Blockage and noise cancellation systems and methods for hearing devices

Abstract

The present disclosure relates to a hearing device comprising an in-ear-canal microphone configured to pick up at least body-conducted sound in an ear canal volume of a user, and a vibration sensor configured to pick up mechanical vibrations generated by the body-conducted sound of the user, such as vibrations through ear canal tissue. A processing unit of the hearing device determines a first compensation signal for cancelling at least body-conducted sound in the ear canal volume of the user based on sound picked up by the microphone in the ear canal. The processing unit determines, based on the vibration signal provided by the vibration sensor, a second compensation signal for cancelling at least the body-conducted sound in the ear canal volume of the user.

Description

Technical Field

[0001] The present disclosure relates to a hearing device, which includes an in-ear canal microphone configured to pick up at least body-conducted sounds in an ear canal volume of a user and a vibration sensor configured to pick up mechanical vibrations generated by the body-conducted sounds of the user, such as by vibrations of ear canal tissue. A processing unit of the hearing device determines a first compensation signal for eliminating at least the body-conducted sounds in the ear canal volume of the user based on the sounds picked up by the in-ear canal microphone. The processing unit of the hearing device determines a second compensation signal for eliminating at least the body-conducted sounds in the ear canal volume of the user based on a vibration signal provided by the vibration sensor. Background Art

[0002] The occlusion effect is an unnatural perception of a user's own voice caused by inserting a housing, such as an ear mold or shell, into the user's ear canal. This arrangement of the housing results in partial or complete occlusion of the user's ear canal, leaving at least a partially blocked ear canal volume in front of the user's eardrum.

[0003] Depending on the individual geometry of the user's ear canal, the occlusion effect can cause low-frequency amplification of up to 30 dB, with the effect being most pronounced for frequencies below about 500 Hz. Historically, the occlusion problem has been alleviated by providing hearing devices with so-called open fittings, in which a sound path is intentionally included around or through the housing. However, there are many fitting situations where open fittings are not feasible, for example due to gain or output power limitations, or when the ear canal must be sealed for protective purposes. Active occlusion cancellation (AOC) has been demonstrated to be a viable alternative to open fittings. AOC uses an adaptive filter to reduce the occlusion effect by calculating a compensation signal that is added to the receiver input. The compensation signal acts to suppress or eliminate unwanted (low) frequency sounds in the user's ear canal.

[0004] EP3340653B1 discloses a hearing device with an AOC circuit, the AOC circuit comprising a first adaptive filter and a second adaptive filter. The first adaptive filter is arranged in the feedback path of the AOC circuit and utilizes the ear canal audio signal sensed by the ear canal microphone. The latter detects the sound pressure in the blocked ear canal volume of the user. Summary of the invention

[0005] A first aspect of the invention relates to a hearing device (50) comprising:

[0006] - an ambient microphone configured to pick up ambient sounds at the user's ear and respond by generating an ambient audio signal (x1),

[0007] - an in-ear canal microphone configured to pick up sounds, including body-conducted sounds, in the ear canal volume in front of the user's eardrum and respond by generating an in-ear canal audio signal,

[0008] - a vibration sensor configured to pick up mechanical vibrations generated at least by body-conducted sound of the user and to respond by generating a vibration signal,

[0009] a processing unit configured to process the ambient audio signal (x1) according to a predetermined signal processing algorithm to generate a processed audio signal (u),

[0010] - a receiver configured to emit output sound into an ear canal volume of a user in response to a receiver input; and

[0011] a feedback path comprising a first filter configured to provide, based on the intra-ear canal audio signal, a first compensation signal for cancelling at least body-conducted sound in the ear canal volume of the user,

[0012] - a second filter configured to: simulate a transfer function of an in-ear canal audio signal input from the receiver to the in-ear canal microphone,

[0013] - a feed-forward path comprising a third filter configured to provide, based on the vibration signal, a second compensation signal for cancelling at least body-conducted sound in an ear canal volume of a user.

[0014] The processing unit may comprise a digital signal processor (DSP) and / or a microprocessor, such as a software programmable DSP or a software programmable microprocessor. The software programmable DSP or microprocessor may be configured to execute a plurality of program instructions configured to implement at least a portion of the signal processing algorithms, functions, steps, and features of the hearing device according to the first and second aspects of the present invention, in particular those associated with the active occlusion cancellation or suppression (AOC) device of the hearing device and the optional noise cancellation or suppression, as described in detail below with reference to the accompanying drawings. The processing unit may additionally comprise one or more dedicated (e.g., hard-coded) digital state machines configured to handle, for example, certain signal processing functions of the AOC device, as described in detail below with reference to the accompanying drawings.

[0015] An embodiment of the hearing device further comprises:

[0016] - a fourth filter configured to provide, based on the ambient microphone signal, a third compensation signal for cancelling noise sounds, eg transmitted via acoustic leakage around the housing of the hearing device or via the ambient audio signal into the ear canal volume of the user.

[0017] The skilled person will appreciate that utilizing at least two different compensation signals, namely an intra-ear canal audio signal originating from sensed sound in the ear canal volume of a user and a vibration signal originating from mechanical tissue vibrations caused by body-conducted sound, represents different and, for example, complementary estimates of undesirable body-conducted sound in the ear canal volume of the user. Such utilization of at least two different compensation signals provides improved cancellation of body-conducted sound in the ear canal volume of a user, thereby improving the accuracy of the estimate of body-conducted sound in the ear canal volume, for a number of reasons, as described in further detail below with reference to the accompanying drawings.

[0018] In some embodiments, at least one of the first filter, the second filter, the third filter, and the fourth filter may remain fixed during normal operation of the hearing device, and be adjusted or adapted offline, for example during manufacture of the hearing device or during an initialization phase of the hearing device and its AOC device at a dispenser's desk associated with the initial fitting of the hearing device to a user. Initialization of at least one of the first filter, the second filter, the third filter, and the fourth filter may alternatively be performed by the processing unit at power-up of the hearing device, after which at least one of the first filter, the second filter, the third filter, and the fourth filter remains fixed during normal operation of the hearing device. In other embodiments, at least one of the first filter, the second filter, the third filter, and the fourth filter is adapted during normal operation of the hearing device, i.e. an adaptive filter. The adaptation of at least one of the first filter, the second filter, the third filter, and the fourth filter may include calculating and repeatedly updating a plurality of filter coefficients of at least one of the first filter, the second filter, the third filter, and the fourth filter according to an optimization algorithm such as LMS, NMLS, etc.

[0019] An initialization phase for at least one of the first filter, the second filter, the third filter, and the fourth filter may include injecting a detection signal (such as a random noise signal or a noise sequence) into an ambient microphone and / or an in-ear microphone and / or a vibration sensor of the hearing device to determine a transfer function estimate of at least one of the first filter, the second filter, the third filter, and the fourth filter.

[0020] According to an embodiment of the hearing device, the processing unit is configured to:

[0021] - subtracting the first compensation signal from the processed audio signal (u) by means of a first subtractor,

[0022] - subtracting the second compensation signal from the processed audio signal (u) by means of a first subtractor; and

[0023] - Apply the output of the first subtractor to the receiver input.

[0024] According to an embodiment of the hearing device, the processing unit comprises a second subtractor comprising an output configured to: generate an error signal (v') by subtracting the output of the second filter from the in-ear canal audio signal (m); and apply the error signal (v') to the input of the first filter.

[0025] According to an embodiment of the hearing device, the first subtractor is configured to subtract the third compensation signal from the processed audio signal (u).

[0026] According to an embodiment of the hearing device, the processing unit is configured to minimize the energy or power of the error signal (v') within a predetermined frequency range, such as above 50 Hz or between 20 Hz and 1 kHz, eg between 100 Hz and 400 Hz.

[0027] According to an embodiment of the hearing device, the processing unit is configured to minimize the energy or power of the error signal (v') by:

[0028] - adapt or adjust the transfer function of the first filter to maximize the real part of (1+B*R),

[0029] - adjusting or tuning the transfer function of the second filter to minimize the error signal (v'),

[0030] - adjusting or modifying the transfer function of the third filter to minimize the error signal (v'); and optionally

[0031] - adjusting or adjusting the transfer function of the fourth filter to minimize the error signal (v'), wherein

[0032] B is the transfer function of the first filter;

[0033] R is the transfer function from the receiver input (y) to the audio signal in the ear canal (m).

[0034] According to an embodiment of the hearing device, the processing unit is configured to minimize the energy or power of the error signal (v') by minimizing a norm (such as a 1-norm or a 2-norm) of the error signal (v'); wherein the error signal (v') is represented according to equation (1)

[0035]

[0036] in:

[0037] A is the transfer function of the second filter;

[0038] B is the transfer function of the first filter;

[0039] C is the transfer function of the third filter;

[0040] D is the transfer function of the fourth filter;

[0041] G is the transfer function of the processing unit;

[0042] R is the transfer function from the receiver input to the audio signal (m) in the ear canal;

[0043] H1 is the transfer function from ambient sound to ambient audio signal (x1);

[0044] H2 is the transfer function from ambient sound to the ear canal microphone signal (m);

[0045] H3 is the transfer function from the vibration signal source (e.g., the user's vocal cords) to the vibration sensor signal (x2);

[0046] H4 is the transfer function from the vibration source to the ear canal microphone (m).

[0047] According to an embodiment of the hearing device, the processing unit is configured to adjust the transfer function of the first filter and to adjust the transfer function of the third filter during normal operation of the hearing device. The processing unit may be configured to keep the transfer function of the second filter fixed, i.e. not adjust the transfer function, during normal operation of the hearing device. According to some embodiments of the hearing device, the processing unit is configured to adjust the transfer function of the fourth filter during normal operation of the hearing device.

[0048] The skilled person will appreciate that adjustment of one or more filters of the hearing device during normal operation will generally result in superior blocking and / or noise cancellation of the AOC arrangement of the hearing device, since the corresponding estimates of the transfer functions of the first, second, third, and fourth filters may have superior accuracy due to being able to track the time-varying electromechanical and acoustic characteristics of the in-situ hearing device as mounted on a user.

[0049] According to an embodiment of the hearing device, the processing unit is configured to:

[0050] - adjusting the transfer function of the second filter by cross-correlating the processed audio signal (u) and the error signal (v') to calculate the first gradient direction,

[0051] - applying the first gradient direction in a first optimization algorithm such as LMS or NLMS; and

[0052] - adjusting the transfer function of the third filter by filtering the vibration signal (x2) with the transfer function of the second filter to provide a processed output signal,

[0053] - cross-correlating the processed output signal and the error signal (v') to calculate a second gradient direction; and

[0054] - Applying the second gradient direction in a second optimization algorithm such as LMS or NLMS.

[0055] Various exemplary embodiments of a hearing device include a housing, such as a housing shaped and sized to be partially or completely placed in an ear canal of a user. The housing includes:

[0056] - an external directional surface including a sound inlet for an ambient microphone,

[0057] - an inner directional tip facing the ear canal volume (65) of the user and supporting the sound outlet of the receiver,

[0058] - a side surface configured to bring the vibration sensitive section of the vibration sensor into physical contact with the ear canal of a user during normal use of the hearing device.

[0059] A second aspect of the invention relates to a method of suppressing at least body-conducted sound in an ear canal volume of a user of a hearing device, comprising:

[0060] - Pick up the ambient sound at the user's ears to generate a corresponding ambient audio signal (x1),

[0061] - processing the ambient audio signal (x1) according to a predetermined signal processing algorithm to generate a processed audio signal (u),

[0062] - picking up sound in the ear canal volume by means of an in-ear canal microphone to generate a corresponding in-ear canal audio signal (m), wherein the sound comprises at least body-conducted sound,

[0063] - picking up the mechanical vibration of the user's ear canal tissue through the vibration sensor and generating a corresponding vibration signal (x2),

[0064] - emitting output sound into the ear canal volume of the user through the receiver in response to the receiver input (y),

[0065] - based on the intra-ear canal audio signal (m), cancelling at least body-conducted sound in the ear canal volume (65) of the user by means of a first compensation signal generated by a first filter of the feedback path,

[0066] - adjusting or tuning the second filter to simulate a transfer function (R) of an in-ear canal audio signal (m) from a receiver input (y) to an in-ear canal microphone,

[0067] - based on the vibration signal (x2), at least body-conducted sound in the ear canal volume of the user is eliminated by a second compensation signal generated by a third filter of the feed-forward signal path.

[0068] One embodiment of a method of suppressing at least body-conducted sound in an ear canal volume comprises generating a receiver input (y) by:

[0069] - subtracting the first compensation signal from the processed audio signal (u),

[0070] - Subtracting the second compensation signal from the processed audio signal (u).

[0071] An embodiment of the method of suppressing at least body-conducted sound in an ear canal volume comprises adjusting a plurality of filter coefficients of a third filter during initialization of the hearing device and / or during normal operation of the hearing device, and adjusting a plurality of filter coefficients of a first filter during initialization of the hearing device and / or during normal operation of the hearing device.

[0072] One embodiment of a method of suppressing at least body-conducted sound in an ear canal volume comprises:

[0073] - placing the hearing device in normal operation, normal operation comprising processing the ambient audio signal (x1) and transmitting a corresponding receiver output sound when the hearing device is mounted in or at the ear of the user,

[0074] - simultaneously or in parallel adjusting the respective transfer functions of the first filter and the third filter and optionally adjusting the transfer function of the fourth filter. BRIEF DESCRIPTION OF THE DRAWINGS

[0075] Other and further aspects and features of the invention will become apparent from a reading of the following detailed description of the embodiments.

[0076] The drawings illustrate the design and use of embodiments of hearing devices, wherein similar elements are referenced to common reference numerals. The drawings are not necessarily drawn to scale. In order to better understand how the above and other advantages are obtained, a more particular description of the embodiments shown in the drawings will be given. These drawings depict only typical embodiments and are therefore not to be considered limiting of their scope.

[0077] Figure 1 a schematic diagram showing an exemplary hearing device comprising an active occlusion suppression device or circuit according to an embodiment of the present invention,

[0078] Figure 2 a block diagram showing an exemplary hearing device including details of an active occlusion suppression circuit or device,

[0079] Figure 3 A first embodiment of an exemplary hearing device 50 including certain computational models, functions, and algorithms of an active occlusion suppression circuit or device is shown in schematic format,

[0080] Figure 3Aa second embodiment of an exemplary hearing device including certain computational models, functions, and algorithms of an active occlusion suppression circuit or device is shown in schematic format; and

[0081] Figure 4 and Figure 5 Block diagrams collectively illustrating certain exemplary embodiments of adaptive filters, functions, and algorithms for an exemplary hearing device. DETAILED DESCRIPTION

[0082] The skilled person will appreciate that the drawings are schematic and simplified for clarity and that in some cases only details necessary for understanding embodiments of the exemplary hearing devices may be shown, while other details have been omitted.

[0083] Figure 1 A schematic diagram of an exemplary hearing device 50 is shown. The hearing device 50 comprises an ambient microphone 105 for picking up ambient sound at the hearing device 50 when mounted at, in, or on an ear 107 of a hearing device user. The ambient microphone 105 responds to the ambient sound by generating an ambient audio signal. The ambient audio signal is preferably sampled and digitized in an A / D converter (not shown) before further processing in the digital domain. The A / D converter may be integrated within the housing of the ambient microphone or integrated with the processing unit 135 on a common semiconductor substrate.

[0084] The hearing device 50 includes an in-ear canal microphone 115 that is configured to pick up, detect, or receive sound in a fully or partially blocked ear canal volume 65 in front of the user's eardrum 55. The in-ear canal microphone 115 responds to the picked up sound in the ear canal volume 65 by generating an in-ear canal audio signal. The ear canal audio signal is preferably sampled and digitized in an A / D converter (not shown) in a similar manner to the ambient audio signal.

[0085] The hearing device 50 further comprises a vibration sensor 110 configured to pick up or detect mechanical vibrations 140 conducted by the user's body, such as generated by vibrations of the ear canal tissue 130. The vibration sensor 110 responds to the mechanical vibrations 140 by generating a vibration signal, which is preferably sampled and digitized in an A / D converter (not shown) in a similar manner to the ambient audio signal.

[0086] The hearing device 50 further comprises a receiver 120, such as a miniature speaker, configured to emit an output sound 155 into the ear canal volume 65 of the user in response to a receiver input (y). The receiver 120 may comprise a moving armature speaker, a piezoelectric speaker, or a dynamic speaker, etc. The receiver input (y) is generated by the output of the first subtractor 150, which is configured to provide the receiver input by subtracting certain compensation signals transmitted by the schematically shown active occlusion elimination or suppression device 160, as described below with particular reference to Figure 2 The housing 125 may include a sound inlet ( Figure 2 The sound inlet 227 may be arranged in the outer directional surface 128 of the housing, which is oriented outward from the ear canal 130 of the user toward the external sound environment. The housing 125 may further include a sound outlet ( Figure 2 The housing 125 may include a side surface configured to allow the vibration sensitive wall or membrane of the vibration sensor 110 to physically contact the user's ear canal. A good mechanical fit or contact between the tissue of the user's ear canal 130 and the vibration sensitive membrane may facilitate accurate sensing of vibrations caused by body-conducted sound.

[0087] The processing unit 135 is configured to process the ambient audio signal according to one or more predetermined signal processing algorithms to generate a processed audio signal (u) at the output of the processing unit 135. The processing unit 135 may include a digital signal processor (DSP) and / or a microprocessor, such as a software programmable DSP or a software programmable microprocessor. The software programmable DSP or microprocessor may be configured to execute a plurality of program instructions configured to implement at least a portion of the signal processing algorithms, functions, steps, and features of the hearing device 50 described in detail below. The processing unit 135 may additionally include one or more dedicated (e.g., hard-coded) digital state machines configured to process certain signal processing algorithms (such as fixed filter processing or adaptive filter processing) and / or other functions, steps, and features of the hearing device 50. The processing unit 135 may thus be configured to perform certain calculations of corresponding filter coefficients of one or more adaptive filters, such as those of adaptive filters configured to suppress or eliminate a feedback path of at least body-conducted sound in the ear canal volume 65 of the user based on the in-ear canal audio signal provided by the in-ear canal microphone of the hearing device 50, as described below with reference to Figure 2 Described in further detail.

[0088] The processing unit 135 may be configured to execute a suitable operating system. The operating system may be configured to manage various hardware and software resources of the hearing device 50, such as handling wireless communication interfaces and their protocols. The operating system may schedule computing and control tasks to efficiently use hearing device resources, and may further include accounting software for cost allocation, including power consumption, processor time, memory locations, wireless transmissions, and other resources. The operating system may be stored in a non-volatile memory (not shown) (e.g., flash memory or EEPROM) of the processing unit 135 and retrieved from the non-volatile memory.

[0089] The housing 125 of the hearing device 50 may be, for example, one of many well-known types in the hearing aid industry, such as so-called BTE, ITE, ITC, CIC, or RIC housings. The shape and size of these types of housings are generally suitable for placement at or in the user's ear. The skilled person will understand that the housing 125 may include several physically separate sections, such as a first housing or section arranged behind the user's ear and a second section configured to be arranged in the user's ear canal 130, such as a custom earplug. The skilled person will understand that when the housing is installed in the user's ear canal 130, an acoustic leakage path H2 may exist around or through the housing 125. This acoustic leakage path H2 may be intentional or unintentional, and for example, the purpose of passive occlusion relief is achieved by providing a so-called through-vent of the housing. In both cases, the acoustic leakage path H2 transmits noise sound components from the external environment 109 into the user's ear canal volume 65. Further, body-conducted sound, as schematically represented by reference numeral 165, is emitted into the ear canal volume 65, for example caused by the user's own voice. These generally undesirable noise sounds are mixed with the desired sounds or sound components in the user's ear canal volume 65 via corresponding transmission mechanisms to form a composite sound pressure as schematically indicated by reference numeral 155 .

[0090] The desired or target sound in the ear canal volume 65 of the user is represented by the processed audio signal (R*u) provided at the output of the processing unit 135 multiplied by the transfer function (R) of the receiver 120. The active occlusion cancellation (AOC) device 160 includes an in-ear canal microphone 115 and a vibration sensor 110. The AOC device 160 preferably includes a feedback path that adaptively generates a first compensation signal based on an in-ear canal audio signal (m) generated by the in-ear canal microphone 115 in response to the sound (e.g., complex sound pressure) in the ear canal volume 65 of the user. The AOC device 160 preferably additionally includes a forward path that adaptively generates a second compensation signal derived from a vibration signal generated by the vibration sensor 110. The vibration sensor 110 is configured to pick up mechanical vibrations of the ear canal tissue 130 of the user, wherein the vibrations are generated, for example, by at least body-conducted sound (e.g., by the user's own voice). The skilled person will appreciate that the vibration sensor 110 is substantially insensitive to acoustic sounds (such as sounds in the ear canal volume 65 of the user). The first compensation signal and the second compensation signal are subtracted from the processed audio signal (u) to provide a receiver input (y), as discussed in further detail below. Different estimates of unwanted body-conducted sound in the ear canal volume 65 of the user are represented using at least two different compensation signals (the first being derived from the sound sensed in the ear canal volume 65, and the second being derived from the mechanical tissue vibration caused by the body-conducted sound). The accuracy of the estimate of body-conducted sound in the ear canal volume 65 is improved for a number of reasons through such utilization of at least two different compensation signals. For example, because the vibration signal is not contaminated or polluted by various types of acoustic noise, or is not infected by the processed target signal, it is inevitably transmitted to the ear canal volume 65 of the user and picked up by the in-ear canal microphone 115 as the sound of the in-ear canal audio signal (m). The improvement in the accuracy of the estimate of unwanted body-conducted sound in the ear canal volume 65 of the user results in an improvement in the suppression of body-conducted sound in the ear canal volume 65, thereby reducing the subjective occlusion benefit to the user of the hearing device 50.

[0091] Figure 2 A block diagram of various embodiments of an exemplary hearing device 50 is shown. The hearing device 50 includes the previously discussed components, such as the ambient microphone 105, the processing unit 135, the in-ear canal microphone 115, the vibration sensor 110, the receiver 120, the housing 125, the ambient microphone 105, etc. The acoustic leakage path H2 is also schematically shown, but the skilled person will understand that it may not form part of the hearing device 50 but is a model representation of the transfer function of the leakage path H2. H4 is the transfer function from the vibration source (such as the vocal cords of the user) to the ear canal volume 65.

[0092] The processing unit (135) is configured to process the ambient audio signal (x1) according to one or several predetermined signal processing algorithms to generate a processed audio signal (u). One of the predetermined signal processing algorithms may include a hearing loss compensator or algorithm to provide a hearing loss compensated audio signal as a component of the processed audio signal (u) for compensating for the hearing loss of the user. The hearing loss compensator may include dynamic range compression, such as loss of dynamic range as a function of frequency.

[0093] The hearing device 50 includes the previously discussed feedback path, which includes the first filter 205, the first filter 205 being configured to provide a first compensation signal 219 to a first input of the first subtractor 150 for canceling at least body-conducted sound in the ear canal volume 65 of the user based on the in-ear canal audio signal (m). The feedback path includes a closed feedback loop, the second subtractor 217, the first filter 205, and the first subtractor 150, the closed feedback loop including a transfer function (R) from the receiver input (y) to the in-ear canal audio signal (m), the output of the first subtractor 150 being applied to the input (y) of the receiver to close the feedback loop. The skilled person will appreciate that in practice, the first filter 205 may additionally be operable to suppress other types of unwanted sounds in the ear canal volume 65 of the user via the feedback path. These other types of unwanted sounds may include the previously discussed noise sounds transmitted into the ear canal volume 65 of the user via the acoustic leakage path H2. The effectiveness of this suppression of other types of unwanted sounds in the user's ear canal volume 65 may depend on the spectral and temporal characteristics of the unwanted sounds.

[0094] The second optional filter 203 is configured to simulate a transfer function (R) of an in-ear canal audio signal (m) from a receiver input (y) to an in-ear canal microphone 115. The second filter 203 is thus configured to simulate the receiver 120, the sound path of the in-ear canal volume 65 between the receiver output and the input to the in-ear canal microphone (115), and the individual transfer functions of the in-ear canal microphone 115. The hearing device 50 comprises a first feed-forward path comprising a third filter 211, the third filter 211 being configured to provide a second compensation signal 213 to a second input of the first subtractor 150, for example via an optional further adder 207, for at least cancelling or at least suppressing the level of body-conducted sound in the ear canal volume 65 of the user based on the vibration signal x2. The first feed-forward path is arranged outside the closed feedback loop of the feedback path. The output of the first subtractor 150 is applied as a receiver input (y) as described above, so that the receiver responds by emitting a corresponding output sound or output sound pressure into the ear canal volume 65 of the user.

[0095] Some embodiments of the hearing device 50 include a fourth adaptive filter 209 configured to provide a third compensation signal 210 that is based on the ambient microphone signal x1 and is operable to further improve the suppression of other noise sounds in the ear canal volume 65 of the user in addition to the body-conducted sound 165. As described above, other types of noise sounds may be transmitted from the external environment into the ear canal volume 65 of the user via the acoustic leakage path H2. Other types of noise sounds may include external noise, such as noise that acoustically reaches the ambient microphone 105 from an external source. The external noise may include traffic noise and / or so-called cocktail party noise, which includes a mixture of speech from multiple people in the vicinity of the user of the hearing device.

[0096] The fourth adaptive filter 209 forms part of a second feed-forward path of the hearing device 50 The third compensation signal 210 is preferably applied to a third input of the first subtractor 150 .

[0097] The output of the second subtractor 217 generates an error signal (v') as an input to the first filter 205, as discussed above. The second subtractor 217 thus provides an error signal (v') by subtracting the output 221 of the second filter 203 from the ear canal audio signal (m). The skilled person will appreciate that the processing unit 135 may be configured to perform adjustments of a plurality of filter coefficients of the first filter 205 of the feedback path, as discussed in further detail below. The processing unit 135 may be configured to perform adjustments of a plurality of filter coefficients of the second filter 203, and similarly perform adjustments of a plurality of filter coefficients of the third filter 211 of the feedforward path, as discussed in further detail below. The processing unit 135 may be configured to perform adjustments of a plurality of filter coefficients of the fourth filter 209, as discussed in further detail below. The skilled person will appreciate that the processing unit 135 may be configured to perform corresponding adjustments of at least the first filter 205 and the third filter 211 in parallel or simultaneously during normal operation of the hearing device 50 to obtain a first estimate and a second estimate of body-conducted sound in the ear canal volume 65 of the user.

[0098] The processing unit 135 may be configured to perform corresponding adjustments or adjustments of the first filter 205, the second filter 203, and the third adaptive filter 211 to meet a specific goal of the error signal (v'), such as minimizing the energy or power of the error signal (v'). Minimization of the energy or power of the error signal (v'), or other goals of the error signal (v'), may be performed, for example, for a predetermined audio frequency range of interest, such as for blocking suppression, such as between 20 Hz and 2 kHz, or between 50 Hz and 400 Hz, or below 1 kHz, such as below 500 Hz. The adjustment of each of the first adaptive filter 205, the second filter 203, the third filter 211, and the fourth filter 209 may be performed by the processing unit 135 using a well-known optimization algorithm, but not limited to a least mean square (LMS) algorithm, a normalized least mean square (NLMS) algorithm, a recursive least square (RLS) algorithm, etc.

[0099] Figure 3 A first embodiment of an exemplary hearing device 50 is schematically shown, in particular a first adaptive filter 205 , a second filter 203 operating adaptively during normal operation, a third adaptive filter 211 , and a corresponding calculation model of an optional fourth filter 209 .

[0100] The skilled person will appreciate that the error signal (v') can be approximated by equation (1):

[0101]

[0102] in:

[0103] A is the transfer function of the second filter (203);

[0104] B is the transfer function of the first adaptive filter (205);

[0105] C is a transfer function of the fourth filter (211);

[0106] D is the transfer function of the third filter (209);

[0107] G is the transfer function of the processing unit (135);

[0108] R is the transfer function from the receiver input (y) to the audio signal in the ear canal (m);

[0109] H1 is the transfer function from ambient sound to ambient audio signal (x1);

[0110] H2 is the transfer function from ambient sound to the ear canal volume (65);

[0111] H3 is the transfer function from the vibration signal source (e.g., the user's vocal cords) to the vibration sensor (110); and

[0112] H4 is the transfer function from the vibration source to the ear canal volume (65).

[0113] The skilled person will understand that the audio signal (m) in the ear canal can be approximated by equation (2):

[0114]

[0115] The skilled person will appreciate that the benefit of the active blocking suppression circuit against external noise (i.e., noise acoustically reaching the ambient microphone 105 from an external source), conditional on x2=0 and G=0, can be derived from equations (1) and (2), as represented by the following equation (3):

[0116]

[0117] The skilled person will appreciate that the benefit of the active occlusion suppression circuit against internal noise (such as at least body-conducted sound in the user's ear canal volume (65), for example generated by the user's own voice), corresponding to the condition x1=0, can be derived from equations (1) and (2), as represented by the following equation (4):

[0118]

[0119] If the active occlusion suppression circuit is disabled, i.e., each of the corresponding filter transfer functions A, B, D, and C is equal to 0, then the transfer function to the audio signal (m) in the ear canal is reduced to:

[0120]

[0121] Therefore, the benefit of the active occlusion suppression circuit against external noise according to equation (3) above is increased by setting x2=0 and dividing the in-ear canal audio signal (m) as expressed in equation (2) by m according to equation (5) off The ratio resulting from the latter division represents the amount by which the external noise is attenuated or suppressed, for example, expressed in decibels (dB) or as a natural number as a function of frequency. In other words, if the ratio is significantly less than 1.0 (e.g., less than 0.3 or less than 0.1) at a particular audio frequency of interest, then the blocking suppression at that audio frequency provides a beneficial reduction of the external noise from about 10 dB to 20 dB. On the other hand, if the ratio is close to 1.0 or even worse, greater than 1.0, the active blocking suppression circuit does not provide significant suppression of the external noise, or even worse, increases the level or amount of the external noise.

[0122] The benefit of the active occlusion suppression circuit according to equation (4) above to combat internal sounds including body-conducted sounds in the ear canal volume of the user is obtained by setting x1=0 and dividing the in-ear canal audio signal (m) as expressed in equation (2) by m according to equation (5) off The ratio of the latter division represents the amount by which the internal noise is attenuated or suppressed, for example expressed in decibels (dB) or as a natural number as a function of frequency. Similar to the suppression of external noise discussed above, if the ratio associated with the internal noise at a particular audio frequency or audio frequency range of interest is significantly less than 1.0 (e.g., less than 0.3 or less than 0.1), then the blocking suppression at that frequency or frequency range provides a beneficial reduction of the internal noise from about 10 dB to 20 dB. On the other hand, if the ratio approaches 1.0 or even worse is greater than 1.0, the active blocking suppression circuit does not provide significant blocking suppression, or even amplifies the blocking effect.

[0123] The processing unit 135 may be configured to adjust the transfer function of the second filter 203 to minimize the error signal (v'). Such adjustment of the transfer function of the second filter 203, whether performed at initialization of the active blocking circuit or adaptively during operation of the hearing device, provides a good estimate of R. The function of the second filter 203 is ideally to eliminate or at least suppress the desired output signal (R*u) provided by the receiver 120 from the feedback path in the ear canal audio signal (m). In this way, the subtraction performed by the second subtractor 217 prevents the desired signal (i.e., the processed audio signal (u)) from being suppressed by the feedback path. The minimization of the error signal (v') performed by the second filter 203 includes a third cross-correlator (XCORR) 333, which performs a cross-correlation of the error signal (v') and the processed audio signal (u) to calculate a third gradient direction. The third gradient direction is applied by the processing unit 135 to a third optimization algorithm, such as normalized least mean square (NLMS), recursive least squares (RLS), etc. The adjustment function 331 may be configured to repeatedly calculate and update the filter coefficients of the second adaptive filter 203 during normal use of the hearing device.

[0124] The processing unit 135 may further minimize the error signal (v') by adjusting the transfer function of the first adaptive filter 205 to maximize the real part of the loop response denominator (1+BR) replaced by (1+B*A) during normal operation of the hearing device for calculation purposes. In other words, the calculated transfer function of the second filter 203 may be used as an estimate of the transfer function R and is therefore input to the exemplary LMS adjustment B function 345. Due to the above-mentioned operation of the third cross-correlator 333 and the LMS adjustment 331, the transfer function of the second filter 203 is already available to the processing unit 135 or stored in the processing unit 135. The minimization of the error signal (v') may include updating the filter coefficients of the first adaptive filter 205 by LMS (least mean square) adjustment 345 or using other suitable optimization techniques or algorithms (such as normalized least mean square (NLMS), recursive least squares (RLS), etc.).

[0125] The processing unit 135 can be configured, for example, to minimize the norm (such as the 1-norm or the 2-norm) of the error signal (v') by means of the exemplary LMS adjustment B function 345, while satisfying the constraints on the gain and stability of the closed-loop response of the feedback path. In an alternative embodiment, the first adaptive filter 205 is not directly controlled by the error signal (v'), but is indirectly controlled by the error signal (v') based on the change of the transfer function of the second filter 203. The latter embodiment results in a slower adjustment of the first adaptive filter 205, which is used to suppress the effects of transient changes in the audio signal (m) in the ear canal in a desired manner.

[0126] The processing unit 135 may be configured to maximize the real part of the loop response denominator (1+B*R) within a certain frequency range that is particularly important for blocking rejection (e.g., between 20 Hz and 1 kHz, such as between 50 Hz and 400 Hz). The stability of the closed-loop response of the feedback path is ensured when the Nyquist contour (i.e., the curve spanned by complex values ​​from all frequencies in the z-plane) does not surround zero. This can be achieved by maximizing the real part of (1+B*R) to obtain a large positive value thereof to avoid surrounding the origin of the z-plane.

[0127] The transfer function of the first adaptive filter (205) may be adapted to optimize the closed-loop response of the feedback path using a set of constraints and objectives. The objectives may specify a desired amount of cancellation at a desired frequency, and the constraints limit undesirable side effects. The constraints are defined with respect to:

[0128] 1. As mentioned above, stability is guaranteed when the Nyquist contour does not enclose zero or the origin. In principle, determining Nyquist stability may require a procedure for counting encirclements of the origin (clockwise minus counterclockwise), which may be computationally demanding. However, the criterion may be simplified by setting a positive lower limit for the real part of the complex values, since if the contour uses only positive real values, it cannot simply enclose the origin.

[0129] 2. The maximum peaking of the closed-loop response of the feedback path sets an upper limit for the expected closed-loop gain.

[0130] 3. The maximum loop gain of the closed-loop transfer function of the feedback path sets an upper limit for the expected open-loop gain.

[0131] 4. The maximum gain of the first adaptive filter 205 sets an upper limit for the gain |B| of the filter 205 .

[0132] When the set of constraints is satisfied, the selected adjustment algorithm utilized by the processing unit 135 is adjusted towards a target to improve the cancellation performance, i.e. preferably the constraints are satisfied first. The skilled person will appreciate that all constraints can usually be satisfied simply by reducing the loop gain. The loop gain can be reduced during normal operation of the hearing device using a scalar gain control, so that for reasonable settings there is always a solution that satisfies all constraints.

[0133] The processing unit 135 is further configured to adjust the third filter 211 of the feedforward path to minimize the error signal (v'). The adjustment of the transfer function of the third filter 211 includes filtering the vibration signal x2 through the second filter 203. A copy or instance of the second filter 203 is arranged in series with a first input of a first cross-correlator 313, and the first cross-correlator 313 is associated with the third adaptive filter 211. The technician will understand that the first input of the first cross-correlator 313 represents the vibration signal (x2) filtered by the transfer function A of the second filter 203. The first cross-correlator 313 is configured to cross-correlate the error signal (v') with a copy of the output of the second filter 203 to calculate a first gradient direction. The first gradient direction is applied by the processing unit 135 to a first optimization algorithm such as LMS or NLMS, and is schematically indicated by the adjustment function 311. The adjustment function 311 can be configured to repeatedly calculate and update the filter coefficients of the third adaptive filter 211.

[0134] The processing unit 135 is further configured to adjust the transfer function of the fourth adaptive filter 209 of the second feedforward path to maximize the error signal (v'). A copy of the second filter 203 is arranged between the ambient microphone signal (x1) and the first input of the second cross-correlator 323 associated with the fourth adaptive filter 209. The cross-correlator 323 is configured to cross-correlate the error signal (v') with a copy of the output of the second filter 203 to calculate a second gradient direction. The second gradient direction is applied by the processing unit 135 to a second optimization algorithm such as LMS or NLMS and is schematically indicated by an adjustment function 321. The adjustment function 321 may be configured to repeatedly calculate and update the filter coefficients of the fourth adaptive filter 209.

[0135] Figure 3A A second embodiment of an exemplary hearing device 50 is schematically shown, in particular the corresponding computational models of the first filter 205, the second filter 203 when operating adaptively during normal operation, the third adaptive filter 211, and the optional fourth filter 209. Unless otherwise stated, Figure 3A Each feature of the second embodiment described above is provided with the same Figure 3 The same reference numerals as in the first embodiment are used.

[0136] The second embodiment of the exemplary hearing device 50 can reduce the computational load of the processing unit 135 because multiple instances of the second filter 203 are eliminated. More specifically, the second filter 203 is moved to the opposite side of the first cross-correlator 313 so that the error signal (v') is processed by the time-reversed instance (A*) 203A of the second filter 203 before being applied to the second input of the first cross-correlator 313. The second filter 203 is similarly moved to the opposite side of the second cross-correlator 323 so that the error signal (v') is processed by the time-reversed instance (A*) 203A of the second filter 203 before being applied to the second input of the second cross-correlator 323. In other words, the computational load imparted by the adjustment of the coefficients of the second filter 203 can be shared between the third adaptive filter 211 and the fourth adaptive filter 209. The first time delay block 315 is inserted before the first input of the first cross-correlator 313, and the second time delay block 325 is inserted before the first input of the second cross-correlator 323. The time delay of each of the first and second time delay blocks corresponds to the time delay of AA*, for example, represented as an integer number of samples. The skilled person will appreciate that the transfer function (A) of the second filter 203 is made available to the processing unit 135 via adjustment of the filter coefficients of the first adaptive filter 205. The processing of the error signal (v') in the time-reversed instance (A*) 203A may be performed in the time domain by convolution or in the frequency domain using multiplication.

[0137] Figure 4 and Figure 5 1 and 1 , which are block diagrams of certain embodiments of an exemplary hearing device 50, such as the first and second embodiments of the hearing device discussed above. The block diagrams schematically illustrate the respective topologies of preferred embodiments of the first adaptive filter 205, the second adaptive filter 203, the third adaptive filter 211, and the optional fourth adaptive filter 209. A skilled person will appreciate that, as described in Figure 2 and Figure 3 The first adaptive filter 205, the second filter 203, the third adaptive filter 211, and the optional fourth adaptive filter 209 shown above can be used with Figure 4 and Figure 5 The first adaptive filter 205 and the third adaptive filter 211, and optionally the fourth adaptive filter 209, may have similar topologies and preferably include multi-rate filter topologies or designs to obtain low time delays. In order to obtain low time delays, each of the first adaptive filter 205, the third adaptive filter 211, and the fourth adaptive filter 209 may be configured to process its corresponding input signal on a sample-by-sample basis. The low time delay through each of the filters is critical to the specific elimination performance of the first adaptive filter 205, the third adaptive filter 211, and the fourth adaptive filter 209. The leading filter taps, i.e., the corresponding taps before downsampling in each filter, such as the filter coefficient b0 of the first adaptive filter 205, the filter coefficient d0 of the third adaptive filter 211, and the filter coefficient c0 of the fourth adaptive filter 209, operate at the full sampling rate. In order to minimize processing delays, the full sampling rate should generally be higher than the sampling rate typically used for normal hearing device applications. Exemplary full sampling rates may be above 80 kHz, but even higher full sampling rates (such as at 96 kHz, 192 kHz, and 250 kHz or above) may be advantageous.

[0138] Subsequent filter stages are fed by corresponding down-samplers 209a, 211a, which reduce the sampling rate by a predetermined factor, for example by 4, 8, or 16, for example, a sampling rate between 8 and 16kHz (such as, about 10kHz). This downsampling reduces the complexity of the adaptive filter in question and reduces its power consumption. The corresponding low-pass filters LPF1, LPF2 are preferably moving average filters with low fixed-point complexity, so that a uniform time delay between filter taps is obtained similar to an FIR filter. The group delay between the filter taps as a function of frequency can be constant, just like a normal FIR filter. The amplitude response of the leading filter taps with corresponding filter coefficients b0, d0, and c0 is different for high frequencies. The corresponding low-pass filters, such as H3 before the input of the fourth adaptive filter 209 and H4 before the input of the third adaptive filter 211, can provide anti-aliasing protection for the corresponding adaptive filters 209, 211.

[0139] The low-pass filters H3 and H4 provide additional beneficial effects, such as controlling the frequency response characteristics of the corresponding adaptive filters 209, 211 at high frequencies (e.g., above 5kHz) and / or low frequencies (e.g., below 50kHz or below 20Hz). For high frequencies, low-pass filtering reduces the frequency response inaccuracy caused by the difference between the corresponding leading taps of the adaptive filters 209, 211, which reduces the computational load caused by updating or adjusting the corresponding filter coefficients of the adaptive filters 209, 211. In addition, the low-pass filters H3 and H4 may include corresponding high-pass filters configured to provide further beneficial effects (such as removing DC and preventing subsonic signals from saturating the adaptive filters 209, 211).

[0140] Regarding the characteristics of the third adaptive filter 211 for processing the vibration signal x2, the experimental results and MATLAB simulations reveal the filter taps and the corresponding filter coefficients d0, d1, d2, ..., d N The number of may be greater than 16, such as greater than 31, such as greater than 63, to achieve good cancellation performance in the previously discussed frequency range of interest for blocker suppression. The third adaptive filter 211 may be designed with a group delay between 10 microseconds and 500 microseconds at 1 kHz.

[0141] Regarding the characteristics of the fourth adaptive filter 209 for processing the ambient microphone signal x1 to suppress external acoustic noise, the experimental results and MATLAB simulations reveal the filter taps and the corresponding filter coefficients (c0, c1, c2, ..., c N) may be greater than 16, such as greater than 31, such as greater than 63, to achieve good cancellation performance. The third adaptive filter 211 may be designed with a group delay between 10 microseconds and 100 microseconds at 1 kHz.

[0142] The second filter 203 is preferably configured to process its input 301, which is the processed audio signal (u), in blocks of samples (e.g. blocks of size between 4 and 64 samples). The processing unit 135 may include a buffer 505 ( Figure 4 ), the buffer 505 may be arranged in front of the processing unit 135, for example in series with the optional downsampler 504, or the buffer 505 may actually form an integral part of the processing unit 135. The buffer 505 converts the sample-by-sample format of the ambient audio signal (x1) into corresponding sample blocks of the above-mentioned size and applies these sample blocks to the input of the processing unit 135. The processed audio signal (u) output by the processing unit 135 can therefore be formatted or structured as a sample block and input to the second filter 203 via the signal path 301 for processing the latter. As schematically shown, the processing unit 135 may include a matched rate conversion (MRC) block 303, which matches the sound path by interpolation (up to 4 times the low pass filter H2) and decimation functions LPF1 and LPF2 to directly downsample from, for example, 20.8kHz to 10.4kHz. The matched rate conversion block 303 is preferably configured to provide a corresponding conversion from the processed audio signal (u) to the audio signal mf( Figure 5 ). As a result, when the transfer function A of the second filter (203) matches the transfer function R from the receiver input (y) to the audio signal (m) in the ear canal, the desired output sound (Ru) is largely eliminated from the feedback path. As a result, the cross-correlation between (u') and (v') should therefore preferably be minimal. The matched rate conversion block 303 is preferably configured such that the relative time alignment between the processed audio signal (u) and the error signal (v) is maintained in their downsampled versions (u'), (v') extracted from the respective buffers of the second filter 203 and the first adaptive filter 205.

[0143] The skilled person will appreciate that block-based processing of samples by the processing unit 135 and the second filter 203 is advantageous because block-based processing of audio signals is generally computationally efficient and consumes less power. The block-based processing of the processing unit 135 and the second filter 203 may include various forward and backward frequency domain transforms, such as FFT / iFFT, etc. In the case where the processing unit 135 is based on block-based processing, the processing unit 135 preferably further includes a so-called non-buffer circuit 507 ( Figure 4), which is configured to convert the processed audio signal (u) from a sample block format to a sample-by-sample format, and apply the latter signal format to one or more of the first adaptive filter 205, the third adaptive filter 211, and the fourth adaptive filter 209. The processing performed by the non-buffer circuit 507 is beneficial for obtaining the previously discussed low time delay processing in one or more of the first adaptive filter 205, the third adaptive filter 211, and the fourth adaptive filter 209. The processing unit 135 may include an upsampler 509 connected in series with the output of the non-buffer circuit 507 to increase the sampling frequency of the processed audio signal (u) by an integer (such as 4, 8, or 16, etc.).

Claims

1. A hearing device (50), comprising: - an ambient microphone (105) configured to pick up ambient sound at the user's ear and respond by generating an ambient audio signal (x1), - an in-ear canal microphone (115) configured to pick up sounds, including body-conducted sounds, in the ear canal volume (65) in front of the user's eardrum (55) and respond by generating an in-ear canal audio signal (m), a vibration sensor (110) configured to pick up mechanical vibrations generated at least by body-conducted sound of the user and to respond by generating a vibration signal (x2), - a processing unit (135) configured to process the ambient audio signal (x1) according to a predetermined signal processing algorithm to generate a processed audio signal (u), - a receiver (120) configured to emit output sound into an ear canal volume (65) of the user in response to a receiver input (y); as well as - a feedback path comprising a first filter (205) configured to provide a first compensation signal (219) for cancelling at least the body-conducted sound in the ear canal volume (65) of the user based on the ear canal audio signal (m), - a second filter (203) configured to model a transfer function (R) of an in-ear canal audio signal (m) from the receiver input (y) to the in-ear canal microphone (115), - a feedforward path comprising a third filter (211), the third filter (211) being configured to provide, based on the vibration signal (x2), a second compensation signal (213) for cancelling at least the body-conducted sound in the ear canal volume (65) of the user.

2. The hearing device (50) according to claim 1, wherein the processing unit comprises: - a fourth filter (209) configured to provide, based on the ambient microphone signal (x1), a third compensation signal (210) for cancelling noise sounds, such as those transmitted via acoustic leakage around the housing of the hearing device or via the ambient audio signal (x1) into the ear canal volume (65) of the user.

3. The hearing device according to claim 1 or 2, wherein the processing unit is configured to: - subtracting said first compensation signal (219) from said processed audio signal (u) by means of a first subtractor (150), - subtracting the second compensation signal (213) from the processed audio signal (u) by means of the first subtractor (150); and - applying the output of the first subtractor (150) to the receiver input.

4. The hearing device according to claim 3 comprises a second subtractor (217), the second subtractor (217) comprising an output, the output being configured to: generate an error signal (v') by subtracting the output (221) of the second filter (203) from the intra-ear canal audio signal (m); and apply the error signal (v') to the input of the first filter (205).

5. The hearing device according to any of claims 2-4, wherein the first subtractor (150) is configured to subtract the third compensation signal (210) from the processed audio signal (u).

6. The hearing device according to claim 4 or 5, wherein the processing unit (135) is configured to minimize the energy or power of the error signal (v') within a predetermined frequency range, such as above 50 Hz or between 20 Hz and 1 kHz, for example between 100 Hz and 400 Hz.

7. The hearing device according to claim 6, wherein the processing unit (135) is configured to minimize the energy or power of the error signal (v') by: - adjusting or tuning the transfer function of said first filter (205) so as to maximize the real part of (1+B*R), - adjusting or regulating the transfer function of the second filter (203) so as to minimize the error signal (v'), - adjusting or regulating the transfer function of the third filter (211) to minimize the error signal (v'); and optionally - adjusting or regulating the transfer function of the fourth filter (209) to minimize the error signal (v'), wherein B is the transfer function of the first filter (205); R is the transfer function from the receiver input (y) to the audio signal in the ear canal (m).

8. The hearing device according to claim 7, wherein the processing unit (135) is configured to minimize the energy or power of the error signal (v') by minimizing a norm of the error signal (v'), such as a 1-norm or a 2-norm; wherein the error signal (v') is represented according to equation (1) in: A is the transfer function of the second filter (203); B is the transfer function of the first filter (205); C is the transfer function of the third filter (211); D is the transfer function of the fourth filter (209); G is the transfer function of the processing unit (135); R is the transfer function of the audio signal (m) input from the receiver to the ear canal; H1 is the transfer function from the ambient sound to the ambient audio signal (x1); H2 is the transfer function from the ambient sound to the ear canal microphone signal (m); H3 is the transfer function from the vibration signal source, e.g., the user's vocal cords, to the vibration sensor signal (x2); H4 is the transfer function from the vibration source to the ear canal microphone (m).

9. The hearing device according to any of the preceding claims, wherein the digital signal processing (DSP) is configured to adjust the transfer function of the first filter (205) and to adjust the transfer function of the third filter (211) during normal operation of the hearing device.

10. The hearing device according to any one of claims 7 to 9, wherein the processing unit is configured to: - adjusting the transfer function of the second filter (203) by cross-correlating the processed audio signal (u) and the error signal (v') to calculate a first gradient direction, - applying said first gradient direction in a first optimization algorithm such as LMS or NLMS; and - adjusting the transfer function of the third filter (211) by filtering the vibration signal (x2) with the transfer function of the second filter (203) to provide a processed output signal, - cross-correlating the processed output signal and the error signal (v') to calculate a second gradient direction; and - applying said second gradient direction in a second optimization algorithm, such as LMS or NLMS.

11. A hearing device according to any one of the preceding claims, comprising a housing; the housing (50) comprising: - an external directional surface comprising a sound inlet (227) for the ambient microphone (105), - an inner directional tip facing the ear canal volume (65) of the user and supporting a sound outlet (223) of the receiver (120), - a side surface configured to bring a vibration sensitive section of the vibration sensor (110) into physical contact with the ear canal of the user during normal use of the hearing device.

12. A method of suppressing at least body-conducted sound in an ear canal volume (65) of a user of a hearing device (50), comprising: - picking up the ambient sound at the user's ear to generate a corresponding ambient audio signal (x1), - processing said ambient audio signal (x1) according to a predetermined signal processing algorithm to generate a processed audio signal (u), - picking up sound in the ear canal volume (65) by means of an in-ear canal microphone (115) to generate a corresponding in-ear canal audio signal (m), wherein the sound comprises the at least body-conducted sound, - picking up mechanical vibrations of the user's ear canal tissue through a vibration sensor (110) and generating a corresponding vibration signal (x2), - emitting output sound into the ear canal volume (65) of the user via a receiver (120) in response to a receiver input (y), - based on the intra-ear canal audio signal (m), at least cancelling the body-conducted sound in the ear canal volume (65) of the user by means of a first compensation signal (219) generated by a first filter (205) of a feedback path, - adjusting or adapting a second filter (203) to simulate a transfer function (R) of an in-ear canal audio signal (m) from said receiver input (y) to said in-ear canal microphone (115), - based on the vibration signal (x2), at least the body-conducted sound in the ear canal volume (65) of the user is eliminated by a second compensation signal (213) generated by a third filter (211) of a feed-forward signal path.

13. A method of suppressing at least body-conducted sound in an ear canal volume (65) according to claim 12, comprising generating the receiver input (y) by: - subtracting said first compensation signal (219) from said processed audio signal (u), - subtracting said second compensation signal (213) from said processed audio signal (u).

14. A method of suppressing at least body-conducted sound in an ear canal volume (65) according to claim 12 or 13, comprising: During initialization of the hearing device and / or during normal operation of the hearing device, a plurality of filter coefficients of the third filter (211) are adjusted and a plurality of filter coefficients of the first filter (205) are adjusted.

15. A method of suppressing at least body-conducted sound in an ear canal volume (65) according to any one of claims 12 to 14, comprising: - placing the hearing device (50) in normal operation, the normal operation comprising processing the ambient audio signal (x1) and transmitting the corresponding receiver output sound when the hearing device is mounted in or at the ear of the user, - simultaneously or in parallel adjusting the respective transfer functions of the first filter (205) and the third filter (211), and optionally adjusting the transfer function of the fourth filter (209).

Images