Abstract:
A hearing apparatus and an associated method for suppressing feedback include a microphone emitting a microphone signal and a receiver picking up a receiver signal by subtracting a compensation signal from the microphone signal. The hearing apparatus includes a number of preset static first compensation filters for forming first compensation signals from the receiver signal and a first selection unit, which selects a first compensation signal in such a way that a feedback signal caused by the feedback is minimal in the receiver signal. An advantage thereof is that adaptation artifacts cannot occur.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the priority, under 35 U.S.C. §119, of German Patent Application DE10 2009 031 135.1, filed Jun. 30, 2009; 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 hearing apparatus for suppressing feedback having a microphone emitting a microphone signal and a receiver picking up a receiver signal by subtracting a compensation signal from the microphone signal. The invention also relates to a method for suppressing feedback in a hearing apparatus by subtracting a compensation signal from a microphone signal. 
         [0003]    A frequent problem with hearing apparatuses is feedback between an output of the hearing apparatus and an input, in which such feedback is experienced as interference in the form of whistling.  FIG. 1  illustrates the principle of acoustic feedback using the example of a hearing device or hearing aid  1 . The hearing device  1  includes a microphone  2 , which picks up an acoustic useful signal  10 , converts it to an electrical microphone signal  11  and emits it to a signal processing unit  3 . The microphone signal  11  is, for example, conditioned and amplified in the signal processing unit  3  and emitted to a receiver  4  as a receiver signal  12 . In the receiver  4 , the electrical receiver signal  12  is converted back into an acoustic output signal  13  and emitted to an eardrum  7  of a hearing device wearer. 
         [0004]    The problem is that some of the acoustic output signal  13  reaches the input of the hearing device  1  by way of an acoustic feedback path  14 , is overlaid there with the useful signal  10  and is picked up by the microphone  2  as a sum signal. Corresponding phasing and amplitude of the fed back output signal produce interference in the form of feedback whistle. Attenuation of acoustic feedback is low due to open hearing device coverage in particular, thereby exacerbating the problem. 
         [0005]    Adaptive systems for feedback suppression have been available for some time in order to resolve the problem. With those systems, the acoustic feedback path  14  is simulated digitally. Simulation takes place, for example, through the use of an adaptive compensation filter  5 , which is supplied, for example, by the signal  12  driving the receiver. After filtering in the compensation filter  5 , a filtered compensation signal  15  is subtracted from the microphone signal  11 . This ideally cancels the effect of the acoustic feedback path  14  and an input signal  16  of the signal processing unit  3  with feedback compensation results. 
         [0006]    It is necessary to regulate or adjust the filter coefficients of the adaptive compensation filter  5  for effective feedback suppression. To that end, an analysis unit  6  is used to evaluate the input signal  16  of the signal processing unit  3  and check for possible feedback. The adjustment may cause artifacts to be produced, since additional signal components are generated if the compensation filters  5  are not optimally adaptive. Feedback whistle can also occur if a compensation filter  5  is not adapted optimally. European Patent EP 1 033 063 B1 discloses such a hearing device, with which two adaptive compensation filters operating in parallel are used to improve feedback suppression. 
       SUMMARY OF THE INVENTION 
       [0007]    It is accordingly an object of the invention to provide a hearing apparatus and a method for improved feedback suppression in a hearing apparatus, which overcome the hereinafore-mentioned disadvantages of the heretofore-known apparatuses and methods of this general type. 
         [0008]    The concept of the invention is to select the compensation filter that is suitable for effective feedback suppression from a number of previously set static compensation filters. 
         [0009]    With the foregoing and other objects in view there is provided, in accordance with the invention, a hearing apparatus for suppressing feedback. The hearing apparatus comprises a microphone emitting a microphone signal, a receiver picking up a receiver signal, a plurality of preset static first compensation filters for forming first compensation signals from the receiver signal, and a first selection unit selecting and subtracting a first compensation signal from the microphone signal in such a way that a feedback signal caused by the feedback is minimal in the receiver signal. This has the advantage that no adaptation artifacts can occur. 
         [0010]    In accordance with another feature of the invention, the hearing apparatus can also include an adaptive first compensation filter for forming a further first compensation signal from the receivere signal. As a result, adaptation artifacts only occur if none of the static first compensation filters generates a better resulting signal than the adaptive first compensation filter. 
         [0011]    In accordance with a further feature of the invention, the hearing apparatus can include a preset static second compensation filter for forming a second compensation signal from the receiver signal and a second selection unit connected between the microphone and the first selection unit. The second selection unit subtracts the second compensation signal from the microphone signal, if this allows a feedback signal caused by the feedback to be minimized in the receiver signal. 
         [0012]    In accordance with an added feature of the invention, the second compensation filter can also model a mechanical feedback path within the hearing apparatus. This has the advantage that it is possible to compensate for feedback paths due to the mechanical structure of the hearing apparatus. 
         [0013]    In accordance with an additional feature of the invention, the static first compensation filters can model different acoustic feedback paths. This allows “typical” feedback paths to be suppressed specifically. 
         [0014]    In accordance with yet another feature of the invention, the filter coefficients of the static first compensation filters can be determined by feedback path measurements. This has the advantage that the filter coefficients can be adjusted individually to the use situation of the hearing apparatus. 
         [0015]    In accordance with yet a further feature of the invention, the hearing apparatus can also be a hearing device or hearing aid. 
         [0016]    With the objects of the invention in view, there is also provided a method for suppressing feedback in a hearing apparatus. The method comprises forming first compensation signals from a receiver signal using preset static first compensation filters, and selecting and subtracting one of the formed first compensation signals from a microphone signal in such a way that a feedback signal caused by the feedback is minimal in the receiver signal. 
         [0017]    In accordance with another mode of the invention, the method includes forming a further first compensation signal from the receiver signal through the use of an adaptive first compensation filter. 
         [0018]    In accordance with a further mode of the invention, the method includes forming a second compensation signal from the receiver signal through the use of a preset static second compensation filter and subtracting the second compensation signal from the microphone signal, if this allows a feedback signal caused by the feedback to be minimized in the input signal. 
         [0019]    In accordance with an added mode of the invention, the second compensation filter can also model a mechanical feedback path within the hearing apparatus. 
         [0020]    In accordance with an additional mode of the invention, the static first compensation filters can model different acoustic feedback paths. 
         [0021]    In accordance with a concomitant mode of the invention, the filter coefficients of the static first compensation filters can also be determined by feedback path measurements. 
         [0022]    Other features which are considered as characteristic for the invention are set forth in the appended claims. 
         [0023]    Although the invention is illustrated and described herein as embodied in a hearing apparatus and a method for suppressing feedback in a hearing apparatus, 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. 
         [0024]    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 
         [0025]      FIG. 1  is a schematic and block circuit diagram of a hearing device with feedback suppression according to the prior art; 
           [0026]      FIG. 2  is a basic schematic and block circuit diagram of a hearing device having a number of static compensation filters; 
           [0027]      FIG. 3  is a schematic and block circuit diagram of a further hearing device having a number of static compensation filters; 
           [0028]      FIG. 4  is a basic schematic and block circuit diagram of a hearing device having a number of static compensation filters and an adaptive compensation filter; 
           [0029]      FIG. 5  is a schematic and block circuit diagram of a further hearing device having a number of static compensation filters and an adaptive compensation filter; 
           [0030]      FIG. 6  is a basic schematic and block circuit diagram of a hearing device having a number of static compensation filters, an adaptive compensation filter and an additional wideband static compensation filter; and 
           [0031]      FIG. 7  is a schematic and block circuit diagram of a further hearing device having a number of static compensation filters, an adaptive compensation filter and an additional wideband static compensation filter. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0032]    Referring now in detail to the figures of the drawings and first, particularly, to  FIG. 2  thereof, in which the principle of the invention is illustrated with the aid of a circuit diagram, it is noted that in the exemplary embodiments which follow, the invention is described by using the example of a hearing device, although naturally the descriptions also apply to other hearing apparatuses. A microphone  2  of a hearing device  1  emits a microphone signal  11 , which is picked up by a first selection unit  8 . The microphone signal  11  is subject to a feedback signal, which is formed as a result of acoustic feedback between a receiver  4  of the hearing device  1  and the microphone  2 . In order to suppress the feedback signal, a first compensation signal  151  is subtracted in the selection unit  8 . Ideally, the first compensation signal  151  should compensate fully for the feedback signal. 
         [0033]    Therefore, according to the invention, a number of first compensation signals  151  are generated from a receiver signal  12 , which is present at the output of a signal processing unit  3  of the hearing device  1 , with the aid of static first compensation filters  51 . The receiver signal  12  is also the input signal of the receiver  4 . The first selection unit  8  selects the most suitable compensation signal  151  from an analysis of the microphone signal  11  and the compensation signals  151  and emits the microphone signal, which thus has feedback compensation, as an input signal  16  to the signal processing unit  3 . 
         [0034]    The filter coefficients of the static first compensation filters  51  are set to “typical” feedback paths. The filter coefficients are determined by a hearing device acoustician using measuring techniques through the use of feedback path measurements, for example at the ear of a hearing device wearer. The use of static first compensation filters is possible, because in the everyday environment of a hearing device user there are a finite number of approximately identical wearing conditions and therefore feedback paths. A large proportion of feedback-critical situations can therefore be overcome. 
         [0035]    The use of statically operating first compensation filters  51  means that adaptation artifacts do not occur. In order to avoid artifacts when switching between different first compensation signals  151 , it is possible for a controlled cross-fading to take place between the compensation signals  151  rather than a “hard” switching. 
         [0036]    An application of the principle according to  FIG. 2  is shown in  FIG. 3 .  FIG. 3  shows a circuit diagram of a hearing device  1  having a microphone  2  to pick up sound and a receiver  4  to emit sound to the eardrum of a hearing device wearer. Feedback is eliminated from the microphone signal  11  emitted by the microphone  2  in a first selection unit  8  and the microphone signal  11  is then amplified, for example, in a signal processing unit and emitted as the receiver signal  12 , between the microphone  2  and the receiver  4 . A number of static first compensation filters  51  are used to obtain compensation signals  151  from the receiver signal  12 . The compensation signals  151  are supplied to the first selection unit  8 . 
         [0037]    In the first selection unit  8 , the compensation signals  151  are respectively subtracted from the microphone signal  11  and supplied as input signals  18  to a first switching unit  82 . The first switching unit  82  switches one of the input signals  18  through and emits it as a further input signal  16  to the signal processing unit  3 . The first switching unit  82  is controlled by a first analysis unit  81  with the aid of a first switching signal  19 . To this end, the first analysis unit  81  analyzes the input signals  18  of the first switching unit  82  and the microphone signal  11 . The input signal  18  having the most effective feedback suppression is selected on the basis of the analysis. The analysis unit  81  decides, for example, on the basis of a minimum energy of the input signal  18  or a minimization of a water mark in the input signal  18 , which is impressed onto the receiver signal  12 . 
         [0038]    In order to also be able to counteract feedback paths, which cannot be stored statically in a hearing device, it is possible to combine the static first compensation filters  51  with an additional adaptive first compensation filter. 
         [0039]      FIG. 4  shows the principle of combining static and adaptive compensation filters, by using a circuit diagram. A microphone  2  of a hearing device  1  emits a microphone signal  11 , which is picked up by a first selection unit  8 . The microphone signal  11  is subject to a feedback signal, which is formed as a result of acoustic feedback between a receiver  4  of the hearing device  1  and the microphone  2 . In order to suppress this feedback signal, a first compensation signal  151  is subtracted in the first selection unit  8 . The first compensation signal  151  should ideally be identical to the feedback signal. 
         [0040]    Therefore, according to the invention, a number of first compensation signals  151  are generated from a receiver signal  12  with the aid of static first compensation filters  51 . The receiver signal  12  is present at the output of a signal processing unit  3  of the hearing device  1 . The receiver signal  12  is also the input signal of the receiver  4 . An adaptive first compensation filter  53  also generates a further first compensation signal  151  from the receiver signal  12 . 
         [0041]    The first selection unit  8  selects the most suitable signal from an analysis of the microphone signal  11  and the compensation signals  151  and emits the microphone signal which thus has feedback compensation, as an input signal  16  to the signal processing unit  3 . 
         [0042]    Adaptation artifacts then only occur if none of the static first compensation filters  51  generates a better resulting input signal  18  than the adaptive first compensation filter  53 . In the case of a better static first compensation filter  51 , an adaptation control of the adaptive first compensation filter  53  can also adopt the former&#39;s filter coefficients as a start value for the adaptation. 
         [0043]    An application of the principle according to  FIG. 4  is shown in  FIG. 5 .  FIG. 5  shows a circuit diagram of a hearing device  1  having a microphone  2  to pick up sound and a receiver  4  to emit sound to the eardrum of a hearing device wearer. Feedback is eliminated from the microphone signal  11  emitted by the microphone  2  in a first selection unit  8  and the microphone signal  11  is then amplified, for example in a signal processing unit, and emitted as the receiver signal  12 , between the microphone  2  and the receiver  4 . A number of static first compensation filters  51  and an adaptive first compensation filter  53  are used to obtain compensation signals  151  from the receiver signal  12 . The compensation signals  151  are supplied to the first selection unit  8 . 
         [0044]    In the first selection unit  8 , the compensation signals  151  are respectively subtracted from the microphone signal  11  and supplied as the input signal  18  to a first switching unit  82 . The first switching unit  82  switches one of the input signals  18  through and emits it as the input signal  16  to the signal processing unit  3 . The first switching unit  82  is controlled by a first analysis unit  81  with the aid of a first switching signal  19 . To this end, the first analysis unit  81  analyzes the input signals  18  of the first switching unit  82  and the microphone signal  11 . The input signal  18  having the most effective feedback suppression is selected on the basis of the analysis. The analysis unit  81  decides, for example, on the basis of a minimum energy of the input signal  18  or a minimization of a water mark in the input signal  18 , which is impressed onto the receiver signal  12 . 
         [0045]    The adaptive first compensation filter  53  is controlled with the aid of an analysis unit  6 . The analysis unit  6  evaluates the first compensation signal  151  of the adaptive first compensation filter  53  subtracted from the microphone signal  11  and sets the filter coefficients of the adaptive first compensation filter  53  correspondingly. 
         [0046]    There is also a further, mechanical, feedback path within the hearing device, as well as the changing external acoustic feedback path. This further path is generally only subject to minor fluctuations and is primarily a function of the structure of the hearing device. This mechanical feedback can be suppressed by a further static compensation filter separately from the first compensation filters. This has the advantage that, unlike an adaptive filter, such a filter can be used wideband since it does not produce any artifacts due to potential incorrect adaptation of the filter coefficients. It is therefore possible to achieve greater maximum amplification of the hearing device by obliterating the feedback element due to housing sound. 
         [0047]      FIG. 6  shows the use of an additional static compensation filter, in principle.  FIG. 6  uses a circuit diagram to show a second selection unit  9  in addition to the components described above in  FIG. 4  between the microphone  2  and the first selection unit  8 . A second compensation signal  152  is formed by a static second compensation filter  52  from the receiver signal  12 . The filter coefficients of the second compensation filter are selected in such a way that mechanical feedback in the hearing device housing is suppressed. The selection unit  9  selects whether the microphone signal  11  or a differential signal between the microphone signal  11  and the second compensation signal  152  is present as an input signal  17  at the first selection unit  8 . 
         [0048]      FIG. 7  shows the application of the principle according to  FIG. 6  by way of example.  FIG. 7  shows the circuit diagram of a hearing device  1  according to  FIG. 5 , extended to include a static second compensation filter  52  and a second selection unit  9 . The selection unit  9  includes a second switching unit  92  and a second analysis unit  91 . The compensation signal  152  of the second compensation filter  52  is subtracted from the microphone signal  11  and supplied to the second switching unit  92  as an input signal  20 . The microphone signal  11  itself is present at a further input of the switching unit  92 . The second switching signal  21  of the second analysis unit  92  controls the second switching unit  92 . The second analysis unit  91  identifies whether or not mechanical feedback is present, from a comparison of the microphone signal  11  with the input signal  20 , both of which are supplied to the second analysis unit  91 . The switching through of the signal  20  with reduced feedback is initiated correspondingly and the second switching unit  92  emits an output signal  17  to the first selection unit  8 .