EP2239962B1 - Assembly and method for recognising feedback in hearing aids - Google Patents

Description

The invention relates to a specified in the independent claims arrangement and a method for better detection of feedback in hearing aids.

A common problem with hearing aids is the acoustic feedback between the output of the hearing aid and the input, which is annoying as feedback whistles. FIG. 1 shows the principle of acoustic feedback using the example of a hearing aid 1. The hearing aid 1 comprises a microphone 2, which receives a useful acoustic signal 10, converts it into an electrical microphone signal 11 and outputs it to a signal processing unit 3. In the signal processing unit 3, the microphone signal 11 is, among other things, processed and amplified and output as a receiver signal 12 to a receiver 4. In the receiver 4, the electrical receiver signal 12 is again converted into an acoustic output signal 13 and delivered to the eardrum 7 of a hearing aid wearer.

The problem now is that a part of the acoustic output signal 13 passes through an acoustic feedback path 14 to the input of the hearing device 1, where it is superimposed with the useful signal 10 and recorded as a sum signal from the microphone 2. With a suitable phase position and amplitude of the fed-back output signal, disturbing feedback whistling occurs. In particular, by an open hearing aid supply, the attenuation of the acoustic feedback is low, whereby the problem is exacerbated.

To solve the problem adaptive systems for feedback suppression have been available for some time. In this case, the acoustic feedback path 14 is digitally reproduced. The replication takes place, for example, by means of an adaptive compensation filter 5, which is generated by the receiver signal 12 is fed. After filtering in the compensation filter 5, a filtered signal 15 is subtracted from the microphone signal 11. Ideally, the effect of the acoustic feedback path 14 is thereby canceled.

For an effective feedback suppression, a control of the adaptation of the filter coefficients of the adaptive compensation filter 5 is required. This is done via the so-called step size. It indicates at which speed the adaptive compensation filter 5 adapts to the acoustic feedback path 14. Since there is no meaningful compromise for a set increment, it must be adapted to the current listening situation. Basically, a large step size for a fast adaptation of the filter coefficients to the acoustic feedback path 14 is desirable. However, the disadvantage of large step sizes is the generation of perceptible signal artifacts.

For a far subcritical feedback case, however, the step size should be negligible. But if a critical feedback situation occurs, the step size should be large. This ensures that the filter coefficients of the compensation filter 5 are changed only if their transfer characteristic differs appreciably from the characteristic of the acoustic feedback path 14, i. if there is a need for a post-adjustment. To control the step size, a feedback detection unit 6 is required which detects feedback from the microphone signal 11 or at least roughly estimates the probability or to what extent a feedback is applied to the microphone 2.

1. a) Pegelvergleiche: werden sinusartige Signale (Spitzen im Spektrum) bei höheren Frequenzen gefunden, so kann von Rückkopplungspfeifen ausgegangen werden. Diese Lösung ist einfach und schnell, aber oft sehr ungenau.
2. b) Tonalitätserkennung: der Grad der Tonalität eines Signals wird erkannt, wobei wieder bei höheren Frequenzen auf Rückkopplungspfeifen geschlossen werden kann. Diese Lösung ist etwas genauer als eine reine Pegelbetrachtung, aber auch etwas langsamer.
3. c) Detektion einer Phasenmodulation: dem Ausgangssignal wird eine unhörbare Phasenmodulation aufgeprägt, die am Mikrofon detektiert werden kann. Diese Lösung ist sehr genau, aber langsam.

To control the step size, or to control a feedback suppression in general, several solutions are available. When choosing a suitable solution, it usually takes a trade off between speed and accuracy of detection. Exemplary solutions are:

1. a) Level comparisons: if sinusoidal signals (peaks in the spectrum) are found at higher frequencies, then feedback whistles can be assumed. This solution is simple and fast, but often very inaccurate.
2. b) Tonality detection: the degree of tonality of a signal is detected, which can be concluded at higher frequencies on feedback whistles again. This solution is a bit more accurate than a pure level view, but also a bit slower.
3. c) detection of a phase modulation: the output signal is an inaudible phase modulation impressed, which can be detected on the microphone. This solution is very accurate, but slow.

When selecting a suitable solution, it is necessary to balance the recognition accuracy with the recognition speed. If the feedback detection is fast or set quickly, the error detection rate often increases significantly.

The EP 1 858 289 A1 discloses a hearing apparatus comprising analyzing means for analyzing the resonance behavior of the whole system in response to a modification of the signal processing means and for determining a feedback quantity representing a measure of the feedback from the analysis result. The feedback quantity can be used to control an adaptive compensation filter to compensate for the feedback in its step size.

The DE 199 04 538 C1 discloses a method for feedback detection in a hearing aid, wherein a frequency band is determined, a first signal level in the frequency band is determined, the signal is attenuated on a signal transmission path of the hearing aid and a second signal level of the attenuated signal in the frequency band is determined, and a feedback on the Basis of the determined first and second Signal level is detected. An associated hearing aid has corresponding features.

It is an object of the invention to overcome this disadvantage and to provide arrangements and methods which enable safe and fast feedback detection in hearing devices.

According to the invention, the stated object is achieved with the arrangement and the method of the independent claims.

The invention claims a device for detecting acoustic feedback in a hearing device with a first feedback detection unit receiving a microphone signal of the hearing device, which determines a feedback probability, with a second feedback detection unit receiving the microphone signal of the hearing device, which regulates a threshold value as a function of the occurrence of feedback the threshold value (20) lies between the values "0" for the secure presence of a feedback and "1" for the secure absence of feedback, the first and second feedback detection units (61, 62) having different feedback detection algorithms, and a comparison unit which compares the feedback probability with the threshold value and signals that the threshold value has been exceeded. The advantage of this is that, for example, the feedback suppression in hearing aids can be optimized and the feedback detection can adapt to the characteristics and habits of a hearing aid wearer.

In a further development, the arrangement may comprise a linking unit which combines a feedback detection signal of the second feedback detection unit with the signal which signals an exceeding of the threshold value. In a development, the detection of acoustic feedback in different predetermined frequency bands can be done.

The invention also claims a hearing aid with at least one microphone, with at least one earpiece and with an arrangement according to the invention.

• Ermitteln einer Rückkopplungswahrscheinlichkeit durch eine ein Mikrofonsignal der Hörvorrichtung aufnehmende erste Rückkopplungserkennungseinheit,
• Regeln eines Schwellwerts durch eine das Mikrofonsignal der Hörvorrichtung aufnehmende zweite Rückkopplungserkennungseinheit in Abhängigkeit des Auftretens von Rückkopplungen,
• wobei der Schwellwert (20) zwischen den Werten "0" für das sichere Vorhandensein einer Rückkopplung und "1" für die sichere Abwesenheit einer Rückkopplung liegt,
• wobei die erste und zweite Rückkopplungserkennungseinheit (61, 62) unterschiedliche Rückkopplungserkennungsalgorithmen aufweisen, und
• Signalisieren, wenn die Rückkopplungswahrscheinlichkeit den geregelten Schwellwert überscheitet.

The invention also claims a method for detecting feedback in hearing devices comprising the steps:

• Determining a feedback probability by a first feedback detection unit receiving a microphone signal of the hearing device,
• Controlling a threshold value by a second feedback detection unit receiving the microphone signal of the hearing device as a function of the occurrence of feedbacks,
• the threshold value (20) being between the values "0" for the reliable presence of a feedback and "1" for the secure absence of a feedback,
• wherein the first and second feedback detection units (61, 62) have different feedback detection algorithms, and
• Signaling when the feedback probability exceeds the regulated threshold.

• Verknüpfen eines Rückkopplungserkennungssignals der zweiten Rückkopplungserkennungseinheit mit dem Signalisieren.

The method may also include the following additional step:

• Associating a feedback detection signal of the second feedback detection unit with the signaling.

In a further development of the method, the recognition of acoustic feedbacks in different predeterminable frequency bands can be performed.

Other features and advantages of the invention will become apparent from the following explanations of several embodiments with reference to schematic drawings.

Figur 1:

ein Blockschaltbild eines Hörgeräts mit Rückkopplungsunterdrückung gemäß Stand der Technik,

Figur 2:

ein Prinzipschaltbild einer erfindungsgemäßen Rückkopplungserkennungseinheit mit Gewichtungsfaktor,

Figur 3:

ein Prinzipschaltbild einer erfindungsgemäßen Rückkopplungserkennungseinheit mit Schwellwertregelung,

Figur 4:

ein Blockschaltbild einer erfindungsgemäßen Rückkopplungserkennungseinheit mit Gewichtungsfaktoren und

Figur 5:

ein Blockschaltbild einer erfindungsgemäßen Rückkopplungserkennungseinheit mit Schwellwertregelung.

Show it:

FIG. 1:

1 is a block diagram of a hearing aid with feedback suppression according to the prior art,

FIG. 2:

1 is a block diagram of a feedback detection unit according to the invention with a weighting factor;

FIG. 3:

a block diagram of a feedback detection unit according to the invention with threshold control,

FIG. 4:

a block diagram of a feedback detection unit according to the invention with weighting factors and

FIG. 5:

a block diagram of a feedback detection unit according to the invention with threshold control.

FIG. 2 shows a block diagram of an arrangement for determining a feedback. A microphone signal 11 is fed to both a first and a second feedback detection unit 61, 62. In the first feedback detection unit 61, a faster but error-prone detection algorithm runs, for example by detecting sinusoidal level peaks at high frequencies. In the second feedback detection unit 62 runs a slower, but very low-error and secure detection algorithm, for example by detecting a phase-modulated feedback signal. In the first feedback detection unit 61, a feedback probability 16 is determined as a feedback measure which can take values between "0" and "1". "1" means very likely and "0" means very unlikely. In the second feedback detection unit 62, a weighting factor 17 is determined, which may also be between "0" and "1", where a "1" signals the secure presence of feedback and a "0" the secure absence of feedback.

The feedback probability 16 is then multiplied by the weighting factor 17 thus determined in a multiplier 63 as the arithmetic unit and the output signal 18 is fed to a comparison unit 64. A normalized threshold value 20 is also supplied to an input of the comparison unit 64. The output signal 19 of the comparison unit 64 now signals whether the output signal 18 of the multiplier 63 is greater than the threshold value 20. If so, this is signaled by a logical "1" of the output signal 19 of the comparison unit 64.

The output signal 19 of the comparison unit 64 is then fed to an input of an OR gate 65. Another input of the OR gate 65 is supplied with a feedback detection signal 21 of the second feedback detection unit 62, which signals with a logical "1" when feedback is reliably detected. The OR gate 65 outputs at its output a feedback detection signal 22 which is logic "1" when either the comparison signal 19 of the comparison unit 64 or the feedback detection signal 21 of the second feedback detection unit 62 is logic "1", i. when a feedback is detected in at least one of the two detection branches.

According to the invention, the threshold value 20 can be regulated. This solution according to the invention is based on a block diagram in FIG FIG. 3 shown. A microphone signal 11 is in turn supplied to a first and a second feedback detection unit 61, 62. In the first feedback detection unit 61 runs a faster but erroneous detection algorithm and in the second feedback detection unit 62 runs a slower, but very low-error and secure detection algorithm. In the first feedback detection unit 61, a feedback probability 16 is determined which can assume values between "0" and "1". "1" means very likely and "0" means very much unlikely. In the second feedback detection unit 62, a predetermined threshold value is regulated thereby between "0" and "1", whereas unlike FIG. 2 a "0" indicates the secure presence of feedback and a "1" indicates the secure absence of feedback.

The thus regulated threshold value 20 is now supplied to a comparison unit 64. The feedback probability 16 is likewise supplied to an input of the comparison unit 64. The output signal 19 of the comparison unit 64 then signals whether the feedback probability 16 is greater than the threshold value 20. If so, this is signaled by a logical "1" of the output signal 19 of the comparison unit 64.

The output signal 19 of the comparison unit 64 is now as in FIG. 2 an input of an OR gate 65 is supplied. Another input of the OR gate 65 is a feedback detection signal 21 of the second feedback detection unit 62, which signals with a logical "1" that a feedback has been reliably detected. The OR gate 65 outputs at its output a feedback detection signal 22 which is logic "1" when either the comparison signal 19 of the comparison unit 64 or the feedback detection signal 21 of the second feedback detection unit 62 is logic "1", ie if a feedback in at least one the two detection branches is detected.

FIG. 4 shows that in FIG. 2 described principle in a practical implementation based on a block diagram. A microphone signal 11 of a hearing device is split by a filter bank 8 into n frequency bands 24. The n bands 24 are supplied to both the inputs of a fast first feedback detection unit 61 and a slower but accurate second feedback detection unit 62 with a phase modulation detector 621. Different methods are available for the fast detection unit 61, the n output signals 16 having values between zero and one deliver. The output signals 16 indicate the feedback probabilities for the n frequency bands 24.

The phase modulation detector 621 of the second feedback detection unit 62 detects whether a phase modulation imposed on an output signal of the hearing apparatus is included in the microphone signal 11. Since the detection is expensive, it is performed only for a frequency band 25 selected by band selection logic 620. The detection 21 of the phase modulation, which generally requires some time, must now be available to a controller 622, 623 of n weighting factors 17 at the same time as a band index 26 which indicates in which frequency band 24 the phase modulation was detected. The n weighting factors 17 may assume values between zero and one.

As a regulation 622, 623 of the n weighting factors 17, for example, a simple algorithm is used which ensures that the sum of all weighting factors 17 remains constant. The n weighting factors 17 thus determined are multiplied by the feedback probability 16 in n multipliers 63 and then compared as frequency multiplied signals 18 as multiplied signals 18 with a predefinable threshold value 20 in comparison units 64. If the feedback probability 16 is above the threshold value 20, a logical "1" is output as the output signal 19 of the comparison unit 64.

Finally, all output signals 19 of the comparison units 64 are OR'd with a feedback detection signal 21 of the phase detector 621 in a gate 65. A feedback 22 thus occurs when one of the weighted n feedback probabilities 18 exceeds the threshold value 20, or when the detection 21 of the phase modulation indicates feedback.

1. a) Die Summe der n Gewichtungsfaktoren 17 oder deren quadratischer Mittelwert bleibt konstant, um die absolute Sensibilität der ersten Rückkopplungserkennungseinheit 61 konstant zu halten.
2. b) Die n Gewichtungsfaktoren 17 werden bei jedem Einschalten der Hörvorrichtung in eine "Werkseinstellung" versetzt, da sich das Rückkopplungsverhalten der Hörvorrichtung zum Beispiel durch einen geänderten Sitz oder durch eine leicht geänderte Frisur täglich ändern kann.
3. c) Die Summe der n Gewichtungsfaktoren 17 oder deren quadratischer Mittelwert passt sich an die Häufigkeit der zuverlässigen Detektion von Rückkopplung der zweiten Rückkopplungserkennungseinheit 62 an, um ein instabiles Rückkopplungsverhalten kompensieren zu können.

The regulation of the weighting factors 17 can have the following properties:

1. a) The sum of the n weighting factors 17 or their root mean square value remains constant in order to keep the absolute sensitivity of the first feedback detection unit 61 constant.
2. b) The n weighting factors 17 are set to a "factory setting" each time the hearing device is switched on, since the feedback behavior of the hearing device can change daily, for example as a result of a changed seat or a slightly changed hairstyle.
3. c) The sum of the n weighting factors 17 or their root-mean-square value adapts to the frequency of the reliable detection of feedback of the second feedback detection unit 62, in order to be able to compensate for an unstable feedback behavior.

FIG. 5 shows that in FIG. 3 described principle in a practical implementation based on a block diagram. A microphone signal 11 of a hearing device is split by a filter bank 8 into n frequency bands 24. The n bands 24 are supplied to both the inputs of a fast first feedback detection unit 61 and a slower but accurate second feedback detection unit 62 with a phase modulation detector 621. For fast detection 61, different methods are available in which n output signals can assume 16 values between zero and one. The values are a measure of the feedback probability.

In the second feedback detection unit 62, the detector 621 for phase modulations detects whether an output signal, for example a receiver signal of a hearing aid, impressed phase modulation is again detected at an input, for example a microphone of the hearing aid. Since the detection is very expensive, it is only selected for a single frequency band 25 selected by band selection logic 620 is carried out. The detection 21 of the phase modulation, which usually takes some time, is simultaneously available together with a band index 26, which indicates the frequency band in which the phase modulation was detected, to a regulation 624, 625 of n band-specific threshold values 20. The n thresholds 20 are between zero and one, with a low threshold 20 indicating a high probability of feedback.

As a regulation 624, 625 of the n threshold values 20, a simple algorithm is used, for example, which ensures that the sum of all threshold values 20 remains constant. The thus determined n threshold values 20 are compared with the n feedback probabilities 16 in n comparison units 64.

Finally, all n output signals 19 of the comparison units 64 are OR'd with the feedback detection signal 21 of the phase detector 621 in a gate 65. A feedback is thus indicated when one of the n feedback probabilities 16 exceeds the corresponding threshold 20, or when the phase modulation detector 621 has detected feedback.

1. a) Die Summe der Schwellwerte 20 oder deren quadratischer Mittelwert bleibt konstant, um die absolute Sensibilität der schnellen Detektion konstant zu halten.
2. b) Die Schwellwerte 20 werden bei jedem Einschalten der Hörvorrichtung in eine "Werkseinstellung" versetzt, da sich das Rückkopplungsverhalten der Hörvorrichtung beispielsweise durch einen geänderten Sitz oder durch eine leicht geänderte Frisur täglich ändern kann.
3. c) Die Summe der Schwellwerte 20 oder deren quadratischer Mittelwert passt sich an die Häufigkeit der zuverlässigen Detektion von Rückkopplungen durch die zweite Rückkopplungserkennungseinheit 62 an, um ein instabiles Rückkopplungsverhalten zu kompensieren.

The regulation of the threshold values can have the following properties:

1. a) The sum of the thresholds 20 or their root mean square remains constant in order to keep the absolute sensitivity of the fast detection constant.
2. b) The threshold values 20 are set to a "factory setting" each time the hearing device is switched on, since the feedback behavior of the hearing device can change daily, for example as a result of a changed seat or a slightly changed hairstyle.
3. c) The sum of the thresholds 20 or their root mean square adapts to the frequency of reliable detection of feedback by the second feedback detection unit 62 to compensate for unstable feedback behavior.

The regulation of the threshold values 20 can be effected, for example, by multiplication with ascertained weighting factors.

LIST OF REFERENCE NUMBERS

1

hearing Aid

2

microphone

3

Signal processing unit

4

receiver

5

Adaptive filter

6

Feedback detection unit

7

eardrum

8th

filter bank

10

payload

11

microphone signal

12

earpiece signal

13

output

14

Feedback path

15

Filtered signal

16

Feedback probability of the first feedback detection unit 61

17

weighting factor

18

Feedback probability 16 multiplied by the weighting factor 17

19

Output signal of the comparison unit 64

20

threshold

21

Feedback detection signal of the second feedback detection unit 62

22

Feedback detection signal

24

Band limited microphone signal / frequency band

25

Bandpass signal

26

Frequency band Index

61

First feedback detection unit

62

Second feedback detection unit

63

Arithmetic unit / multiplier

64

comparing unit

65

Link unit / OR gate

620

Band selection logic

621

Phase modulation detector

622

Regulation of weighting factors 17

623

actuator

624

Regulation of thresholds 20

625

actuator

Claims (7)

1. Arrangement for detecting acoustic feedback (22) in a hearing device (1), having:

   - a first feedback detection unit (61) which receives a microphone signal (11) from the hearing device (1), and by means of which the probability of feedback (16) can be determined,

   characterised by:

   - a second feedback detection unit (62) which receives the microphone signal (11) from the hearing device (1), and by means of which a threshold value (20) can be controlled as a function of the occurrence of feedback (21),

   - wherein the threshold value (20) lies between the values "0" indicating the definite presence of feedback and "1" indicating the definite absence of feedback,

   - wherein the first and second feedback detection units (61, 62) have different feedback detection algorithms, and

   - a comparison unit (64), by means of which the feedback probability (16) can be compared to the threshold value (20) and the overshoot of the threshold value can be signalled (19).
2. Arrangement according to claim 1,
   characterised by:

   - a linking unit (65) which is designed to link a feedback detection signal (21) from the second feedback detection unit (62) to the signal (19) which signals an overshoot of the threshold value.
3. Arrangement according to one of the preceding claims,
   characterised in that
   acoustic feedback is detected (22) in different predefinable frequency bands (24).
4. Hearing device (1) having at least one microphone (2) and at least one earphone (4),
   characterised by:

   - an arrangement according to one of the preceding claims.
5. Method for detecting (22) feedback in hearing devices (1), by:

   - detection of feedback probability (16) by a first feedback detection unit (61) which receives a microphone signal (11) from the hearing device (1),

   characterised by:

   - control of a threshold value (20) by a second feedback detection unit (62) which receives the microphone signal (11) from the hearing device (1) as a function of the occurrence of feedback,

   - wherein the threshold value (20) lies between the values "0" indicating the definite presence of feedback and "1" indicating the definite absence of feedback,

   - wherein the first and second feedback detection units (61, 62) have different feedback detection algorithms, and

   - signalling (19) when the feedback probability (16) overshoots the controlled threshold value (20).
6. Method according to claim 5,
   characterised by:

   - linking a feedback detection signal (21) from the second feedback detection unit (62) to the signalling (19).
7. Method according to claim 5 or 6,
   characterised in that
   acoustic feedback is detected (22) in different predefinable frequency bands (24).

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