cancellation with audio hear-through. 
     The hearing device  1100  includes an audio processing facility operably coupled to, or incorporating, the processor  1120 . The audio processing facility includes audio signal processing circuitry (e.g., analog front-end, analog-to-digital converter, digital-to-analog converter, DSP, and various analog and digital filters), a microphone arrangement  1130 , and an acoustic transducer  1132  (e.g., loudspeaker, receiver, bone conduction transducer). The microphone arrangement  1130  can include one or more discrete microphones or a microphone array(s) (e.g., configured for microphone array beamforming). Each of the microphones of the microphone arrangement  1130  can be situated at different locations of the housing  1102 . It is understood that the term microphone used herein can refer to a single microphone or multiple microphones (e.g., a microphone array) unless specified otherwise. 
     At least one of the microphones  1130  may be configured as a reference microphone producing a reference signal in response to external sound outside an ear canal of a user. Another of the microphones  1130  may be configured as an error microphone producing an error signal in response to sound inside of the ear canal. A physical propagation path between the reference microphone and the error microphone defines a primary path of the hearing device  1100 . The acoustic transducer  1132  produces amplified sound inside of the ear canal. The amplified sound propagates over a secondary path to combine with direct noise at the ear canal, the summation of which is sensed by the error microphone. 
     The hearing device  1100  may also include a user interface with a user control interface  1127  operatively coupled to the processor  1120 . The user control interface  1127  is configured to receive an input from the wearer of the hearing device  1100 . The input from the wearer can be any type of user input, such as a touch input, a gesture input, or a voice input. The user control interface  1127  may be configured to receive an input from the wearer of the hearing device  1100 . 
     The hearing device  1100  also includes an active occlusion canceller  1138  and a hear-through processor  1139  both operably coupled to the system processor  1120 . The active occlusion canceller  1138  and the hear-through processor  1139  can be implemented in software, hardware, or a combination of hardware and software. The active occlusion canceller  1138  and the hear-through processor  1139  can be a component of, or integral to, the processor  1120  or another processor coupled to the processor  1120 . The active occlusion canceller  1138  is configured to reduce or eliminate coloration of reproduced sound due to the hearing device  1100  partially or fully blocking the ear canal. The hear-through processor  1139  receives signals from an external microphone  1130  and reproduces the sounds at the acoustic transducer  1132 . As indicated by the line  1141  therebetween, the active occlusion canceller  1138  and the hear-through processor  1139  include adaptive filters that are updated jointly, that is an update to one adaptive filter (e.g., in the hearthrough processor  1139 ) is used to update another adaptive filter (e.g., in the active occlusion canceller  1138 ). Joint optimization implies that the combination of AOC and hear-through will correspond to an open ear transfer function (D o ). The performance of AOC need not change with or without the joint optimization, although the values (e.g., gain) of the hearthrough filter is changed with the joint optimization. 
     The hearing device  1100  can include one or more communication devices  1136 . For example, the one or more communication devices  1136  can include one or more radios coupled to one or more antenna arrangements that conform to an IEEE 802.11 (e.g., Wi-Fi®) or Bluetooth® (e.g., BLE, Bluetooth® 4.2, 5.0, 5.1, 5.2 or later) specification, for example. In addition, or alternatively, the hearing device  1100  can include a near-field magnetic induction (NFMI) sensor (e.g., an NFMI transceiver coupled to a magnetic antenna) or telecoil for effecting short-range communications (e.g., ear-to-ear communications, ear-to-kiosk communications). The communications device  1136  may also include wired communications, e.g., universal serial bus (USB) and the like. 
     The communication device  1136  is operable to allow the hearing device  1100  to communicate with an external computing device  1104 , e.g., a smartphone, laptop computer, etc. The external computing device  1104  includes a communications device  1106  that is compatible with the communications device  1136  for point-to-point or network communications. The external computing device  1104  includes its own processor  1108  and memory  1110 , the latter which may encompass both volatile and non-volatile memory. The external computing device  1104  includes a user interface  1114  that facilitates performing the operations described herein with both the external computing device  1104  and the hearing device  1100 . 
     The external computing device  1104  includes a streaming audio content source  1112  (e.g., streaming audio from microphone, streaming audio from file playback, etc.) that may operate in with the hear-through processor  1139 , e.g., by combining the audio content stream with the hear-through signals. A similar audio content stream may be provided by an external device such as a telecoil signal transmitter, which may or may not include a digital processor. The hearing device  1100  may receive such signals via a telecoil or NFMI, and reproduce the signals as sounds in the processing stream. The active occlusion canceller  1138  and the hear-through processor  1139  may detect the audio content stream and prevent updates to hearthrough filters during such streaming. A similar pausing of the updates may occur in response to own voice detection, which may use microphones  1130  and/or an accelerometer  1134  to detect the user&#39;s voice. 
     The hearing device  1100  also includes a power source, which can be a conventional battery, a rechargeable battery (e.g., a lithium-ion battery), or a power source comprising a supercapacitor. In the embodiment shown in  FIG.  5   , the hearing device  1100  includes a rechargeable power source  1124  which is operably coupled to power management circuitry for supplying power to various components of the hearing device  1100 . The rechargeable power source  1124  is coupled to charging circuitry  1126 . The charging circuitry  1126  is electrically coupled to charging contacts on the housing  1102  which are configured to electrically couple to corresponding charging contacts of a charging unit when the hearing device  1100  is placed in the charging unit. 
     In  FIG.  13   , a flowchart shows a method according to an example embodiment. The method involves performing  1300  adaptive occlusion cancellation in an ear-wearable device using an adaptive filter. An adaptive gain of the adaptive filter is used  1301  to determine a leakage path estimate between an external source and an eardrum of the user through the ear-wearable device. The leakage path estimate is used  1302  to update an adaptive hear-through filter of the ear-wearable device. The updated adaptive hear-through filter is used  1303  for hear-through processing in the ear-wearable device. 
     In  FIG.  14   , a flowchart shows a method according to another example embodiment. The method involves performing  1400  adaptive occlusion cancellation in an ear-wearable device using a first adaptive filter. Hear-though processing is performed  1401  in the ear-wearable device using a second adaptive filter. A leakage path is estimated  1402  between an external source and an eardrum of the user through the ear-wearable device based on an adaptive gain of the first adaptive filter. Adaptive filter parameters of the second adaptive filter is updated  1403  based on the estimate of the leakage path. 
     This document discloses numerous example embodiments, including but not limited to the following: 
     Example 1 is a method, comprising: performing occlusion cancellation in an ear-wearable device using an adaptive occlusion cancellation filter; using an adaptive gain of the adaptive occlusion cancellation filter to determine a leakage path estimate between an external source and an eardrum of a user through the ear-wearable device; using the leakage path estimate to update an adaptive hear-through filter of the ear-wearable device; and using the updated adaptive hear-through filter for hear-through processing in the ear-wearable device. Example 2 includes the method of example 1, wherein using the leakage path to update the hear-through filter jointly optimizes the adaptive occlusion cancellation and the hear-through processing. Example 3 includes the method of example 1 or 2, wherein the adaptive occlusion cancellation filter is a normalized, filtered-x least mean square (Fx-NLMS) filter. 
     Example 4 includes the method of any one of examples 1-3, wherein the updating of the hear-through filter of the ear-wearable device is performed only when an own voice of the user is absent such that only ambient sound leakage in an ear canal of the user is present. Example 5 includes the method of example 4, wherein determining that the own voice is absent utilizes an energy level threshold detection of an audio signal of the ear-wearable device. Example 6 includes the method of example 5, wherein the energy level threshold detection comprises band pass filtering using corner frequencies of 350 Hz and 900 Hz with a smoothing constant of 250 ms. Example 7 includes the method of example 4, wherein determining that the own voice is absent utilizes an inertial measurement unit to detect bone-conducted vibration or physical movement due to the own voice of the user. 
     Example 8 includes the method of any one of examples 1-7, wherein the ear-wearable device inserts an audio content stream into an audio processing path, the updating of the hear-through filter of the ear-wearable device being performed only when the audio content stream is absent. Example 9 includes the method of example 8, wherein the audio content stream originates from a telecoil. 
     Example 10 includes the method of any one of examples 1-9, wherein the hear-through processing uses a targeted insertion gain derived from a fitting of the ear-wearable device to the user. Example 11 includes the method of any one of examples 1-10, further comprising detecting an auto-vent state of the ear-wearable device, wherein transform coefficients of the hear-through filter are changed based on the auto-vent state. Example 12 includes the method of example 11, wherein at least one of the hear-through processing and the adaptive occlusion cancellation is reset when a change of the auto-vent state is detected. Example 13 includes the method of any one of examples 1-12, wherein the adaptive hear-through filter operates in a frequency domain and the adaptive occlusion cancellation filter operates in a time domain, the method further comprising applying a discrete Fourier transform matrix to time-domain filter coefficients of the adaptive occlusion cancellation filter to obtain frequency domain filter coefficients for the adaptive hear-through filter. 
     Example 14 is an ear-wearable device, comprising: an external microphone operable to receive external sound from an external source; an internal microphone configured to receive internal sound from an ear canal of a user; a receiver configured to reproduce sound in the ear canal; and a controller operatively coupled to the external microphone, the internal microphone, and the receiver, the controller operable to: perform occlusion cancellation using an adaptive occlusion cancellation filter; use an adaptive gain of the adaptive occlusion cancellation filter to determine a leakage path estimate between the external source and an eardrum of the user through the ear-wearable device; use the leakage path estimate to update an adaptive hear-through filter of the ear-wearable device; and use the updated adaptive hear-through filter for hear-through processing in the ear-wearable device. 
     Example 15 includes the ear-wearable device of example 14, wherein using the leakage path to update the hear-through filter jointly optimizes the adaptive occlusion cancellation and the hear-through processing. Example 16 includes the ear-wearable device of example 14 or 15, wherein the adaptive occlusion cancellation filter is a normalized, filtered-x least mean square (Fx-NLMS) filter. 
     Example 17 includes the ear-wearable device of any one of examples 14-16, wherein the updating of the hear-through filter of the ear-wearable device is performed only when an own voice of the user is absent such that only ambient sound leakage in an ear canal of the user is present. Example 18 includes the ear-wearable device of example 17, wherein determining that the own voice is absent utilizes an energy level threshold detection of an audio signal of the ear-wearable device. Example 19 includes the ear-wearable device of example 18, wherein the energy level threshold detection comprises band pass filtering using corner frequencies of 350 Hz and 900 Hz with a smoothing constant of 250 ms. Example 20 includes the ear-wearable device of example 17, wherein determining that the own voice is absent utilizes an inertial measurement unit to detect bone-conducted vibration or physical movement due to the own voice of the user. 
     Example 21 includes the ear-wearable device of any one of examples 14-20, wherein the ear-wearable device inserts an audio content stream into an audio processing path, the updating of the hear-through filter of the ear-wearable device being performed only when the audio content stream is absent. Example 22 includes the ear-wearable device of example 21, wherein the audio content stream originates from a telecoil. 
     Example 23 includes the ear-wearable device of any one of examples 14-22, wherein the hear-through processing uses a targeted insertion gain derived from a fitting of the ear-wearable device to the user. Example 24 includes the ear-wearable device of any one of examples 14-23, further comprising an auto-vent, the controller further operable to detect a state of the auto-vent, wherein transform coefficients of the hear-through filter are changed based on the state of the auto-vent state. Example 25 includes the ear-wearable device of example 24, wherein at least one of the hear-through processing and the adaptive occlusion cancellation is reset when a change of the state of the auto-vent is detected. 
     Example 26 includes the ear-wearable device of any one of examples 14-25, wherein the adaptive hear-through filter operates in a frequency domain and the adaptive occlusion cancellation filter operates in a time domain, the controller further operable to apply a discrete Fourier transform matrix to time-domain filter coefficients of the adaptive occlusion cancellation filter to obtain frequency domain filter coefficients for the adaptive hear-through filter. 
     Example 27 is a method comprising: performing occlusion cancellation in an ear-wearable device using a first adaptive filter; performing hear-though processing in the ear-wearable device using a second adaptive filter; estimating a leakage path between an external source and an eardrum of a user through the ear-wearable device based on an adaptive gain of the first adaptive filter; and updating adaptive filter parameters of the second adaptive filter based on the estimate of the leakage path. 
     Example 28 includes the method of example 27, wherein estimating the leakage path jointly optimizes the first and second adaptive filters. Example 29 includes the method of example 27 or 28, wherein the first adaptive filter is a normalized, filtered-x least mean square (Fx-NLMS) filter. Example 30 includes the method of any one of examples 27-29, wherein the updating of the adaptive filter parameters of the second adaptive filter is performed only when an own voice of the user is absent such that only ambient sound leakage in an ear canal of the user is present. Example 31 includes the method of example 30, wherein determining that the own voice is absent utilizes an energy level threshold detection of an audio signal of the ear-wearable device. Example 32 includes the method of example 30, wherein determining that the own voice is absent utilizes an inertial measurement unit to detect bone-conducted vibration or physical movement due to the own voice of the user. 
     Example 33 includes the method of any one of examples 27-32, wherein the ear-wearable device inserts an audio content stream into an audio processing path, the updating of the adaptive filter parameters of the second adaptive filter being performed only when the audio content stream is absent. Example 34 includes the method of any one of examples 27-33, further comprising detecting an auto-vent state of the ear-wearable device, wherein transform coefficients of the second adaptive filter are changed based on the auto-vent state. Example 35 includes the method of any one of examples 27-34, wherein the second adaptive filter operates in a frequency domain and the first adaptive filter operates in a time domain, the method further comprising applying a discrete Fourier transform matrix to time-domain filter coefficients of the first adaptive filter to obtain frequency domain filter coefficients for the second adaptive filter. Example 36 is an apparatus comprising a controller operable to perform the method of any one of examples 27-35 and comprising the ear-wearable device. 
     Although reference is made herein to the accompanying set of drawings that form part of this disclosure, one of at least ordinary skill in the art will appreciate that various adaptations and modifications of the embodiments described herein are within, or do not depart from, the scope of this disclosure. For example, aspects of the embodiments described herein may be combined in a variety of ways with each other. Therefore, it is to be understood that, within the scope of the appended claims, the claimed invention may be practiced other than as explicitly described herein. 
     All references and publications cited herein are expressly incorporated herein by reference in their entirety into this disclosure, except to the extent they may directly contradict this disclosure. Unless otherwise indicated, all numbers expressing feature sizes, amounts, and physical properties used in the specification and claims may be understood as being modified either by the term “exactly” or “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the foregoing specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by those skilled in the art utilizing the teachings disclosed herein or, for example, within typical ranges of experimental error. 
     The recitation of numerical ranges by endpoints includes all numbers subsumed within that range (e.g.  1  to  5  includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5) and any range within that range. Herein, the terms “up to” or “no greater than” a number (e.g., up to 50) includes the number (e.g., 50), and the term “no less than” a number (e.g., no less than 5) includes the number (e.g., 5). 
     The terms “coupled” or “connected” refer to elements being attached to each other either directly (in direct contact with each other) or indirectly (having one or more elements between and attaching the two elements). Either term may be modified by “operatively” and “operably,” which may be used interchangeably, to describe that the coupling or connection is configured to allow the components to interact to carry out at least some functionality (for example, a radio chip may be operably coupled to an antenna element to provide a radio frequency electric signal for wireless communication). 
     Terms related to orientation, such as “top,” “bottom,” “side,” and “end,” are used to describe relative positions of components and are not meant to limit the orientation of the embodiments contemplated. For example, an embodiment described as having a “top” and “bottom” also encompasses embodiments thereof rotated in various directions unless the content clearly dictates otherwise. 
     Reference to “one embodiment,” “an embodiment,” “certain embodiments,” or “some embodiments,” etc., means that a particular feature, configuration, composition, or characteristic described in connection with the embodiment is included in at least one embodiment of the disclosure. Thus, the appearances of such phrases in various places throughout are not necessarily referring to the same embodiment of the disclosure. Furthermore, the particular features, configurations, compositions, or characteristics may be combined in any suitable manner in one or more embodiments. 
     The words “preferred” and “preferably” refer to embodiments of the disclosure that may afford certain benefits, under certain circumstances. However, other embodiments may also be preferred, under the same or other circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful and is not intended to exclude other embodiments from the scope of the disclosure. 
     As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” encompass embodiments having plural referents, unless the content clearly dictates otherwise. As used in this specification and the appended claims, the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise. 
     As used herein, “have,” “having,” “include,” “including,” “comprise,” “comprising” or the like are used in their open-ended sense, and generally mean “including, but not limited to.” It will be understood that “consisting essentially of,” “consisting of,” and the like are subsumed in “comprising,” and the like. The term “and/or” means one or all of the listed elements or a combination of at least two of the listed elements. 
     The phrases “at least one of,” “comprises at least one of,” and “one or more of” followed by a list refers to any one of the items in the list and any combination of two or more items in the list.