WO2000033634A2

WO2000033634A2 - Method for providing the transmission characteristics of a microphone arrangement and microphone arrangement

Info

Publication number: WO2000033634A2
Application number: PCT/CH2000/000190
Authority: WO
Inventors: Hans-Ueli Roeck
Original assignee: Phonak Ag
Priority date: 2000-03-31
Filing date: 2000-03-31
Publication date: 2000-06-15
Also published as: JP2003516646A; DE50009746D1; AU2000234142B2; WO2000033634A3; DK1269576T3; CA2404863A1; CA2404863C; EP1269576B1; AU3414200A; EP1269576A1

Abstract

Two output signals (A1a and A1b) of a microphone arrangement (1) are divided (7), whereby said signals are differently dependent on the direction of incidence (ζ) of acoustic signals. A product from the division result (A7) and the weighting factor (α) is saturated (12) and subtracted from a signal value (A) which can be inputted. The subtraction result is multiplied with the output signal of the microphone arrangement (1) which is the denominator signal for the division (7). A desired directivity is produced between the result signal (Sout) of the multiplication and the direction of incidence (ζ) on the microphone arrangement (1) of incident acoustic signals according to the weighting factor (α) of the saturation value (B) and of the subtraction value (A).

Description

Method for specifying the transmission characteristics of a microphone arrangement and microphone arrangement

The present invention relates to a method according to the preamble of claim 1 and a microphone arrangement according to that of claim 9.

In the reception and processing technology of acoustic signals, there is often a need to implement microphone arrangements with a transmission characteristic which, in a predetermined or predefinable function of the direction of incidence of the acoustic signals, generate the electrical output signal. In particular, there is a need to implement microphone arrangements with predetermined or predeterminable directional characteristics, in which acoustic signals from predetermined directional areas have a greater effect on the output signal from other directional areas, up to arrangements with reception characteristics that are practically focused in one direction.

A variety of approaches are known for realizing such transmission characteristics. For example, in this regard, reference is made to WO99 / 04598 or US 09/146784 (φ multiplication) or WO99 / 09786 or US 09/168184 (φ filter guidance) from the same applicant, according to which the phase shift generally affects microphone arrangements acoustic signals and their targeted processing, desired transmission characteristics of microphone arrangements can be obtained.

It is the object of the present invention to propose a further procedure in order to implement a desired transmission characteristic in the aforementioned sense.

According to the invention, this object is achieved by a method of the type mentioned in the introduction, in which at least two submicrophone arrangements are provided on the microphone arrangement,

Confirmation copy Their transmission characteristics differ depending on their electrical output signals as a function of said direction and that the output signal is formed as a function of a product saturated to a predetermined or predeterminable value, with the quotient of the output signals of the submicrophone arrangements as a factor.

If we speak of "saturation" in the context of the present application, this means that the value of a mathematical function under consideration is clipped when a predetermined value is reached, so that it remains constant, contrary to the course of the mathematical function, when this value is reached.

Although a saturation of the mentioned product, i.e. of the weighted quotient, to a minimum value may be sensible, it is preferably proposed that the product, in any case also, be saturated to a maximum value.

Furthermore, the second factor of the saturated product can have any value other than zero, which means that it can also have the value 1.

In a further preferred embodiment it is proposed that the function mentioned comprises a difference between an optionally adjustable constant and the saturated product, the value of the constant preferably being selected to be at least approximately equal to the saturation value.

Furthermore, the quotient mentioned is preferably determined from the amplitude values of the output signals, without taking their phase position into account.

In a particularly preferred embodiment of the method according to the invention, the quotient mentioned is used in the context of the following function:

in what mean

S: output signal of the microphone arrangement

A: A predefined or predefinable signal value

| c _N |: amplitude value of the output signal of a first submicrophone arrangement, the transmission characteristics of which have maximum amplification at an angle of incidence, where the characteristic to be formed should also have maximum amplification

| c _z |: amplitude value of the output signal of the second submicrophone arrangement

satB: Saturation of the quotient to a predetermined or predeterminable maximum signal value B

α: Predeterminable or predefined factor.

In a particularly preferred embodiment, in particular as part of the use of the method according to the invention for hearing aids, the transmission characteristics of the submicrophone arrangements are selected such that they each have maximum signal amplifications for acoustic signals incident from essentially inverse directions.

A microphone arrangement of the type mentioned at the outset is characterized in that the processing unit comprises a weighted quotient formation unit with a Denominator input, a numerator input and a weighting input, numerator and denominator inputs being operatively connected to an input of the processing unit, the weighted quotient formation unit further producing an output signal saturated to a maximum and / or a minimum value at its output, which Output is operatively connected to the output of the processing unit.

Preferred embodiments of the microphone arrangement according to the invention are specified in claims 10 to 18.

The method according to the invention and the microphone arrangement according to the invention are particularly suitable for use on hearing aids.

Although it is entirely possible to implement the method according to the invention and the microphone arrangement according to the invention by means of signal processing in the time domain, signal processing in the frequency domain is carried out in a preferred embodiment, using time domain / frequency domain converters or frequency domain / time domain converters.

The invention is subsequently explained using figures, for example. These show:

Figures la and b, for example, the transmission characteristics of two (a and b) sub-microphone arrangements used according to the invention;

2 over the angular axis φ according to FIGS. 1 a and 1 b, in dB the formation of a quotient function Q from the characteristics according to FIGS. 1 a and 1 b and the saturation of this quotient function to the maximum value 0 dB; 3, starting from the saturated quotient function explained with reference to FIG. 2, the same saturated quotient function in linear gain scaling and the formation of a function F from the difference between said saturated quotient function with respect to a fixed value;

FIG. 4 in a representation analogous to FIGS. 1 a and 1 b, shaded, a transmission characteristic implemented according to the invention;

5 shows a representation analogous to FIG. 4, a further transmission characteristic implemented according to the invention, and

6 in the form of a simplified signal flow / function block diagram, the realization of a microphone arrangement according to the invention.

On the basis of FIGS. 1 to 3, the procedure according to the invention is to be illustrated on the basis of simple transfer characteristics without any claim to scientific accuracy, corresponding to first order cardiids. On the basis of this clear and simple procedure, the person skilled in the art is given instructions on how, according to the invention, a desired transmission characteristic can also be realized on the basis of more complex transmission functions.

A first submicrophone arrangement has, with regard to its transmission or amplification characteristic with regard to acoustic signals incident on it from the direction φ, the three-dimensional transmission characteristic shown in FIG. FIG. 1b shows, analogously to FIG. La, the transmission characteristic of a second submicrophone arrangement, which with respect to the axis π / 2; 3π / 2 is a mirror image of the transmission characteristic of the first sub- microphone arrangement. The transfer characteristic according to FIG. La is denoted by c _N , that according to lb by c _z .

In FIG. 2, the magnitude of the transmission characteristics c _N and c _{z is shown} qualitatively and in dB over the angular axis φ according to FIGS.

In the case of acoustic unit signals arriving at the two submicrophone arrangements, the transmission characteristics shown in FIGS. 1a and 1b simultaneously correspond to the respective signal values on the output side of the submicrophone arrangements under consideration.

According to the invention, a quotient is now formed from these two output signals, which is likewise denoted by c _N or c _z , for example

The result of this quotient formation is the function Q, shown in dash-dotted lines in FIG. 2, with a pole at φ = π. With real quotient formation, the one at the zero of the denominator function | c _N | the resulting pole is intercepted anyway, ie the quotient function Q is saturated.

The quotient function is preferably saturated to a predetermined or predeterminable value B, according to FIG. 1 preferably to the value "one", with the maximum value of the transfer functions according to FIGS. 1 a, b being "one".

If one now assumes that the denominator transmission characteristic, in the present case c _N , is that which is the dominant one for the transmission characteristic result to be achieved, that is to say a transmission characteristic which has a high signal gain in an angular range, in which also the realizing desired characteristics high signal Should have strengthening, the advantage of forming the quotient according to the invention is already evident. From this transmission characteristic, which is dominant for the desired result, a pole point of the quotient results in the zero angle range. However, the zero point angle range of the dominant transmission characteristic or those angle ranges with reduced signal amplification will be those which are to be changed, ie “improved”, in order to obtain the desired characteristic. There is the possibility to intervene simply, namely by saturation a predeterminable or predefined constant value of the quotient function.

For reasons of clarity, the quotient function Q _sat ι saturated to "1" is now entered in FIG. 3 with linear gain scaling. From this it can furthermore be seen that in the unsaturated angular ranges, in this case between 0 and π / 2 and between 3π / 2 and 2π, the saturated quotient function Q _sat i has the course of a directional transmission characteristic. If pronounced directional characteristics are now to be achieved for the desired transmission characteristic to be realized, then the range of the quotient function set according to the invention to the specified saturation value, using the example described “one”, is used to achieve a defined minimum gain of the desired transmission characteristic there, ie in this angular range In the example presented, this is achieved in that the saturated quotient function is subtracted from a predetermined or predeterminable fixed value A, for example and preferably in the example presented with the value “one”. This results in the function shown again in solid form in FIG. 3

F = A - Q _satB

or as a special case and preferred case, the function F = 1 - Q satl •

From this it can be seen that a transfer function has been achieved, F, which is only in the angular range

, 3π

0 <φ <π - and - <φ <2 π 2 2

has a non-vanishing signal amplification.

With regard to the procedure according to the invention, the following can now be carried out:

• Basically, the transmission characteristic to be implemented is implemented on the output side of the microphone arrangement according to the invention as a function of the quotient of the output signals of two submicrophone arrangements with different transmission characteristics, which is saturated to a predetermined or predeterminable maximum value.

It is preferred, and as will be shown, that the quotient function Q, as a factor, is multiplied by a further predetermined or adjustable weighting factor before the resulting product saturates. In the example presented with reference to FIGS. 1 to 3, the weighting factor mentioned is 1.

Furthermore, it can be quite advantageous to saturate the product from the mentioned factor and the quotient, at least also when predetermined minimum values are reached.

•• The formation of the quotient can take place directly by forming the quotient of the signal amplitude values, without taking phase into account. •• Although the saturated product can possibly be used in the form of another function, generally as F = F [(α 'Q) s ß] / the preferred satinized product from a given product is preferred for the realization of a directional characteristic or predeterminable fixed value is subtracted.

As will be shown later, the possibility of varying the desired directional characteristic is obtained in a very simple manner by varying the fixed value mentioned and / or the multiplicative factor α of the saturated product.

In principle, all known microphones and their combinations can be used as sub-microphone arrangements, which, as required in the operating position and as required with respect to the direction of incidence φ of acoustic signals, have different transmission characteristics.

•• In particular for the implementation of directional characteristics, sub-microphone arrangements are preferably used whose transmission characteristics are identical, but are inversely directed with respect to the direction of incidence of acoustic signals.

•• Such microphone arrangements can be implemented in particular according to the known “delay and add” principle.

The inverse-acting microphone arrangements just mentioned can in particular also be implemented in this embodiment with two microphones, the outputs of which, as will be shown below, are each time-delayed and appropriately added to form the two sub-microphone arrangements. • It goes without saying that further development of the procedure according to the invention with three or more submicrophone arrangements makes it possible to implement highly complex transfer functions and transfer function combinations.

In summary, the transfer function that is preferably used according to the invention is reproduced again, namely:

In FIG. 4, * ⁼ Practice rtragu ^"ngsfunkt% ion is d ^L arge provides that has been formed from inversely directed, identical Kardoid transmission characteristics Ca according to the invention, in accordance with the transfer function

The resulting transmission characteristic is shown in FIG. 5 if:

FIG. 6 shows, for example, a microphone arrangement operating according to the method according to the invention on the basis of a simplified signal flow / function block diagram, in particular also for use on a hearing aid.

6, an arrangement 1 with at least two sub-microphone arrangements 1 a and 1 b is provided on the input side of the microphone arrangement according to the invention. At their outputs A _ia and A _ü , output _signals appear as a function of the direction φ of acoustic impinging on the input-side microphones Signals. As shown in Fig. 6, the two Submikrophonanordnungen may well be realized by means of a single pair of microphones whose outputs are coupled to one another according to the technique "delay and add" It is essential that _b basically signals at the outputs A _ia and Aι with. Different transmission characteristics with respect to the direction φ incoming acoustic signals are generated.

The outputs A _ia and A _lb are preferably routed to the time range / frequency range converter units FFT 3a and 3b, if, as preferred, the subsequent signal processing in the frequency range is to take place. The outputs mentioned are operatively connected to inputs E _5a and E _5b of amount formation units 5a and 5b. As shown, the outputs of the aforementioned amount formation units are routed to the denominator and numerator inputs N and Z of a division unit 7. Multiplied by a weighting unit 9 by a weighting factor α which can be predetermined at a control input S ₉ , the output A _{7 is} operatively connected to the one input E _{ila of} a subtraction unit 11.

As outlined in dashed lines in FIG. 6, division unit 7 and weighting unit 9 form a weighted quotient formation unit 10. The factor α that can be set on the weighting unit 9, for example, shown in FIG. 6, can have any values that differ from 0.

As shown schematically in FIG. 6, the signal at the output A _{9 of} the weighted quotient formation unit 10 is fed to a saturation unit 12, the output of which is only fed to the input E _11a . At the saturation unit 12, which can of course be integrated integrally with the weighted quotient formation unit 10, the output signal of the weighted quotient formation unit 10 is down (in

Block 12 of Fig. 6 indicated by dashed lines) and / or up to a predetermined or predeterminable value B - as schematic shown on the table set at the entrance sat _B - saturated. This preferably also at least to a maximum value. At the subtraction unit 11, the signal present there is subtracted from a fixed value A set or adjustable at the second input _E11b . The output A _{X1 of} the subtraction unit 11 is _operatively connected to the one input E _{i3a of} a multiplication unit 13, with the second input E _{ι3b of} which the output signal of the submicrophone arrangement la which is also operatively connected to the denominator input N of the division unit 7 is operatively connected. If necessary to change the saturation angle range explained with reference to FIGS. 1 to 3, the denominator signal, optionally also the numerator signal, can be fed to the input N or the input Z of the division input 7, as shown in dashed lines at 15.

The output signal S ₀ ut of the microphone arrangement according to the invention appears on the output side of the multiplication unit 13. It has the desired transmission characteristic as a function of the spatial angle φ with which acoustic signals strike the microphone arrangement 1 on the input side.

As already mentioned, are preferred for the

Transmission characteristics of the submicrophone arrangements la and lb selected identical, directionally inverse characteristics. By setting the weighting factor α, the saturation value B, the fixed value A, and possibly further weighting factors such as β, the desired transmission characteristic is set on the output signal S _ou t.

The method according to the invention and the microphone arrangement according to the invention are excellently suited for use on hearing aids, in particular also because of the low signal processing effort and, as was shown with reference to FIGS. 3 and 4, the possibility of signal transmission from undesired directions of incidence, such as from behind in terms of of a worn hearing aid to suppress. For hearing aids, preference is given to using rather those with hypercardoid characteristics H _ca (FIG. 5) instead of sub-microphone arrangements with cardoid characteristics Ca.

Claims

Claims:

1. A method for specifying the transmission characteristic, with which acoustic signals incident on a microphone arrangement are converted into an electrical output signal as a function of their direction of incidence, characterized in that at least two submicrophone arrangements are provided on the microphone arrangement, the transmission characteristics of which are said in function Direction are different depending on their electrical output signals and that the output signal is formed as a function of a product saturated to a predetermined or predeterminable value, with the quotient of the output signals of the submicrophone arrangements as a factor.

2. The method according to claim 1, characterized in that the product is saturated to a maximum value.

3. The method according to claim 1 or 2, characterized in that the second factor of the saturated product can take any value other than zero.

4. The method according to any one of claims 1 to 3, characterized in that the function comprises a difference between a - optionally adjustable - constant (A) and the saturated product, the value of the constant (A) preferably being at least approximately equal to that Saturation value (B) is selected.

5. The method according to any one of claims 1 to 4, characterized in that the quotient of the amplitude values of the

Output signals is determined.

6. The method according to any one of claims 1 to 5, characterized in that the output signal is formed according to the following function

in what mean

S: output signal of the microphone arrangement

A: A predefined or predefinable signal value

| c _N |: amplitude value of the output signal of a first submicrophone arrangement, the transmission characteristic of which at a

Angle of incidence has maximum gain, where the characteristic to be formed should also have maximum gain.

| c _z j: amplitude value of the output signal of the second submicrophone arrangement

satB: Saturation of the product [] to a predetermined or predeterminable maximum signal value B

α: Predeterminable or predefined factor of the product.

7. The method according to any one of claims 1 to 6, characterized in that the transmission characteristics of the submicrophone arrangements have maximum amplifications for acoustic signals incident from essentially inverse directions.

8. The method according to claim 7, characterized in that the transmission characteristics are cardoid or, preferably, hypercardoid-shaped.

9. Microphone arrangement with at least two sub-microphone arrangements, the transmission characteristics of which with respect to the rattle direction of incoming signals are different and the outputs of which are led to inputs of a processing unit with one output, characterized in that the processing unit comprises a weighted quotient formation unit with a denominator input, a numerator input ?? and a weighting input, the numerator and denominator inputs being operatively connected to an input of the processing unit, the weighted quotient formation unit also producing an output signal saturated at a maximum and / or a minimum value at its output, which output with the output of the processing unit is connected.

10. Microphone arrangement according to claim 9, characterized in that the output signal of the weighted quotient formation unit is saturated to a maximum signal value.

11. Microphone arrangement according to one of claims 9 or 10, characterized in that the weighting input any weighting factor other than zero is supplied fixed or adjustable.

12. Microphone arrangement according to one of claims 9 to 11, characterized in that the output of the weighted quotient formation unit is operatively connected to the output of the processing unit via a difference formation unit.

13. Microphone arrangement according to claim 12, characterized in that a fixed or adjustable signal is supplied to a second input of the difference formation unit, the value of which is preferably at least approximately equal to a saturation value of the saturated output signal of the weighted quotient formation unit.

14. Microphone arrangement according to one of claims 9 to 13, characterized in that the inputs of the processing unit are each guided over amount-forming units before they are operatively connected to the numerator or denominator inputs of the quotient formation unit.

15. Microphone arrangement according to one of claims 9 to 14, characterized in that the output of the weighted quotient formation unit is operatively connected to the one input of a multiplication unit, the second input of which is operatively connected to the output of the submicrophone arrangement which is operatively connected to the denominator input of the quotient formation unit and that the output of the multiplication unit is operatively connected to the output of the processing unit.

16. Microphone arrangement according to claims 13 and 15, characterized in that the output of the difference formation unit is operatively connected to the one input of the multiplication unit.

17. Microphone arrangement according to one of claims 9 to 16, characterized in that between the outputs of the submicrophone arrangements and the inputs of the processing unit per time / frequency domain converter are provided.

18. Microphone arrangement according to one of claims 9 to 17, characterized in that the submicrophone arrangements have cardoid or hypercardoid characteristics, preferably the latter.

19. Use of the method according to one of claims 1 to 8 or the arrangement according to one of claims 9 to 18 for hearing aids.