EP2226795B1 - Hearing aid and method for reducing noise in a hearing aid - Google Patents

Description

The invention relates to a hearing device and a method for reducing a noise for a hearing device. The term hearing device is understood in particular to mean a hearing device. In addition, however, the term includes other portable acoustic devices such as headsets, 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 (ITE), 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, for. 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 into 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

A signal processing unit of a hearing device can also be designed to reduce unwanted noise in a microphone signal of the hearing device. With such a noise reduction, an auditory quality of the acoustic signal output from the hearing aid can be improved. For example, a noise may originate from noise sources in an environment of the equipment carrier. It is therefore detected by the microphones of the hearing aid together with the sound that is to be processed as useful sound from the hearing aid for the equipment wearer.

Noise reduction is in many cases achieved by using an input signal, e.g. a microphone signal or even for individual spectral components of the microphone signal, continuously an attenuation factor is calculated. An attenuation factor can have a value between 0 and 1. A small value results whenever a noise dominates in an input signal of the noise reduction. An attenuation factor is often calculated on the basis of an estimate for a signal-to-noise ratio. An example of such a noise reduction is the Wiener Filter.

An improved output eventually results when the input signal is multiplied by the corresponding attenuation factor. Also, for noise reduction algorithms where a damping factor is not explicitly calculated, a corresponding damping value can be determined. This value then results as the ratio of a value of an output signal produced by the noise reduction to the corresponding value of the input signal.

For reducing a noise in a microphone signal, different methods are known. All methods have in common that they must be able to distinguish between a useful sound and a noise.

Between a useful sound and a noise can be effectively distinguished in many cases when it is checked for an input signal, whether the input signal is stationary in the statistical sense. Many sounds, such as The noise of a ventilation, their statistical properties namely, in comparison to, for example, a voice of a person speaking often very slowly. Therefore, it is assumed in these methods that stationary sections of the input signal are to be associated with unwanted noise and can be correspondingly attenuated.

Disadvantage of such a noise reduction for stationary noise, however, is that it can be damped with poor non-stationary noise. Non-stationary noise is referred to herein as transient noise. An example of a transient noise is the cracking of a door that is slamming or the clattering of clanging dishes. Another disadvantage of many methods of reducing stationary noise is that they produce unwanted artifacts in the processed signal in transient noise.

Another way to distinguish between a useful sound and a noise is used in a multi-microphone arrangement. Thus, an incident direction can be determined, from which a sound or spectral components of a sound strike the arrangement. Depending on the direction of incidence, a distinction is made between useful sound sources and noise sources.

In order for a direction of incidence of a sound to be determined, however, the sound must be spatially directed. In other words, sound waves of the sound must show a propagation direction. Only then can a sound be assigned a spatial position of a sound source with respect to the microphone arrangement. Allocation becomes increasingly difficult as more reverb mixes with a direct sound source sound. Much reverb occurs especially in closed rooms. A disadvantage of a noise reduction for spatially directed noise is thus that it is only suitable for noise, for which an incident direction of the noise can be determined.

From the publication DE 199 44 467 A1 a method for reducing acoustic noise is known. In these generic methods, signals are received via a plurality of microphones and processed with at least one of the stored noise reduction algorithms. If the noise situation matches the requirements of the at least one noise reduction algorithm, the interference signals are reduced compared to the useful signals. The noise reduction algorithms can be switched on and off separately. In the analysis of the signals, characteristic parameters for the noise field are determined, which are assigned to the individual noise reduction algorithms as typical parameters, and depending on the characteristic parameters, the associated noise reduction algorithm is selected.

In addition, the document reveals US 2006/0120540 A1 a method of processing acoustic signals. Adaptive noise cancellation is used in parallel with wind noise reduction. The wind noise suppression is activated when the wind noise exceeds a predetermined level.

In the publication US 6,751,325 B1 a method for processing microphone signals in a hearing aid is described. The microphone signals are subjected to side signal reduction and return signal reduction, and mixed in response to signal analysis.

Furthermore, in the document EP 0 883 325 A2 a multi-strategy array processor is described. Each processor has a different signal-to-noise performance. Depending on the ambient noise, the outputs of the processors are summed to obtain a signal in the beam direction of a microphone array.

It is an object of the present invention to provide an improved noise reduction for a hearing device, with which both stationary and transient noises in an input signal of the hearing device can be damped.

The object is achieved by a hearing device according to claim 1. The object is also achieved by a method according to claim 6. Advantageous developments of the invention are given by the dependent claims.

The hearing device according to the invention has a first reduction device for reducing stationary noise of an input signal and a second reduction device for reducing interference noise spatially directed relative to the hearing device. Furthermore, a hearing device according to the invention has a selection device for selecting the first and / or the second reduction device for an output signal to be formed from the input signal.

• Analysieren eines Eingangssignals,
• Auswählen zwischen oder Kombinieren von einer Geräuschreduktion für stationäre Störgeräusche und einer Geräuschreduktion für räumlich gerichtete Störgeräusche in Abhängigkeit von dem Ergebnis der Analyse und
• Erzeugen eines Ausgangssignals aus dem Eingangssignal mittels der ausgewählten Geräuschreduktion oder der kombinierten Geräuschreduktionen.

With such a hearing device, a method according to the invention for reducing a noise for a hearing device can be applied, comprising the following steps:

• Analyzing an input signal,
• Selecting or combining a noise reduction for stationary noise and a noise reduction for spatially directed noise depending on the result of the analysis and
• Generating an output signal from the input signal using the selected noise reduction or the combined noise reduction.

With the hearing device and the method for reducing a noise can be attenuated advantageously stationary noise with a specialized noise reduction for stationary noise. At the same time, however, whenever the noise reduction for stationary noise is inappropriate for attenuating a certain noise, it is possible to resort to the advantages of noise reduction for spatially directed noise.

The invention is based on the finding that in particular a transient noise with a reduction device for reducing spatially directed noise can often be damped much more effectively than is possible with a reduction device for reducing stationary noise.

The selector selects between the reducers depending on a criterion for the stationarity of the input signal. A criterion for stationarity can simply be the information as to whether an input signal is stationary in the statistical sense or not. However, the criterion can also be a continuous measure.

According to the hearing device, the method according to the invention is developed in an advantageous manner, by analyzing the input signal for stationarity.

By determining a stationarity of the input signal, it can be decided in a particularly reliable manner whether a noise reduction for stationary noise or a noise reduction for spatially directed noise results in an output signal with a better auditory quality.

A hearing device according to the invention is advantageously further developed if the selection device evaluates as a criterion for the stationarity a value of a damping factor of the first reduction unit or an estimated value for a signal-to-noise ratio of the first reduction unit. Accordingly, the inventive method can be further developed. By evaluating the attenuation factor or the signal-to-noise ratio estimate, there is the advantage that it can reliably be determined from these quantities when reducing noise based on the first reduction unit is not sufficiently accomplished to achieve high auditory quality ,

The hearing device according to the invention is further developed in an advantageous manner if the two reduction devices are designed to perform the respective reduction and the selection device to perform the selection for a plurality of different frequency bands. This results in a particularly high auditory quality of the output signal. The method according to the invention can be developed accordingly.

A further advantage results if in the hearing device according to the invention the damping factor of the first reduction unit is limited to small values by an anchor gain value and if by the second reduction unit a Damping is generated, which corresponds to a value for a damping factor less than the anchor gain value. An anchor gain value is to be understood as a minimum value which is used for damping instead of the damping factor of the first reduction device whenever a calculation for this damping factor according to a noise reduction algorithm yields a value smaller than the anchor gain value , By applying an anchor gain value for the attenuation factor of the first reduction unit and at the same time allowing smaller values for the attenuation by the second reduction unit, the hearing aid is able to effectively attenuate both stationary and transient noises in an input signal without the auditory quality of the output signal is affected, for example, by artifacts generated by the noise reduction. A corresponding development of the method according to the invention is likewise possible.

Furthermore, the hearing device according to the invention is further developed in an advantageous manner in the case of the hearing device, when the selection results in a change from one of the two reduction devices to the other reduction device, blending the selection device from one reduction device to the other reduction device. A cross-fade here means that it is not instantaneously switched, for example, from the second reduction unit to the first reduction unit, when the input signal has initially behaved in an instantaneous manner and then it is recognized that it is now stationary. Instead of an instantaneous changeover or switching over, the effect of the cross-fading is rather to mix, for example, attenuation factors of both reduction units or output signals calculated with both reduction units during a transition that is limited in time. Mixing can be done, for example, by weighted addition. The method according to the invention can be developed accordingly.

Crossfading reduces audible switching effects when switching between the two reduction units.

The second reduction device is designed to attenuate signals of a sound when the sound hits the hearing device from a predetermined direction. Accordingly, the method according to the invention is further developed in that the sound reduction for spatially directed interference noises signals of a sound are attenuated when the sound is received from a predetermined direction.

A predetermined direction provides the advantage that artifacts in the output signal are avoided for noise reduction for spatially directed noise. This contributes to a high auditory quality of the output signal.

FIG 1

eine Darstellung eines schematischen Aufbaus eines Teils eines Hinter-dem-Ohr-Hörgeräts aus dem Stand der Technik,

FIG 2

einen Signalflussplan für ein Hörgerät gemäß einer Ausführungsform einer erfindungsgemäßen Hörvorrichtung und

FIG 3

Diagramme, in denen jeweils ein zeitlicher Verlauf von einer Größe gezeigt ist, wobei sich alle Verläufe bei einem Hörgerät gemäß einer weiteren Ausführungsform einer erfindungsgmäßen Hörvorrichtung ergeben.

The invention will be explained in more detail below with reference to examples. To show:

FIG. 1

FIG. 4 is an illustration of a schematic structure of a portion of a prior art behind-the-ear hearing aid; FIG.

FIG. 2

a signal flow diagram for a hearing aid according to an embodiment of a hearing device according to the invention and

FIG. 3

Diagrams in each of which a time course of one variable is shown, wherein all courses in a hearing aid result according to a further embodiment of a hearing device according to the invention.

The examples illustrate preferred embodiments of the invention.

In FIG. 2 is shown as in a hearing aid that is in FIG. 2 not shown further, from an input signal by means of a signal processing 6, an output signal is generated. In the output signal, a noise contained in the input signal is reduced.

The input signal for the signal processing 6 is decomposed by a filter bank 7 into its spectral components. This means here that for different frequency bands contained therein portions of the input signal are determined. The values for the determined spectral components are transferred to a noise reduction 8 for stationary noises and a noise reduction 9 for spatially directed noises. The spectral components are in the example of FIG. 2 independently processed by the signal processing 6. In FIG. 2 Therefore, only the signal flow chart for values of a single spectral component is shown. This is symbolized by simple connecting lines between the blocks of the signal flow diagram. The remaining spectral components are processed in the signal processing 6 in a comparable manner.

From the noise reduction 8 for stationary noises, an attenuation factor is calculated, which is adjusted as a function of the input signal with time. By means of a limiter 10, the calculated damping factor is set to an anchor gain value if the calculated damping factor is less than the anchor gain value. In the example, the anchor gain value provides a 10 dB attenuation. In other words, the gain of the input signal is -10 dB due to the achor gain value. The possibly corrected attenuation factor output by the limiter 10 is offset with the input signal. In FIG. 2 Thus, the output of the limiter 10 is a processed signal.

The method used in the noise reduction 8 for calculating the damping factor in combination with the limiter 10 generates a low-artifact, quiet sound impression of the processed signal in that for stationary noise, the reduction of a fixed lower bound, the anchor-gain value, not lower. In stationary noise, this maximum value of the reduction is also usually achieved, so that there is a nearly constant damping. This causes the quiet sound impression.

The noise reduction 9 for spatially directed noise is able to attenuate the signal of a sound that hits the equipment carrier from behind. At the same time, the signal of a sound source remains undamped by the noise reduction 9, when the device carrier turns straight to this sound source. The sound then hits the gear tray from the front.

The input signal is a multi-channel signal. It is composed of several microphone signals of a microphone arrangement of the hearing aid. In FIG. 2 It is not indicated in any particular way that the connecting lines between the blocks of the signal flow diagram can be multi-channel connections.

The directional damping by the noise reduction 9 is achieved by a so-called beamforming, which combines corresponding spectral components of the different channels. The attenuation of a noise caused by the noise reduction 9 may be more than 10 dB in particular. The damping is therefore not limited in the case of noise reduction 9. In the example of FIG. 2 The noise reduction 9, like the limiter 10, outputs a processed signal which is single-channeled.

From the two processed signals, namely that of the limiter 10 and the noise reduction 9, an output signal is formed by a mixer 11. This output signal is then converted by a synthesis unit 12 into an audio signal.

The mixer 11 is controlled by an analysis unit 13. The analysis unit 13 examines each spectral component of the Input signal as to whether he is stationary in a statistical sense or not. For periods of time for which the spectral components are stationary, the mixer 11 is controlled so that only the processed signal of the limiter 10 is output as an output signal to the synthesis unit 12. If, however, a spectral component is unsteady, the mixer 11 switches over to the output of the noise reduction 9. If this results in a change from the output of the noise reduction 9 back to the limiter 10, it is not simply switched back. Instead, the analysis unit 13 controls the mixer 11 in such a way that, within a period of one second, it is gradually faded in from the output of the noise reduction 9 to the output of the limiter 10.

The analysis unit 13 not only examines the spectral components of the input signal. Also, the attenuation factor calculated by the noise reduction 8 is observed. This is in FIG. 2 symbolized by a dashed box. If the attenuation factor for a spectral component has a value less than or equal to the anchor gain value, then the analysis unit 13 indicates that the spectral component is stationary. Similarly, if the damping factor is above the anchor gain, then it is decided upon instationarity. Since the signal of the filter bank 7 is also directly observed by the analysis unit 13, further analysis steps can be carried out in order to recheck the analysis which was carried out on the basis of observation of the damping factor.

The five diagrams D1 to D5 in FIG. 3 show temporal courses of each one size, as they are for one in FIG. 3 not shown hearing aid revealed. In all five diagrams horizontally running time axes are scaled identically, so that simultaneous changes of the quantities in FIG. 3 lie on a common vertical axis.

Diagram D1 shows a time profile of a spectral portion 14 of a microphone signal originating from one of several microphones of the hearing aid. The time profile of the spectral component represents an input signal in the sense of the invention. The spectral component 14 behaves stationary in a statistical sense in a total of three time segments 15a, 15b, 15c. Namely, in the periods 15a, 15b, 15c, the spectral component has a constant statistical average and a constant variance. The microphone signal is determined for the periods of time 15a, 15b, 15c predominantly by a fan whose uniform noise is detected by the microphones of the hearing aid.

In two time periods 16a, 16b, the stationary signal of the fan noise is drowned out by a sound signal. This results in a total of the time segments 16a, 16b, a transient course of the spectral component 14. The first sound signal detected in the period 16a, it is the speech signal of a speaker. The speaker faces a wearer of the hearing aid. Thus, the voice of the speaker from the front hits the intended worn hearing aid. The transient course during the period 16b is caused by the popping of a door that falls behind the wearer of the hearing aid in a lock. The sound generated by the random door thus hits the hearing aid from behind.

In the diagram D2, the course 17 of a gain V is shown, as it is caused by a noise reduction in the hearing aid for stationary noise for the spectral portion 14. An attenuation factor of the noise reduction is limited by a limiter to an anchor gain value at the bottom. This results in a minimum value of the gain V of -10 dB. This minimum value has the gain V in the periods 15a, 15b, 15c when the spectral component 14 is stationary. In the time segments 16a, 16b, for which the spectral component 14 is transient, the noise reduction effects for stationary noise here almost no damping. The spectral component 14 is attenuated, that is, transmitted with a gain V of almost 0 dB by the noise reduction for stationary noise.

In the diagram D3 an analysis result 18 of an analysis unit is shown, which corresponds to the in FIG. 2 similar to the analysis unit 13 shown. It was correctly recognized by the analysis unit that the spectral component 14 behaves unsteadily in the time segments 16a and 16b. The analysis result 18 therefore changes from "stationary" to "unsteady" for the time segments 16a and 16b. In Diagram D3, these two possible analysis results are "stat." and "instat." abbreviated. The analysis result 18 is based here on the profile 17 of the gain V. The analysis result 18 shows that the profile of the spectral component 14 here becomes subdivided into two mutually exclusive classes, namely in time segments 15a, 15b, 15c, in which the signal is classified as stationary, and in periods 16a, 16b in which the signal is classified as transient.

In the diagram D4, a curve 19 of a gain V 'is shown, which is caused by a likewise present in the hearing aid noise reduction for spatially directed noise in the spectral component 14. By this second method for noise reduction, a signal of a sound that strikes the wearer of the hearing aid from the front is not attenuated. In contrast, a signal of sound striking the back of the hearing aid wearer is attenuated by up to 20 dB due to the cardioid characteristic of a beamformer of noise reduction for spatially directed noise. For the noise reduction for spatially directed noise but can also be provided a lower limit. For example, this limit can be -18 dB.

The gain V ', unlike the gain V, is not limited to small values. That's why she can be special even smaller than -10 dB fail. However, their course is also not constant for those time segments 15a, 15b, 15c in which the spectral component 14 is stationary. The course 19 is uneven in the time intervals 15a, 15b, 15c, because a reverberation in the surroundings of the device carrier causes the noise of the fan to strike the microphones of the hearing device from a constantly changing direction.

The speech signal of the speaker striking the hearing aid from the front in the period 16a is not audibly changed by the noise reduction for spatially directed noise. Namely, the gain V 'for the period 16a is almost 0 dB. In contrast, the pop of the door, which strikes the wearer's wearer from behind in the period 16b, is very effectively suppressed with a gain V 'of -20 dB.

Diagram D5 shows a profile 20 of an overall gain V '' which results during the processing of the spectral component by the signal processing 6. The processed spectral component is combined together with the parallel processed spectral components to form an output signal from which a hearing signal for the wearer of the hearing aid is formed by the hearing aid. The curve 20 results from a selection between the results of the noise reduction, by which the gain V is effected, and the noise reduction, by which the gain V 'is effected. The selection is made according to the analysis result 18. In this case, the noise reduction for stationary noise is selected for the time intervals 15a, 15b and 15c, so that a nearly constant gain of -10 dB results for the overall gain V ". For the periods 16a and 16b, the noise reduction is selected for spatially directed noise. Accordingly, there is a very effective damping for the pop of the door in the period 16b. The gain V '' is then -20 dB. On the other hand, the speech signal detected during the period 16a becomes is not distorted, so that the wearer of the hearing aid can understand the speaker well.

For the overall gain V ", there is no limit to small values. Nevertheless, the steady-state gain for fixed sounds is always fixed, namely the limit of -10 dB for noise reduction for stationary noise. This limitation thus forms an anchor for the overall gain V "in the case of stationary noise. Starting from the anchor value, the total gain V '' may shift to higher values when transient sound is coming from the front. However, it can also be changed to smaller values if a transient sound comes from behind. In a stationary noise, therefore, a lower limit is effective, in a transient sound, however, not. This gives the wearer of the hearing aid a quiet sound impression at the same time high attenuation for unsteady noise.

Overall, the wearer of the hearing aid thus perceives an output signal which has a better auditory quality than in a hearing aid in which only a simple noise reduction is provided.

LIST OF REFERENCE NUMBERS

1

hearing aid housing

2

microphone

3

Signal processing unit

4

receiver

5

battery

6

signal processing

7

filter bank

8th

noise reduction

9

noise reduction

10

limiter

11

mixer

12

synthesis unit

13

analysis unit

14

spectral component

15a, 15b, 15c

period

16a, 16b

period

17

course

18

analysis result

19

course

20

course

D1 to D5

diagram

V, V '

reinforcement

V '

overall gain

Claims (6)

1. Hearing apparatus having

   - a first reduction device (8) for reducing steady-state interference noise in an input signal,

   - a second reduction device (9) for reducing interference noise directed three-dimensionally with regard to the hearing apparatus, and

   - a selection device (11, 13) for selecting the first (8) and/or the second (9) reduction device for an output signal that can be formed from the input signal,

   - wherein the selection device (11, 13) takes a criterion for the steady-state nature (18) of the input signal as a basis for selection,

   - wherein the second reduction device (9) is designed to attenuate signals for a sound if the sound hits the hearing apparatus from a predetermined direction,

   characterized
   in that the selection device (11, 13) selects the first reduction device (8), which is designed to reduce steady-state interference noise in the input signal, when the input signal is in the steady state, and selects the second reduction device (9) when the input signal is transient.
2. Hearing apparatus according to Claim 1,
   in which the selection device (11, 13) evaluates a value (17) of an attenuation factor (V) of the first reduction unit (8) or an estimate for a signal-to-noise ratio of the first reduction unit (8) as a criterion for the steady-state nature (18).
3. Hearing apparatus according to either of the preceding claims, in which the two reduction devices (8, 9) are designed to perform the respective reduction and the selecting device (11, 13) is designed to perform the selection for multiple different frequency bands (14).
4. Hearing apparatus according to one of the preceding claims, in which the attenuation factor (V) of the first reduction unit (8) is limited to small values by an anchor gain value and in which the second reduction unit (9) can produce an attenuation (V') that corresponds to a value for an attenuation factor smaller than the anchor gain value.
5. Hearing apparatus according to one of the preceding claims, in which, if the selection results in a change from one of the two reduction devices to the other reduction device, then the selection device changes over from one reduction device to the other reduction device.
6. Method for reducing interference noise for a hearing apparatus, having the steps of:

   - analysis (13) of an input signal (14) with regard to a steady-state nature (18),

   - selection (11) between or combination (11) of a first noise reduction (8) for reducing steady-state interference noise in the input signal and a second noise reduction (9) for reducing interference noise in the input signal that is directed three-dimensionally with regard to the hearing apparatus on the basis of the result (18) of the analysis, wherein the second noise reduction (9) attenuates signals for a sound when the sound hits the hearing apparatus from a predetermined direction, and

   - production of an output signal from the input signal (14) by means of the selected noise reduction (8, 9) or the combined noise reductions (8, 9), characterized in that

   - the first noise reduction (8) is selected when the input signal is in the steady state, and the second noise reduction (9) is selected when the input signal is transient.

Images