Abstract:
A method performs signal processing in a binaural hearing device that has first and second hearing aids with first and second microphones producing first and second signals and with first and second sound generators. The first and second signals ascertain a direction of a main sound source. A deviation in the direction from a frontal direction prompts the hearing aid that is closer to the main sound source to be defined as the local hearing aid and the hearing aid that is more remote from the main sound source to be a remote hearing aid. The local hearing aid, in one frequency band, filters the first signal using an angle-dependent first filter factor, and thus produces a first filtered signal. The first signal, the second signal and/or the direction of the main sound source is used for determining an adaptation coefficient, a first adapted signal and a local directional characteristic.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the priority, under 35 U.S.C. §119, of German application DE 10 2015 211 747.2, filed Jun. 24, 2015; the prior application is herewith incorporated by reference in its entirety. 
       BACKGROUND OF THE INVENTION 
     Field of the Invention 
       [0002]    The invention relates to a method for signal processing in a binaural hearing device having a first hearing aid and a second hearing aid. The first hearing aid has a first microphone for producing a first signal and a first sound generator, and the second hearing aid has a second microphone for producing a second signal and a second sound generator. 
         [0003]    A binaural hearing device usually contains one hearing aid per ear of the user, each of the two hearing aids containing a microphone and an electroacoustic transducer for sound generation. The signals picked up by the two microphones can then be used to form a directional characteristic on the basis of their spacing, it being possible for the directional characteristics in the respective output signal that is output to the electroacoustic transducer to be different for both hearing aids so as to attain better spatial perception. In this case, the term microphone used here and below is intended to be understood to mean both an individual microphone, which is then particularly and essentially an omnidirectional microphone, that is to say a single microphone, and a microphone that contains a plurality of single microphones, particularly two single microphones, and that as such already has a directional characteristic through the interconnection of the single microphones, that is to say is a directional microphone. In other words, in the latter case, a hearing aid then has a monaural directional microphone system. 
         [0004]    In a conversation situation with multiple interlocutors that surround the user of a hearing device in various directions, it is possible, given a significant noise level in the surroundings, for adaptation of the binaural directional characteristic to contribute to isolating the voice signals from individual interlocutors and hence improve comprehension of the voice signal that comes from a particular target interlocutor for the user of the binaural hearing device. Interfering noise in proximity to the target interlocutor can be reduced in this case in the same way as conversation contributions from other interlocutors if they are identified as not being the relevant useful signal at that moment. This is achieved by virtue of the directional characteristic being oriented in a comparatively narrow angle range, for example with a total angular aperture of 90 degrees or even just 45 degrees, in the frontal direction of the user. 
         [0005]    Usually, adaptation of the binaural directional characteristic requires precise knowledge of the position of the target sound source or target interlocutor, or, synonymously, of the exact direction from which the useful signal comes. For operation of hearing devices, it is usually assumed in this case that the position of the target sound source is in the frontal direction, which is to say approximately 0 degrees relative to the line of vision of the user. A binaural directional characteristic with an orientation of 0 degrees and an angular aperture of 90 degrees or even just 45 degrees then suppresses a large proportion of the background noise, which first of all improves the signal-to-noise ratio for the useful signal coming from the target interlocutor. Furthermore, voice signals from other interlocutors outside the angle range in which the directional characteristic has a high sound sensitivity are also suppressed as appropriate. Such a hearing situation, which is generally referred to as a “cocktail party situation”, can arise for a user of a hearing device whenever a conversation is to be held in the presence of other people who are themselves holding conversations with one another. 
         [0006]    In a normal conversation situation, the interlocutor makes small movements that may be in an angle range of up to 10 or even up to 20 degrees. Similarly, the user of the binaural hearing device may also make natural head movements by virtue of his gestures in a conversation, which head movements can lead to similar angular deviations in his frontal direction relative to the interlocutor. These movements can noticeably attenuate the voice signal from the interlocutor in the conversation on account of the narrow angular aperture of the directional characteristic. Since particularly head movements by the user of the binaural hearing device during a conversation situation are often fast and barely perceptible to the user himself, and this means that fluctuations in the signal level from the binaural hearing device are correspondingly brief, the auditory perception by the user can be significantly impaired, and, particularly on account of the relatively high concentration that is required as a result of the fluctuations in the sound level, may even be perceived as disagreeable. 
         [0007]    Published, non-prosecuted German patent application DE 10 2013 207 149 A1 discloses a hearing aid system having at least two hearing aids and also a method for operation of said hearing aid system. The hearing aid system contains particularly a signal processing apparatus for processing audio signals and a signal connection for transmitting a first audio signal from each hearing aid to the signal processing apparatus. The signal processing apparatus rates a signal component from the preferential direction in relation to the head of the wearer in the first audio signals, and the signal processing device uses the first audio signals to produce a first binaural directional microphone signal and sets the directional characteristic thereof on the basis of the rating. In this situation, other useful signals, e.g. vocal contributions in a discussion, are prevented from being suppressed. 
         [0008]    Published, European patent application EP 2 928 210 A1 proposes a binaural hearing system, containing a left and a right hearing aid, with noise suppression and with a user interface. The left and right hearing aids contain at least two input units that, in a number of frequency bands and time entities, provide a representation of an input signal in the time domain, and a noise suppression system having a multichannel “beamformer” that is connected to the input units and produces a directional signal. The wearer of the hearing system can use the user interface to prescribe directivity for a target signal. 
       SUMMARY OF THE INVENTION 
       [0009]    The invention is based on the object of specifying for a binaural hearing device a method that, in a hearing situation with a main sound source against a noisy background, prevents fluctuations in the signal level on the basis of relative movements by the main sound source in relation to a user of the binaural hearing device as quickly and efficiently as possible. 
         [0010]    The invention achieves the cited object by method for signal processing in a binaural hearing device having a first hearing aid and a second hearing aid. The first hearing aid has a first microphone for producing a first signal and a first sound generator, and the second hearing aid has a second microphone for producing a second signal and a second sound generator. The first signal and the second signal are taken as a basis for at least approximately ascertaining a direction of a main sound source. A deviation in the direction of the main sound source from a frontal direction of the binaural hearing device prompts the hearing aid that is closer to the main sound source in each case to be defined as the local hearing aid and the hearing aid that is more remote from the main sound source to be defined as the remote hearing aid. 
         [0011]    In this case, in the local hearing aid, at least in one frequency band, the first signal is filtered using at least one first angle-dependent filter, that is to say by applying an angle-dependent filter factor, and this produces a filtered first signal. The first signal and/or the second signal and/or the direction of the main sound source is/are taken as a basis for determining an adaptation coefficient. An adapted first signal is produced from the first signal and the filtered first signal on the basis of the adaptation coefficient, and a local directional characteristic of a reproduction signal that is to be output by the sound generator of the local hearing aid is determined from the adapted first signal and the second signal. Refinements that are advantageous and in some cases inventive in themselves are the subject matter of the subclaims and of the description below. 
         [0012]    In this context, at least approximate ascertainment of the direction of the main sound source is intended to be understood to mean particularly that a plurality of angle ranges are determined or prescribed and that the angle ranges with which the direction of the main sound source can be associated are ascertained. In particular, this can involve one of the angle ranges being associated with the frontal direction of the binaural hearing device, and hence containing a zero angle on the angle scale on which the division into the angle ranges is based. In this case, a deviation in the direction of the main sound source from the frontal direction of the binaural hearing device can occur by virtue of the direction of the main sound source being associated with a different angle range than the one corresponding to the frontal direction. In this case, the frontal direction of the binaural hearing device can be defined preferably by the plane of symmetry of the two hearing aids during operation when worn properly by the user. 
         [0013]    In particular, it is also possible for a frontal angle range and a right and left deviation range to be defined in this case, so that the approximate determination of the direction of the main sound source in this case means the association of the main sound source either with the frontal angle range or with one of the two deviation ranges. Filtering of the first signal using at least one angle-dependent first filter factor particularly includes multiplication of the first signal by an angle-dependent first filter factor in a relevant frequency band. However, the first signal can likewise also be convoluted with a vector-value filter factor in the time domain or in a frequency domain, in order to produce the first filtered signal. 
         [0014]    To determine the adaptation coefficient in a frequency band, the first signal needs to be associated either with the local hearing aid or with the remote hearing aid, and the second signal needs to be associated with the hearing aid that then remains. The adaptation coefficient in a local hearing aid specifies whether and, if need be, to what extent in the local hearing aid a first signal needs to be adapted to suit the second signal by producing the first adapted signal from the first signal and the first filtered signal. By way of example, this involves the first adapted signal being formed by mixing the first signal and the first filtered signal, e.g. in the form of a weighted sum. In particular, the first adapted signal will be formed by a convex sum of the first signal and the first filtered signal with the adaptation coefficient as convexity parameter. In this case, the adaptation coefficient lies between 0 and 1, the first filtered signal being forwarded directly for a value of 1, corresponding to complete adaptation of the first signal, whereas no adaptation takes place for a value of 0. 
         [0015]    In this case, the angle-dependent first filter factor that is used to filter the first signal in order to produce the first filtered signal takes account of the fact that, in the case of a deviation in the direction of the main sound source from the frontal direction, a minimum time shift caused by the propagation time difference firstly arises between the first signal and the second signal. This shift can initially be approximated as a phase shift. In addition, secondly, shadowing effects arise in the cited case of the angular deviation as result of the head of the user of the binaural hearing device, as result of which the remote hearing aid has a weaker signal level. The filtering of the first signal using the first filter factor compensates for the phase difference and the volume differences between the first signal and the second signal for the direction of the main sound source, as result of which the main sound source can initially be considered to be a frontal source for the further signal processing in the local hearing aid on account of the aligned level and the aligned phase in the first signal and in the second signal. 
         [0016]    In a hearing situation for the user of the binaural hearing device in which a voice signal from an interlocutor needs to be reproduced as clearly as possible while background noise, such as other voice signals, need to be suppressed as far as possible, the binaural directional characteristic is in most cases oriented very narrowly to the front in order to reduce the undesirable sound signals as result of the lower sound sensitivity in those directions that do not correspond to the voice signal from the interlocutor, which is considered to be the useful signal. Since the binaural directional characteristic, that is to say the directional characteristic formed on the basis of signal components from the two microphones, is now formed in the reproduction signal from one of the sound generators at a time, on the basis of the first adapted signal and the second signal, and the directional deviation of the main sound source from the frontal direction has effectively been corrected in the two cited signals, a voice signal from an interlocutor is no longer attenuated by the narrow binaural directional characteristic given relative movements between the interlocutor and the user of the binaural hearing device. 
         [0017]    In the case of such relative movements as can arise as result of brief head movements by the user of the binaural hearing device or as a result of spontaneous gestures by the interlocutor, the interlocutor is, in simple terms, always “returned to the frontal direction” by virtue of the adaptation of the first signal to suit the second signal. A particular advantage in this case is that the adaptation of the first signal to suit the second signal, which corrects the effects of the relative movements between the user and an interlocutor, can be effected regardless of the formation of the binaural directional characteristic, and hence does not influence the algorithm of the latter. 
         [0018]    If need be, after the formation of the binaural directional characteristic in the local hearing device from the first adapted signal and the second signal, the reproduction signal can still be appropriately reworked in order to achieve as realistic as possible a spatial perception of the signal from the main sound source. 
         [0019]    Preferably, the approximate direction of the main sound source and/or the adaptation coefficient is/are ascertained in at least one frequency band on the basis of the signal levels of the first signal and the second signal. In particular, this can be affected on a frequency band by frequency band basis, with only a subset of frequency bands being used for the final determination of the direction of the main sound source. Direction determination on the basis of the differences in the level of the first signal and of the second signal can be implemented particularly simply and quickly. In particular, it is also possible for the signal level of the sum of the first signal and the second signal to be used in order to be able to take account of any phase cancellation effects too. 
         [0020]    Alternatively, in at least one frequency band, the value of an angle-dependent second filter factor can be prescribed at least for a left deviation angle, a zero angle and a right deviation angle. A signal can be selected from the first signal and the second signal and needs to be multiplied by the second filter factor for the purpose of orientation, which produces a respective oriented signal. An angle-dependent interference power can be ascertained from the difference between the oriented signal and the other signal, and an angle-dependent total power can be ascertained from the sum of the oriented signal and the other signal. A normalized angle-dependent interference power can be ascertained from the angle-dependent interference power and the angle-dependent total power, and a comparison of the normalized angle-dependent interference powers can be taken as a basis for ascertaining the approximate direction of the main sound source and/or an adaptation coefficient at least for the left deviation angle, the zero angle and the right deviation angle. 
         [0021]    In this case, prescribing the second filter factor for a left deviation angle, a zero angle and a right deviation angle corresponds to splitting the space into three angle ranges, the direction of the main sound source being determined approximately by classification into one of the three angle ranges. This classification is now performed as described below. 
         [0022]    Since the selected signal is multiplied by the second filter factor—at least for the left deviation angle, the zero angle and the right deviation angle in each case—it is oriented in line with the other signal. In this case, this orientation is effected such that, for the angle that is used as a parameter in the angle-dependent second filter factor, the two signals do not have any significant phase and volume differences. If the difference is now formed from the oriented signal and the other signal, then any sound signal from that direction that is used as an angle parameter in the second filter factor is approximately cancelled out. For this angle, the angle-dependent interference power is close to zero. 
         [0023]    So as now to be able to compare the angle-dependent interference power for the three cited angle ranges with one another, the interference power still needs to be normalized beforehand using the total power that is formed from the summed signal containing the adapted signal and the other signal. In this case the angle-dependent interference power and the angle-dependent total power preferably need to be computed as the absolute value or square of the absolute value of the difference or the sum of the oriented signal and the other signal. 
         [0024]    The direction of a main sound source can then be identified as that direction in which the normalized angle-dependent interference power is at a minimum. A priori, this can also be performed for more than three angle ranges, but for most applications it is sufficient to distinguish between the frontal region and two deviation regions distributed symmetrically to the left and right. 
         [0025]    A further advantage in this case is found to be when, in a plurality of frequency bands, the comparison of the normalized angle-dependent interference powers is taken as a basis in each case for determining a frequency-band-dependent direction parameter at least for the left deviation angle, the zero angle and the right deviation angle, wherein the approximate direction of the main sound source is ascertained from the frequency-band-dependent direction parameters. By way of example, this can be affected by a possibly weighted mean value of the direction parameters. Preferably, determination of the direction of the main sound source is performed only in those frequency bands in which a significant directional dependency of the sound signal from the main sound source can be expected. By using direction parameters from multiple frequency bands, it is possible to compensate for or minimize errors in the direction determination, which can arise on account of fluctuations, for example. 
         [0026]    Preferably, the first filter factor for producing the first filtered signal and the second filter factor have the same frequency dependency for the respective frequency band and have the same angle dependency at least for the left deviation angle, the zero angle and the right deviation angle. This means that adapting the first signal to suit the second signal, that is to say angle-dependent orientation, involves the use of filter factors having the same functional dependency as for ascertaining the direction of the main sound source. 
         [0027]    In an advantageous refinement of the invention, in the local hearing aid, a first filtered signal is produced in each of a plurality of frequency bands and the first filtered signal is taken as a basis for producing a first adapted signal, wherein, as the frequency of the frequency band for producing the first filtered signal for the first filter factor rises, the angle increases monotonously in each case in the direction of the main sound source. What is meant by a monotonous increase is particularly that the angle that is used for the first filter factor can be chosen to be constant for multiple successive frequency bands, with a smaller angle for the first filter factor being chosen for a group of low frequency bands and a larger angle for the first filter factor being chosen for a group of higher frequency bands. This takes account of the circumstance that the directional dependency of signal components in lower frequency bands is usually lower, which means that the need for angle-dependent adaptation has less of an effect in this case than in higher frequency bands, in which standard useful signal components has a much higher directional dependency that should preferably be taken into account. 
         [0028]    Expediently, the absolute value of the first filter factor is ≦1 in each case. This is favorable particularly for the case in which the first signal, which can be adapted to suit the second signal by the first filter factor, is formed by the signal from the local hearing aid. The signal that is recorded by the microphone of the remote hearing aid has a lower volume level on account of shading effects due to the head of the user. This is represented by a first filter factor, the absolute value of which is chosen to be ≦1. The first filtered signal undergoes no raising of the level as result of the filtering process. The selection concerning whether the signal from the microphone of the local hearing aid or the signal from the microphone of the remote hearing aid is to be chosen as the first signal that needs to be adapted to suit the second signal can be made particularly on the basis of the current hearing situation in this case. Specifically in noisy surroundings, the “local signal” preferably needs to be adapted to suit the “remote signal”, since, in this case, the adaptation process does not raise the level of the signal still further, which means that oversaturation can be avoided. 
         [0029]    A further advantage is found to be when, in a reproduction signal for the local hearing device, the first angle-dependent filter factor and/or the adaptation coefficient is/are taken as a basis for performing compensation for a volume and a phase difference when the first signal is produced by the microphone of the local hearing aid. In this case of adaptation, the “local signal” is effectively provided with the phase and volume reference of the remote hearing aid in the local hearing aid. For the reproduction signal from the local hearing aid, this referencing to the remote hearing aid needs to be compensated for in order to be able to obtain a spatial perception that is as realistic as possible for the user of the hearing aid. 
         [0030]    The invention further cites a binaural hearing device having a first hearing aid and a second hearing aid. The first hearing aid has a first microphone for producing a first signal and a first sound generator, and the second hearing aid has a second microphone of a second signal and a second sound generator. At least one signal processing unit is provided that is set up to perform the method described above. The advantages cited for the method and developments thereof can be applied to the binaural hearing device mutatis mutandis in this case. 
         [0031]    Other features which are considered as characteristic for the invention are set forth in the appended claims. 
         [0032]    Although the invention is illustrated and described herein as embodied in a method for signal processing in a binaural hearing device, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. 
         [0033]    The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         [0034]      FIGS. 1A-1C  show diagrammatic, plan views of a user of a binaural hearing device in a conversation situation with an interlocutor; 
           [0035]      FIG. 2  is a block diagram of a flow of a method for direction-dependent adaptation of signals in the binaural hearing device for the conversation situation shown in  FIG. 1 ; 
           [0036]      FIG. 3  is a block diagram of a further refinement of the method shown in  FIG. 2 ; 
           [0037]      FIG. 4  is a block diagram of an approximate determination of a direction of an interlocutor using an angle-dependent interference power; and 
           [0038]      FIGS. 5A-5C  are plan views of adapted directional characteristics of the binaural hearing device in the conversation situation shown in  FIG. 1A-1C . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0039]    Corresponding parts and parameters are provided with the same reference symbols throughout the figures. 
         [0040]    The influence of the movements of a user of the binaural hearing device in a conversation, or of the movements of an interlocutor, on the signal level of the voice signal from the interlocutor is shown in  FIGS. 1A to 1C .  FIG. 1A  shows a user  1  of a binaural hearing device  2  who is in a conversation with an interlocutor  4 . In this case, the interlocutor  4  is positioned in a frontal direction  6  of the user  1 . Owing to the narrow directional characteristic  8  of the binaural hearing device, interjections from the other interlocutors  10  to  13  are barely perceived by the user  1 . In  FIG. 1B , the main interlocutor  4  of the user  1  has moved slightly to the side, for example owing to a relieving movement. If the user  1  now follows the movement of the interlocutor  4  not directly by changing his line of vision but rather only with his eyes, this results in the voice signal from the main interlocutor  4  being slightly attenuated on account of the movement of the main interlocutor within the directional characteristic  8  of the binaural hearing device  2 . There is a similar occurrence in  FIG. 1C , in which the user  1  turns his line of vision slightly while the main interlocutor  4  maintains his position. In this case too, the result is that the relative movement means that the main interlocutor  4  is no longer positioned in the center of the directional characteristic  8 , as result of which his voice signal undergoes attenuation. 
         [0041]      FIG. 2  schematically shows a block diagram of the flow of a method  20  for signal processing in a binaural hearing device  2 . The binaural hearing device  2  contains a first hearing aid  22  and a second hearing aid  24 , which each contain a microphone, which is not shown in the drawing. The microphone of the first hearing aid  22  produces a first signal  26  from sound, and the microphone of the second hearing aid  24  correspondingly produces a second signal  28 . On the basis of the first signal  26  and the second signal  28 , a direction identifier  30  can establish that the interlocutor  4  of the user  1 , who in this case forms the main sound source  32 , is not oriented in the frontal direction  6  of the user  1  but rather has a certain angular deviation  34  relative thereto. As result of this angular deviation  34 , the second hearing aid  24 , which is closer to the interlocutor  4 , is defined as the local hearing aid  36 , while the first hearing aid  22 , which is more remote from the interlocutor  4 , is defined as the remote hearing aid  38 . In the individual frequency bands  39 , the first signal  26  is now multiplied by a first filter factor  40  each time in the local hearing aid  36 , as result of which a first filtered signal  32  is first produced. 
         [0042]    In the direction identifier  30 , the direction of the interlocutor  4  is taken as a basis for determining an adaptation coefficient  44 , and then a first adapted signal  46  is produced from the first signal  26 , the first filtered signal  42  and the adaptation coefficient  44 . In this case, the first adapted signal  46  is formed as a weighted overlay containing the first filtered signal  42  and the first signal  26 , for example, the adaptation coefficient  44  being used for the weighting. The first adapted signal  46  and the second signal  28  are then used to form the directional characteristic  48  that the reproduction signal  50  that is to be output via the sound generator of local hearing aid  36  needs to have in the relevant frequency band. 
         [0043]      FIG. 3  shows an alternative refinement of the method  20  shown in  FIG. 2 . In the case that exists here, the local hearing aid  36  can be associated with the first hearing aid  22 , while the remote hearing aid  38  can be associated with the second hearing aid  24 . In this case too, the first signal  26  is adapted to suit the second signal  28  by virtue of the first signal  26  first of all being multiplied by a first filter factor  40  on a frequency band by frequency band basis, which produces a filtered first signal  42  that is used by means of the adaptation coefficient  40  that was determined in the direction identifier  30  to form the first adapted signal  46 . The first adapted signal  46  is then used with the second signal  28  as an input variable in the forming directional characteristic  48 . Since the first hearing aid  22  selected in this case was the local hearing aid  36  that is closer to the interlocutor  4  of the user  1 , but the first signal  26  is being adapted in respect of the reference of the remote hearing aid  38 , the adaptation coefficient  44  and the first filter factor  40  can be used to perform compensation  52  for the volume and the phase difference on the reproduction signal  50  in order to restore the spatial perception as far as possible. 
         [0044]      FIG. 4  shows a block diagram of an approximate direction determination  30  for the voice signal from an interlocutor, who is not shown in more detail. For the space in front of the user  1  of the binaural hearing device, a left deviation angle  56   a,  a zero angle  56   b  and a right deviation angle  56   c  are prescribed, which divides the space in front of the user into three angle ranges. For the left deviation angle  56   a,  the zero angle  56   b  and the right deviation angle  56   c,  angle-dependent second filter parameters  40   a,    40   b,    40   c  are prescribed each time in a frequency band  39 . In this case, these can have the same angle dependency as the first filter parameter  40  in the respective frequency band  39 . From the first signal  26  and the second signal  28 , one signal in this case the first signal  26 , is selected that needs to be oriented to the other signal, that is to say in this case the second signal  28 . 
         [0045]    To this end, the first signal  26  is first of all multiplied by the respective second filter parameter  40   a,    40   b,    40   c  for each of the cited angles  56   a,    56   b,    56   c,  as result of which an angle-dependent oriented signal  60   a,    60   b,    60   c  is formed in each case. For each of the cited angles  56   a,    56   b,    56   c,  an angle-dependent interference power  62   a,    62   b,    62   c  and an angle-dependent total power  64   a,    64   b,    64   c  are now formed from the oriented signal  60   a,    60   b,    60   c  with the second signal by difference and sum formation. The angle-dependent interference power  62   a,    62   b,    62   c  is normalized in each case by dividing the associated angle-dependent total power  64   a,    64   b,    64   c  thereby, as result of which a normalized angle-dependent interference power  66   a,    66   b,    66   c  is obtained for each of the angles  56   a,    56   b,    56   c  from the first signal  26  and the second signal  28 . 
         [0046]    The normalized angle-dependent interference powers  66   a,    66   b,    66   c  are then compared with one another. The orientation of the first signal  26  to the second signal  28  is such that a sound that comes each time from the direction of the angle  56   a,    56   b,    56   c  used for orientation does not lead to a significant angle-dependent interference power  62   a,    62   b,    62   c  on account of the difference formation. Therefore, a direction parameter  68  that is used for approximate direction determination for the voice signal from the interlocutor can be ascertained on the basis of that angle among the left deviation angle  56   a,  the zero angle  56   b  and the right deviation angle  56   c  for which the normalized angle-dependent interference power  66   a,    66   b,    66   c  is at a minimum. On the one hand, the direction parameter  68  can then be used in the relevant frequency band directly to determine the adaptation coefficient  44 , and on the other hand, direction parameters  68  for multiple frequency bands  39  can be averaged in order to use this to associate the voice signal from the interlocutor, which is the main sound signal for the user  1 , with one of the three cited angles. 
         [0047]      FIGS. 5A-5C  each show a plan view of the conversation situation shown in  FIGS. 1A-1C  and the adaptations of the directional characteristics  8 ,  48  to suit the movements of the interlocutor  4  and to suit the movements of the user  1 . In  FIG. 5A , the interlocutor  4  is standing head-on to the user; an adaptation of the directional characteristics  8  is not necessary. In  FIG. 5B , the interlocutor  4  has made a slight sideways movement. The local directional characteristic  48  of the local hearing aid  36  follows this movement, while the directional characteristic  8  of the remote hearing aid  38  continues to be oriented in the frontal direction  6 . As result, the voice signal from the interlocutor continues to be captured well by the local directional characteristic  48 , whereas the shift in respect of the directional characteristic  8  of the remote hearing aid  38  means that the voice signal is attenuated in the reproduction signal therefrom. A similar situation is shown in  FIG. 5C , in which the user  1  has now slightly turned his frontal direction  6  relative to the interlocutor  4 . The local directional characteristic  48  of the local hearing aid does not follow this turn, however, but rather continues to be oriented to the interlocutor  4 , so that the voice signal from the latter does not experience any kind of attenuation in the reproduction signal from the local hearing aid  36 . 
         [0048]    Although the invention has been illustrated and described in more detail by the preferred exemplary embodiment, the invention is not restricted by this exemplary embodiment. Other variations can be derived therefrom by a person skilled in the art without departing from the scope of protection of the invention. 
         [0049]    The following is a summary list of reference numerals and the corresponding structure used in the above description of the invention:
     1  User     2  Binaural hearing device     4  Interlocutor     6  Frontal direction     8  Directional characteristic     10 - 13  Interlocutor     20  Method     22  First hearing aid     24  Second hearing aid     26  First signal     28  Second signal     30  Direction identifier     32  Main sound source     34  Angular deviation     36  Local hearing aid     38  Remote hearing aid     39  Frequency band     40  First filter factor     40   a - c  Second filter factor     42  First filtered signal     44  Adaptation coefficient     46  First adapted signal     48  Local directional characteristic     50  Reproduction signal     52  Compensation     56   a  Left deviation angle     56   b  Zero angle     56   c  Right deviation angle     60   a - c  Oriented signal     62   a - c  Angle-dependent interference power     64   a - c  Angle-dependent total power     66   a - c  Normalized angle-dependent interference power     68  Direction parameter