EP2104376A2 - Method for active occlusion reduction with plausibility test and corresponding hearing aid - Google Patents

Abstract

The method involves receiving sound in an auditory canal (11) by a microphone (17) by outputting microphone signals. The signals are filtered by a loop filter (18). The filtered signals are feedback to an input of a receiver. Part of transducer transmission function defined for a transmission path (19) from the input of the receiver via the canal to the output of the microphone, is measured. The filter is adjusted based on the function, which is subjected to an automatic plausibility check. The filter is only altered if the function is plausible according to a predefined criterion. An independent claim is also included for a hearing aid for active occlusion reduction.

Description

The present invention relates to a method for active occlusion reduction in a hearing device. In this case, a sound in an auditory canal is recorded by a microphone with the output of a corresponding microphone signal and the recorded microphone signal is filtered by means of an adaptive filter. The filtered microphone signal is fed back to an input of a receiver, which is used to output sound into the ear canal. At least a portion of a transducer transfer function defined for the transmission path from the earphone input to the ear canal to the microphone output is measured, and the adaptive filter is adjusted in response to it. A hearing device here means any sound-emitting device that can be worn in or on the ear, such as a hearing aid, a headset, headphones and the like.

Hearing aids are portable hearing aids that are used to care for the hearing impaired. In order to meet the numerous individual needs, different types of hearing aids such as behind-the-ear hearing aids (BTE), hearing aid with external receiver (RIC: receiver in the canal) and in-the-ear hearing aids (IDO), e.g. Concha hearing aids or canal hearing aids (ITE, CIC). The hearing aids listed by way of example are worn on the outer ear or in the ear canal. In addition, bone conduction hearing aids, implantable or vibrotactile hearing aids are also available on the market. The stimulation of the damaged hearing takes place either mechanically or electrically.

Hearing aids have in principle as essential components an input transducer, an amplifier and an output transducer. The input transducer is usually a sound receiver, z. As a microphone, and / or an electromagnetic Receiver, e.g. B. an induction coil. The output transducer is usually used as an electroacoustic transducer, z. As miniature speaker, or as an electromechanical transducer, z. B. bone conduction, realized. The amplifier is usually integrated in a signal processing unit. This basic structure is in FIG. 1 shown using the example of a behind-the-ear hearing aid. In a hearing aid housing 1 for carrying behind the ear, one or more microphones 2 for receiving the sound from the environment are installed. A signal processing unit 3, which is also integrated in the hearing aid housing 1, processes the microphone signals and amplifies them. The output signal of the signal processing unit 3 is transmitted to a loudspeaker or earpiece 4, which outputs an acoustic signal. The sound is optionally transmitted via a sound tube, which is fixed with an earmold in the ear canal, to the eardrum of the device carrier. The power supply of the hearing device and in particular the signal processing unit 3 is effected by a likewise integrated into the hearing aid housing 1 battery. 5

An unpleasant effect when wearing a hearing aid is that your own voice sounds unnatural. This is due to the fact that one's own voice is led via bone conduction into the auditory canal and there causes a certain sound pressure, especially at lower frequencies. If the auditory canal is open, the corresponding pressure waves can be directed to the outside. However, if the auditory canal is closed by the hearing aid, a high sound pressure builds up here, which is called an occlusion effect and, since it is unnatural, is perceived as unpleasant.

A generic method for active occlusion reduction in hearing aids is from the document WO 2004/021740 A1 'and the publication WO 2006/037156 A1 known. The transducer transfer function from the input of the listener via the ear canal to the output of the ear canal microphone is described in detail in the first-mentioned document. It can be determined very accurately in situ with the hearing aid as a measuring device. The Transformer transfer function is complex, ie a function of magnitude and phase versus frequency.

In a not fully adaptive active occlusion reduction implementation, the measured transducer transfer function is used to determine in a computer the optimal configuration of digital signal processing for active occlusion reduction. In principle, this optimization process could also be completely automatic. However, there is the problem that in certain situations, the algorithm is irreversibly incorrectly changed, or that a lot of computing time is needed. In these situations, a manual intervention is necessary or helpful.

The object of the present invention is thus to further automate an adaptive implementation of an active occlusion reduction.

According to the invention, this object is achieved by a method for active occlusion reduction in a hearing device by recording a sound in an ear canal through a microphone with output of a corresponding microphone signal, filtering the microphone signal by means of an adjustable filter, feeding back the filtered microphone signal to an input of a listener who for outputting sound into the ear canal, measuring at least a portion of a transducer transmission function defined for the transmission path from the earphone input via the ear canal to the microphone output, and adjusting the tunable filter in response to the transducer transmission function, the transducer transmission function undergoing an automatic plausibility check and the adjustable filter is only changed if the transducer transfer function is plausible according to a predetermined criterion. The term "adjustable" does not exclude that a Tel of the filter is adaptive, ie is automatically adaptable by an adaptation rule.

In addition, the invention provides a hearing device with active occlusion reduction comprising a receiver for sound output in an auditory canal, a microphone for recording a sound in the ear canal and for outputting a corresponding microphone signal, an adjustable filter for filtering the microphone signal, wherein the filtered microphone signal to the input a measuring device for measuring at least a part of a Wandlerübertragungsfunktion which is defined for the transmission path from the entrance of the listener via the ear canal to the output of the microphone, and an adjusting means for adjusting the adjustable filter in response to the transducer transfer function, and a testing device for the automatic plausibility check of the transducer transfer function, wherein the adjustable filter is only changeable by the adjusting means when the transducer transfer function according to a vo criterion is plausible.

Advantageously, it is checked according to the present invention before the adaptation of Okklusionsreduktionsalogrithmus whether the measured transducer transfer function is plausible. This ensures that the algorithm that determines the optimal configuration does not run into an exceptional situation that makes it difficult or impossible for it to come out. This prevents a too large solution space for the algorithm or an excessive amount of unnecessary computation time.

Preferably, the measured part of the transformer transfer function for the plausibility check is smoothed. Thus, certain measurement uncertainties can be compensated.

Furthermore, it may be advantageous if the transducer transmission function is measured in a first frequency range and extrapolated in a second frequency range on the basis of the measured data using a model. So that can For example, a safely measurable range can be used to estimate a less secure area to be measured for the converter function or the plausibility check.

According to an embodiment variant, the transducer transmission function can be assessed as not plausible if its magnitude in a given frequency range is less than a predetermined threshold. Thus, for example, a blockage of the hearing device with cerumen can be detected.

In addition, the transducer transfer function can also be considered implausible if its phase is within a predetermined frequency range below a predetermined minimum phase. This can also be checked, for example, if one of the components involved is defective or the measurement signal was too quiet.

Furthermore, the transducer transfer function may be considered implausible if its value, including magnitude and phase, is outside a given tolerance tube in the space defined by the coordinates, phase and frequency. With such a tolerance tube, it can be detected whether the hearing device works correctly within a certain scope. However, the tolerance tube can also be used to keep the computing time for the change of the algorithm within a certain range. For example, if the transducer transfer function is not in a very tight tolerance tube, changing the algorithm may quickly bring about a small change in the fit of the hearing aid in the ear, and a longer computation time can be avoided.

FIG 1

den prinzipiellen Aufbau eines Hörgeräts gemäß dem Stand der Technik;

FIG 2

eine Prinzipskizze eines In-dem-Ohr-Hörgeräts mit den wesentlichen Komponenten zur aktiven Okklusionsreduktion;

FIG 3

eine hochpassartige Wandlerübertragungsfunktion und

FIG 4

ein Blockdiagramm zur erfindungsgemäßen Plausibilitätsprüfung für Wandlerübertragungsfunktionen.

The present invention will be further explained with reference to the accompanying drawings, in which:

FIG. 1

the basic structure of a hearing aid according to the prior art;

FIG. 2

a schematic diagram of an in-the-ear hearing aid with the essential components for active occlusion reduction;

FIG. 3

a high-pass type transformer transfer function and

FIG. 4

a block diagram of the inventive plausibility check for transformer transmission functions.

The embodiments described in more detail below represent preferred embodiments of the present invention.

In FIG. 2 is an ITE hearing aid 10 shown in cross section, as it is inserted into an ear canal 11. The ear canal 11 is closed by a tympanic membrane 12. Between the eardrum 12 and the eardrum end of the ITE hearing aid 10 results in a closed space 13. The seclusion of this space leads to the known, unpleasant Okklusionseffekten.

The ITE hearing aid 10 has an outwardly directed microphone 14 in order to record the ambient sound (see microphone 2 of FIG FIG. 1 ). The microphone signal is forwarded to a signal processing unit 15, which processes and amplifies the signal in the usual way (compare signal processing unit 3 of FIG FIG. 1 ). In the usual way, the processed signal is supplied to a receiver 16 or 4, which converts the signal into a sound and emits it into the auditory canal 13. Due to the own voice, an unnaturally high noise sound pressure arises in the ear canal space 13 due to the occlusion by the ITE hearing device 10 (for example also in the case of an earpiece of a BTE hearing device). This can be passively activated by a vent or active with the in FIG. 2 Reduce the circuitry shown (short: occlusion reduction). With an auditory canal microphone 17, the sound in the ear canal space 13, which contains the increased proportion due to their own voice, is recorded. The output signal of the auditory canal microphone 17 is fed back via a loop filter 18 to the input of the receiver 16 with a negative sign, possibly via further digital signal processing elements (eg AD converters). The single transfer functions are R, V, M and S. This results in the feedback function 1 / (1+ RVMS). This applies, for example, to keep less than 1 for a frequency range of 200 to 300 Hz. The transfer functions R of the earpiece 16 and M of the auditory canal microphone 17 are specified device-specific. The transfer function V represents the acoustic signal path in the auditory canal space 13 from the earpiece 16 to the auditory canal microphone 17. It depends on the individual shape of the auditory canal 11, on the depth of insertion of the ITE hearing device 10, on the shell shape of the ITE device 10, but also on the degree of occlusion. However, for a particular wearing situation, this transfer function V is fixed. On the other hand, the transfer function S of the loop filter 18 is variable. It is, for example, the one in the publication WO 2004/021740 A1 adapted manner, so that the occlusion effect is reduced as much as possible. For this purpose, the transducer transmission function of the transmission path 19 from the input of the handset 16, through the ear canal space 13 to the output of the ear canal microphone 17, ie the product RVM, measured. This measured transducer transfer function RVM of the transmission path 19 is complex, ie both the amplitude and the phase of a signal is influenced during the transmission. Depending on the feature (eg hearing device is too loose), it is better to evaluate the amplitude, the phase information or other properties of the measured transducer transfer function RVM.

However, it may be the case that the system itself is out of order or unable to operate properly. This is the case, for example, when the handset 16 or auditory canal microphone 17 has failed, or the sound output of the handset 16 and / or the sound output of the auditory canal microphone 17 is blocked by cerumen. In such cases, the transformer transfer function is not plausible. With a Plausibility check these cases can be detected. It follows the principle of the block diagram of Fig. 4 , In this case, the transducer transfer function is measured in a first step S1. Under certain circumstances, the measurement data scatter strongly, so that according to step S2 a smoothing of the raw data of the measured transfer function is necessary. Furthermore, it may be necessary to extrapolate the measured data. For certain frequencies, especially low frequencies, it is usually difficult to determine the transducer transfer function. The accuracy for this frequency range can be increased by determining model-based parameters in a higher frequency range and applying this model in the poorly measurable frequency range.

The extrapolation of the transformer transfer function can be performed using the example of a first order high pass according to FIG. 3 be explained. The transfer function of a first-order high pass is completely described by the corner frequency f _g . If it is known that a first-order high pass is present in an unknown system to be measured, only the corner frequency f _g needs to be determined. The model parameter corner frequency f _g is determined by taking measurement data from a frequency range classified as "reliable". In the example of FIG. 3 is the phase φ and the amplitude A of a high-pass first order including the corner frequency f _g shown. The data in the high-frequency range are classified as reliable and therefore the amplitude A and the phase φ is drawn there with a solid line. The course of the transducer transfer function in the lower frequency range, however, is uncertain due to the measurements. With the reliable data from the high-frequency range, the parameter corner frequency f _g is determined by varying the cut-off frequency f _{g of} a parameterizable high-pass transfer function such that the measured data coincide as far as possible with the correctly parameterized high-pass transfer function. The high-pass transfer function thus found is now used for the non-reliably measurable, here the low, frequency ranges (see dashed amplitude). and phase history in FIG. 3 ). Thus, the measured and supplemented by extrapolation transformer transfer function for the plausibility check can now be evaluated.

When the transmission path 19 is blocked from the input of the listener 16 to the output of the auditory canal microphone 17, the amount of the transfer function RVM is small for a certain frequency range. With regard to the plausibility, it is therefore necessary to extract the amplitude of the transfer function or to evaluate its value in accordance with step S3. As a result, cases can be detected in which the handset 16 or the ear canal microphone 17 are defective. But it may also be blocked the acoustic transmission path from the listener to the microphone, z. B. by clogging with cerumen.

Furthermore, according to step S4, the phase of the transducer transfer function can be extracted. With regard to the plausibility check, it is known that the phase can not assume any values at low frequencies in the range of 100 Hz. Through a series of high passes (listener, microphone, analogue microphone preamplifier) a minimum phase is given at low frequencies. The typical value of the minimum phase can be specified depending on the converter. If there is a lower measured phase than the minimum phase, the measurement result itself does not have to be in order. For example, the measurement signal may have been too quiet if the S / N ratio was temporarily too low. In this case, the measurement must be repeated with a louder measurement signal in order to obtain a valid measurement result.

Under certain circumstances, the measured transducer transfer function according to step S1 or a transfer function prepared according to step S2 can also be evaluated directly, which is indicated by the arrow S5 in FIG FIG. 4 is indicated. In most cases, however, it is favorable to perform a normalization of the transfer function at an arbitrary frequency for the evaluation, which is indicated by step S6 in FIG FIG. 4 is indicated.

The data obtained from steps S3 to S6 can now be compared, for example, with certain threshold values or evaluated on the basis of specific criteria in accordance with step S7. For example, as mentioned, the phase can be compared to a minimum phase. Also, the amount of the transfer function should not be below a minimum amount for a larger frequency range. The normalized measured or extrapolated transfer function, which in fact represents a spatial curve in the amplitude-phase frequency space, can be compared, for example, with a tolerance tube around this curve. If the tolerance hose is never left, the measured transfer function is accepted as valid or plausible. Thus, based on the comparison of step S7 in step S8, a decision is made as to whether the transfer function is valid or not valid or plausible or not plausible. Only after decided plausibility is the occlusion reduction optimized by adapting the loop filter S.

The advantage of this approach is that only meaningful transducer transfer functions are used for determining the optimal configuration of the signal processing (in particular the loop filter). The optimization algorithm is thus protected from converging into an unfavorable state by an inappropriate transducer transfer function. Overall, this leads to a limitation of the solution space for the algorithm and thus to a shortening of the computation time. Furthermore, given certain properties of the measured transfer function, an indication of the cause of the fault can be given. Thus, for example, the indication of a leak can be given if the cutoff frequency of the high-pass transfer function is relatively high.

Claims (7)

A method for active occlusion reduction in a hearing by - Recording a sound in an ear canal (13) by a microphone (17) with the output of a corresponding microphone signal, Filtering the microphone signal by means of an adjustable filter (18), - Feedback the filtered microphone signal to an input of a handset (16), which serves for sound output into the ear canal (13), - Measuring at least a part of a transducer transfer function (RVM), which is defined for the transmission path (19) from the input of the listener (16) via the ear canal (13) to the output of the microphone (17), and Adjusting the adjustable filter (18) in dependence on the transformer transfer function (RVM), characterized in that - The transformer transfer function is subjected to an automatic plausibility check and - The adjustable filter (18) is only changed if the transducer transfer function (RVM) is plausible according to a predetermined criterion. The method of claim 1, wherein the measured part of the transducer transfer function (RVM) for the plausibility check is smoothed. The method of claim 1 or 2, wherein the transducer transfer function (RVM) is measured in a first frequency range and thus extrapolated in a second frequency range. Method according to one of the preceding claims, wherein the transducer transfer function (RVM) is considered implausible if its amount in a predetermined frequency range is less than a predetermined threshold. Method according to one of the preceding claims, wherein the transducer transfer function (RVM) is considered implausible if its phase is within a predetermined frequency range below a predetermined minimum phase. Method according to one of claims 1 to 3, wherein the transducer transfer function (RVM) is considered implausible if its value including magnitude and phase outside a predetermined tolerance hose in the space, which is defined by the coordinates of magnitude, phase and frequency. Comprising hearing device with active occlusion reduction a receiver (16) for sound output in an auditory canal (13), a microphone (17) for picking up a sound in the ear canal (13) and outputting a corresponding microphone signal, - An adjustable filter (18) for filtering the microphone signal, wherein the filtered microphone signal is fed back to the input of the listener (16), - A measuring device for measuring at least a part of a transducer transfer function (RVM), which is defined for the transmission path (19) from the input of the listener (16) via the ear canal (13) to the output of the microphone (17), and a setting device for setting the adjustable filter (18) as a function of the transducer transfer function (RVM),
marked by - A test device for automatic plausibility test of the transformer transfer function (RVM), wherein - The adjustable filter (18) by the adjusting means is changeable only if the transducer transfer function (RVM) is plausible according to a predetermined criterion.

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