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

Abstract

An audio system (AS) for an ear-worn playback device (HP) comprises: a compensation filter (C) configured to generate a third compensation signal (CS3) by applying a filtering operation to an audio signal (IN); and an error compensation unit (ECU) configured to generate a compensated error signal (EM) based on the third compensation signal (CS3) and a disturbed audio signal (E) from an error microphone (FB_MIC). The audio system (AS) further comprises: a first noise filter (F) configured to adapt based on the compensated error signal (EM); and a detection unit (DET) configured to estimate an acoustic leakage condition based on the first noise filter (F) or based on the disturbed audio signal (E) and an audio output signal. The compensation filter (C) is configured to adapt based on the acoustic 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 (such as a headset), where the ear-worn playback device includes a speaker.

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

[0003] Various ANC methods utilize feedback (FB) microphones, feedforward (FF) microphones, or a combination of feedback and feedforward microphones. Effective FF and FB ANC is achieved by tuning filters or by conditioning the audio signal according to given system acoustics (eg, via an equalizer).

[0004] Hybrid noise cancelling headphones are well known. For example, a microphone is placed in 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 so that it is acoustically decoupled from the headphone driver.

[0005] For each system to work effectively, the headset preferably creates a near-perfect seal against the user's ear / head that does not change while the device is worn and is consistent for any user. Any change in this seal due to a poor fit will change the acoustics and ultimately the performance of the ANC. This seal is typically between the ear cushion and the user's head, or between the rubber tip of the earbud and the wall of the ear canal.

[0006] With most noise cancelling headphones and earbuds, efforts are made to maintain a consistent fit while being worn and from one user to another to ensure that the headset acoustics do not change and that the noise filters are always well matched. However, "leaky" earbuds and headphones (which do not form a seal between the earpad / earbud and the ear) can differ greatly in acoustics when worn by different people. Additionally, the earbuds may perform differently as they move in the user's ears due to typical daily head movements. Therefore, with any leaky headphones or earbuds, some adjustments will need to be made to ensure that the filters are always well matched to the acoustics.

[0007] The object to be achieved is to provide an improved concept for adjusting an active noise control algorithm according to the acoustic leakage conditions of an ear-worn playback device, such as headphones, earbuds or a mobile phone.

[0008] This object is achieved by the subject matter of the independent claims. Embodiments and developments of improved concepts are defined in the dependent claims.

[0009] The improved concept is based on the idea that during normal use of the ear-worn playback device, the degree of acoustic leakage is estimated, i.e., the degree of acoustic leakage between the ear-worn playback device and the user's ear canal is determined. Therefore, the leakage condition is generally used to enhance the user's sound experience, for example, by removing unwanted parts of the sound signal transmitted to the user's ear canal via a noise control algorithm. The unwanted part can be ambient noise, the degree of which depends on the degree of acoustic leakage, for example. In order to achieve sufficient noise control without attenuating the desired signal, such as an audio signal (such as a music signal), the improved concept also uses a compensation filter that matches the driver of the ear-worn playback device with the FB microphone response transfer function so that effective signal removal can be performed to obtain the best noise control result.

[0010] In contrast, currently, the tuning of noise control filters (such as feedforward filters and feedback filters) for conventional earplugs and headphones is only performed once during or at the end of the production of the ANC device, for example by measuring the acoustic characteristics of the device. In particular, during the calibration process, some measurement fixture (such as an artificial head) is used, in the ear canal of which a microphone is installed to perform the tuning. The measurements, which include the playback of 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 must be performed for each of the ANC devices under the control of the processing device, which is very time-consuming, especially when a larger volume of ANC devices needs to be calibrated.

[0011] In the following, the improved concept will be explained, sometimes with headphones or earplugs as an example of a playback device. However, it should be understood that this example is non-limiting and will also be understood by technicians of other types of playback devices that can have different acoustic leakage conditions during user use. In general, the term "playback device" should include all types of audio reproduction devices.

[0012] In an embodiment of an audio system for an ear-worn playback device (such as a headset, earplug, mobile phone, cell phone, etc.) according to an improved concept, the system includes a speaker configured to generate a speaker signal based on an audio output signal. The system also includes an error microphone configured to generate an interfered audio signal based on ambient noise and the speaker signal. Another microphone of the audio system is configured to generate a noise signal based on ambient noise. The audio system also includes a first noise filter, which is configured to generate a first compensation signal by applying a filtering operation to the noise signal, and adapts based on the compensated error signal.

[0013] The audio system according to the improved concept also includes a first mixer configured to generate an audio output signal by superimposing an audio signal, a first compensation signal, and a second compensation signal. The compensation filter of the audio system is configured to generate a third compensation signal by applying a filtering operation to the audio signal and is adapted based on an acoustic leakage condition. The second noise filter is configured to generate a second compensation signal by applying a filtering operation to an intermediate compensation signal, the intermediate compensation signal being generated by subtracting the third compensation signal from the disturbed audio signal.

[0014] The audio system further comprises an error compensation unit configured to generate a compensated error signal based on the disturbed audio signal and the third compensation signal. In addition, the audio system further comprises a detection unit configured to estimate the acoustic leakage condition based on a response of the first noise filter or based on the disturbed audio signal and the audio output signal.

[0015] For example, a speaker of an audio system is disposed in a housing of a playback device so that the first space is disposed on the sound emission priority side of the speaker. The housing may have an opening for coupling the first space to the user's ear canal space. 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 earplug with the user's ear, the front space will also be coupled to the surrounding environment via acoustic leakage. This acoustic leakage varies from person to person, depending on how the earphone is placed in the ear at a particular time. The error microphone is, for example, a feedback error microphone, which is disposed in the first space so that it detects the sound output from the speaker and the ambient sound (i.e., ambient noise). For example, it is disposed close to the opening.

[0016] Furthermore, a second space is arranged in the housing on a side of the loudspeaker facing away from the preferred sound emission side. 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. The further microphone can be, for example, a feed-forward microphone, which is arranged, for example, outside the rear space (i.e. outside the housing) in order to primarily sense the ambient noise.

[0017] The first noise filter is, for example, a feedforward noise filter, and is configured to generate a first compensation signal by filtering a noise signal from a feedforward microphone. The feedforward active noise control FF ANC algorithm detects ambient noise outside the headset via the feedforward microphone, processes it via the first noise filter, and provides an anti-noise signal and a first compensation signal to the speaker, so that the anti-noise signal and the noise signal are superimposed at the position of the ear to produce noise cancellation. Specifically, the residual noise ERR at the position of the ear and / or the error microphone can be characterized by the following formula:

[0018] Err=AE-AFFM·F·DE,

[0019] Where AE is the acoustic transfer function from environment to ear, AFFM is the transfer function from environment to FF microphone, F is the FF filter, and DE is the acoustic transfer function from driver to ear.

[0020] To minimize the residual noise, effective FF ANC requires matching the first noise filter F to the target acoustic response:

[0021]

[0022] For example, the second noise filter is a feedback noise filter and is configured to generate a second compensation signal by filtering the intermediate compensation signal, which may correspond to the interfered audio signal, wherein the desired signal (e.g., audio signal) or a signal derived from the desired signal (i.e., the third compensation signal) is subtracted. In other words, the intermediate compensation signal is mainly (if not only) composed of a portion of the interfered audio signal, which portion of the interfered audio signal is generated by the ambient noise through the error microphone, hereinafter referred to as the noise portion.

[0023] The first mixer is configured to generate an audio output signal provided to the speaker by superimposing the audio signal, the first compensation signal and the second compensation signal. In this case, the first compensation signal and the second compensation signal correspond to signals that destructively interfere with ambient noise between the speaker and the error microphone and / or an ear canal of a user of the ear-worn playback device.

[0024] For example, the compensation filter is similar to the filter described in US 2017 / 0140746 A1. According to the improved concept, the compensation filter in the present disclosure has a dual purpose. For these two purposes, the compensation filter applies a filtering operation to the audio signal for generating a third compensation signal, so that the third compensation signal mainly or only consists of a part of the disturbed audio signal generated from the loudspeaker signal and detected by the error microphone, hereinafter referred to as the loudspeaker part.

[0025] Firstly, this provides a music compensation mechanism for compensating the audio signal attenuated by the feedback active noise control FB ANC algorithm, since in this case the second noise filter applies the filter function mainly or exclusively to the noise portion of the disturbed audio signal. In particular, the intermediate compensation signal provided to the second noise filter mainly or exclusively consists of the noise portion of the disturbed audio signal together with only a negligible loudspeaker portion, if any.

[0026] Secondly, for the music removal mechanism, the third compensation signal is provided to an error compensation unit, which generates a compensated error signal from the disturbed audio signal and from the third compensation signal. For example, the error compensation unit adapts the third compensation signal so that it matches the loudspeaker portion of the disturbed audio signal. In particular, the error compensation unit generates a compensated error signal that includes the noise portion of the disturbed audio signal and at most only a negligible contribution of the loudspeaker portion.

[0027] Therefore, the compensated error signal is used to adapt the response of the first noise filter, for example by a detection unit or a tuning unit, so that the ambient noise detected by the further microphone can be removed from the disturbed audio signal (i.e. the signal detected by the error microphone) in a more effective manner, for example by a feed-forward active noise control algorithm FF ANC as described above. To this end, an exact matching of the response of the first noise filter of an effective FF-ANC therefore requires a nearly perfect compensated error signal that only includes the noise contribution of the disturbed audio signal.

[0028] In practice, the acoustic transfer functions can vary depending on the fit of the headphone. For leaky headphones with highly variable leakage coupling the front room acoustically to the surroundings, the transfer functions AE, DE and the acoustic transfer function DFBM from the driver to the error microphone vary substantially, making it necessary to adapt at least the first noise filter, and optionally the second noise filter, in response to the acoustic signal in the ear canal to minimize the error.

[0029] From the adapted response of the first noise filter or the transfer function from the driver to the error microphone, the acoustic leakage condition can be detected and estimated by the detection unit. For example, the detection unit is configured to compare the audio output signal with the disturbed audio signal and estimate the acoustic leakage condition based on the result of the comparison (e.g., based on the deviation between the two signals).

[0030] Alternatively or additionally, the detection unit is configured to monitor a response of the first noise filter and estimate the acoustic leakage condition based on the response. For example, the detection unit is configured to compare the response of the first noise filter with a predetermined response for estimating the acoustic leakage condition.

[0031] Therefore, the acoustic leakage condition is used to adapt the compensation filter. For example, the response of the compensation filter is adapted according to the current or changing acoustic leakage. For example, the response of the compensation filter is configured to match the driver response between the speaker and the error microphone that depends on the sound leakage. In this way, an effective noise control algorithm as described above can be implemented to enhance the sound experience of the user of the ear-worn playback device.

[0032] In some embodiments, the error compensation unit comprises a second mixer configured to generate a compensated error signal by subtracting a removal signal based on the third compensation signal from the disturbed audio signal.

[0033] In order to make the third compensation signal match the noise part of the disturbed audio signal as closely as possible, the error compensation unit in these embodiments is configured to further adjust the third compensation signal to achieve a better match of the driver to the error microphone response, for example by applying a further filter function.

[0034] In some embodiments, the error compensation unit further comprises a filter element, which is configured to generate a removal signal from the third compensation signal. In addition, in order to generate the removal signal, the filter element can be configured to apply a filtering operation to the third compensation signal. Alternatively or additionally, in order to generate the removal signal, the error compensation unit can be configured to control an adjustable gain of the filter element according to the third compensation signal and the compensated error signal.

[0035] For example, the error compensation unit includes a feedback loop configured to control the filter element (e.g., an adjustable gain and / or response of the filter element) based on the deviation between the compensated error signal and the third compensation signal. This enables the third compensation signal to effectively match the speaker portion of the disturbed audio signal. In this way, the noise portion of the disturbed audio signal can be effectively isolated as the compensated error signal.

[0036] In some embodiments, the error compensation unit is configured to control the adjustable gain by applying an error minimization algorithm, in particular a least mean square algorithm, to the third compensation signal and the compensated error signal.

[0037] In case the determined leakage conditions are inaccurate, for example during or before the adaptation process of the audio system, the filter parameters of the compensation filter may be partially inaccurate. In these cases, the error minimization algorithm can especially lead to additional accuracy and / or faster adaptation.

[0038] In some embodiments, the second noise filter is further configured to adapt based on leakage conditions.

[0039] In these embodiments, the response of the second noise filter (ie the feedback filter) is also adapted based on the current or changing acoustic leakage conditions. This allows to further improve the efficiency of the active noise control, since the performance of the FB ANC can depend heavily on the acoustic leakage conditions.

[0040] In some embodiments, the detection unit is configured to estimate the leakage condition based on the disturbed audio signal and the audio output signal when the ratio between the speaker signal and the ambient noise exceeds a set threshold. In addition, the detection unit in these embodiments is configured to estimate the leakage condition based on the first noise filter, in particular the filter parameters of the first noise filter.

[0041] Depending on the sound pressure level of the loudspeaker signal, and thereby on the contribution of the ambient noise in the disturbed audio signal, the determination of the acoustic leakage may be more accurate in one way than in another. For example, if an audio signal is output from the loudspeaker at a high sound pressure level compared to the ambient noise level, the determination of the acoustic leakage condition via the driver response may be more accurate than if a low level audio signal or no audio signal is output from the loudspeaker. In the latter case, the leakage is more accurately determined via the response of the first filter. Therefore, the detection unit in these embodiments is configured to determine the ratio between the loudspeaker signal and the ambient noise, and based on the determination, estimate the acoustic leakage condition according to a corresponding method.

[0042] In some embodiments, the leakage condition characterizes acoustic leakage between the environment of the playback device and a space defined by the user's ear canal and a cavity of the playback device.Here, the cavity is arranged on a sound emission priority side of the speaker.

[0043] In some embodiments, estimating the leakage condition includes determining a leakage value.

[0044] A convenient way to describe the acoustic leakage condition is to determine an actual leakage value, which quantifies the acoustic leakage condition currently existing. For example, the leakage value is calculated as a normalized value between 0 and 1, scaling the determined acoustic leakage to a predetermined maximum acoustic leakage and / or minimum acoustic leakage. A leakage value of 0 indicates the minimum possible acoustic leakage or no leakage, and a leakage value of 1 indicates the maximum acceptable acoustic leakage, i.e., when the playback device has a very large leakage between the front space and the surrounding environment.

[0045] In some embodiments, the compensation filter is adapted based on a comparison of the leakage condition to reference leakage conditions in a lookup table.

[0046] For example, the lookup table comprises a number of predetermined acoustic leakage conditions, such as calibrated leakage values ​​measured at different acoustic leakage conditions associated with parameters of the compensation filter. The detection unit or the tuning unit may comprise a memory with said lookup table and be configured to adapt the response of the compensation filter by setting one of the associated parameters according to the estimated acoustic leakage condition.

[0047] The lookup table can be coarse, for example it includes five predetermined acoustic leakage conditions. Then, if the estimated leakage condition is between two predetermined acoustic leakage conditions, the detection unit or the tuning unit can be configured to interpolate the parameters of the compensation filter from two adjacent points of the lookup table. This process is sufficient for the music compensation mechanism.

[0048] However, for the music removal mechanism, a higher level of isolation of the noise portion of the disturbed audio signal is essential. Therefore, for the music removal mechanism, an error compensation unit is employed in order to reduce the significant error between the response of the compensation filter and the driver response. This achieves a significantly improved accuracy in removing the music signal from the disturbed audio signal during the generation of the compensation error signal.

[0049] It seems obvious to use an error compensation unit for music compensation and music removal mechanisms (e.g., via an adjustable gain of the compensation filter itself) for highly optimized music compensation and music removal filters, however, this is actually disadvantageous. Specifically, any adaptation of the music compensation filter (e.g., via an adaptation gain) requires an error signal to feedback any deviation from the target response, as described above for some embodiments. If the adjustable gain is the gain of the compensation filter itself, the operation of the feedback loop configured to reduce the speaker portion used to generate the compensated error signal can result in the desired adaptation of the gain of the compensation filter to match the driver response, thereby effectively removing as much of the speaker signal as possible from the disturbed audio signal. However, the operation of the feedback loop can also result in a reduction in the gain of the compensation filter to reduce the amount of audio signal reaching the second noise filter. This is an undesirable effect because from the user's perspective, the audio signal (e.g., music) is significantly attenuated.

[0050] Therefore, the proposed solution of a lookup table for the music compensation mechanism eliminates this conflict and also simplifies the process since the operation adaptation process requires an additional calculation step for implementing a safety measure to ensure stability. Since there is no direct reference, a lookup table for the music compensation mechanism with a small error of, for example, 1 dB is acceptable. That is, when noise cancellation is turned off, the user will perceive the sound spectrum from the headphone as slightly different relative to the driver response, however, this difference is so small that it is barely noticeable in normal operation and is small compared to the spectral difference caused by the varying leakage.

[0051] In contrast, if a similar small error exists in the music removal mechanism between the noise portion of the disturbed audio signal and the third compensation signal, the attenuation or removal of the loudspeaker signal used to generate the compensated error signal will be significantly reduced. Since the third compensation signal is to be subtracted from the disturbed audio signal, i.e. the third compensation signal is directly compared with the disturbed audio signal, a near perfect match is required to obtain a good attenuation. Therefore, an additional adaptation stage implemented by the error compensation unit is used for the music removal mechanism.

[0052] The object is also solved by an ear-worn playback device, the ear-worn playback device comprising an audio system according to one of the above-described embodiments. For example, the ear-worn playback device is a headset or an earplug. In general, the term playback device includes all types of audio reproduction devices. Where the term music is specified, it should be understood that this term can include any known signal, such as a voice recording.

[0053] The object is also solved by a signal processing method for an ear-worn playback device, the ear-worn playback device having a speaker that generates a speaker signal based on an audio output signal, having an additional microphone configured to generate a noise signal based on ambient noise, and having an error microphone configured to generate an interfered audio signal based on the speaker signal and the ambient noise. The method comprises: generating a first compensation signal by applying a filtering operation of a first noise filter to the noise signal; generating an audio output signal by superimposing the audio signal, the first compensation signal and the second compensation signal; and generating a third compensation signal by applying a filtering operation of the compensation filter to the audio signal. The method also comprises generating a second compensation signal by applying a filtering operation of a second noise filter to an intermediate compensation signal, the intermediate compensation signal being generated by subtracting the third compensation signal from the interfered audio signal.

[0054] The method also includes generating a compensated error signal based on the disturbed audio signal and a third compensation signal, estimating a leakage condition based on the first noise filter or the disturbed audio signal and the audio output signal, adapting the first noise filter based on the compensated error signal, and adapting the compensation filter based on the leakage condition.

[0055] From the above-described embodiments of the audio system, other embodiments of the signal processing method will be apparent to the skilled person.

[0056] The improved concept will be described in more detail below with the aid of the accompanying drawings. In all the accompanying drawings, elements with the same or similar functions have the same reference numerals. Therefore, it is not necessary to repeat their description in the following description of the accompanying drawings.

[0057] In the attached picture:

[0058] Figure 1 shows a schematic diagram of a headset;

[0059] Figure 2 A block diagram of a general adaptive ANC system is shown;

[0060] Figure 3 An example representation of a "leaky" type earplug is shown;

[0061] Figure 4 An example headset worn by a user is shown with multiple sound paths from ambient sound sources;

[0062] Figure 5 An example representation of an ANC-enabled cell phone is shown; and

[0063] Figure 6 A block diagram of an exemplary embodiment of an audio system for an ear-worn playback device according to an improved concept is shown.

[0064] Figure 1 A schematic diagram of an ANC-enabled playback device in the form of a headset HP is shown, which in this example is designed as an earmuff or ear-wrapped headset. Only the portion of the headset HP corresponding to a single audio channel is shown. However, it will be apparent to those skilled in the art that it will be extended to a stereo headset. The headset HP includes a housing HS carrying a speaker SP, a feedback noise microphone or an error microphone FB_MIC, and an ambient noise microphone or a feedforward microphone FF_MIC. The error microphone FB_MIC is specifically guided or arranged so that it records both ambient noise and the sound played on the speaker SP. Optionally, the error microphone FB_MIC is arranged close to the speaker, for example, close to the edge of the speaker SP or close to the membrane of the speaker. Alternatively, the error microphone FB_MIC can be arranged close to the ear canal of the user of the headset HP. The ambient noise / feedforward microphone FF_MIC is specifically guided or arranged so that it mainly records ambient noise from outside the headset HP.

[0065] When the user wears the headphone HP, the error microphone FB_MIC may be used according to the improved concept to provide an error signal, which is a basis for determining the wearing condition or acoustic leakage condition of the headphone HP.

[0066] exist Figure 1In an embodiment of the invention, an adaptation unit ADP, which may include a detection unit DET, a tuning unit TU and / or an error compensation unit ECU according to the improved concept, is located inside the headset HP for performing various signal processing operations, examples of which will be described in the following disclosure. The tuning unit TU, the detection unit DET and the error compensation unit ECU may be arranged as a single unit or separately. They may also be placed outside the headset HP, for example in an external device located in a mobile phone or telephone or in the wires of the headset HP.

[0067] Figure 2 A block diagram of a generic adaptive 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 an adaptation unit ADP. The noise signal recorded with the feedforward microphone FF_MIC is also provided to a feedforward filter F for generating an anti-noise signal output via a loudspeaker SP. At the error microphone FB_MIC, the sound output from the loudspeaker SP is combined with the ambient noise and recorded as an error signal, which comprises the remaining part of the ambient noise after ANC. The sound adaptation unit ADP uses the error signal to adjust the filter response of the feedforward filter.

[0068] Figure 3 An example representation of a "leaky" type earplug is shown, i.e. an earplug with 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, indicated as "acoustic leakage" in the figure.

[0069] Figure 4 An example configuration of a headset HP with multiple sound paths worn by a user is shown. Figure 4 The headset HP shown in is an example of any ear-worn playback device of the noise-canceling audio system AS, and can, for example, include in-ear headphones or earbuds, on-ear headphones or over-ear headphones. In addition to the headset, the ear-worn playback device can also be a mobile phone or similar device.

[0070] The headset HP in this example has 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 a better overview, the internal processing details of the headset HP are not shown here.

[0071] exist Figure 4In the configuration shown, there are multiple sound paths, each of which can be represented by its own 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 the 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 path between the speaker SP of the headphone (which 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 the driver to the ear response function. The third acoustic transfer function AE represents the acoustic path between the ambient sound source and the eardrum ED through the user's ear canal EC, and can be referred to as the environment to the ear response function. The fourth acoustic transfer function AFBM represents the acoustic path between the ambient sound source and the feedback noise microphone FB_MIC, and can be referred to as the environment to the feedback response function. The driver response defined in the present disclosure is caused by the first acoustic transfer function DFBM and the fourth acoustic transfer function AFBM, i.e., the total sound signal detected by the error microphone FB_MIC.

[0072] Regarding the ambient noise microphone FF_MIC, the fifth acoustic transfer function AFFM represents an acoustic path between an ambient sound source and the ambient noise microphone FF_MIC, and may be referred to as an ambient-to-feedforward response function.

[0073] The response function or transfer function of the headset 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 F, which filter functions can be parameterized as a noise cancellation filter during operation.

[0074] For a better overview, Figure 4 Any processing of the microphone signal or any signal transmission is omitted. However, processing the microphone signal to perform ANC can be implemented in a processor located inside the headset or other ear-worn playback device, or in a dedicated processing unit outside the headset. The processor or processing unit can be called an adaptation unit. If the processing unit is integrated into the playback device, the playback device itself can form an audio system AS that enables noise cancellation. If the processing is performed externally, the external device or processor together with the playback device can form an audio system AS that enables 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 by wire or wirelessly.

[0075] In various embodiments, the FB or error microphone FB_MIC may be located in a dedicated cavity, such as detailed in application EP17208972.4 by AMS.

[0076] Now refer to Figure 5 , another example of a noise cancellation enabled audio system AS is presented. In this example embodiment, the system is formed by a mobile device, such as a mobile phone MP, comprising a playback device having a loudspeaker SP, a feedback or error microphone FB_MIC, an ambient noise or feedforward microphone FF_MIC and an adaptation unit ADP for performing, in particular, ANC and / or other signal processing during operation.

[0077] In another embodiment (not shown), the headset HP (e.g. Figure 1 or Figure 4 The headset HP shown is connectable to a mobile phone MP, wherein signals from microphones FB_MIC, FF_MIC are transmitted from the headset to the mobile phone MP, in particular to a processor PROC of the mobile phone, for generating an audio signal to be played on a loudspeaker of the headset. For example, depending on whether the headset is connected to a mobile phone, ANC is performed using components inside the mobile phone (i.e. loudspeaker and microphone) or using the loudspeaker and microphone of the headset, thereby using different sets of filter parameters, respectively.

[0078] Several implementations of the improved concept will be described below in conjunction with specific use examples. However, it is obvious to those skilled in the art that the details described for the implementations can still be applied to other implementations.

[0079] Figure 6 A block diagram of a hybrid ANC audio system AS according to an improved concept is shown. The audio system AS comprises an error microphone FB_MIC and a feedforward microphone FF_MIC. The noise signal N from the feedforward microphone FF_MIC is provided to a feedforward type first noise filter F for generating a first compensation signal CS1 as an anti-noise signal, which is provided to a first mixer M1. At the error microphone FB_MIC, the loudspeaker signal SPS is combined with the ambient noise NOISE and recorded as a disturbed audio signal E, which comprises the remainder of the ambient noise after ANC.

[0080] The disturbed audio signal E is provided to the third mixer M3, which performs music compensation processing, that is, subtracting the third compensation signal CS3 from the disturbed audio signal E, and providing the obtained intermediate compensation signal to the feedback type second noise filter B for generating another anti-noise signal (second compensation signal CS2). For subtraction, the third mixer M3 can be an additive mixer, which includes, for example, a signal inverter on one of its inputs. The second compensation signal CS2 is superimposed with the audio signal IN (e.g., a music signal) and the first compensation signal CS1 by the first mixer M1 to generate an audio output signal, which is converted into a speaker signal SPS through the speaker SP.

[0081] The third compensation signal CS3 is generated from the audio signal IN through the compensation filter C. As described above, the third compensation signal CS3 is provided to the third mixer M3 in addition to the error compensation unit ECU for music removal processing. In detail, the error compensation unit ECU is configured to adjust the third compensation signal CS3 so that it matches the speaker part of the interfered audio signal E. The second mixer M2 of the error compensation unit ECU generates a compensated error signal EM by subtracting the adjusted compensation signal from the interfered audio signal E, so that the compensated error signal EM includes only or substantially only the noise part of the interfered audio signal E.

[0082] An adjusted compensation signal is generated from the third compensation signal CS3 by applying the filtering operation of the adjustable filter element X to the third compensation signal CS3. For example, the adjustable filter element X is gain-adjustable and is adjusted by a feedback loop comprising a control unit CTRL, which compares the third compensation signal CS3 and the compensated error signal EM and adjusts the gain of the adjustable filter element X based on the comparison. To this end, for example, the control unit CTRL applies an error minimization algorithm (e.g., a least mean square algorithm).

[0083] The response of the first noise filter F is adjusted according to the compensated error signal EM so that the residual noise portion in the disturbed audio signal E is more effectively removed by the first compensation signal CS1 (ie by the FF ANC).

[0084] The detection unit DET is configured to estimate the acoustic leakage condition from the response of the first noise filter F or from the disturbed audio signal E and the audio output signal. The detection unit DET estimates the acoustic leakage condition, for example, from the driver response (i.e. the disturbed audio signal E and the audio output signal) if the level of the audio signal IN exceeds a predetermined threshold relative to the level of the ambient noise NOISE or the noise N, otherwise estimates the acoustic leakage condition from the response of the first noise filter F. In order to determine whether the threshold is exceeded, the detection unit can be configured, for example, to measure the level of the audio portion relative to the noise portion of the disturbed audio signal E.

[0085] Regarding the estimation of the acoustic leakage condition by the driver response, the detection unit can be configured to compare the audio output signal with the disturbed audio signal and to estimate the acoustic leakage condition based on a result of the comparison, for example based on a deviation between the two signals.

[0086] Regarding the estimation of the acoustic leakage condition by the response of the first noise filter F, the detection unit can be configured to monitor the adjustable response of the first noise filter F and estimate the acoustic leakage condition based on the response. For example, the detection unit is configured to compare the response of the first noise filter F with a predetermined response to estimate the acoustic leakage condition.

[0087] The detection engine DET can be configured to generate a leakage value for quantifying the actual leakage condition of the earplug. Therefore, the leakage value is provided to the tuning unit TU for adjusting the response of the compensation filter C to match the driver response (i.e., the transfer function from the loudspeaker SP to the error microphone FB_MIC). For example, the tuning unit TU includes a memory with a lookup table, which includes a plurality of reference leakage values ​​and respective associated filter responses. The tuning unit TU is then configured to adjust the response of the compensation filter C by setting one of the associated filter responses according to the leakage value received from the detection unit DET. If the leakage value received from the detection unit DET is between two of the reference leakage values, the tuning unit TU can also be configured to interpolate to obtain the adaptation result of the compensation filter C.

[0088] Furthermore, the tuning unit TU can also be configured to adjust the response of the second noise filter B depending on the leakage value received from the detection unit DET (eg based on a second look-up table).

[0089] The combination of the tuning unit TU, the detection unit DET and the error compensation unit ECU basically constitutes Figure 1 , Figure 2 and Figure 5 The adaptation unit ADP is shown and can be configured, for example, as a combined ASIC in a single package.

[0090] like Figure 6 The illustrated embodiment of the audio system AS implements ANC including FB ANC and adaptive FF ANC, and matches the compensation filter C to the driver response, so that both music compensation and music removal processing can be performed to achieve enhanced ANC while taking into account acoustic leakage and without attenuating the desired input signal IN. Optionally, the FB ANC can also be adaptive based on the leakage situation.

[0091] Reference numerals

[0092] HP Headphones

[0093] HS Housing

[0094] SP Driver or Speaker

[0095] FB_MIC Error microphone or feedback microphone

[0096] FF_MIC Ambient microphone or feed-forward microphone

[0097] F First noise (feedforward) filter

[0098] B Second Noise (Feedback) Filter

[0099] C Compensation filter

[0100] ADP Adapter Unit

[0101] CTRL Control Unit

[0102] DET Detection Unit

[0103] EC ear canal

[0104] ECU Error Compensation Unit

[0105] ED eardrum

[0106] M1, M2, M3 mixers

[0107] TU Tuning Unit

[0108] X Tunable Filter Components

[0109] DFBM drive to feedback response function

[0110] DE Driver to Ear Response Function

[0111] AE Environment to Ear Response Function

[0112] AFBM environment to feedback response function

[0113] AFFM Environment to Feedforward Response Function

[0114] NOISE Environmental noise

[0115] MP Mobile Phone

[0116] CS1, CS2, CS3 compensation signals

[0117] E Interfered audio signal

[0118] EM compensated error signal

[0119] IN Input signal

[0120] N Noise signal

[0121] SPS speaker signal

Claims

1. An audio system (AS) for an ear-worn playback device (HP), the audio system comprising - a speaker (SP) configured to generate a speaker signal (SPS) based on the audio output signal; - an error microphone (FB_MIC) configured to generate an interfered audio signal (E) based on the ambient noise (NOISE) and the speaker signal (SPS); - a further microphone (FF_MIC) configured to generate a noise signal (N) based on the ambient noise (NOISE); - a first noise filter (F) configured to - generate a first compensation signal (CS1) by applying a filtering operation to the noise signal (N); as well as - adapting based on the compensated error signal (EM); - a first mixer (M1) configured to generate an audio output signal by superimposing the audio signal (IN), the first compensation signal (CS1) and the second compensation signal (CS2); - a compensation filter (C) configured to - generate a third compensation signal (CS3) by applying a filtering operation to the audio signal (IN); and -Adaptation based on acoustic leakage conditions; a second noise filter (B) configured to generate a second compensation signal (CS2) by applying a filtering operation to an intermediate compensation signal, the intermediate compensation signal being generated by subtracting a third compensation signal (CS3) from the disturbed audio signal (E); - an error compensation unit (ECU) configured to generate a compensated error signal (EM) based on the disturbed audio signal (E) and a third compensation signal (CS3); as well as a detection unit (DET) configured to estimate an acoustic leakage condition based on a first noise filter (F) or based on a disturbed audio signal (E) and an audio output signal, wherein - applying an adjustable gain to the third compensation signal (CS3) in order to generate a compensated error signal (EM); and - To generate the intermediate compensation signal, no adjustable gain is applied to the third compensation signal (CS3).

2. The audio system (AS) according to claim 1, wherein The compensation filter (C) is configured to match a leakage-dependent driver response between a loudspeaker (SP) and an error microphone (FB_MIC).

3. An audio system (AS) according to claim 1 or 2, wherein: The error compensation unit (ECU) comprises a second mixer (M2) configured to generate a compensated error signal (EM) by subtracting a removal signal based on a third compensation signal (CS3) from a disturbed audio signal (E).

4. The audio system (AS) according to claim 3, wherein The error compensation unit (ECU) further comprises a filter element (X) configured to generate a removal signal from the third compensation signal (CS3).

5. The audio system (AS) according to claim 4, wherein In order to generate the removal signal, the filter element (X) is configured to apply a filtering operation to the third compensation signal (CS3).

6. The audio system (AS) according to claim 4, wherein To generate the removal signal, the error compensation unit (ECU) is configured to control an adjustable gain of the filter element (X) as a function of the third compensation signal (CS3) and the compensated error signal (EM).

7. The audio system (AS) according to claim 6, wherein The error compensation unit (ECU) is configured to control the adjustable gain through a feedback loop.

8. The audio system (AS) according to claim 6, wherein The error compensation unit (ECU) is configured to control the adjustable gain by applying an error minimization algorithm to the third compensation signal (CS3) and the compensated error signal (EM).

9. The audio system (AS) according to claim 1 or 2, wherein: The second noise filter (B) is further configured to adapt based on leakage conditions.

10. The audio system (AS) according to claim 1 or 2, wherein: The detection unit (DET) is configured to estimate a leakage condition based on: - in case the ratio between the loudspeaker signal (SPS) and the ambient noise (NOISE) exceeds a set threshold, based on the disturbed audio signal (E) and the audio output signal; and - Otherwise based on the first noise filter (F).

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

12. An audio system (AS) according to claim 1 or 2, wherein: Estimating the leakage condition includes determining a leakage value.

13. The audio system (AS) according to claim 1 or 2, wherein: The compensation filter (C) is adapted based on a comparison of the leakage condition with reference leakage conditions in a look-up table.

14. The audio system (AS) according to claim 1 or 2, wherein: The detection unit (DET) is configured to estimate an acoustic leakage condition based on a first noise filter (F) and based on a disturbed audio signal (E) and an audio output signal.

15. The audio system (AS) according to claim 6, wherein The error compensation unit (ECU) is configured to control the adjustable gain by applying a least mean square algorithm to the third compensation signal (CS3) and the compensated error signal (EM).

16. The audio system (AS) according to claim 1 or 2, wherein: The detection unit (DET) is configured to estimate a leakage condition based on: - in case the ratio between the loudspeaker signal (SPS) and the ambient noise (NOISE) exceeds a set threshold, based on the disturbed audio signal (E) and the audio output signal; and - Otherwise based on the filter parameters of the first noise filter (F).

17. An ear-worn playback device (HP) comprising an audio system (AS) according to claim 1 or 2.

18. A signal processing method for an ear-worn playback device (HP), the ear-worn playback device (HP) having a speaker (SP) generating a speaker signal (SPS) based on an audio output signal, having a further microphone (FF_MIC) configured to generate a noise signal (N) based on an ambient noise (NOISE), and having an error microphone (FB_MIC) configured to generate an interfered audio signal (E) based on the speaker signal (SPS) and the ambient noise (NOISE), the method comprising - generating a first compensation signal (CS1) by applying a filtering operation of a first noise filter (F) to the noise signal (N); - generating an audio output signal by superimposing the audio signal (IN), the first compensation signal (CS1) and the second compensation signal (CS2); - generating a third compensation signal (CS3) by applying a filtering operation of the compensation filter (C) to the audio signal (IN); as well as - generating a second compensation signal (CS2) by applying a filtering operation of a second noise filter (B) to an intermediate compensation signal generated by subtracting a third compensation signal (CS3) from the disturbed audio signal (E); - generating a compensated error signal (EM) based on the disturbed audio signal (E) and a third compensation signal (CS3); - estimating a leakage condition based on a first noise filter (F) or based on the disturbed audio signal (E) and the audio output signal; - adapting the first noise filter (F) based on the compensated error signal (EM); and - adapting the compensation filter based on the leakage conditions, wherein applying an adjustable gain to a third compensation signal (CS3) in order to generate a compensated error signal (EM); and To generate the intermediate compensation signal, no adjustable gain is applied to the third compensation signal (CS3).

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