Abstract:
A method for influencing, e.g., for decreasing, the treble reproduction of an audio signal for reproduction obtained from a received signal, the received field strength and reception quality of the received signal being evaluated and, as a function thereof, the transfer function of at least one filter unit that can be impinged upon by the audio signal being controlled, as well as a circuit assemblage or arrangement for performing such a method for the modification of treble reproduction, so that, among other things, reproduction of the interference may always be reliably concealed and so that no noticeable and/or irritating “flutter” effects may occur. The method may include processing of the output signals of at least two reception interference detectors, and processing of the received field strength may be accomplished respectively in at least one first processing branch operating at a first, e.g. variable, sampling rate and/or in at least one second processing branch operating at a second sampling rate, and the first sampling rate may be set lower than the second sampling rate, so that the treble reproduction can be damped for longer time periods by the first processing branch than the second processing branch.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a method for influencing, e.g., for decreasing, the treble reproduction of an audio signal for reproduction obtained from a received signal, the received field strength and reception quality of the received signal being evaluated and, as a function thereof, the transfer function of at least one filter unit that can be impinged upon by the audio signal being controlled. The present invention further relates to a circuit assemblage for influencing, e.g., for decreasing, the treble reproduction of an audio signal for reproduction obtained from a received signal, the received field strength and reception quality of the received signal being capable of evaluation and, as a function thereof, the transfer function of at least one filter unit that can be impinged upon by the audio signal being controllable.  
         BACKGROUND INFORMATION  
         [0002]    In interference-affected reception areas, interference resulting, e.g., from multi-path propagation is clearly perceptible when a frequency-modulated (FM) station is received. A lesser perception of such interference can be achieved by decreasing the treble reproduction.  
           [0003]    In some systems, this decrease in treble reproduction may be controlled by evaluating the received field strength and/or the reception quality, the transfer function of a filter in the audio signal branch being controlled in proportion thereto. In this context, the treble may be quickly canceled and also quickly switched back in.  
           [0004]    In this connection, however, rapidly canceling the treble and switching it back may be disadvantageous in that reproduction of the interference cannot always and reliably be concealed, with the occurrence of noticeable and irritating effects such as “flutter.” In addition, with the conventional methods and circuit assemblages it may not be possible to coordinate the modification in treble reproduction with a reduction in channel separation.  
         SUMMARY OF THE INVENTION  
         [0005]    It is, therefore, an object of an exemplary method of the present invention to provide a method with regard to the modification of treble reproduction, in such a way that reproduction of the interference may be reliably concealed, and no noticeable and/or irritating “flutter” effects occur, and in this connection, to coordinate the modification in treble reproduction with a reduction in channel separation.  
           [0006]    This object may be achieved by way the exemplary methods and circuit arrangements described herein.  
           [0007]    According to the exemplary method and/or exemplary embodiment of the present invention, the control system therefore encompasses a portion operating at a slow processing speed (e.g., first processing branch as first “HiCut” stage), and a portion operating at a higher processing speed (e.g., second processing branch as second “HiCut” stage).  
           [0008]    The technical significance of this subdivision is that in a highly interference-affected reception area, the treble reproduction needs to be damped for a longer period, up to approximately thirty seconds (so-called “HiCut”). Switching of the various HiCut stages may need to occur slowly in this context so that the switching is not perceptible. This function may be implemented by the control system having a slow processing speed, i.e. by the first processing branch.  
           [0009]    With sporadically occurring interference, however, a long cancellation of treble reproduction may be more noticeable than the interference itself. In this case the treble is canceled only briefly, and also quickly switched back in. This function is implemented by the control system having a fast processing speed, i.e. by the second processing branch. If the treble reproduction is reduced quickly and often, however, this procedure may become too noticeable.  
           [0010]    In the transition region between frequent interference and sporadic interference, a combination of slow control and fast control may be used. According to an exemplary method and/or an exemplary embodiment of the present invention, a treble diminution with a slow time constant is performed and, additively, a short-duration fast treble diminution, with low dynamics, upon occurrence of the interference.  
           [0011]    Accordingly, this signifies that the treble diminution (i.e. decrease in treble reproduction of the audio signal to be reproduced) brought about by means of the slow control system and/or fast control system is overlain by a maximum selection operation.  
           [0012]    If interference is occurring only sporadically or in isolated fashion, the treble diminution resulting from the slow control system is small, and in some circumstances the treble diminution in fact disappears, i.e. is not present at all. In this case only the fast control system, responding for short periods, is active.  
           [0013]    In the case of interference occurring moderately frequently, the treble diminution of the slow control system will be set to a moderate value. In this case there is a greater treble diminution while the fast control system is responding.  
           [0014]    If interference is occurring frequently, there are two possibilities: if the dynamics of the slow control system and the fast control system are identical, what results after the maximum selection operation is the signal of the slow control system; if, on the other hand, the dynamics of the slow control system are lower than the dynamics of the fast control system, then short diminutions equivalent in value to the difference in dynamics between the two control systems will be summed even in the context of frequently occurring interference.  
           [0015]    According to an exemplary embodiment and/or exemplary method, the first processing branch may operate at a first sampling rate on the order of 0 Hz to approx. 950 Hz, so that the treble reproduction may be damped by means of the first processing branch for periods of up to approximately thirty seconds.  
           [0016]    Independently thereof or in combination therewith, the second processing branch may operate at a second sampling rate on the order of approx. 9.5 kHz, since this second sampling rate should be set as high as possible for almost zero-delay reaction to reception interference. In this manner, the treble reproduction by means of the second processing branch can be damped for periods substantially shorter than thirty seconds.  
           [0017]    The exemplary method and the exemplary embodiment of the present invention relates to an approach (which is believed to be unknown) to diminishing the perception of interference in an interference-affected reception area. With this approach, in a context of interference-affected reception, not only may the treble reproduction damped, but the stereo channel separation may also be simultaneously reduced.  
           [0018]    In a manner, in the exemplary method and/or exemplary embodiment of the present invention, the two control systems (influencing, i.e. damping, the treble reproduction, and reducing the stereo channel separation) are coupled to one another in such a way that the same detectors and threshold decisions are used for the slow portion (e.g., first processing branch) of the HiCut control system and for the slow portion of the channel separation control system, ruling out any divergence of these two control systems.  
           [0019]    The exemplary method and/or exemplary circuit arrangement of the present invention further relates to influencing, e.g., decreasing, the treble reproduction of an audio signal for reproduction obtained from a received broadcast signal in at least one broadcast receiver. The at least one broadcast receiver may have digital IF (intermediate frequency) processing, for example, at least one “DigiCeiver” (e.g., digital receiver) or “Digital Car Radio,” for example, of the Blaupunkt company. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]    [0020]FIG. 1 shows a schematic block diagram of an exemplary embodiment of a circuit assemblage, arrangement or system according to the present invention.  
         [0021]    [0021]FIG. 2A shows a schematic diagram of a first and second threshold value decision in the first processing branch of the exemplary embodiment of the circuit assemblage of FIG. 1.  
         [0022]    [0022]FIG. 2B shows a schematic diagram in which the third threshold values in the first processing branch of the circuit assemblage of FIG. 1 are correlated with the pointers in the first processing branch of the exemplary embodiment of the circuit assemblage of FIG. 1.  
         [0023]    [0023]FIG. 3 shows a schematic diagram of an exemplary embodiment of an asymmetrical ramp with a short rise time and long decay time.  
         [0024]    [0024]FIG. 4A shows a schematic diagram of a characteristic curve in a first exemplary embodiment.  
         [0025]    [0025]FIG. 4B shows a schematic diagram of a characteristic curve in a second exemplary embodiment.  
         [0026]    [0026]FIG. 5A shows a schematic diagram of a fourth and fifth threshold value decision in the second processing branch of the exemplary embodiment of the circuit assemblage or arrangement of FIG. 1.  
         [0027]    [0027]FIG. 5B shows a schematic diagram in which the sixth threshold values in the second processing branch of the exemplary embodiment of the circuit assemblage or arrangement of FIG. 1 are correlated with the pointers in the second processing branch of the exemplary embodiment of the circuit assemblage or arrangement of FIG. 1.  
         [0028]    [0028]FIG. 6 shows a schematic diagram of the setting of the eight available filter curves (“HiCut”) according to an exemplary embodiment.  
         [0029]    [0029]FIG. 7A shows a schematic comparison of the operating principle of an exemplary embodiment of the present invention in situations where interference occurs infrequently.  
         [0030]    [0030]FIG. 7B shows a schematic comparison of the operating principle of an exemplary embodiment of the present invention in situations where interference occurs infrequently.  
         [0031]    [0031]FIG. 7C shows a schematic comparison of the operating principle of an exemplary embodiment of the present invention in situations where interference occurs infrequently.  
         [0032]    [0032]FIG. 7D shows a schematic comparison of the operating principle of an exemplary embodiment of the present invention in situations where interference occurs infrequently.  
         [0033]    [0033]FIG. 7E shows a schematic comparison of the operating principle of an exemplary embodiment of the present invention in situations where interference occurs moderately frequently.  
         [0034]    [0034]FIG. 7F shows a schematic comparison of the operating principle of an exemplary embodiment of the present invention in situations where interference occurs moderately frequently.  
         [0035]    [0035]FIG. 7G shows a schematic comparison of the operating principle of an exemplary embodiment of the present invention in situations where interference occurs moderately frequently.  
         [0036]    [0036]FIG. 7H shows a schematic comparison of the operating principle of an exemplary embodiment of the present invention in situations where interference occurs moderately frequently.  
         [0037]    [0037]FIG. 71 shows a schematic comparison of the operating principle of an exemplary embodiment of the present invention in situations where interference occurs very frequently.  
         [0038]    [0038]FIG. 7J shows a schematic comparison of the operating principle of an exemplary embodiment of the present invention in situations where interference occurs very frequently.  
         [0039]    [0039]FIG. 7K shows a schematic comparison of the operating principle of an exemplary embodiment of the present invention in situations where interference occurs very frequently.  
         [0040]    [0040]FIG. 7L shows a schematic comparison of the operating principle of an exemplary embodiment of the present invention in situations where interference occurs very frequently. 
     
    
     DETAILED DESCRIPTION  
       [0041]    The exemplary embodiment and/or exemplary method of the present invention illustrated in FIGS. 1 through 7L involves a circuit assemblage  100  for influencing, e.g., decreasing, the treble reproduction of an audio signal (left stereo channel  90 , right stereo channel  98 ; see FIG. 1), obtained from a frequency-modulated (FM) broadcast signal and intended for reproduction. The audio signals may be prepared or supplied by an external source, e.g., for radio programs, e.g., also for news and for traffic reports.  
         [0042]    According to an exemplary method according to the present invention, receiving field strength  12  and the reception quality of the received broadcast signal are evaluated, and in a manner proportional thereto the transfer function of a filter unit  94  impinged upon by audio signal  90 ,  92  is controlled in such a way that there emerges from filter unit  94  a filtered audio signal (left channel  96  of the stereo channel; right channel  98  of the stereo channel) in which the interference caused by multi-path propagation is less perceptible or in fact is essentially no longer perceptible.  
         [0043]    According to an exemplary embodiment of a circuit assemblage  100 , signal processing is accomplished in two processing branches  204  and  507  that are physically and functionally separate from one another, i.e. after two upstream reception interference detectors, e.g., after a high-pass detector  10   a  and after a 19-kHz amplitude-modulation (AM) detector  10   b , circuit assemblage  100  has a first processing branch  204  which operates at a first variable sampling rate, and a second processing branch  507  which operates at a second sampling rate that differs from, i.e. is higher than, the first sampling rate.  
         [0044]    The result of this different setting of the two sampling rates is that the output signals of the two reception interference detectors  10   a ,  10   b , and the signal of received field strength  12 , are respectively processed in such a way that the treble reproduction can be damped for longer time periods by means of first processing branch  204  than by means of second processing branch  507 .  
         [0045]    First to be described below will be the control system having a slow processing speed that is depicted in an exemplary embodiment in the top half of FIG. 1, i.e. first processing branch  204  provided for longer time periods. In this “slow control system,” the sampling rate can be set between 0 Hz and 950 Hz.  
         [0046]    First control/processing unit  204  has conveyed to it the respective output signals of reception interference detector  10   a  and reception interference detector  10   b , and field strength  12 . The signals of reception interference detectors  10   a  and  10   b  are delivered, after respective weighting that occurs in a weighting unit  20   a  and  20   b , respectively, to a separate threshold decision in a respective threshold value unit  22   a  and  22   b , as shown in FIG. 2A where the abscissa or right-hand axis represents time t, the ordinate or vertical axis represents output signal of reception interference detectors  10   a ,  10   b , and the horizontal line represents the threshold value. (FIG. 2A is divided into two pages for reasons having only to do with illustration technique and not with content.) This threshold value decision decides whether the interference in question is pronounced and clearly perceptible.  
         [0047]    After the threshold decision, the two signals are subjected to a logical OR operation in a first logic unit  24 . The output signal thereby obtained serves as the input signal for an asymmetrical ramp, provided by a first ramp unit  26  (see FIG. 1) and depicted in FIG. 3, that has a fast rise time and a slow decay time (in FIG. 3 as well, time t is plotted on the abscissa or right-hand axis).  
         [0048]    After this, the output signal coming from ramp unit  26  is conveyed to a reset/hold unit  28  that can exhibit the following operating states:  
         [0049]    (a) Normal state: Output=input;  
         [0050]    (b) Hold state: Output is held at its value regardless of the input;  
         [0051]    (c) Reset: Output=0.  
         [0052]    Additionally, in the exemplary embodiment of a control system with slow processing speed depicted in the top half of FIG. 1, i.e. in first processing branch  204  provided for longer time periods, field strength signal  12  is conveyed by means of a first characteristic curve unit  30  to a characteristic curve whose approximate profile is shown in FIGS. 4A and 4B, where the abscissa or right-hand axis represents the received field strength signal  12  and the ordinate or vertical axis represents the output signal of first characteristic curve unit  30 .  
         [0053]    At an infinitesimal or low received field strength  12  a large output signal is generated, and at a higher received field strength  12  a small output signal or a zero output signal is generated. The intermediate region of the output signal extending between infinitesimal received field strength  12  and high received field strength  12  exhibits, for example:  
         [0054]    a proportionately decaying profile after a constant value at low received field strength  12  (see FIG. 4A); or  
         [0055]    a proportionately decaying profile from the outset (see FIG. 4 b ).  
         [0056]    The signal after the characteristic curve is once again conveyed to a reset/hold unit  32  that has substantially the same properties as the first reset/hold unit  28  downstream from interference detectors  10   a ,  10   b.    
         [0057]    From the respective signals after the two reset/hold blocks  28  and  32 , the maximum M 1  (see FIGS. 1 and 2B, where FIG. 2B is divided into two pages for reasons having only to do with illustration technique and not with content) is obtained in a first comparator unit  40 . This maximum M 1  is in turn forwarded to the threshold value decision occurring in threshold unit  42 .  
         [0058]    Here the input signal of threshold unit  42  is compared to nine thresholds [ 44 . 0 ], [ 44 . 1 ], [ 44 . 2 ], [ 44 . 3 ], [ 44 . 4 ], [ 44 . 5 ], [ 44 . 6 ], [ 44 . 7 ], [ 44 . 8 ]. In each processing cycle, however, three threshold decisions are performed, checking whether:  
         [0059]    (i) the input signal is greater than the currently stored threshold;  
         [0060]    (ii) the input signal is greater than the next-greatest threshold; or  
         [0061]    (iii) the input signal is less than the currently stored threshold.  
         [0062]    The threshold [ 44 . 0 ], [ 44 . 1 ], [ 44 . 2 ], [ 44 . 3 ], [ 44 . 4 ], [ 44 . 5 ], [ 44 . 6 ], [ 44 . 7 ], [ 44 . 8 ] can thus be:  
         [0063]    (i) maintained (permissible change Δ 1 =0; see FIG. 1);  
         [0064]    (ii) increased by one step (permissible change Δ 1 =+1; see FIG. 1); or  
         [0065]    (iii) decreased by one step (permissible change Δ 1 =−1; see FIG. 1).  
         [0066]    Threshold values [ 44 . 0 ] and [ 44 . 8 ] represent the limits of the numerical region and provide a boundary (see FIG. 2B). The decrease in the threshold by one step (permissible change Δ 1 =−1; see FIG. 1) can occur only if a dead time tt has elapsed (-&gt;reference character tt′ in FIG. 2B). This dead time is counted when the input signal is less than the current threshold (see FIG. 2B). If the input signal is greater than the current threshold for one processing cycle, the dead time tt is reset (see FIG. 2B).  
         [0067]    This will be explained with reference to the example below, based on threshold values [ 44 . 0 ]= 0 , [ 44 . 1 ]= 2000 , [ 44 . 2 ]= 4000 , [ 44 . 3 ]= 6000 , [ 44 . 4 ]= 8000 , [ 44 . 5 ]= 10 , 000 , [ 44 . 6 ]= 12 , 000 , [ 44 . 7 ]= 20 , 000 , [ 44 . 8 ]= 32 , 768 , and a threshold currently set to [ 44 . 3 ]=6,000.  
         [0068]    (i) If the input value is 7,000, the input signal (=input value) is then greater than the currently stored threshold [ 44 . 3 ]=6,000, but not greater than the next-greatest threshold [ 44 . 4 ]=8,000 (and of course not less than the currently stored threshold [ 44 . 3 ]=6,000), so that the threshold can be maintained (permissible change Δ 1 =0; see FIG. 1), i.e. the new current threshold is still [ 44 . 3 ]=6,000.  
         [0069]    (ii) If the input value is 9,000, the input signal (=input value) is then not only greater than the currently stored threshold [ 44 . 3 ]=6,000 but also greater than the next-greatest threshold [ 44 . 4 ] (and of course not less than the currently stored threshold [ 44 . 3 ]=6,000), so that the threshold can be increased by one step (permissible change Δ 1 =+1; see FIG. 1), i.e. the new current threshold is then [ 44 . 4 ]=8,000.  
         [0070]    (iii.a) If, on the other hand, the input value is 5,000 and the dead time tt has not elapsed, the input signal (=input value) is then not greater than the currently stored threshold [ 44 . 3 ]=6,000 and therefore also not greater than the next-greatest threshold [ 44 . 4 ]=8,000, but instead is less than the currently stored threshold [ 44 . 3 ]=6,000; since the dead time tt has not expired, the currently stored threshold does not change but continues to be [ 44 . 3 ]=6,000.  
         [0071]    (iii.b) If, on the other hand, the input value is 1,000 and the dead time tt has elapsed, the input signal (=input value) is then not greater than the currently stored threshold [ 44 . 3 ]=6,000 and therefore also not greater than the next-greatest threshold [ 44 . 4 ]=8,000, but instead is less than the currently stored threshold [ 44 . 3 ]=6,000, so that the threshold can be decreased by one step (permissible change Δ 1 =−1; see FIG. 1), i.e. the new current threshold is [ 44 . 2 ]=4,000.  
         [0072]    The new threshold value ascertained according to (i), (ii), (iii.a), or (iii.b) then has allocated to it one pointer [46] (see FIG. 2B) of the available pointers [ 46 . 0 ], [ 46 . 1 ], [ 46 . 2 ], [ 46 . 3 ], [ 46 . 4 ], [ 46 . 5 ], [ 46 . 6 ], [ 46 . 7 ] to a filter coefficient table  82 ; for example, pointer [ 46 . 2 ] corresponds to threshold [ 44 . 2 ], as is shown in the diagram shown in FIG. 2B.  
         [0073]    Now that an exemplary embodiment of the control system with a slow processing speed depicted in the top half of FIG. 1, i.e. first processing branch  204  provided for longer time periods, has been considered, the exemplary embodiment of the control system with a fast processing speed depicted in the bottom half of FIG. 1, i.e. second processing branch  507  provided for shorter time periods, will be considered below. With this “fast control system,” the sampling rate is, e.g., 9.5 kHz, since this sampling rate is as high as possible for almost zero-delay reaction to reception interference.  
         [0074]    Since fast control system  507  (e.g., second processing branch  507 ) may be similar to slow control system  204  (e.g., first processing branch  204 ), unnecessary repetition will be eliminated by discussing below the differences between first processing branch  204  and second processing branch  507 . Otherwise, the statements, descriptions, and explanations presented above are also applicable to second processing branch  507  and the reference characters allocated to second processing branch  507  may be selected to be higher by an additive constant, e.g., equal to 30 more than the reference characters allocated to first processing branch  204 .  
         [0075]    Second processing branch  507  has no reset/hold blocks, instead, a scaling unit  58  is inserted in the path coming from the two reception interference detectors  10   a ,  10   b  to comparator unit  70 .  
         [0076]    In addition, generation of the current threshold values [ 74 . 0 ], [ 74 . 1 ], [ 74 . 2 ], [ 74 . 3 ], [ 74 . 4 ], [ 74 . 5 ], [ 74 . 6 ], [ 74 . 7 ], [ 74 . 8 ] has a slightly different characteristic, in that threshold values [ 74 . 0 ], [ 74 . 1 ], [ 74 . 2 ], [ 74 . 3 ], [ 74 . 4 ], [ 74 . 5 ], [ 74 . 6 ], [ 74 . 7 ], [ 74 . 8 ] once again can be:  
         [0077]    (i) maintained (permissible change Δ 2 =0; see FIG. 1);  
         [0078]    (ii) increased by one step (permissible change Δ 2 =+1; see FIG. 1); or  
         [0079]    (iii) decreased by one step (permissible change A 2 =−1; see FIG. 1).  
         [0080]    However, unlike in slow control system  204 , it can also be increased by two steps (permissible change Δ 2 =+2; see FIG. 1). A dead time tt does not exist in fast control system  507  (see FIG. 5B).  
         [0081]    The identified threshold value [ 74 . 0 ], [ 74 . 1 ], [ 74 . 2 ], [ 74 . 3 ], [ 74 . 4 ], [ 74 . 5 ], [ 74 . 6 ], [ 74 . 7 ], [ 74 . 8 ] once again has allocated to it one pointer [ 76 ] (see FIG. 5B) of the available pointers [ 76 . 0 ], [ 76 . 1 ], [ 76 . 2 ]. [ 76 . 3 ], [ 76 . 4 ], [ 76 . 5 ], [ 76 . 6 ], [ 76 . 7 ] to the same filter coefficient table  82  as in the case of slow control system  204 . For example, pointer [ 76 . 3 ] may correspond to threshold value [ 74 . 3 ], as shown in the diagram according to FIG. 5B.  
         [0082]    After slow control system  204  and fast control system  507  are combined, i.e. after control unit  80 , further processing is performed at a fast processing speed. The respectively generated pointers [ 46 ] and [ 76 ] are conveyed in comparator unit  80  to a maximum selection operation.  
         [0083]    The output signal of comparator unit  80  contains the identified pointer M 3  (see FIG. 1) to filter coefficient table  82 , i.e. the maximum of the allocated first pointer [ 46 ] of first processing branch  204  and the allocated second pointer [ 76 ] of second processing branch  507  (depending on whether first pointer [ 46 ] or second pointer [ 76 ] is greater).  
         [0084]    That filter coefficient [ 84 ] of the available filter coefficients (e.g., filter curve steps [ 84 . 0 ], [ 84 . 1 ], [ 84 . 2 ], [ 84 . 3 ], [ 84 . 4 ], [ 84 . 5 ], [ 84 . 6 ], [ 84 . 7 ]) to which the identified pointer M 3  points is then transferred to HiCut filter  94  and set. The diagram in FIG. 6, where the abscissa or right-hand axis represents the frequency in kHz (logarithmic scale) and the ordinate or vertical axis represents the damping in decibels, shows an exemplary embodiment of the setting of the eight available filter curves (e.g., “HiCut” filter curves) labeled in FIG. 6 with the numerals 0, 1, 2, 3, 4, 5, 6, and 7.  
         [0085]    Because filter coefficients [ 84 . 0 ], [ 84 . 1 ], [ 84 . 2 ], [ 84 . 3 ], [ 84 . 4 ], [ 84 . 5 ], [ 84 . 6 ], [ 84 . 7 ] are controlled using an identified pointer M 3  in memory, the control system is independent of the nature and disposition of filter  94  since, in a manner essential to the invention, one or more filter coefficients [ 84 . 0 ], [ 84 . 1 ], [ 84 . 2 ], [ 84 . 3 ], [ 84 . 4 ], [ 84 . 5 ], [ 84 . 6 ], [ 84 . 7 ] can selectably be allocated to the identified pointer. This may have the advantage that the control system is substantially independent of the audio processing system, and in addition, a nonlinear allocation of the control variable to the filter curves in HiCut filter  94  can be achieved.  
         [0086]    It should additionally be mentioned that the absence of reset/hold blocks in second processing branch  507  and the presence of reset/hold blocks  28 ,  32  in first processing branch  204  may be related to the technical condition of causing, in first processing branch  204 , a rapid reset or hold of the current setting.  
         [0087]    If a highly interference-affected station is being received, the HiCut function will strongly damp the treble. When the station is then changed, that new station needs to be receivable immediately with no treble diminution. The reset functionality is used for that purpose.  
         [0088]    The hold functionality is used to freeze the status of the slow HiCut function during a Radio Data System alternative-frequency (RDS AF) test. Holding the setting ensures that the auditory impression before the AF test does not differ from the auditory impression after the AF test.  
         [0089]    Lastly, the exemplary method according to the present invention will be illustrated once again with reference to FIGS. 7A through 7L, where the abscissa or right-hand axis in FIGS. 7A through 7L represents time t. The ordinate or vertical axis in FIGS. 7A, 7E,  7 I represents the output signal of reception interference detectors  10   a ,  10   b  and the horizontal line in FIGS. 7A, 7E,  7 I represents the threshold value. The ordinate or vertical axis in FIGS. 7B, 7F,  7 J represents the signal for “fast control system” i.e. in second processing branch  507 , the ordinate or vertical axis in FIGS. 7C, 7G,  7 K represents the signal for “slow control system” i.e. in first processing branch  204  and the ordinate or vertical axis in FIGS. 7D, 7H,  7 L represents the signal after maximum selection, i.e. signal resulting from maximum selection.  
         [0090]    In this connection, the left portion of the exemplary embodiment shown in FIGS. 7A, 7B,  7 C, and  7 D relates to the case of sporadic interference, the center portion of the exemplary embodiment shown in FIGS. 7E, 7F,  7 G, and  7 H relates to the instance of moderate or average interference frequency, and the right portion of the exemplary embodiment shown in FIGS. 7I, 7J,  7 K, and  7 L refers to the instance of very frequent interference.  
         [0091]    In the case of interference occurring in only sporadic or isolated fashion (see FIG. 7A), the treble diminution by way of the slow control system is small, and in some circumstances the treble diminution in fact disappears, i.e. is not present at all (see FIG. 7C). In this case, only the fast control system that responds for short periods is active (see FIG. 7B), resulting in the signal shown in FIG. 7D after maximum selection.  
         [0092]    In the case of frequent interference (see FIG. 7), there are two possibilities: if the dynamics of the fast control system (see FIG. 7J) and the dynamics of the slow control system (see FIG. 7K) are identical, what results after selection of the maximum is the signal of the slow control system (see FIG. 7L); if, on the other hand, the dynamics of the fast control system (see FIG. 7J) are greater than the dynamics of the slow control system (see FIG. 7K), then short diminutions equivalent in value to the difference in dynamics between the two control systems will be summed even in the context of frequently occurring interference (see FIG. 7L).  
         [0093]    In the transition region (see FIGS. 7E, 7F,  7 G,  7 H) between sporadic interference (see FIGS. 7A, 7B,  7 C,  7 D) and frequent interference (see FIGS. 7I, 7J,  7 K,  7 L), there is a combination of the fast control system (see FIG. 7F) and the slow control system (see FIG. 7G). In this case, a treble diminution with a slow time constant is performed, and a short-duration fast treble diminution with low dynamics is additively performed only upon occurrence of the interference.  
         [0094]    This signifies that the treble diminution (e.g., decrease in the treble reproduction of audio signal  90 ,  92  for reproduction) brought about by means of the fast control system (see FIG. 7F) and/or by means of the slow control system (see FIG. 7G) has a maximum selection operation (see FIG. 7H) overlaid on it. In the case of moderately frequent interference, the treble diminution of the slow control system (see FIG. 7G) will therefore be set to a moderate value. In this case a greater treble diminution is obtained while the fast control system is responding (see FIG. 7F).  
         [0095]    List of Reference Characters  
         [0096]    [0096] 100  Circuit assemblage  
         [0097]    [0097] 10   a  First reception interference detector  
         [0098]    [0098] 10   b  Second reception interference detector  
         [0099]    [0099] 12  Received field strength  
         [0100]    [0100] 20   a  First weighting unit  
         [0101]    [0101] 20   b  Second weighting unit  
         [0102]    [0102] 22   a  First threshold value unit  
         [0103]    [0103] 22   b  Second threshold value unit  
         [0104]    [0104] 24  First logic unit, e.g., first OR logic unit  
         [0105]    [0105] 26  First ramp unit  
         [0106]    [0106] 28  First reset/hold unit  
         [0107]    [0107] 30  First characteristic curve unit  
         [0108]    [0108] 32  Second reset/hold unit  
         [0109]    [0109] 40  First comparator unit  
         [0110]    [0110] 42  Third threshold value unit  
         [0111]    [ 44   i ] New first threshold value (i=0; 1; 2; 3; 4; 5; 6; 7; 8)  
         [0112]    [ 46   j ] Available first pointer (j=0; 1; 2; 3; 4; 5; 6; 7)  
         [0113]    [ 46 ] Allocated first pointer  
         [0114]    [0114] 50   a  Third weighting unit  
         [0115]    [0115] 50   b  Fourth weighting unit  
         [0116]    [0116] 52   a  Fourth threshold value unit  
         [0117]    [0117] 52   b  Fifth threshold value unit  
         [0118]    [0118] 54  Second logic unit, in particular second OR logic unit  
         [0119]    [0119] 56  Second ramp unit  
         [0120]    [0120] 58  Scaling unit  
         [0121]    [0121] 60  Second characteristic curve unit  
         [0122]    [0122] 70  Second comparator unit  
         [0123]    [0123] 72  Sixth threshold value unit  
         [0124]    [ 74   i ] New second threshold value (i=0; 1; 2; 3; 4; 5; 6; 7; 8)  
         [0125]    [ 76   j ] Available second pointer (j=0; 1; 2; 3; 4; 5; 6; 7)  
         [0126]    [ 76 ] Allocated second pointer  
         [0127]    [0127] 80  Third comparator unit  
         [0128]    [0128] 82  Filter coefficient table  
         [0129]    [ 84   j ] Available filter coefficient (j=0; 1; 2; 3; 4; 5; 6; 7)  
         [0130]    [ 84 ] Allocated filter coefficient  
         [0131]    [0131] 90  Audio signal (left channel of stereo channel) before filter unit  94   
         [0132]    [0132] 92  Audio signal (right channel of stereo channel) before filter unit  94   
         [0133]    [0133] 94  Filter unit  94   
         [0134]    [0134] 96  Audio signal (left channel of stereo channel) after filter unit  94   
         [0135]    [0135] 98  Audio signal (right channel of stereo channel) after filter unit  94   
         [0136]    [0136] 204  First processing branch with first sampling rate  
         [0137]    [0137] 507  Second processing branch with second sampling rate  
         [0138]    Δ 1  Permissible change in first processing branch  204   
         [0139]    Δ 2  Permissible change in second processing branch  507   
         [0140]    M 1  Maximum value in first processing branch  204   
         [0141]    M 2  Maximum value in second processing branch  507   
         [0142]    M 3  Maximum of allocated first pointer ( 46 ) and  
         [0143]    allocated second pointer [ 76 ] 
         [0144]    t Time  
         [0145]    tt Dead time  
         [0146]    tt? 0  Dead time? 
         [0147]    tt′ Dead time elapsed