WO1999004598A1

WO1999004598A1 - Method for electronically selecting the dependency of an output signal from the spatial angle of acoustic signal impingement and hearing aid apparatus

Info

Publication number: WO1999004598A1
Application number: PCT/IB1998/001069
Authority: WO
Inventors: Joseph Maisano
Original assignee: Phonak Ag
Priority date: 1997-07-16
Filing date: 1998-07-14
Publication date: 1999-01-28
Also published as: EP0997055A1; TR200000119T2; CA2296414C; AU7928198A; DK0997055T3; DE69805526T2; EP0802699A2; EP0802699A3; IL133999A0; AU749652B2; NZ502350A; ATE218025T1; JP2001510975A; CA2296414A1; IL133999A; CN1267444A; EP0997055B1; DE69805526D1; KR20010021877A

Abstract

An acoustical beam former is proposed with at least two acoustical/electrical converters (2a, 2b) in a predetermined physical distance. The mutual phasing of the output signals of the two converters is detected (27) and is multiplied by a constant or frequency-dependent factor. In dependency (46, 48) from multiplied phasing and from at least one of the output signals of the converters (2a, 2b) there is generated an electric output signal which has a dependency from spatial impinging direction of acoustical signals to the converters (2a, 2b), as if the two converters were located at a virtual distance from each other which is different and especially considerably larger than the real physical distance they are mutually located.

Description

Method for electronically selecting the dependency of an output signal from the spatial angle of acoustic signal impingement and hearing aid apparatus

The present invention is generically directed on a technique according to which acoustical signals are received by at least two acoustical/electrical converters as e.g. by multidirectional microphones, respective output signals of such converters are electronically computed by an electronic transducer unit so as to generate an output signal which represents the acoustical signals weighted by a spatial characteristic of amplification. Thus, the output signal represents the received acoustical signal weighted by the spatial amplification characteristic as if reception of the acoustical signals had been done by means of e.g. an antenna with an according reception lobe or beam. Thus, the present invention is generically directed on an electronically preset, possibly electronically adjusted and tailored reception "lobe".

Figure 1 most generically shows such known technique for such "beam forming" on acoustical signals. Thereby, at least two multidirectional acoustical/electrical converters 2_a and 2_b are provided, which both - per se - convert acoustical signal irrespective of their impinging direction θ and thus substantially unweighted with respect to impinging direction θ into first and second electrical output signals A_r and A_j . The output signals A_x and A₂ are fed to an electronic transducer unit 3 which generates from the input signals A_1# A₂ an output signal A,,. As shown within the block of unit 3 the signals A_1/2 are treated to result in the result signal A_ which represents either of A_x or _j, but additionally weighted by the spatial amplification function F^θ). Thus, acoustic signals may selectively be am- plified dependent from the fact under which spatial angle θ they impinge, i.e. under which spatial angle the transducer arrangement 2a, 2b "sees" an acoustical source. Thereby, such known approach is strictly bound to the physical location and intrinsic "lobe" of the converters as provided.

One approach to perform signal processing within transducer unit 3 shall be exemplified with the help of Fig. 2. Thereby, all such approaches are based on the fact that due to a predetermined mutual physical distance p_p of the two converters 2_a and 2_b, there occurs a time-lag dt between reception of an acoustical signal at the converters 2_a, 2_b.

Considering a single frequency - ω - acoustical signal, received by the converter 2_a, this converter will generate an output signal

(1) A_x = A ' sinωt,

whereas the second transducer 2_b will generate an output signal according to

(2) A_j = A ^• sinω(t+dt),

whereat dt is given by

p_psinθ (3) dt = — c therein, c is the sound velocity.

By time-delaying e.g. A_x by an amount

and forming the result signal A,, from the difference of time- delayed signal A_x ' - as a third signal - namely from

(5) A_x ' = A ^• sinω(t+τ), and

(2) A₂ = A ^• sinω(t+dt),

there results, considered at the frequency ω, a spatially car- doid weighted output signal A,, as shown in the block of transducer unit 3 :

(6) IA = \ A_X ' - A = 2A sin(ω(τ-dt) /2)

= 2A sin(ω (τ-p_p*sinθ/c) /2) .

At θ = 90° A_. becomes zero and

at θ = -90° A,, becomes

(7) A^ = 2A sin ω p_p/c.

Such processing of the output signals of two omnidirectional order converters leads to a first order cardoid weighing func- tion F₁(θ) as shown in Fig. 3. By respectively selecting converters with higher order acoustical to electrical conversion characteristic i.e. "lobe" and/or by using more than two converters, higher order - m - weighing functions F_m(θ) may be realised.

In Fig. 4 there is shown the amplitude A^^-characteristic, resulting from first order cardoid weighing as a function of frequency f = ω/2π. Additionally, the respective function for a second order cardoid weighing function F₂(θ) is shown. Thereby, there is selected a physical distance p_p of the two converters 2_a and 2_b of fig. 1 to be 12 mm. As may clearly be seen at a frequency f_r which is

(8) f_r = c/(4p_p)

maximum amplification occurs of +6 dB at the first order cardoid and of +12 dB at a second order cardoid. For p_p = 12 mm, f_r is about 7 kHz.

From fig. 4 a significant roll-off for low and high frequencies with respect to f_r is recognised, i.e. a significant decrease of amplification.

Techniques for such or similar type of beam forming are e.g. known from the US 4 333 170 - acoustical source detection -, from the European patent application 0 381 498 directional microphone - or from Norio Koike et al . , "Verification of the Possibility of Separation of Sound Source Direction via a Pair of Pressure Microphones", Electronics and Communications in Ja- pan, Part 3, Vol. 77, No. 5, 1994, page 68 to 75.

Irrespective of the prior art techniques used for such beam forming with at least two converters, the distance p_p is an important entity as may be seen e.g. from formula (8) and directly determines the resulting amplification/angle dependency.

Formula (8) may be of no special handicap if such a technique is used for narrow band signal detection or if no serious limits are encountered for geometrically providing the at least two converters at a large mutual physical distance p_p.

Nevertheless, and especially for hearing aid applications, the fact that f_r is inversely proportional to the physical distance p_p of the transducers is a serious drawback, due to the fact that for hearing aid applications the audio frequency band up to about 4 kHz for speech recognition should be detectable by the at least two transducers which further should be mounted with the shortest possible mutual distance p_p. These two requirements are in contradiction: The lower f_r shall be real- ised, the larger will be the distance p_p required.

It is thus a first object of the present invention to remedy the drawbacks encountered with respect to p_p-dependency of known acoustical "beam forming" .

The first object of the present invention is reached by provid- ing a method for electronically selecting the dependency of an electric output signal of an electronic transducer unit from spatial direction wherefrom acoustical signals impinge on at least a first and a second acoustical/electrical converter, connected to the inputs of said transducer unit, thereby input- ting first and second electric signals thereto, which comprises the steps of

• generating at least one third electric signal in dependency from mutual phasing of the first and the second electric signals, said phasing being multiplied by a constant or a fre- quency-dependent factor and further from a fourth electric signal which depends from at least one of the first and the second electric signals;

• generating the output signals of the transducer unit in dependency of the third signal and further from a fifth elec- trie signal which is dependent from at least one of the first and the second electric signals .

Thereby, it becomes possible, irrespective of the actual physical mutual distance of the two converters, to select said de- pendency, thereby pre-selecting same and possibly tuning and adjusting same, to result in a dependency as if the at least two converters were physically arranged at completely different physical positions than they really are.

In a first preferred manner of realising the inventive method the fourth electric signal is selected to be linearly dependent only from one of the first and second electric signals, thereby being preferably directly formed by such first or second electric signal.

Nevertheless, in a today's more preferred manner of realising the inventive method, the fourth electric signal is dependent on both first and second electric signals . In a preferred form the fourth electric signal has a predetermined or adjustable "lobe" characteristic, i.e. dependency from spatial impinging direction. Thereby in a preferred form of "lobe" realisation the fourth electric signal is generated by delaying one of the first and second signals and then summing the delayed signal and the other, undelayed signal of said first and second signals. Thereby, the fourth electric signal per se has an ampli- fication to impinging angle dependency and thus defines - as was said - for a "lobe", as an example according to a dependency as was discussed with the help of the figs. 1 to 4.

In a further preferred form of realising the inventive method, either per se or combined with either method to generate the fourth signal as just stated, and especially combined with generating the fourth signal with a "lobe" -characteristic, it is proposed to generate the fifth electric signal in direct or linear dependency of at least one of the first and second elec- trie signals, thereby preferably using one the said first and second electric signals as the fifth electric signal.

Thereby, and again per se or combined with either method of generating the fourth electric signal, especially combined with generating the fourth electric signal with a "lobe" -dependency, it is proposed to generate the fifth electric signal as well with a "lobe" dependency from spatial impinging angle, which is realised in a first form by delaying one of the first and second signals and summing the delayed signal and the other of said first and second signals. Thereby, it becomes clear that the fourth electric signal, generated to define for a "lobe" characteristic, may directly be used as the fifth electric signal, having then the same "lobe" -characteristic .

In a further, clearly preferred realisation form of the inven- tive method and combined with any of the preferred realisation forms stated up to now and throughout the further description, it is proposed to generate the first and second electric signals in their respective spectral representation, thereby generating the at least one third electric signal in dependency of mutual phasing of respective spectral components of the first and second signals and multiplied by a constant frequency-independent or by frequency-dependent factors .

In a further preferred mode of operation, the frequency- dependent multiplication factors are selected to be inversely proportional to frequency, at least in a first approximation.

With an eye specifically on hearing aid applications, wherefore the present method is most suited, but may be clearly applied to others, it is proposed that the real physical distance of the first and second converters to be at most 20 mm, whereby the virtual distance, which is at least dependent from the phasing multiplication factor, is selected to be larger than the mutual physical distance of the two converters, in other words dependency of the transducer unit ' s output signal from spatial angle becomes so as if, physically, converters were provided at considerably larger mutual distances than they really are. It goes without saying, that such technique is of very high advantage in any space-restricted applications, as especially in hearing aid applications.

To resolve the object mentioned above and to realise especially a hearing aid, whereat, irrespective of the physical position of at least two acoustical/electrical converters, a desired reception lobe may be tailored and possibly adjusted according to the needs, is realised inventively by an acoustical/electrical transducer apparatus comprising at least two acoustical/electrical converters spaced from each other by a predetermined physical distance, whereby the at least two converters generate, respectively, first and second electrical output signals and wherein the outputs of said acoustical/electrical convert- ers are operationally connected to an electronic transducer unit, which generates an output signal dependent from said first and second output signals of said converters by an amplification function which function is dependent from spatial angle under which said converters receive acoustical signals, comprising:

- a phase difference detection unit, the inputs thereof being operationally connected to the outputs of said converters and generating at its output a phase difference-dependent signal, - a phase processing unit, one input thereof being operationally connected to the output of said phase difference- detection unit, at least one second input of said processing unit being operationally connected to a factor-value- selecting source, a third input of said phase processing unit being operationally connected to at least one of the inputs of said at least two converters, said phase processing unit generating an output signal at its output according to a signal at said third input with a phasing according to a sig- nal at said one input and at said at least one second input,

- a beam-former processing unit with at least two inputs, one input being operationally connected to the output of said phase-processing unit, the second input being operationally connected to at least one output of said at least two con- verters .

Under all the aspects of the invention there is thus possible to realise

(9) p_v > p_p.

This especially for low-space applications, as especially for hearing aid applications.

Thereby, there is introduced the virtual distance p_v of transducers, i.e. the distance of converters which would have to be physically realised to get an angle dependency as realised inventively.

Thereby, according to formula (8) , f_r may be shifted to lower frequencies : It becomes possible to realise f_r values well in the audiofrequency band for speech recognition (< 4 kHz) with physical distances of microphones, which are considerably smaller than this was possible up to now.

Multiplying the phase difference by a constant factor does nevertheless not affect the roll-off according to fig. 4. This roll-off is significantly improved, leading to an enlarged frequency band B_r according to fig. 4 if - as was said - the predetermined function of frequency is selected as a function which is at least in a first approximation inversely proportional to the frequency of the acoustic signal.

For instance for the first order cardoid according to fig. 3 and fig. 4, there may be reached a flat frequency characteristic between 0,5 and 4 kHz and thus a significantly enlarged frequency band B_r with well-defined roll-offs of amplification at lower and higher frequencies by accordingly selecting the frequency dependent function to be multiplied with the phase difference .

Other objects of this invention will become apparent as the de- scription proceeds in connection with the accompanying drawings, of which show:

Fig. 1: A functional block diagram of a two-transducer acoustic receiver with directional beam forming according to prior art;

Fig. 2: one of prior art beam forming techniques as may be incorporated in the apparatus of fig. 1, shown in block diagram form; Fig. 3: a two-dimensional representation of a three- dimensional cardoid beam, i.e. amplification characteristic as a function of incident angle of acoustical signals;

Fig. 4: the frequency dependency of the maximum amplification value according to fig. 3 for first and second order cardoid functions;

Fig. 5: a pointer diagram resulting from the technique ac- cording to fig. 2, still prior art;

Fig. 6: a pointer diagram based on fig. 5 (prior art) , but according to the inventive method, which is performed by an inventive apparatus;

Fig. 7: a simplified block diagram of a first realisation form of an inventive apparatus, especially of an in- ventive hearing aid apparatus, wherein the inventive method is implemented;

Fig. 8: a simplified block diagram of a today preferred realisation form of the inventive method and apparatus;

Fig. 9: a simplified block diagram of an inventive apparatus, operating according to the inventive method, in a generalised form;

Fig. 10: a generic signal-flow/functional block diagram of an inventive apparatus operating according to the inventive method; Fig. 11: the measured directivity characteristics resulting from the inventive method and inventive apparatus according to fig. 8;

Fig. 12: a second directivity characteristics in a representa- tion according to fig. 11, resulting from the inventive method and apparatus according to fig. 8.

As was mentioned above, in the figs. 1 to 4 known beam forming techniques were based on at least two acoustical/electrical transducers spaced from each other and directly on their mutual physical distance p_p.

In fig. 5 there is shown a pointer diagram according to (6) .

The basic idea of the present invention shall be explained now with the help of the still simplified one - ω - frequency example. The inventively realised pointer diagram is shown in fig. 6. The phase difference ω ' dt between signal A^ and A_x according to fig. 6 is

PpSinθ

(10) ω ' dt = ω ^• = Δφ. c

This phase difference is determined and is multiplied by a value dependent from frequency, thus with the respective value of a function M(ω) , which may be also a constant M₀ ≠ 1.

By phase shifting one of the two signals A_lf P^ according to the respective pointers in fig. 6, e.g. of A₂ by

M_ω ' Δφ or by M₀ ' Δφ,

there results the phase shifted pointer A_2V. This pointer would have also occurred if dt had been larger by an amount according to M_ω or M₀, thus if a "virtual transducer" had been placed distant from transducer l_a by the virtual distance p_v, for which:

(11) p_v = M_ra ^■ p_p or

(12) p_v = M₀ ^• p_p.

As we consider one single frequency for simplicity we may write M = M

With virtual τ_v

(13) τ_v = M_ω ^• τ and

sinθ

(3_V) dt_v = M_ω

we get according to the present invention:

(l_v) A-_L = A_1V = Asinωt

(2_V) A_2V = Asinω (t+dt_v) = Asinω (t+M_ωdt)

(5_V) A_1V = Asinω (t+M_ωτ)

(6_V) _v = 2Asin((M_ω ^■ ω(τ-dt)/2)

With (8) we further get:

c 1_ ^{frv =} 4 _ωPp M_ω ^fr*

Therefrom, we may see that for a given p_p, which would lead to a too high f_r, f_rV is reduced by the factor M_ω, taken M_ω > 1. In fig. 7 there is schematically shown a first preferred realisation form of an inventive apparatus in a simplified manner, especially for implementing the inventive method into an inventive hearing aid apparatus. Thereby, the output signals of the acoustical/electrical transducer 2_a and 2_b are fed to respective analogue to digital converters 20a, 20b, the outputs thereof being input to time domain to frequency domain - TFC - converter units as to Fast-Fourier Transform units 22a and 22b. A spectral phase difference detecting unit 27 spectrally detects phase difference Δφ_n for all n spectral frequency components which are then multiplied by a set of constants c_n. If M is a function of ω, M_ω, then the c_n can be different for different frequencies, and represent a frequency dependent function or factor. If on the other hand the phase differences Δφ_n are multiplied by the same c₀ = c_n ≠ 1 this accords with using a constant M₀.

This multiplication according to (3_V) is done at a spectral multiplication unit 28. Signal A_x in its spectral representation is then spectrally phase shifted at a spectral phase shifter unit 29 by the multiplied spectral phase difference signals output by multiplier unit 28.

According to fig 7 the signal A_t in its spectral representation and inventively, spectrally phase shifted - A₁(ω,Δφ'_n) - is computed in a spectral computing unit 23 together with A₂ in its spectral representation, as if transducer 2a was distant from transducer 2b by a distance p_v = M_ωp_p The resulting spec- trum is transformed back by a frequency to time domain converter - FTC - as by an Inverse-Fast-Fourier-Transform unit 24 to result in A^. Thereby, other beam forming techniques than that described with the help of figs 1 to 4, i.e. using the time delaying technique - transformed in the frequency domain - may be used in unit 23.

Nevertheless the time delaying technique is preferred.

With an eye on fig. 4 it has been explained that by inventively introducing "virtual" converters with a virtually enlarged mutual distance, it becomes possible to shift the high gain frequency f_r towards lower frequencies, which is highly advantageous especially for hearing aid applications. This is already reached if instead of a frequency dependent function M_ω, a constant M₀ is multiplied with the phase difference as explained.

In a preferred mode of the invention the frequency dependent function M_ω is selected to be, at least in a first approximation,

1 (14) M_ω ~ — ω

Thereby, it is reached that, different from fig. 4, there will be no roll-off and the gain in target direction will be constant over the desired frequency range. By appropriately selecting the function M_ω it is e.g. possible to reach a flat characteristic within a predetermined frequency range, e.g. between 0.5 and 4 kHz with defined roll-offs at lower and higher frequencies. With appropriately selecting the function M_(a practically any kind of beam forming can be made.

For generating higher order cardoid weighing functions it is absolutely possible to additionally use the not phase-shifted output signal A_x - as shown in fig. 7 by dotted line - as com- puting input signal to unit 23 too, thus "simulating" three converters .

Fig. 8 shows a today's preferred embodiment of an inventive apparatus in a functional-block/signal-flow representation in analogy to the representation of fig. 7. Blocks and signals which were already explained with the help of fig. 7 are defined in fig. 8 by the same reference numbers.

The phase spectrum at the outside of multiplication unit 28, Aφ'_ι...n i^s added at a summing unit 29' to a signal A_{kr ι...π}(ω,θ), also in spectral representation, which signal has a preselected dependency from impinging angle θ, as especially a first or higher order cardoid dependency.

To realise that signal A_{kr x n}(ω_{x n},θ) and following the explanation with respect to figures 2 to 4, the output signal A_λ (ω ) , and A^ω) in their spectral representation, are led to a beam- former unit 32, which may be integrated in beam-former unit 23' and which e.g. is built up according to the beam-former of fig. 2. Thereby, it must be clearly stated that instead of the beam- former 32 as shown in fig. 8 other kinds of beam-former result- ing in different than first order cardoid characteristics may be implemented there .

The spectrum A_fcr>1____n(co_1..n θ) is then phase-shifted by the phase adding unit 29' by Δφ ' _{x n}, resulting in an output signal of that unit 29' which is the spectrum A _{#1 n} (ω_{x n}, Δφ ' _{λ n}, θ) as shown in fig. 8. The signal A_{kr l π}(ω_{1 n},θ) as well as the output signal of summing unit 29' are led to the beam-former unit 23 ' , where they are preferably again summed as shown at 33. At the output of beam-former unit 32 a signal is generated with a real cardoid dependency from impinging angle θ, whereas at the output of unit 29', and thus after phase shifting, a dependency function with respect to impinging angle θ is realised according to virtually positioned converters. When summing, as with the unit 33 within beam-former unit 23 ' , there results a dependency of the output signal A,, from impinging angle θ according to a second order cardoid if the real cardoid dependency at the output of unit 32 is a first order cardoid.

Thus, in a more generic representation, as shown in fig. 9, the phase difference spectrum at the output of unit 27 is subjected to a phase shifter unit 35, where it is modified as per c_x to

The generalised phase shifter 35 may receive directly one of the output signals of one of the two converters 2a, 2b and/or a signal which results from beam forming from the said converter output signals to be phase shifted. In fig. 9 this is represented by the signal path fed back from beam former 37 to the phase shifter 35. This feedback accords, with an eye on fig. 8, to the signal path between beam former 32 and summing unit 29' . According to fig. 9 beam former unit 32 of fig. 8 is integrated in the overall beam former unit 37.

The beam former 37 in its generalised form of fig. 9 receives at least one of the output signals of the converters 2a, 2b and the output signal of the generalised phase shifter 35.

It is evident for the skilled artisan that

• more than two real converters may be used and/or • more than one M_ω function or of c₀ or c_{x n} sets may be used to produce more than one "virtual transducer" signal from one or from more than one real converter signals respectively.

With selecting the number of physical and virtual converters, their characteristics and virtual "relocation" of these converters, the spatial weighing function may be selectively tailored.

The present invention under its principal object makes it possible to realise practically any desired beam forming with at least two converters separated by only a predetermined small distance, due to the fact that electronically there is provided a virtual mutual converter location of the physically provided converter .

Thereby, roll-off may be significantly reduced by such virtual transducer, which is especially established with realising a virtual distance of the converter which is dependent from frequency, especially inversely dependent. By selecting a fre- quency-M_ω-dependent virtual distance of the converters, virtually an array of frequency-selective converters is established. For a hearing aid apparatus the real distance between the at least two transducers, i.e. microphones, is selected to be 20 mm at most, preferably less.

Fig. 10 shows in most generic form the principle proceeding and apparatus structure as according to the present invention and common to all embodiments of the invention as described above.

First and second electric signals S and S₂, which are derived from the output signals of the at least two acoustical/electrical converters 2_a, 2_b, are input to the transducer unit 3. Within unit 3 , there is provided a phase difference detection unit according to unit 27 of figures 7, 8 or 9. The phase difference detection unit 27 has respective inputs which are operationally connected to the inputs of unit 3 and- thus to the outputs of the converters 2a, 2b. The output of the phase difference detection unit 27 is operationally connected to an input of a phase processing unit 40 shown in dashed-dotted lines in fig. 10. The phase processing unit has a second input, which is connected to a factor value-selecting source 42, generating a constant or frequency-dependent factor h. A third input of the phase processing unit is operationally connected as schematically shown by combining unit 44 in an "AND" or in an "EX- OR" dependency to respective outputs of the at least two converters 2_a and 2_b. The phase processing unit 40 generates an output signal, S₃, in accordance with a signal, S₄, applied to the third input of the processing unit 40 and in accordance with the signals applied to the first - from 27 - and second - from 42 - inputs to the phase processing unit .

The signal at the first input of the phase processing unit, which is operationally connected to the output of the phase difference detection unit, is multiplied - by unit 28 - by the constant or frequency-dependent factor, and, at a signal combining unit 46, the output signal of the processing unit, signal S₃, is thus generated in dependency from mutual phasing of the output signals of the converters, multiplied by a constant or frequency-dependent factor and from signal S₄ as applied to the third input of the processing unit 40, which latter signal S₄ is dependent from at least one of the output signals of the converters 2_a, 2_b. In unit 46 the dependency F_τ of signal S₃ from both, signal S₄ and multiplied phasing signal as at the output of unit 28, is generated.

The signal S₃, which accords to A_x(ω) of fig. 7 or to

^A _kr,_ι..._n (^ωι...n/θ) °f figs . 8 and 9, is input to a beam former processing unit 48 according to unit 23 or 23' or 37, as of the figs. 7 to 9. The beam former processing unit comprises a second input to which S₅, dependent from at least one of the output signals of the converters 2_a, 2_b is fed. Latter signals are thus operationally connected as schematically shown by block 50 in an "EX-OR" or in an "AND" combination to the beam former processing unit 48.

In fig. 11 there is shown the "lobe" or directivity characteristic - in dB - which was measured at an inventive apparatus according to fig. 8 at single frequency 1 kHz of acoustical signals impinging on the two acoustical/electrical converters 2_a, 2_b. In this apparatus there was valid:

converters 2_a, 2_b: omnidirectional microphones,

KNOWLES EK 7263

Physical distance p_p: 12 mm

τ: 35 μsec .

c: 2 at 1 kHz and at 4 kHz

There resulted a directivity index as defined in SPEECH COMMUNICATION 20 (1996) , 229 to 240, Microphone array systems for hands-free telecommunication, Gary W. Elco of 8.83.

In fig. 12 the result is shown at an inventive apparatus which was used for the measurement according to fig. 11, but at 4 kHz single frequency acoustical impinging signals. The directivity index became 7.98.

There results from proceeding according to fig. 8 a directivity characteristics according to a second order cardoid. This would conventionally have to be realised by means of four acoustical/electrical converters as of 2_a and 2_b, which four converters define for a spacing of 24 mm between respective two of the four converters. Thus, it might be seen that with the inventive method and apparatus with only two acoustical/electrical con- verters with a mutual spacing of 12 mm a directivity result is reached as if four acoustical/electrical converters had been used with mutual spacing of 24 mm.

Claims

Claims :

1. A method for electronically selecting the dependency of an electric output signal of an electronic transducer unit from spatial direction wherefrom acoustical signals impinge on at least a first and a second acoustical/electrical converter operationally connected to the input of said transducer unit and thereby inputting first and second electric signals thereto, comprising the steps of

ΓÇó generating at least one third electrical signal in dependency from mutual phasing of said first and second electric signals multiplied by a constant or a frequency-dependent factor and further from a fourth electric signal which is dependent from at least one of said first and second electric signals;

ΓÇó generating said output signal of said transducer unit in de- pendency of said third electric signal and a fifth electric signal being dependent from at least one of said first and second electric signals.

2. The method of claim 1, thereby generating said fourth electric signal as a signal dependent from said first or second electric signal.

3. The method of claim 1, thereby generating said fourth electric signal as dependent from said first and said second electric signals.

4. The method of claim 1, thereby generating said fourth electric signal as a signal with a predetermined or adjustable dependency from said spatial direction, as with a cardoid dependency.

5. The method of claim 1, thereby generating said fourth electric signal by delaying one of said first and second electric signals and summing the delayed signal and the other of said first and second signals.

6. The method of one of claims 1 to 4 , thereby generating said fifth electric signal as being dependent from one of said first and second electric signals.

7. The method of one of claims 1 to 4 , thereby generating said fifth electric signal as dependent from both said first and said second electric signals.

8. The method of one of claims 1 to 5 or 7 , thereby generating said fifth electric signal as a signal with a predetermined or adjustable dependency from said spatial direction, as with a cardoid dependency.

9. The method of one of claims 1 to 5 or 7 or 8 , thereby generating said fifth electric signal by delaying one of said first and of said second signals and summing said delayed signal and the other of said first and second signals.

10. The method of one of claims 1 to 9 , thereby generating said fourth electric signal by generating said fifth electric signal .

11. The method of one of claims 1 to 10, thereby generating said first and second electric signals in their respective spectral representation and generating said at least one third electric signal in dependency of mutual phasing of respective spectral components of said first and second signals, multiplied by said factor and in dependency of said fourth electric signal .

12. The method of one of claims 1 to 11, thereby selecting said factor as inversely proportional to frequency.

13. An acoustical/electrical transducer apparatus comprising at least two acoustical/electrical converters spaced from each other by a predetermined physical distance, whereby the at least two converters generate, respectively, first and second electrical output signals and wherein the outputs of said acoustical/electrical converters are operationally connected to an electronic transducer unit, which generates an output signal dependent from said first and second output signals of said converters by an amplification function which function is dependent from spatial angle under which said converters receive acoustical signals, comprising:

- a phase difference detection unit, the inputs thereof being operationally connected to the outputs of said converters and generating at its output a phase difference-dependent signal,

- a phase processing unit, one input thereof being operationally connected to the output of said phase difference- detection unit, at least one second input of said processing unit being operationally connected to a factor-value- selecting source, a third input of said phase processing unit being operationally connected to at least one of the outputs of said at least two converters, said phase processing unit generating an output signal at its output according to a signal at said third input with a phasing according to a signal at said one input and at said at least one second input,

- a beam-former processing unit with at least two inputs, one input being operationally connected to the output of said phase-processing unit, the second input being operationally connected to at least one output of said at least two converters .

14. The apparatus of claim 13, wherein said factor value- selecting source generates a constant or frequency-dependent signal values.

15. The apparatus of claim 13 or 14, wherein said third input of said phase-processing unit is operationally connected to one output of said at least two converters .

16. The apparatus of one of claims 13 to 15, wherein said third input of said phase-processing unit is connected to the output of a beam former unit, the inputs thereof being operationally connected to the outputs of said at least two converters .

17. The method of claim 16, said beam former unit comprising a further summing unit, one input thereof being operationally connected to an output of one of said at least two converters, the other input thereof being operationally connected via a time-delay unit to the output of the other of said at least two converters .

18. The apparatus of one of claims 13 to 17, wherein said second input of said beam-former processing unit is operationally connected to one of said at least two converters .

19. The apparatus of one of claims 13 to 18, wherein said second input of said beam-former processing unit is operationally connected to the output of a summing unit, one input thereof being connected via a time-delaying unit to the output of one of said at least two converters, a second input of said summing unit being operationally connected to the output of said second one of said at least two converters .

20. The apparatus of one of claims 13 to 19, wherein the outputs of said at least two converters are operationally con- nected to the inputs of a further summing unit, one thereof via a time-delay unit, the output of said further summing unit being operationally connected to said third input of said phase- processing unit and to said second input of said beam-former processing unit.

21. The apparatus of one of claims 13 to 20, wherein the outputs of said at least two converters are generated via respective analogue to digital converters and time domain to frequency domain transform units, said phase-difference detection unit, said phase-processing unit and said beam-former process- ing unit operating in frequency domain, the output of said transducer unit being generated via a frequency domain to time domain conversion unit.

22. The apparatus of one of claims 13 to 21, being a hearing aid apparatus, said at least two converters having a mutual physical distance of at most 20 mm.