EP1465453B1 - Automatic adjustment of a directional microphone system with at least three microphones - Google Patents

Description

The invention relates to a method for automatic microphone adjustment in a directional microphone system having at least three omnidirectional microphones, wherein for generating a directional characteristic in each case two omnidirectional microphones are connected to a first and a second directional microphone first order.

Furthermore, the invention relates to a directional microphone system having at least a first, a second and a third omnidirectional microphone, wherein the first and the second omnidirectional microphone to a first directional microphone first order and the second and the third omnidirectional microphone to a second directional microphone of the first order are interconnected ,

Hearing impaired people often suffer from a reduced ability to communicate in noise. To improve the signal / noise ratio directional microphone arrays have been used for some time, the benefits to the hearing impaired is undisputed. The exclusion of backward received interference signals as well as the focus on frontally incident sounds facilitate a better understanding in everyday situations.

From the WO 00/76268 A2 is a hearing aid with three omnidirectional microphones known. From two microphones in each case a directional microphone of the first order is formed by inverting and delaying the microphone signal generated by a microphone and then adding both microphone signals. Similarly, by delaying and inverting the microphone signal formed by a first order directional microphone and then adding one to another Directional microphone formed first order microphone signal a directional microphone with directional characteristics of the second order (directional microphone second order) are formed.

Particularly in directional microphones of higher order, the problem arises that the systems are extremely sensitive to detuning of the transfer function of the microphones by amount and phase, e.g. caused by aging as well as by pollution effects. While in the application of directional microphones of first order in hearing aids often an amplitude tuning of the microphones is sufficient, in directional microphones of higher order, the phase position of the individual microphones must also be very closely matched.

From the DE 198 22 021 A1 is a hearing aid with automatic microphone adjustment and a method for operating such a hearing aid known. In the known hearing aid, a difference element for subtracting mean values of the output signals of the microphones and a differential element downstream analysis / control unit for controlling the amplification of the output signal of at least one microphone is provided. The regulation of the amplification takes place in such a way that the mean values of the microphone signals are brought into agreement. In the microphone adjustment, only the amplitudes of the microphones are adjusted.

From the DE 199 18 883 C1 is a hearing aid with directional microphone characteristic known. In the hearing aid for amplitude and / or phase alignment of two omnidirectional microphones the microphones downstream high passes are adjusted in their lower limit frequencies. In each case, the lower limit frequency of a microphone is adjusted by a microphone connected downstream high pass of the cutoff frequency of the other microphone.

From the DE 198 49 739 A1 For example, a hearing device and an adaptive method for adjusting the microphones of a directional microphone system in the hearing device are known. In order to avoid unwanted forgery of the directional microphone characteristic in a directional microphone system with at least two microphones by non-matched microphones, characteristics of the signals of both microphones are detected via a comparison element, a control element and an actuator and aligned with each other at a detected deviation.

A disadvantage of the known method for microphone adjustment in directional microphones is their insufficient effect in microphone mismatches, which are caused in particular by aging and pollution effects.

Object of the present invention is therefore to provide a method for automatic microphone adjustment in a directional microphone system and a directional microphone system that allow without external intervention during normal operation of the directional microphone system to adapt the amplitude response as well as the phase response of the microphones of the directional microphone system.

• Abgleichen der Amplituden der von den omnidirektionalen Mikrofonen erzeugten Mikrofonsignale,
• Abgleichen der Amplituden der von den Richtmikrofonen erster Ordnung erzeugten Mikrofonsignale durch Phasenverschiebung wenigstens eines von einem der drei omnidirektionalen Mikrofone erzeugten Mikrofonsignale.

This object is achieved by a method for automatic microphone adjustment in a directional microphone system having at least three omnidirectional microphones, two omnidirectional microphones being connected to a first or a second directional microphone of the first order in order to generate a directional characteristic, with the following method steps:

• Matching the amplitudes of the microphone signals generated by the omnidirectional microphones,
• Balancing the amplitudes of the microphone signals generated by the first-order directional microphones by phase shifting at least one microphone signals generated by one of the three omnidirectional microphones.

Furthermore, the object is achieved by a directional microphone system having at least a first, a second and a third omnidirectional microphone, wherein two omnidirectional microphones are connected to a first directional microphone first order and a second directional microphone first order, wherein level measuring means for determining the time-averaged signal level are provided by the omnidirectional microphones and the microphone signals generated by the first-order directional microphones, wherein an amplitude control means for adjusting the amplitudes in at least two of the three microphone signals generated by the omnidirectional microphones in dependence of the detected signal levels and wherein a phase control means for adjusting the phase of the microphone signal generated by at least one omnidirectional microphone as a function of the signal detected by the level measuring devices in the directional microphones of the first order level is present.

By electrically interconnecting at least three omnidirectional microphones directional microphones with directional characteristics of second and higher order (directional microphones of the second and higher order) can be formed. In particular, a directional microphone of the first order can be built up by electrically interconnecting two omnidirectional microphones, and a directional microphone of the second order can be set up by electrically interconnecting two directional microphones of the first order. In the case of electrical interconnection, usually a microphone signal is inverted and delayed in time and added to a further microphone signal of the same order.

In a first method step, the invention provides an amplitude adjustment of the microphone signals generated by the omnidirectional microphones of the microphone system. To adjust the amplitude, a measure of the time-averaged sound field energy is respectively obtained from the microphone signals in the case of the microphone signals. The microphone signals are then adjusted so that after the adjustment, the time-averaged Sound field energy in all microphone signals at least approximately coincident. As a measure of the time-averaged sound field energy is preferably the signal level. However, other dimensions, eg the RMS value, can also be used. For adjustment, a control or regulation of the respectively obtained from a microphone signal measure of the time-averaged sound field energy can be done. For example, individual microphone signals are multiplied or filtered by a factor. Furthermore, the gain in the microphones downstream amplifiers can be changed. The first method step or the entire method according to the invention can be performed in narrowband in several channels or broadband.

The first method step causes the amplitudes of the microphone signals to be adjusted at a certain point in the signal paths of the microphones.

While it is often sufficient to adjust the amplitude of the microphones when using directional microphones of the first order, the phase position of the individual microphones must also be taken into account in directional microphones of higher order. It is less the absolute phase of the microphone signals, but rather their relative phase shift from each other of interest.

At least two first order directional microphones are required to form a second order directional microphone system. These in turn can be constructed by pairing at least three omnidirectional microphones. The amplitudes of the three omnidirectional microphones are adjusted as described above in a first method step. In a second method step, the amplitudes of the directional microphones are matched first order. For this purpose too, a measure of the time-averaged sound field energy, for example the signal level, is obtained and matched from the microphone signals of the directional microphones of the first order. In difference However, to the omnidirectional microphone signals, the adjustment is done not by an amplitude or gain adjustment of the microphone signals of the directional microphones of the first order, but by phase shifting at least one microphone signal generated by an omnidirectional microphone. The phase of this microphone signal is varied until the directional microphones of the first order in their amplitude response match as exactly as possible. Since the omnidirectional microphones are already matched in their amplitudes, the amplitudes of the directional microphones of the first order only match exactly when the phase shift between each two omnidirectional microphones, which are connected to a directional microphone system of the first order, match. This results in their signal transmission behavior largely symmetrical directional microphones of the first order.

The invention offers the advantage that the phasing of individual microphones required in a directional microphone system of higher order is attributed to a relatively easy amplitude balance to be realized. Furthermore, the microphone adjustment can be done during normal operation of the directional microphone system. In addition, several signal sources may be present during the microphone adjustment and arranged arbitrarily in the room.

The method described for a second-order directional microphone system can analogously also be extended to directional microphone systems of higher order. The method is also not limited to three omnidirectional microphones as signal inputs. Thus, even with more than three omnidirectional microphones directional microphones of the first (and higher) order can be formed and aligned. As a rule, there is no absolute phase adjustment by means of the invention, but rather a relative phase adjustment in the case of microphone pairs which are interconnected to form a microphone of the next higher order. The method can be broadband or narrowband in only one frequency range or multiple parallel frequency channels.

A directional microphone system constructed symmetrically with respect to the external geometry facilitates the implementation of a method according to the invention. Thus, the sound inlet openings of the omnidirectional microphones are advantageously located on a straight line, wherein adjacent sound inlet openings each have the same distance from each other. Then, e.g. Due to the geometry-related transit time differences of the individual microphone signals for microphone matching are not excluded. Since in the method according to the invention the time-averaged sound field energy is determined and adjusted from the microphone signals, runtime differences play no role, which arise, for example, in that a microphone with a sound inlet located further forward with respect to a signal source receives a sound signal earlier than a microphone with a rearward sound inlet opening.

The method for adjusting the relative phase error between individual pairs of microphones can be extended to the effect that the absolute phase of individual microphones or directional microphones is matched with the same order. This shall be described below without limiting the generality in the case of directional microphones of the first order which have been adjusted according to the method described above.

A first and a second directional microphone of the first order are adjusted according to the method described above. Furthermore, it is assumed that at least one source of interference is present in the rear region of a hearing device wearer, ie in the range between 90 ° and 270 ° with respect to the straight-ahead viewing direction (0 ° direction), which can almost always be assumed in real environmental situations. Then the phase in the microphone signal of an omnidirectional Microphones of the first directional microphone in a limited range of values changed so that the amplitude of the microphone signal of the first directional microphone of the first order decreases with respect to the amplitude of the microphone signal of the second directional microphone first order. The limited value range of the phase shift is determined so that the incision of the sensitivity of the directional microphone (Notch) by the phase shift in the rear region between 90 ° and 270 ° remains. Preferably, the phase is adjusted so that the amplitude of the microphone system of the first directional microphone of the first order has a minimum compared to the amplitude of the microphone signal of the second directional microphone of the first order. Physically, this means that the Notch is set in the first directional microphone system so that an interference signal (or interference signals) from the rear area is suppressed as possible. Subsequently, the two directional microphones of the first order are reconciled by also in the second directional microphone first order a phase shift in the microphone signal of an omnidirectional microphone of the second directional microphone first order is adjusted so that the two directional microphones are aligned again.

The above-described approach may also be modified such that the phase in the microphone signal of an omnidirectional microphone of the first directional microphone is changed only a small step in the direction that reduces the amplitude of the first directional microphone of the first order compared to the amplitude of the second directional microphone , For example, the step size can be set to shift the notch by 2 ° with each step. Then the two directional microphones of the first order are adjusted again as described above. This procedure is repeated until the amplitude in the microphone signal of the first directional microphone of the first order compared to the amplitude of the microphone signal of the second directional microphone first order only insignificantly reduce. Both directional microphones are then optimally aligned to the interference signal or the interference signals.

This procedure leads to a comparison of the absolute phase position of the omnidirectional microphones. Also, this phase adjustment is advantageously attributed to a relatively easy to implement amplitude balance.

Figur 1

ein Richtmikrofonsystem zweiter Ordnung nach dem Stand der Technik,

Figur 2

ein Richtmikrofonsystem gemäß der Erfindung und

Figur 3

ein hinter dem Ohr tragbares Hörhilfegerät mit einem Richtmikrofonsystem gemäß der Erfindung.

Further details and advantages of the invention will become apparent from the following description of an embodiment. Showing:

FIG. 1

a second-order directional microphone system according to the prior art,

FIG. 2

a directional microphone system according to the invention and

FIG. 3

a behind the ear portable hearing aid with a directional microphone system according to the invention.

FIG. 1 shows a constructed of three omnidirectional microphones 1, 2 and 3 directional microphone system with directional characteristics of the second order (directional microphone system second order). The two omnidirectional microphones 1 and 2 form a first directional microphone of the first order. Here, the resulting from the omnidirectional microphone 2 microphone signal is delayed in a delay element 4 and inverted in an inverter 5, before being added by the summer 8 to the microphone signal of the omnidirectional microphone 1. Likewise, the microphone signal of the omnidirectional microphone 3 is delayed in a delay element 6, inverted in an inverter 7 and added in a summer 9 to the microphone signal of the omnidirectional microphone 2. As with the omnidirectional microphones 2 and 3, the microphone signal of the second directional microphone of the first order formed by the two omnidirectional microphones 2 and 3 is subsequently delayed in a delay element 10, in an inverter 11 inverted and finally added in a summer 12 to the microphone signal of the first directional microphone of the first and the second omnidirectional microphone formed first order. In the second-order directional microphone system thus formed, the precise expression of the directional characteristic, which can be illustrated in a directional diagram, can be varied by different settings of the signal delays in the delay elements 4, 6 and 10.

As well as FIG. 1 also shows FIG. 2 a directional microphone system second order, which is composed of only three omnidirectional microphones 21, 22 and 23 and thereby takes into account in particular the limited space for use in a hearing aid. From the microphone pair 21, 22, a first directional microphone of the first order is formed in the summer 25 by delaying the microphone signal generated by the omnidirectional microphone 22 and inverting it in a delay and inverter unit 24 and then summing it to the microphone signal produced by the omnidirectional microphone 21. Likewise, the microphone pair 22, 23 also forms a second directional microphone of first order by delaying and inverting the microphone signal generated by the omnidirectional microphone 23 in the delay and inverter unit 26 and then adding the microphone signal generated by the omnidirectional microphone 22 in the summer 27. To carry out the method according to the invention, the signal delays in the delay and inverter units 24 and 26 are initially set equal. In a first method step of the method according to the invention, firstly the amplitudes of the microphone signals generated by the three omnidirectional microphones 21, 22 and 23 are adjusted. For this purpose, the time-averaged signal levels are first obtained from the microphone signals in the level measuring devices 28, 29 and 30. The measured signal levels are fed to an amplitude control device 31. This controls in at least two of the three microphone signal paths existing multipliers 32 and 33, so that deviations from the Microphone signals detected time-averaged signal level can be compensated. As a result, the amplitude response of the three omnidirectional microphones 21, 22 and 23 is aligned. Subsequently, the time-averaged signal levels of the microphone signals generated by the two directional microphones of the first order are obtained by level measuring means 34 and 35. These signal levels are supplied to a control unit 36. The control unit 36 controls a phase compensation filter 38, by which a phase shift in the microphone signal generated by the omnidirectional microphone 22 is adjusted such that the same time-averaged signal levels are measured by the two level measuring devices 34 and 35. This means that the phase error present in the two microphone pairs becomes equal (relative phase adjustment). Due to the same signal transmission behavior, the two microphone pairs are therefore ideally suited for the formation of a directional microphone of the second order. For this purpose, the microphone signal generated by the second directional microphone of the first order can be delayed in the delay and inverter unit 39 and added in the summer 40 to the microphone signal of the first directional microphone of the first order.

The invention has the advantage that the phase alignment of the microphones has been attributed to an amplitude balance that is easy to implement. The adjustment can be done under real environmental conditions, with any number of sound sources may be present.

A continuation of the method according to the invention provides that, following the previously performed microphone adjustment, the phase of the microphone signal generated by the omnidirectional microphone 21 is adjusted by controlling the phase compensation unit 37 by the control unit 36 such that the one measured by the level measuring devices 34 and 35 Signal level of the first-order directional microphones reduces the signal level of the first directional microphone compared to the signal level of the second directional microphone.

Physically, this reduction is due to the fact that the notch of the first directional microphone of the first order, that is, the incision in the directional characteristic, which shows the direction of least sensitivity, is better aligned with the one or more interferers present in the respective environmental situation. The phase variation is limited to a range of values, so that the Notch can be adjusted only in a certain angular range, e.g. Between 90 ° and 270 ° relative to the straight-ahead viewing direction of a hearing device wearer (0 ° direction). Subsequently, the phase compensation unit 38 is adjusted so that the signal levels of the microphone signals of the directional microphones of the first order again match as closely as possible, that is, the second directional microphone of the first order is adapted again to the first directional microphone of the first order.

The last-mentioned procedure can be run through once for the microphone adjustment, wherein the phase shift in the predetermined value range is adjusted so that the signal level of the first directional microphone is minimal relative to the signal level of the second directional microphone. The first directional microphone is then optimally adapted to the interference signals in the specific environment situation and the second microphone is then tracked accordingly. The disadvantage here, however, is the additional effort that must be operated to determine the minimum. Therefore, an alternative embodiment provides that the notch of the first directional microphone first order is gradually rotated in small steps, for example 2 °, in the direction in which a reduction of the signal level with respect to the signal level of the microphone signal of the second directional microphone results first order. Then the two directional microphones of the first order are adjusted again as described above. This procedure is repeated until at most a slight reduction in the signal level of the microphone signal of the first directional microphone of the first order can be achieved.

Overall, this continuous cyclic algorithm represents a three-stage control loop, with the aid of which the three omnidirectional microphones can be adjusted according to magnitude and phase. It can be a uniform small step size or an adaptive step size can be used. The realization of the phase compensation units can be done for example by delay elements or digital filters. By means of digital filters, it is possible to achieve a broadband or different phase compensation for different frequency ranges.

Preferably, the last-described absolute phasing of the microphones is performed only when the signal levels in the current environmental situation exceed a certain threshold. Then, as a rule, it can be assumed that interference signals are also present. However, this is not a disadvantage, since in ambient situations with only very low signal levels, a directivity and thus obtained noise removal are only of minor importance anyway.

The second-order directional microphone system formed for the embodiment of a three-omnidirectional microphones can also be analogously transmitted to directional microphone systems with more than three omnidirectional microphones and higher than second order.

FIG. 3 shows a behind the ear portable hearing aid 50 with a directional microphone system according to the invention. The hearing aid 50 includes a battery chamber 51 for arranging a battery 52 for powering the hearing aid 50, a signal processing electronics 53 and an MTO switch 54 for switching off the hearing aid 50 (switch position 0) and for switching on and switching the reception between the directional microphone system (switch position M ) and a telecoil (switch position T).

The directional microphone system of the hearing aid device 50 comprises three omnidirectional microphones 55, 56 and 57, to each of which a sound inlet opening 58, 59 and 60 is assigned. The sound inlet openings 58-60 are arranged laterally on the hearing aid 50 in the embodiment. They are at least approximately on a straight line 61 and have approximately the same distance from each other. Unlike in the exemplary embodiment shown, the sound inlet openings 58-60 could also be arranged on the upper side of the housing, as is usual with hearing aids that can be worn behind the ear.

According to the invention, in the hearing aid 50 worn behind the ear, the microphone adjustment can be carried out with the hearing aid worn in real environmental conditions. As a result, in particular dirt and aging phenomena of the microphones 55-57 in the hearing aid 50 are compensated.

To carry the hearing aid 50 behind the ear, the hearing aid 50 is provided in a known manner with a support hook 62. An acoustic input signal supplied to the hearing aid 50 is converted into electrical input signals in the microphones 55-57, processed in the signal processing electronics 53, and finally converted back into an acoustic signal in a receiver 63 and (not shown) by the wearing hook 62 and a sound tube connected thereto Auditory hearing aid wearer supplied.

Claims (14)

1. Method for automatically equalizing microphones in a directional microphone system with at least three omnidirectional microphones (21, 22, 23; 55, 56, 57), with respectively two omnidirectional microphones (21, 22; 22, 23; 55, 56; 56, 57) being interconnected to form a first and a second first-order directional-microphone in order to generate a directional characteristic, comprising the following method steps:

   - equalizing the amplitudes of the microphone signals generated by the omnidirectional microphones (21, 22, 23; 55, 56, 57),

   - equalizing the amplitudes of the microphone signals generated by the first-order directional-microphones by phase shifting at least one microphone signal generated by one of the three omnidirectional microphones (21, 22, 23; 55, 56, 57).
2. Method according to Claim 1, wherein the omnidirectional microphones (55, 56, 57) each have at least one sound entrance port (58, 59, 60), and said ports are arranged along an at least substantially straight line (61) and spaced apart equidistantly.
3. Method according to Claim 1 or 2, wherein a measure of the time-averaged acoustic field energy is respectively obtained from the microphone signals in order to equalize the amplitudes of the microphone signals generated by the omnidirectional microphones (21, 22, 23; 55, 56, 57), and the signal transfer functions of the omnidirectional microphones (21, 22, 23; 55, 56, 57) are adjusted by setting means downstream of the microphones (21, 22, 23; 55, 56, 57) to that effect that the measures of the time-averaged acoustic field energy, respectively established from a microphone signal, at least substantially correspond for all three microphone signals.
4. Method according to Claim 3, wherein the signal level is established as a measure of the time-averaged acoustic field energy.
5. Method according to Claim 3 or 4, wherein the signal transfer functions of the omnidirectional microphones (21, 22, 23; 55, 56, 57) are respectively set by multiplying the microphone signals by a factor.
6. Method according to one of Claims 1 to 5, wherein a measure of the time-averaged acoustic field energy from the microphone signals from the first-order directional-microphones is respectively obtained and equalized in order to equalize the amplitudes of the microphone signals generated by the first-order directional-microphones.
7. Method according to Claim 6, wherein the signal level is established as a measure of the time-averaged acoustic field energy.
8. Method according to one of Claims 1 to 7, with a first, a second and a third omnidirectional microphone (21, 22, 23; 55, 56, 57), with the first and the second omnidirectional microphone (21, 22; 55, 56) being interconnected to form a first first-order directional-microphone and the second and the third omnidirectional microphone (22, 23; 56, 57) being interconnected to form a second first-order directional-microphone in order to generate a directional characteristic, wherein a phase shift of the microphone signal generated by the first or the second omnidirectional microphone (21, 22; 56, 57) is brought about to that effect that the amplitude of the microphone signal generated by the first first-order directional-microphone is reduced with respect to the amplitude of the microphone signal generated by the second first-order directional-microphone, and wherein the amplitudes of the first-order directional-microphones are subsequently re-equalized by shifting the phase of the microphone signal generated by the second or the third omnidirectional microphone (22, 23; 56, 57).
9. Method according to Claim 8, wherein the phase shift within a prescribable value range is brought about to that effect that the amplitude of the microphone signal generated by the first first-order directional-microphone is minimized with respect to the amplitude of the microphone signal generated by the second first-order directional-microphone.
10. Method according to Claim 8, wherein the method steps are repeated until a termination criterion is met.
11. Method according to one of Claims 1 to 10, wherein the microphone signals generated by the omnidirectional microphones (21, 22, 23; 55, 56, 57) are subdivided into frequency bands, and the microphone equalization is respectively carried out in a frequency band.
12. Directional microphone system with at least a first, a second and a third omnidirectional microphone (21, 22, 23; 55, 56, 57), with respectively two omnidirectional microphones (21, 22; 22, 23; 55, 56; 56, 57) being interconnected to form a first and a second first-order directional-microphone, characterized in that there are level-measuring arrangements (28, 29, 30; 34, 35) for establishing the time-averaged signal levels of the microphone signals generated by the omnidirectional microphones (21, 22, 23; 55, 56, 57) and by the first-order directional-microphones, with there being an amplitude control arrangement (31) for setting the amplitudes of at least two of the three microphone signals generated by the omnidirectional microphones (21, 22, 23; 55, 56, 57) as a function of the established signal levels and with there being a phase control arrangement for setting the phase of the microphone signal generated by at least one omnidirectional microphone (21, 22; 55, 56) as a function of the signal levels established by the level-measuring arrangements (34, 35) in the first-order directional-microphones.
13. Directional microphone system according to Claim 12, wherein there is a phase control arrangement (36) for setting the phases of the microphone signals generated by at least two omnidirectional microphones (21, 22; 55, 56) as a function of the signal levels established by the level-measuring arrangements (34, 35) in the first-order directional-microphones.
14. Arrangement of a directional microphone system according to Claim 12 or 13 in a hearing aid (50).

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