Audio system and signal processing method for ear-worn playback device

Abstract

An audio system (AS) for an ear-worn playback device (HP) includes a speaker (SP), an error microphone (FB_MIC) configured to primarily sense sound output from the speaker (SP), and another microphone (FF_MIC) configured to primarily sense ambient sound. The system also includes a first noise filter (FNF) coupling the other microphone (FF_MIC) to the speaker (SP), a second noise filter (SNF) coupling the error microphone (FB_MIC) to the speaker (SP), and an adaptation engine (ADP). The adaptation engine is configured to adapt a response of the first noise filter (FNF) according to an error signal from at least the error microphone (FB_MIC), estimate a leakage condition according to the response of the first noise filter (FNF), and adapt a response of the second noise filter (SNF) according to the estimated leakage condition.

Description

[0001] The present disclosure relates to an audio system and a signal processing method, both of which are used for an ear-worn playback device including a speaker, such as an earphone.

[0002] Today, a large number of headphones, including in-ear headphones, employ technologies that enhance the user's sound experience, such as noise cancellation technology. For example, such noise cancellation technology is called active noise control or ambient noise cancellation, both of which are abbreviated as ANC. ANC typically utilizes recorded ambient noise, which is processed to generate an anti-noise signal, which is then combined with a useful audio signal to be played on the headphone's speakers. ANC can also be used in other audio devices, such as handheld devices or mobile phones.

[0003] Various ANC methods use feedback (FB) microphones, feedforward (FF) microphones, or a combination of feedback and feedforward microphones. Effective FF and FB ANC is achieved based on the given system acoustics, for example by tuning filters or by adjusting the audio signal via an equalizer.

[0004] Hybrid noise cancelling headphones are well known. For example, a microphone is placed inside a space that is acoustically coupled directly to the eardrum, usually near the front of the headphone driver. This is called a feedback (FB) microphone. A second microphone (a feedforward (FF) microphone) is placed outside the headphone, such that the second microphone is acoustically decoupled from the headphone driver.

[0005] In order for each system to work effectively, the earphones preferably make a near-perfect seal against the ear / head that does not change while the device is worn and is consistent for any user. Any change in the seal due to a poor fit will change the acoustics and ultimately the ANC performance. This seal is typically between the ear cushion and the user's head or between the rubber sleeve and the ear canal wall for an in-ear headphone.

[0006] For most noise canceling headphones and earphones, an effort is made to maintain a consistent fit while being worn and between users to ensure that the earphone acoustics do not change and always have a good match to the noise filters. However, "leaky" earphones and headphones, which leave no seal between the ear pad / earcup and the ear, have large variations in acoustics when worn by different people. Furthermore, due to typical everyday head movements, the acoustics can change for the user as the earphone moves in the user's ear. Therefore, for any leaky headphone or earphone, some fitting is required to ensure that the filters are always matched acoustically.

[0007] Some headphones and earphones already feature some form of off-ear detection (i.e., detecting whether the user is wearing the earphone). This is usually achieved through a variety of means including optical proximity sensors, pressure sensors, and capacitive sensors. However, off-ear detection is only able to distinguish between two extreme acoustic leakage states, i.e., whether the earphone is on the ear or off the ear. In addition, the listed solutions all require the addition of additional sensors to the device for this purpose alone.

[0008] The object to be achieved is to provide an improved concept for detecting acoustic leakage of ear-worn playback devices, such as headphones, earphones or mobile handsets.

[0009] This object is achieved by the subject matter of the independent claims. Embodiments and developments of the improved concept are defined in the dependent claims.

[0010] The improved concept is based on the idea of ​​estimating the leakage condition in terms of the degree of leakage so that the obtained estimate can be used to enhance the sound experience of the user, i.e. remove unwanted parts of the sound signal transmitted to the ear canal of the user. For example, the enhancement can be achieved by adjusting the noise control algorithm based on the estimated leakage condition. For example, the FF and FB filters of a hybrid noise cancellation handset can be tuned according to the degree of acoustic leakage.

[0011] In contrast, currently the tuning of the above-mentioned filters is only performed once during or at the end of the production of the ANC device, for example by measuring the acoustic properties of the device. In particular, the tuning is performed during a calibration process using some measurement fixture, such as an artificial head with a microphone in the ear canal of the artificial head. The measurements, which include playing some test sounds, are coordinated by some processing device, which can be a personal computer or the like. In order to achieve the best ANC performance for each ANC device produced, dedicated measurements have to be performed for each of the ANC devices under the control of the processing device, which is time-consuming, especially if a large volume of ANC devices is to be calibrated.

[0012] Furthermore, to date, FB ANC has not been implemented into leaky in-ear headphones and headsets, where there can be highly variable acoustic leakage between the front volume and the surrounding environment. Implementing FB ANC into these playback devices as a fixed (i.e., non-adaptive) system would result in poor or even non-existent noise cancellation in the presence of significant leakage around the in-ear headphones. Therefore, for leaky playback devices, only adaptive FB ANC is feasible. However, conventional adaptation processes known for FF ANC systems cannot be applied to FB ANC systems, since FB ANC systems are inherently likely to become unstable in the face of changes in acoustic leakage.

[0013] In one embodiment of an audio system according to the improved concept, the audio system is to be used in an ear-worn playback device (such as headphones, in-ear headphones, mobile phones, handheld devices, etc.), and the system includes a speaker, an error microphone configured to mainly sense the sound output from the speaker and some ambient sounds, and another microphone configured to mainly sense ambient sounds. The audio system also includes a first noise filter coupling the other microphone to the speaker, a second noise filter coupling the error microphone to the speaker, and an adaptation engine.

[0014] In the following, the improved concept will be described, sometimes with headphones or earphones as an example of a playback device. However, it should be understood that this example is not limiting, and that other types of playback devices that can experience different leakage conditions during user use should also be understood by those skilled in the art. Generally speaking, the term playback device should include all types of audio reproduction devices.

[0015] For example, a speaker of an audio system is arranged in a housing of a playback device so that a first space is arranged on a preferred side of sound emission of the speaker. The housing may have an opening for coupling the first space to an ear canal space of a user. The housing may also include a front vent covered with an acoustic resistor and coupling the first space to the surrounding environment. Due to the imperfect fit of the in-ear headphones to the user's ears, the front space will also be coupled to the surrounding environment via acoustic leakage. This acoustic leakage varies from person to person and depends on how the in-ear headphones are placed in the ears at a particular time. An error microphone is arranged in the first space so that the error microphone detects the sound output from the speaker as well as the ambient sound. For example, it is arranged close to the opening.

[0016] Furthermore, a second space is arranged in the housing on the side of the speaker facing away from the preferred side of the sound emission. The second space is acoustically coupled to the surroundings via a rear vent of the housing, which can also be covered with an acoustic resistor. A further microphone is arranged, for example, outside the rear space (i.e. outside the housing) in order to primarily sense the ambient sound.

[0017] The adaptation engine is configured to adapt a response of the first noise filter according to an error signal from at least the error microphone, to estimate a leakage condition from the response of the first noise filter, and to adapt a response of the second noise filter according to the estimated leakage condition.

[0018] In some embodiments, the audio system is configured to perform noise cancellation. For example, the additional microphone is a FF microphone, and the first noise filter is of the FF noise cancellation type. In addition, the error microphone is a FB microphone, and the second noise filter is of the FB noise cancellation type.

[0019] In such a system, the FF microphone is arranged in the earphone or on the outside of the earphone, so that the microphone mainly senses the ambient sound and preferably only senses a negligible part of the sound output by the speaker. On the other hand, the FB microphone is arranged in the earphone, so that the microphone senses the ambient sound and the sound output by the speaker. In order to provide FF ANC, in this case, the adaptation engine is configured to record the error signal from the FB error microphone and adjust the response of the FF filter coupled between the FF microphone and the speaker. Optionally, the adaptation engine is also configured to adjust the response of the FF filter according to the signal from the FF microphone as well.

[0020] In detail, FF ANC requires matching the filter F to the target acoustic response:

[0021]

[0022] Where AE is the acoustic transfer function from the environment to the ear, AFFM is the transfer function from the environment to the FF microphone, and DE is the transfer function from the driver (or speaker) to the ear.

[0023] From the adjusted response of the FF filter (e.g., from the amplitude of the FF filter), the adaptation engine obtains leakage condition information characterizing acoustic leakage of the playback device, which acoustic leakage is caused, for example, by variable placement of the playback device in the user's ear. For example, a low gain FF filter response indicates a small acoustic leakage, while a high gain FF filter response constitutes a large acoustic leakage.

[0024] Therefore, the adaptation engine adjusts the response of the FB filter based on the obtained leakage condition. In this way, adaptive FB ANC is achieved, in which the response of the FB filter is adapted whenever the acoustic leakage changes. In detail, FB ANC can be calculated by the following formula:

[0025]

[0026] Where B is the response of the FB filter coupling the FB microphone to the loudspeaker, and DFBM is the transfer function of the acoustic driver to the FB microphone. Adjusting the response of the FB filter based on the state of the FF filter as described provides an effective solution for hybrid ANC with an adapted FF loop and an adapted FB loop.

[0027] For leaky ANC playback devices, the described FB loop response can change rapidly based on the changing acoustic leakage, whereby the driver response and the response of the FB filter can also change rapidly. Compared to conventional systems, and in particular compared to systems that adapt both FB ANC and FF ANC independently, the improved concept prevents the FB filter adaptation from becoming unstable on the path to a target stable state. Furthermore, adapting the FB ANC in relation to the already adapted FF ANC has the advantage of saving resources by minimizing processing, which is particularly advantageous for battery-powered wireless devices.

[0028] In other embodiments, the adaptation engine is further configured to evaluate the performance of the noise cancellation by determining an energy ratio between the signal of the error microphone and the signal of the further microphone.

[0029] The approximation of ANC is performed by monitoring the energy at the FB microphone relative to the energy at the FF microphone. For example, the ANC performance is approximately equal to the energy of the FB signal divided by the energy of the FF signal. In this way, a threshold can be defined for starting the adaptation engine to adapt the second noise filter.

[0030] In some embodiments, the adaptation engine is further configured to compare the signal level of the further microphone to the signal level of the error microphone and to evaluate the accuracy of the estimated leakage condition based on the comparison of the signal levels.

[0031] For example, a ratio of signal levels, such as corresponding to the performance of an ANC process, may indicate whether an estimated leak condition is accurate.

[0032] In other embodiments, the adaptation engine is further configured to enable and disable the second noise filter based on the accuracy of the estimated leakage condition.

[0033] For example, if the estimated leakage condition does not correspond to the actual leakage condition, ie, if the estimated leakage condition is inaccurate, it may be necessary to deactivate the second noise filter to avoid instabilities.

[0034] In some embodiments, the leakage condition characterizes acoustic leakage between an environment of the audio system and a space defined by an ear canal of a user and a cavity of the audio system, wherein the cavity is disposed on a preferential side of sound emission of a speaker.

[0035] "Leaky" in-ear headphone designs are often preferred because they are relatively compact and comfortable to wear, while still providing the user with the desired level of sound performance. However, these in-ear headphone designs do not completely seal the in-ear headphone's interior space and ear canal from the surrounding environment. For an effective ANC process, the resulting acoustic leakage must be accurately characterized to achieve the desired ANC performance.

[0036] In some embodiments, the adaptation engine is configured to estimate the leakage condition by comparing the adapted response of the first noise filter to predetermined minimum and / or maximum responses.

[0037] During the design or calibration process (i.e., at the factory), the minimum leakage acoustic transfer function and the maximum leakage acoustic transfer function can be predetermined for the playback device. The predetermined minimum value corresponds to low leakage or no leakage, for example, and the predetermined maximum value corresponds to high leakage or a playback device not on the user's ear.

[0038] The amplitude response of the first noise filter can then be compared with the predetermined minimum and maximum responses, from which the leakage condition can be obtained. For example, an adapted response of the first noise filter close to the predetermined minimum response indicates a small acoustic leak. Similarly, an adapted response of the first noise filter close to the predetermined maximum response corresponds to a large acoustic leak.

[0039] In other embodiments, comparing the adapted response of the first noise filter with a predetermined minimum and / or maximum response is performed in the frequency domain.

[0040] In some embodiments, the adaptation engine is configured to estimate leakage conditions at one or more different frequencies or frequency ranges.

[0041] Typically, the magnitude response filter is evaluated only in a frequency band of interest (e.g., an audio band). Therefore, the adaptation engine in these embodiments is configured to evaluate and compare only the filter response in the frequency band of interest and, for example, ignore the filter response outside the frequency band. For example, only the filter response is evaluated and compared to a predetermined response of 100 Hz to 1 kHz.

[0042] For example, the adaptation engine evaluates the adapted FF filter response at multiple different frequencies (e.g., at least three different frequencies within the audio band) and compares it with a predetermined minimum and / or maximum response. The amplitude of the adapted FF filter response is monitored and averaged at at least three frequencies. The amplitude is then compared with a predetermined maximum and / or minimum leakage response averaged over the same at least three frequencies. The result of the comparison is therefore used to determine the leakage condition of the system.

[0043] In some implementations, the adaptation engine is configured to estimate the leakage condition by determining a leakage value.

[0044] A convenient way to describe the leakage condition and adjust the FB filter based on the leakage condition is to determine an actual leakage value that quantifies the acoustic leakage condition. The leakage value can be, for example, a value from 0 to 1, where 0 indicates the smallest possible acoustic leakage or no leakage, and 1 indicates the maximum acceptable acoustic leakage, i.e., in the case where the playback device has a very large leakage between the front room and the environment.

[0045] In other embodiments, the adaptation engine is further configured to estimate the leakage condition by estimating the temporary leakage value at the corresponding different frequencies or frequency ranges based on the amplitude value of the response of the first noise filter within the range defined by the predetermined minimum and maximum responses at each of a set of different frequencies or frequency ranges. In addition, the adaptation engine in these embodiments is further configured to calculate the leakage value based on the temporary leakage value.

[0046] In order to obtain a more accurate result of the leakage value describing the leakage condition, as a first step, a temporary leakage value can be determined. Determining the temporary leakage value means, for example, determining a temporary leakage value at the frequency by comparing the adapted FF filter response with a predetermined minimum and / or maximum response at each different frequency. The target leakage value can then be a function of the temporary leakage value. For example, the leakage value is calculated as the average value of the temporary leakage values.

[0047] In some embodiments, a threshold may be defined below which the adaptation engine initiates adaptation of the response of the second noise filter.

[0048] For example, because the ANC performance may move quickly around a threshold due to small changes in leakage conditions over time, the single threshold may also be replaced by two thresholds in order to create a hysteresis behavior for initiating adaptation by the adaptation engine.

[0049] In some embodiments, the adaptation engine is configured to adapt the response of the second noise filter by setting one of the predefined filter groups as the second noise filter. For example, the second noise filter is a parallel arrangement of two parallel filters with different filter coefficients. In such an embodiment, the adaptation engine is configured to select any parallel filter as the second noise filter by setting the adjustable gain of one of the parallel filters (i.e. the activated parallel filter) to 1 and setting the adjustable gain of another parallel filter (i.e. the inactivated parallel filter) to 0. In addition, the memory of the audio system stores a plurality of filter coefficient groups (e.g., at least 10 coefficient groups), which correspond to different predefined filters that can be applied to different acoustic leakage conditions. For example, each of the predefined filter groups is assigned to different leakage conditions. Then, the adaptation engine is also configured to load such predefined filters as parallel filters. For example, the adaptation engine loads the predefined filters as parallel filters (i.e., inactivated parallel filters) with an instantaneous adjustable gain of 0.

[0050] For example, if the leakage condition changes, the replaced predefined filter can become a more suitable second noise filter. Therefore, in this case, the adaptation engine loads the new filter coefficients corresponding to the new suitable predefined filter as an inactivated parallel filter, and then switches the adjustable gain of the parallel filter, so that the newly loaded parallel filter becomes the second noise filter, while the other parallel filters now have an adjustable gain of 0, thereby becoming inactivated parallel filters. For example, when further changes in the leakage condition are detected and a new suitable predefined filter in the predefined filter group is determined, the filter coefficients of the latter can be modified by the adaptation engine in the same manner.

[0051] In other embodiments, the adaptation engine is further configured to adapt the response of the second noise filter by selecting a subsequent filter in the predefined filter bank according to the currently selected second noise filter.

[0052] In order to prevent the FB ANC from becoming unstable due to a sharp change in the response of the second noise filter or the FB filter, for example, the adaptation engine can be configured to change the filter coefficients only in small steps, i.e., set the predefined filter as a second noise filter adjacent to the currently selected second noise filter in terms of leakage conditions. For example, each predefined filter in the predefined filter group is assigned to a different leakage value describing the leakage condition, so that the predefined filter group can be sorted in terms of the assigned leakage value.

[0053] For example, if the currently selected second noise filter corresponds to a leakage value of 0.3, and a change in the leakage condition requires switching to a predefined filter corresponding to a leakage value of 0.5, the adaptation engine may be configured to set the predefined filter corresponding to a leakage value of 0.4 as the second noise filter in a first step, and to set the predefined filter corresponding to a leakage value of 0.5 as the second noise filter in a second step. In some systems, this may significantly reduce the risk of reaching instability due to sudden and significant changes in filter responses (such as feedback filter responses).

[0054] In some embodiments, the adaptation engine is further configured to adapt the response of the second noise filter by setting subsequent filters in the predefined filter bank by fading, in particular crossfading, from the currently selected second noise filter to subsequent filters in the predefined filter bank.

[0055] In order to ensure smooth transition when switching to a subsequent filter from a filter, the adaptation engine can be configured to change to the subsequent filter in the predefined filter group by fading. For example, the filter in the predefined filter group currently selected as the second noise filter is gradually faded out by reducing its adjustable gain from 1 to 0 step by step, and the subsequent filter in the predefined filter group gradually fades in, that is, its adjustable gain is gradually increased from 0 to 1. This process is generally referred to as crossfading. Changing the filter by the described fading can help prevent the noise elimination process from reaching instability due to the sudden change of the filter response.

[0056] In other embodiments, the adaptation engine is further configured to adapt a response of the second noise filter by adjusting a global gain during the fade.

[0057] In addition to fading the predefined filter by fading out and fading in the corresponding adjustable gain of the predefined filter, the global adjustable gain can be used to globally fade and / or globally enable and disable the second noise filter. For example, if a fade operation as described above occurs, the global adjustable gain can be set to a value less than 1 or even 0 to further reduce the risk of instability during the response change of the second noise filter. After completing the change operation, that is, after the exemplary cross-fade operation, the global adjustable gain can be set back to 1, which means that the second noise filter is fully enabled after switching. For example, in the case of an FB ANC process when a suboptimal currently set second noise filter is detected, since the performance of the FBANC has been suboptimally performed, and the reduction of the described global adjustable gain only negligibly further reduces the performance, a global adjustable gain of, for example, 0.8 can be set.

[0058] In various embodiments, the adaptation engine may be configured to interpolate between high leakage filters and low leakage filters according to leakage conditions as detailed in ams application EP 17189001.5.

[0059] In some embodiments, the audio system further comprises a combiner configured to generate a response of the second noise filter based on a combination of an output of the first interpolation filter amplified by a first adjustable gain factor and an output of the second interpolation filter amplified by a second adjustable gain factor. In these embodiments, the adaptation engine is further configured to adapt the response of the second noise filter by adjusting at least one of the first adjustable gain factor and the second adjustable gain factor.

[0060] For example, the second noise filter is the result of interpolation between two interpolation filters (i.e., the first interpolation filter and the second interpolation filter). For example, the first interpolation filter optimizes low leakage conditions (e.g., leakage value is 0), while the second interpolation filter optimizes high leakage conditions (e.g., leakage value is 1). Therefore, in this example, the two interpolation filters are tuned by the adaptation engine of the control combiner so that for the maximum leakage condition, the first adjustable gain factor is set to 0, while the second adjustable gain factor is set to 1. Correspondingly, for the minimum leakage condition, the first adjustable gain factor is set to 1, while the second adjustable gain factor is set to 0.

[0061] For intermediate leakage conditions, the adaptation engine controls the combiner to set the first adjustable gain factor and the second adjustable gain factor according to the estimated leakage condition. For example, in the described example, the second adjustable gain factor is configured to be set equal to the estimated leakage value, and the first adjustable gain factor is configured to be set equal to 1 minus the estimated leakage value. In this example, the leakage value describes the degree of the leakage condition, where 0 corresponds to no acoustic leakage or minimum acoustic leakage and 1 corresponds to maximum acoustic leakage. Therefore, the first adjustable gain and the second adjustable gain are both limited to 0 to 1, and the sum of the two gains is always 1, so as not to cause any instability. The design of the first interpolation filter and the second interpolation filter is such that for a specified leakage setting, any gain combination set by the leakage value cannot become unstable.

[0062] In some implementations, the audio system may include more than two interpolation filters that are combined to generate the second noise filter.

[0063] In other embodiments, the combiner is further configured to generate a response of the second noise filter based on the combination amplified by the supplementary adjustable gain factor. In these embodiments, the adaptation engine is further configured to adapt the response of the second noise filter by adjusting the supplementary adjustable gain factor.

[0064] As described above, in these embodiments, the supplementary adjustable gain factor as the global gain factor of the second noise filter can also further reduce the risk of instability during the response change of the second noise filter. For example, when the adaptation engine adapts the first adjustable gain and the second adjustable gain of the interpolation filter, the supplementary adjustable gain factor is set to a value less than 1.

[0065] In some embodiments, the adaptation engine is configured to adapt the response of the second noise filter such that a stable operation of the response of the second noise filter is maintained.

[0066] For example, the response of the second noise filter is generated by a gain factor (such as a global gain factor according to one of the above embodiments). In such an embodiment, the stability criterion for the operation of the second noise filter can be that the product of the acoustic transfer function (i.e., the transfer function from the loudspeaker to the error microphone) and the response of the second noise filter (i.e., the gain factor) is less than 1 at the frequency where the loop phase flips (i.e., exceeds ±180°). The global gain can be set to 0 until the second noise filter can operate stably.

[0067] Alternatively, for an embodiment in which the response of the second noise filter is generated based on a combination of multiple filters (such as an interpolation filter according to one of the above embodiments), the stability criterion for the operation of the second noise filter in such an embodiment may be that the sum of the adjustable gain factors is always less than or equal to 1. In addition, if the response of the second noise filter is adjusted by setting one of the predefined filter banks as the second noise filter as described above, stability may be maintained by setting an intermediate stage between two adjacent predefined filters in the predefined filter bank as the second noise filter. The intermediate stage is, for example, an intermediate filter (i.e., a selected one of the predefined filter banks), characterized in that the response is less than the currently selected second noise filter and greater than the subsequent second noise filter.

[0068] In some embodiments, the audio system further comprises a proximity sensor configured to detect proximity between the audio system and the user's ear canal, wherein the adaptation engine is further configured to estimate the leakage condition from the response of the first noise filter and the proximity.

[0069] To enhance the accuracy of the estimated leak condition, an additional proximity sensor may be employed to independently estimate a second leak condition that can be compared with the estimated leak condition estimated based on the response of the first noise filter to assess accuracy. Likewise, the estimated leak condition and the second estimated leak condition may be combined to generate a better approximation of the actual leak condition.

[0070] In some embodiments, the audio system includes a playback device. In addition, in some embodiments, the adaptation engine is included in the housing of the playback device. The playback device can be a headphone or an in-ear headset, especially a "leaky" headphone or in-ear headset.

[0071] From the above-described audio system embodiments, further embodiments of the method of the present invention will become apparent to those skilled in the art.

[0072] The improved concept is described in more detail below with the aid of the accompanying drawings. In all the accompanying drawings, the same reference numerals are used for elements having the same or similar functions. Therefore, it is not necessary to repeat the description thereof in the following drawings.

[0073] In the attached picture:

[0074] Figure 1 A schematic diagram of a headset is shown;

[0075] Figure 2 A block diagram of a generic adaptive ANC system is shown;

[0076] Figure 3 An example representation of a "leaky" type in-ear headphone is shown;

[0077] Figure 4 An example headset worn by a user is shown, the headset having multiple sound paths from ambient sound sources;

[0078] Figure 5 An example representation of an ANC-enabled handheld device is shown;

[0079] Figure 6 shows a block diagram of an adaptive hybrid ANC system according to the improved concept; and

[0080] Figure 7 A signal diagram showing the amplitude response of the adapted noise filter is shown.

[0081] Figure 1A schematic diagram of an ANC-enabled playback device in the form of headphones HP is shown, which in this example are designed as over-ear headphones or surround headphones. Only a portion of the headphones HP corresponding to a single audio channel is shown. However, the extension to stereo headphones will be obvious to a person skilled in the art. The headphones HP include a housing HS carrying a loudspeaker SP, a feedback noise microphone or error microphone FB_MIC and an ambient noise microphone or feedforward microphone FF_MIC. The error microphone FB_MIC is particularly guided or arranged so that it records ambient noise and the sound played through the loudspeaker SP. Preferably, the error microphone FB_MIC is arranged close to the loudspeaker, for example close to the edge of the loudspeaker SP or close to the membrane of the loudspeaker. The ambient noise / feedforward microphone FF_MIC is particularly guided or arranged so that it mainly records ambient noise from outside the headphones HP.

[0082] Depending on the type of ANC to be performed, the ambient noise microphone FF_MIC can be omitted if only feedback ANC is performed. When the user wears the headset HP, the error microphone FB_MIC can be used according to the improved concept to provide an error signal, which is the basis for determining the wearing condition or leakage condition of the headset HP.

[0083] exist Figure 1 In an embodiment, the adaptation engine ADP is located inside the headset HP for performing various signal processing operations, examples of which are described in the following disclosure. The adaptation engine ADP can also be placed outside the headset HP, for example, in an external device located in a mobile handset or phone or in the cable of the headset HP.

[0084] Figure 2 A block diagram of a generic adaptation ANC system is shown. The system comprises an error microphone FB_MIC and a feedforward microphone FF_MIC, both of which provide their output signals to the adaptation engine ADP. The noise signal recorded with the feedforward microphone FF_MIC is further provided to a feedforward filter FNF for generating an anti-noise signal output via a speaker SP. At the error microphone FB_MIC, the sound output from the speaker SP is combined with the ambient noise and recorded as an error signal comprising the remainder of the ambient noise after ANC. The sound adaptation engine ADP uses the error signal to adjust the filter response of the feedforward filter.

[0085] Figure 3 An example representation of a "leaky" type in-ear earphone is shown, i.e. an in-ear earphone characterized by some leakage between the surroundings and the ear canal EC. In particular, there is a sound path between the surroundings and the ear canal EC, which is indicated as "acoustic leakage" in the figure.

[0086] Figure 4 An example configuration of headphones HP with multiple sound paths worn by a user is shown. Figure 4 The earphone HP shown in is an example of any ear-worn playback device of the audio system enabling noise cancellation, and can for example include in-ear headphones or earbud headphones, on-ear headphones or earmuff headphones. In addition to earphones, the ear-worn playback device can also be a mobile phone or similar device.

[0087] The headset HP in this example features a loudspeaker SP, a feedback noise microphone FB_MIC and an optional ambient noise microphone FF_MIC, which is designed as a feed-forward noise cancellation microphone, for example. For better understanding, the internal processing details of the headset HP are not shown here.

[0088] exist Figure 4 In the configuration shown, there are multiple sound paths, each of which can be represented by a corresponding acoustic response function or acoustic transfer function. For example, the first acoustic transfer function DFBM represents the sound path between the speaker SP and the feedback noise microphone FB_MIC, and can be referred to as a driver-to-feedback response function. The first acoustic transfer function DFBM may include the response of the speaker SP itself. The second acoustic transfer function DE represents the acoustic sound path between the speaker SP of the headset that may include the response of the speaker SP itself and the eardrum ED of the user exposed to the speaker SP, and can be referred to as a driver-to-ear response function. The third acoustic transfer function AE represents the acoustic sound path between the ambient sound source and the eardrum ED through the user's ear canal EC, and can be referred to as an environment-to-ear response function. The fourth acoustic transfer function AFBM represents the acoustic sound path between the ambient sound source and the feedback noise microphone FB_MIC, and can be referred to as an environment-to-feedback response function.

[0089] If there is an ambient noise microphone FF_MIC, the fifth acoustic transfer function AFFM represents the acoustic path between the ambient sound source and the ambient noise microphone FF_MIC, and may be referred to as an ambient-to-feedforward response function.

[0090] The response function or transfer function of the earphone HP, in particular between the microphones FB_MIC and FF_MIC and the loudspeaker SP, can be used together with the feedback filter function B and the feedforward filter function FNF, which can be parameterized as a noise cancellation filter during operation.

[0091] The headset HP as an example of an ear-worn playback device can be embodied as both microphones FB_MIC and FF_MIC are activated or enabled, so that hybrid ANC can be performed or as a FB ANC device, where only the feedback noise microphone FB_MIC is activated and the ambient noise microphone FF_MIC does not exist or is at least not activated. Therefore, in the following, if a signal or acoustic transfer function involving the ambient noise microphone FF_MIC is used, it is assumed that the microphone exists, otherwise it is assumed that the microphone is optional.

[0092] For a better overview, Figure 4 Any processing of the transmission of the microphone signal or any signal is omitted. However, in order to perform ANC, the processing of the microphone signal can be implemented in a processor located within the headset or other ear-worn playback device or in a dedicated processing unit outside the headset. The processor or processing unit can be referred to as an adaptation engine. If the processing unit is integrated into the playback device, the playback device itself can form an audio system enabled with noise cancellation. If the processing is performed externally, the external device or processor together with the playback device can form an audio system enabled with noise cancellation. For example, the processing can be performed in a mobile device (such as a mobile phone or a mobile audio player), and the headset is connected to the mobile device with or without a wire.

[0093] In various embodiments, the FB or error microphone FB_MIC may be located in a dedicated cavity, as detailed, for example, in ams application EP 17208972.4.

[0094] Now refer to Figure 5 , presents another example of an audio system with noise cancellation enabled. In this example embodiment, the system is formed by a mobile device (such as a mobile phone MP) comprising a playback device with a loudspeaker SP, a feedback or error microphone FB_MIC, an ambient noise or feedforward microphone FF_MIC and an adaptation engine ADP for performing, in particular, ANC and / or other signal processing during operation.

[0095] In another embodiment not shown, the earphone HP (e.g. Figure 1 or Figure 4 ) can be connected to a mobile phone MP, wherein the signals from the microphones FB_MIC, FF_MIC are transmitted from the headset to the mobile phone MP (in particular the processor PROC of the mobile phone) for generating an audio signal to be played through the loudspeaker of the headset. For example, depending on whether the headset is connected to a mobile phone, the ANC is performed using the internal components of the mobile phone (i.e. the loudspeaker and microphone) or using the loudspeaker and microphone of the headset, so that different sets of filter parameters are used in each case.

[0096] In the following, several embodiments of the improved concept will be described in conjunction with specific use cases. However, it is obvious to those skilled in the art that the details described for one embodiment may still be applied to one or more of the other embodiments.

[0097] Figure 6 A block diagram of an adaptive hybrid ANC system according to an improved concept is shown. The system includes an error microphone FB_MIC and a feedforward microphone FF_MIC, both of which provide their output signals to an adaptation engine ADP. The noise signal recorded by the feedforward microphone FF_MIC is further provided to a feedforward first noise filter FNF for generating an anti-noise signal output via a speaker SP. At the error microphone FB_MIC, the sound output from the speaker SP is combined with the ambient noise and recorded as an error signal including the remainder of the ambient noise after ANC. The error signal is output to a feedback second noise filter SNF for generating an additional anti-noise signal that is added to the anti-noise signal and also output via the speaker SP. The error signal is also provided to a sound adaptation engine ADP for adjusting the filter response of the feedforward filter FNF.

[0098] Furthermore, the adjustment of the feedforward filter FNF is also used to determine the leakage condition. For example, the response of the feedforward filter FNF is evaluated and compared with the known leakage condition to determine a leakage value that quantifies the leakage condition of the in-ear headphone. Thus, the adaptation engine ADP uses the leakage value to adjust the filter response of the feedback filter SNF.

[0099] Figure 7 A signal diagram is shown which shows the frequency-dependent response amplitude of the adapted FF filter and the predetermined or pre-calculated low leakage (i.e., minimum) and high leakage (i.e., maximum) filter response amplitudes. For example, the low leakage FF filter response corresponds to a wearing state with no leakage, i.e., no acoustic leakage between the ear canal and the surrounding environment, while the high leakage FF filter response corresponds to a maximum, i.e., a state with a large amount of acoustic leakage between the ear canal and the surrounding environment. Then, as shown in the exemplary response of the adapted FF filter, the adaptation of the FF filter for the intermediate leakage condition results in a filter response between these two predetermined responses. For example, a typical range of possible amplitudes of the FF filter response between the minimum and maximum values ​​is about 15 dB.

[0100] The adaptation engine ADP may be configured to evaluate the response of the adapted FF filter and compare the response to the Figure 7. The predetermined minimum and maximum responses at three different frequencies marked as thick vertical lines in FIG. 4 are compared. In this example, the adapted FF filter is closer to a low leakage response, indicating a leakage condition slightly above the minimum value. A leakage value quantifying the leakage condition can be determined, for example, as a value from 0 to 1, where 0 indicates a minimum value and 1 corresponds to a maximum leakage condition.

[0101] Furthermore, the adaptation engine ADP may be configured to detect and evaluate a ratio of the energy at the FB microphone FB_MIC relative to the energy at the FF microphone FF_MIC and determine the accuracy of the estimated leakage value based on the ratio. A typical error range for the leakage value is about 5%, which constitutes sufficient accuracy for setting the FB filter based on the leakage value. For example, if the accuracy of the leakage value is below a certain threshold, the adaptation engine ADP may be configured to suspend the FB ANC.

[0102] Description of Reference Numerals

[0103] HP Headphones

[0104] HS housing

[0105] SP Speakers

[0106] FB_MIC Error or feedback microphone

[0107] FF_MIC Feed-forward Microphone

[0108] FNF First noise or feedforward filter

[0109] SNF Second Noise or Feedback Filter

[0110] ADP Adaptation Engine

[0111] EC ear canal

[0112] ED eardrum

[0113] F Feedforward filter function

[0114] B Feedback filter function

[0115] DFBM drive to feedback response function

[0116] DE Driver to Ear Response Function

[0117] AE environment to ear response function

[0118] AFBM environment to feedback response function

[0119] AFFM Environment to Feedforward Response Function

[0120] MP Mobile Phone

Claims

1. An audio system (AS) for an ear-worn playback device (HP), the audio system comprising: - loudspeaker (SP); - an error microphone (FB_MIC) configured to sense the sound output from the speaker and the ambient sound (SP); - a further microphone (FF_MIC) configured to sense ambient sound; - a first noise filter (FNF) coupling said further microphone (FF_MIC) to said loudspeaker (SP); - a second noise filter (SNF) coupling the error microphone (FB_MIC) to the loudspeaker (SP); and - an adaptation engine (ADP) configured to - adapt a response of said first noise filter (FNF) according to an error signal from at least said error microphone (FB_MIC); - estimating a leakage condition based on the response of said first noise filter (FNF); and - adapting the response of said second noise filter (SNF) according to the estimated leakage conditions, Therein, the adaptation engine (ADP) is configured to estimate the leakage condition by comparing the adapted response of the first noise filter (FNF) with a predetermined minimum response and / or maximum response.

2. An audio system (AS) according to claim 1, wherein Comparing the adapted response of the first noise filter (FNF) with the predetermined minimum response and / or maximum response is performed in the frequency domain.

3. An audio system (AS) according to claim 1 or 2, wherein: The adaptation engine (ADP) is configured to estimate leakage conditions at one or more different frequencies or frequency ranges.

4. An audio system (AS) according to claim 1 or 2, wherein: The adaptation engine (ADP) is configured to estimate the leakage condition by determining a leakage value.

5. The audio system (AS) according to claim 4, wherein The adaptation engine (ADP) is further configured to estimate the leakage condition by: - based on the magnitude values ​​of the response of said first noise filter (FNF) within a range defined by a predetermined minimum response and a maximum response at each of a set of different frequencies or frequency ranges, estimating temporary leakage values ​​at the respective different frequencies or frequency ranges; and - calculating the leakage value based on the temporary leakage value.

6. The audio system (AS) according to claim 5, wherein The adaptation engine (ADP) is further configured to estimate the leakage condition by calculating the leakage value as an average of the temporary leakage values.

7. An audio system (AS) according to claim 1 or 2, wherein: The adaptation engine (ADP) is configured to adapt a response of the second noise filter (SNF) by setting one of a predefined filter bank as the second noise filter (SNF).

8. The audio system (AS) according to claim 7, wherein Each of the predefined filter banks is assigned to a different leakage condition.

9. The audio system (AS) according to claim 8, wherein The adaptation engine (ADP) is further configured to adapt a response of the second noise filter (SNF) by selecting a subsequent filter of the predefined filter bank in dependence on the currently selected second noise filter (SNF).

10. The audio system (AS) according to claim 9, wherein With respect to the assigned leakage condition, the subsequent filters in the predefined filter bank are adjacent to the currently selected second noise filter (SNF).

11. The audio system (AS) according to claim 7, wherein The adaptation engine (ADP) is further configured to adapt a response of the second noise filter (SNF) by setting subsequent filters in the predefined filter bank by fading from the currently selected second noise filter (SNF) to subsequent filters in the predefined filter bank.

12. The audio system (AS) according to claim 11, wherein The adaptation engine (ADP) is further configured to adapt a response of the second noise filter (SNF) by adjusting a global gain during the fading.

13. The audio system (AS) according to claim 1 or 2, - it also comprises a combiner (CO) configured to generate a response of the second noise filter (SNF) based on a combination of an output of the first interpolation filter (FIF) amplified by a first adjustable gain factor and an output of the second interpolation filter (SIF) amplified by a second adjustable gain factor; and -in, The adaptation engine (ADP) is further configured to adapt a response of the second noise filter (SNF) by adjusting at least one of the first adjustable gain factor and the second adjustable gain factor.

14. The audio system (AS) according to claim 13, wherein - the combiner (CO) is further configured to generate a response of the second noise filter (SNF) based on the combination amplified by means of a complementary adjustable gain factor; and - said adaptation engine (ADP) is further configured to adapt a response of said second noise filter (SNF) by adjusting said supplementary adjustable gain factor.

15. An audio system (AS) according to claim 1 or 2, configured to perform noise cancellation.

16. The audio system (AS) according to claim 15, wherein The adaptation engine (ADP) is further configured to evaluate the performance of the noise cancellation by determining an energy ratio between the signal of the further microphone (FF_MIC) and the signal of the error microphone (FB_MIC).

17. An audio system (AS) according to claim 1 or 2, wherein: - the further microphone (FF_MIC) is a feed-forward error microphone and the first noise filter (FNF) is of the feed-forward noise cancellation type; and - the error microphone (FB_MIC) is a feedback error microphone and the second noise filter (SNF) is of the feedback noise cancellation type.

18. An audio system (AS) according to claim 1 or 2, wherein: The adaptation engine (ADP) is further configured to - compare the signal level of the further microphone (FF_MIC) with the signal level of the error microphone (FB_MIC); and - Assessing the accuracy of the estimated leak condition based on the comparison of these signal levels.

19. The audio system (AS) according to claim 18, wherein The adaptation engine (ADP) is further configured to enable and disable the second noise filter (SNF) depending on the accuracy of the estimated leakage condition.

20. The audio system (AS) according to claim 1 or 2, wherein: The leakage condition characterizes a leakage between the environment of the audio system (AS) and a space defined by an ear canal of a user and a cavity of the audio system (AS), wherein the cavity is arranged on a preferential side of a sound emission of the loudspeaker (SP).

21. An audio system (AS) according to claim 1 or 2, - it also comprises a proximity sensor (PS) configured to detect the proximity between the audio system (AS) and the ear canal of a user; wherein, - said adaptation engine (ADP) is further configured to estimate said leakage condition based on a response of said first noise filter (FNF) and said proximity.

22. An audio system (AS) according to claim 1 or 2, comprising a playback device (HP).

23. An audio system (AS) according to claim 22, wherein The adaptation engine (ADP) is comprised in a housing of the playback device (HP).

24. An audio system (AS) according to claim 1 or 2, wherein: The playback device (HP) is a headset or an in-ear headset.

25. An audio system (AS) according to claim 1 or 2, wherein: The adaptation engine (ADP) is configured to adapt the response of the second noise filter (SNF) such that a stable operation of the response of the second noise filter (SNF) is maintained.

26. An audio system (AS) according to claim 1 or 2, wherein: The further microphone (FF_MIC) detects a negligible level of sound output from the speaker (SP).

27. An audio system (AS) according to claim 1 or 2, wherein: The error microphone (FB_MIC) detects a negligible level of the ambient sound.

28. The audio system (AS) according to claim 7, wherein The adaptation engine (ADP) is further configured to adapt the response of the second noise filter (SNF) by setting subsequent filters in the predefined filter bank by crossfading from the currently selected second noise filter (SNF) to the subsequent filters in the predefined filter bank.

29. A signal processing method for an ear-worn playback device (HP), the ear-worn playback device comprising a speaker (SP), an error microphone (FB_MIC) for sensing sound output from the speaker (SP), and a further microphone (FF_MIC) for sensing ambient sound, the method comprising: - generating an error signal via the error microphone (FB_MIC); - adapting a response of a first noise filter (FNF) coupled between the further microphone (FF_MIC) and the loudspeaker in dependence on at least the error signal; - estimating a leakage condition based on the response of said first noise filter (FNF); and - adapting the response of a second noise filter (SNF) coupled between the error microphone (FB_MIC) and the loudspeaker (SP) according to the leakage condition, Therein, the leakage condition is estimated by comparing the adapted response of the first noise filter (FNF) with a predetermined minimum response and / or maximum response.

30. The method of claim 29, wherein: Estimating the leakage condition includes determining a leakage value.

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