EP0963684B1 - Method and corresponding system for influencing the stereo channel separation of an audiosignal - Google Patents

Description

State of the art

The invention relates to a method for influencing the Stereo channel separation of an audio signal to be played back and a radio receiver to carry out the inventive method according to the genus of independent claims.

Modern radio transmitters emit radio signals whose Signal format the transmission of stereophonic audio signals enables and on the receiver side the surround sound stereophonic playback can be clearly heard.

If there is a broadcast signal to be received at the receiving location only with a low field strength, this advantage goes lost because interference-free channel separation has a minimum reception field strength one received at the receiving location Broadcast signal required. Therefore, radio receivers, especially car radios, with a switching for a long time or smooth transition from stereophonic to monophonic Playback equipped by the reception field strength of a received broadcast signal. In such Radio receivers will drop when the reception field strength the channel separation is automatically reduced.

Often, in addition to the fluctuation of the reception field strength of a received broadcast signal further reception interference such as B. Multi-way reception of a set Radio station on. With such reception conditions also with the mentioned stereo radio receivers which the smooth mono-stereo transition to optimal Channel separation is set, disadvantageously noticeable that the good stereo reproduction when entering a multi-path reception area abruptly and often only for short periods Routes is disturbed. You therefore have stereo capabilities Radio receiver with a detector for interference such. B. Equipped multi-path reception of the set transmitter, whose output signal controls a switch that the Receiver is forced to monophonic playback of the received radio signal switches.

EP 0 617 519 A2 describes a circuit arrangement for known such a radio receiver, in which from the Receiving field strength of a received broadcast signal on the Received field strength signal is derived in which continues to come from the received broadcast signal Interference signal indicating reception interference is derived, and in which the signal indicating the reception field strength and the interference signal multiplicative to form a Influencing the stereo channel separation of a audio signal to be reproduced using a stereo decoder supplied factor can be linked.

On routes with short-term multi-path reception, e.g. B. on streets with high-rise buildings or in mountainous areas Areas occur alternating between one-way reception and Multi-way reception often on and within a very short time lead to corresponding frequent changes from one Stereo playback for monophonic playback of a Stereo broadcast. This effect has long been considered so annoying felt that motorists in mountainous areas Switch off the stereo decoder when receiving modern stereo stations and do without stereo playback altogether.

Finally, radio receivers are able to Evaluation of by means of the radio data system (RDS) transmitted information known for the purpose of Optimization of the reception quality of a received Broadcast program briefly from a currently set one Transmission frequency to an alternative transmission frequency over which the same program is broadcast, be tuned being on the alternative during the stay Transmission frequency determines their reception quality and then the receiver on the transmission frequency with the best reception conditions is set. The information The alternative transmission frequency is used, for example the AF- (alternative Frequencies) data taken.

Tuning the radio receiver to an alternative Transmitting frequency, the reception field strength of which of the originally set transmission frequency may differ, causes sudden and therefore disturbing changes in the Stereo channel separation of a reproduced audio signal.

Advantages of the invention

The inventive method and the inventive Broadcast receiver with the characteristics of independent Claims have the advantage that with strongly fluctuating Reception conditions or frequently occurring Reception interference, such as B. multipath, fast and frequent changes between stereophonic and monophonic Playback and the associated negative auditory impression in favor of a partially or completely monophonic Playback can be suppressed.

Advantageous embodiments of the invention The method and the radio receiver according to the invention specified in the dependent claims.

It is particularly advantageous to use the characteristic curves for evaluation which indicates the reception field strength of a broadcast signal Execute field strength signals in the form of staircase functions, since this in the case of a realization of the invention Method or the radio receiver according to the invention in digital technology are particularly easy to implement.

It is especially in the case of digital signal processing also an advantage, the frequency of interference signal to be realized by means of a counter which if a fault occurs and if there is no Disturbance is decremented because of that counter required clock in a simple manner, for example from the System clock z. B. from the bit clock of the digital involved Signals can be derived.

After all, it is particularly beneficial to Radio receivers for receiving radio data signals automatic to optimize reception quality Carry out alternative frequency tests for the duration of one Alternative frequency tests the channel separation auxiliary signal P on to keep its last value and possibly only after to change the alternative frequency test because it is strong Fluctuations in stereo channel separation in the course of Alternative frequency tests can be avoided.

drawings

Embodiments of the invention are in the drawings shown and are explained in more detail below.

FIG. 1 shows a block diagram of the part of an invention essential to the invention Broadcast receiver, Figure 2 shows an example of a Realization of the second evaluation circuit 6, Figure 3 a Realization possibility for the stereo decoder 11, FIG. 4 an example of a first in the first Evaluation circuit 4 realized characteristic, Figure 5 a second realized in the third evaluation circuit Characteristic curve and Figure 6 shows an example of that in the second Evaluation circuit 6 realized monotonically falling characteristic 62.

Description of an embodiment

An embodiment of the part essential to the invention of a radio receiver according to the invention for implementation of the method according to the invention is shown in FIG. 1.

At two outputs of a stereo decoder 11, the one in at itself known by demodulating a received Broadcast signal, stereo multiplesx signal MPX is supplied, audio signals for a left and a right channel (l, r) removable.

Formation of the audio signals for the left and the right Stereo channels l and r from the stereo multiplex signal MPX based on the embodiment shown in Figure 3 for the stereo decoder 11 described. The stereo multiplex signal MPX is processed in two signal paths, by low-pass filtering 113 of the stereo multiplex signal from this the sum signal (L + R) is isolated. In one second signal path is by in-phase multiplication 111 with one from, for example, one in the stereo multiplex signal contained 19kHz pilot tone obtained 38kHz subcarrier and then eliminating undesirable Mixed products using a low pass 112 Difference signal (L - R), which is the difference of the signals for contains the left and right audio channels.

After weighting 114 of the difference signal (L-R) by a factor D (0 D D 1 1), the weighted difference signal is added (116) to form a signal I for the left audio channel to the sum signal (L + R) and to form a signal r subtracted from the sum signal for the right audio channel (115). So it applies l = (L + R) + D (LR) and r = (L + R) -D (LR), where for D = 1 maximum stereo channel separation and for D = 0 there is a purely monophonic reproduction.

Thus, a change in the factor D, the Generation is the subject of the following considerations any stereo channel separation between purely monophonic and Set purely stereophonic playback.

One in a first signal path 1 to 3 Weighting circuit included inventive arrangement 1 are different reception disorders like Fluctuations in field strength, multi-path reception and interference noise indicating interference signals (ST) supplied, which are dependent the ranges of values they occupy and theirs desired influence on the stereo channel separation of a audio signal to be reproduced individually weighted and Formation of a common interference signal linked together, be added up in the present case.

The common interference signal is a threshold value decision 2 supplied by it with a predetermined threshold is evaluated so that the outcome of the Threshold decision 2 when the specified one is exceeded Threshold value due to the common interference signal from one first changes to a second state. In the present The case is for the first and the second state Values 1 and 0 selected.

The output of the threshold decision 2 is one Edge control 3 for controlling the slope of the supplied signal supplied. This is done in such a way that their output signal, hereinafter referred to as the first interference auxiliary signal s denotes when the output of the Threshold decision maker two from the first to the second Condition suddenly takes on a fourth value and as soon as the output of the threshold decision 2 at first Value decreases after a predetermined time function z. B. to the third value within a few 10 ms goes back. The predefined time function is in the present Case realized in the form of a linear course, it can but it can also be provided that the first auxiliary auxiliary signal s after a non-linear, for example exponential Course to the third value and thus towards stereophonic playback returns.

In a second signal path of the arrangement according to the invention becomes a field strength signal indicating the reception field strength (FST) a first evaluation circuit 4 to form a first field strength auxiliary signal x, which is the reception field strength of the received radio signal identifies, supplied. The Field strength signal FST is in the present case by Rectification and low pass filtering of the Intermediate frequency signal that by mixing down the Received signal is obtained in the intermediate frequency level, generated. In the first evaluation circuit 4 Field strength signal FST with a monotonically increasing, in In the present case, the linear characteristic is evaluated so that for higher reception field strengths, higher values for the first Field strength auxiliary signal x result. For high input values the characteristic curve has a saturation range, so that for very high reception field strengths, no changes to the first field strength auxiliary signal x. The range of values the first field strength auxiliary signal lies in present case between the values 0 for a very low reception field strength FST and 1 for high and highest Reception field strengths. An example of one in the first Evaluation circuit 4 realized non-linear characteristic is shown in Figure 4.

A third signal path 5 to 8 comprises a second evaluation circuit 6 for forming a signal which characterizes the frequency of reception disturbances, ie the number of disturbances per unit of time, _hereinafter referred to as second disturbance auxiliary signal P _disturbance , to which the first disturbance auxiliary signal s is supplied.

An embodiment of the second evaluation circuit 6 is shown in Figure 2. This includes one in present case of digital signal processing clocked counter 61, the first interference auxiliary signal s is fed. When the first auxiliary auxiliary signal s in the fourth, the presence of a reception disorder indicating state, the counter 61 becomes a fifth incremented predetermined value while it is absent a reception disturbance by a sixth predetermined value is decremented. The clock T fed to the counter is in present case from the sampling clock for the demodulated Received signal derived, so that the counter 61 in synchronism the samples of the stereo multiplex signal MPX works. Alternatively, it is also possible to use the clock T by means of to generate a separate clock generator.

The counter reading 61 is evaluated by means of a monotonically falling characteristic curve 62, so that for high counter readings Z of the counter 61 at the output of the second evaluation _circuit 6 there are low values for the second auxiliary auxiliary signal P _disturbance at low counter readings Z. An example of the characteristic curve 62 is shown in FIG. 6, from which the relationship between the counter reading Z of the counter 61 and the second auxiliary _fault signal P _disturb can be seen.

In an _{exemplary embodiment} which is _{simplified compared to} the _exemplary embodiment shown in FIG. 1, the second _interference auxiliary signal P _interference obtained in this way, which indicates the frequency of reception _{interference, corresponds to} the second auxiliary signal P _soll , from which a channel separation auxiliary signal P is obtained by means of a tracking circuit 8.

The tracking circuit 8 works so that for values of the second auxiliary signal P _soll , which are smaller than a current value of the channel auxiliary signal P, the value of the channel separation auxiliary signal P quickly decreases to the value of the second auxiliary signal P _soll , while for values of second auxiliary signal P _should , which are greater than a current value of the channel separation auxiliary signal P, the channel separation auxiliary signal P slowly after a predetermined time function, in the present case after an exponential function first very quickly, then increasing slowly, to the value of the second Auxiliary signal P _should approximate.

For a radio receiver that is for the purpose of Reception optimization of a received radio program Carry out alternative frequency test, suitable further training it is provided during an alternative frequency test or a jump to an alternative frequency that Channel separation auxiliary signal P on the frequency hopping or Alternative frequency test immediately preceding value hold. Only after completing the jump to an alternative Frequency (in the case of a frequency change towards a better one receiving transmission frequency) or the alternative frequency test the tracking circuit 8 for tracking the Channel separation auxiliary signal P reactivated.

As an alternative to deactivating tracking 8 for the duration of a frequency hopping or alternative frequency test, the second auxiliary signal P _{should also be} frozen to its value immediately preceding such an event.

In the embodiment of the arrangement according to the invention shown in Figure 1, the third signal path further comprises a third evaluation circuit 5, in which the field strength signal FST to form a second field strength auxiliary signal P _FST with a second monotonically increasing characteristic, an example of which is shown in Figure 5 , Is evaluated.

The second auxiliary field-strength signal P _FST and the second auxiliary interference signal P _sturgeon are for forming a second auxiliary signal P _to a link 7 is supplied, in which in the present case, _sturgeon, the minimum of the two supplied second auxiliary signals P formed P _FST, and the second Auxiliary signal P _{is to be} equated with the smaller of the two auxiliary signals P _disturb , P _FST .

In a variant of the present exemplary embodiment, provision is made for the first link 7 to be carried out as a multiplication, so that the second auxiliary signal _results as the product P _disturbance XP _{FST of} the two second auxiliary signals P _disturbance , P _FST supplied.

The first auxiliary auxiliary signal the first auxiliary field strength signal x and the channel separation auxiliary signal P are in one second link 9, 10 to form the stereo channel separation influencing factor linked together. In the present case, this is the first auxiliary auxiliary signal s and the first field strength auxiliary signal x to form a first auxiliary signal in a first multiplier 9 multiplied together. The first so formed Auxiliary signal y is then used to form factor D in a second multiplier 10 with the channel separation auxiliary signal P weighted.

The following mode of operation of a radio receiver according to the invention is achieved in this way. The factor D is directly proportional to the first field strength auxiliary signal, so that the reception field strength of the received radio signal has a direct effect on the stereo channel separation. In the case of strong reception interference lying above a threshold value, the first interference auxiliary signal s fades from stereophonic to monophonic reproduction. Finally, via the channel separation auxiliary signal P, either the frequency of interference in the form of the second auxiliary signal P _interference (with high frequency of interference) or the reception field strength in the form of the second field strength auxiliary signal P _FST (with low reception field strength), depending on which one of the two variables signaled poorer reception, based on the stereo channel separation in the sense of a reduction thereof.

The signals ST indicating the disturbances mentioned at the beginning are generated in a manner known per se as follows.

A signal indicating fluctuations in field strength is ΔFST for example, by constantly comparing the current one Receiving field strength signal, z. B. by Rectification of the intermediate frequency signal can be generated with the slowly changing field strength signal FST derivable. In the simplest case it can Signal ΔFST indicating field strength fluctuations Subtraction of the current field strength from the field strength signal FST are formed.

A noise indicating signal can e.g. B. by Evaluation of the high-frequency signal components, e.g. B. Beyond 60 kHz, which are contained in the stereo multiplex signal MPX, be won.

An interference signal indicating multipath reception is known in the prior art Way z. B. by evaluating the symmetry of the sidebands of the 38 kHz subcarrier HT can be derived, with an asymmetry suggests multipath reception.

As shown in FIGS. 4 to 6, the characteristic curves realized in the evaluation circuits 4 to 6 are designed in the form of staircase functions, which are shown in broken lines in FIGS. 4 and 5, so that the number of possible output values and thus also the word length of the signals x, s, P _sturgeon , P _FST finite and with a small number of stages is low. By executing the characteristic curves as staircase functions with a small number of steps, it is possible to represent them using fewer comparators.

Claims (12)

1. Method for influencing the stereo channel separation of an audio signal which is to be reproduced and is obtained from a received radio signal in a radio receiver, where a sum signal (L+R) and a difference signal (L-R) are logically combined with one another in a stereo decoder (11) to form signals for a left-hand and a right-hand channel (l, r) of the audio signal, where a factor (D) supplied to the stereo decoder (11) is used to influence the stereo channel separation between the signals on the audio channels (l, r), where a first auxiliary field-strength signal (x) characterizing the reception field strength of the received radio signal is formed from the reception field strength of the received radio signal, preferably using a monotonously rising characteristic curve which has a saturation region for high input values, and where a first auxiliary interference signal (s) indicating interference is formed from at least one signal which indicates reception interference and is derived from the received radio signal, the first auxiliary field-strength signal (x), the first auxiliary interference signal (s) and a further signal (P) being logically combined with one another in order to form the factor (D), characterized in that the further signal (P) is an auxiliary channel-separation signal formed from the second auxiliary interference signal (PINTERF), the second auxiliary interference signal (PINTERF) being derived from the first auxiliary interference signal (s), preferably using a monotonously falling characteristic curve, and characterizing the number of instances of reception interference per unit time.
2. Method according to Claim 1, characterized in that a second auxiliary field-strength signal (PFST) indicating the reception field strength of the received radio signal is formed from the reception field strength of the received radio signal, preferably using a monotonously rising characteristic curve, and in that the second auxiliary field-strength signal (PFST) is logically combined with the second auxiliary interference signal (PINTERF), preferably for the purpose of forming the minimum of the two second auxiliary signals (PFST, PINTERF), in order to form the auxiliary channel-separation signal (P).
3. Method according to one of Claims 1 or 2, characterized in that the first auxiliary field-strength signal (x) is multiplied by the first auxiliary interference signal (s) in order to form a first, further auxiliary signal (y), and in that the auxiliary signal (y) is multiplied by the auxiliary channel-separation signal (P) in order to form the factor (D).
4. Method according to one of Claims 1 to 3, characterized

   in that, for the purposes of reception optimization on the radio receiver, an alternative transmission frequency which differs from a currently received transmission frequency and is intended to be used to transmit the same programme is temporarily set, and, during the time spent on the alternative transmission frequency, the reception quality thereof is determined,

   and in that, for the duration of the change from the current transmission frequency to the alternative transmission frequency and from the alternative transmission frequency to the current transmission frequency and/or for the duration prescribed by determining the reception quality, a second, further auxiliary signal (P_nom), which either corresponds to the second auxiliary interference signal (PINTERF) or is formed from a logic combination of the second auxiliary interference signal (PINTERF) and the second auxiliary field-strength signal (PFST), or the auxiliary channel-separation signal (P) derived from the second auxiliary signal is held at the value which immediately precedes the frequency change.
5. Radio receiver having an arrangement for carrying out the method according to Claim 1, having a stereo decoder (11) for forming audio signals for the left-hand and the right-hand channel (l, r) from a sum signal (L+R) and a difference signal (L-R), where a supplied factor (D) can be used to influence the channel separation between the left-hand and the right-hand audio channel (l, r), having a first signal path (1 to 3), in which a first auxiliary interference signal (s) is formed from at least one signal which indicates reception interference and is derived from the received radio signal, having a second signal path, in which a first auxiliary field-strength signal (x) characterizing the reception field strength of the received radio signal is formed from the reception field strength of the received radio signal using a first evaluation circuit (4), characterized in that a third signal path (5 to 8) for generating an auxiliary channel-separation signal (P) is provided which comprises a second evaluation circuit (6), in which a second auxiliary interference signal (PINTERF) characterizing the number of instances of reception interference per unit time is formed from the first auxiliary interference signal (s), and in that a second logic combination circuit (9, 10) is provided in which the auxiliary channel-separation signal (P) derived from the second auxiliary interference signal (PINTERF) is logically combined with the first auxiliary interference signal (s) and the first auxiliary field-strength signal (x).
6. Radio receiver according to Claim 5, characterized in that the second logic combination circuit (9, 10) comprises two multipliers (9, 10), with the first auxiliary field-strength signal (x) and the first auxiliary interference signal (s) being supplied to the first multiplier (9) in order to form an auxiliary signal (y), and the auxiliary signal (y) and the auxiliary channel-separation signal (P) being supplied to the second multiplier (10) in order to form the factor (D).
7. Radio receiver according to Claim 6, characterized in that the third signal path comprises a third evaluation circuit (5), which is used to derive a second auxiliary field-strength signal (PFST) from the reception field strength of the reception signal, and in that a first logic combination circuit (7) is provided for logically combining the second auxiliary field-strength signal (PFST) with the second auxiliary interference signal (PINTERF) to form the auxiliary channel-separation signal (P), preferably for the purpose of determining the minimum of the supplied second auxiliary field-strength and interference signals (PFST, PINTERF).
8. Radio receiver according to one of Claims 5 to 7, characterized in that the first signal path comprises a threshold-value decision maker (2) in order to evaluate the at least one signal indicating interference, the output of said threshold-value decision maker changing from a first to a second state, preferably from the value 1 to the value 0, if the at least one signal indicating interference exceeds a prescribed threshold value.
9. Radio receiver according to Claim 8, characterized in that the output of the threshold-value decision maker (2) is supplied to an edge controller (3) in order to control the edge gradient of the supplied signal, the output of the edge controller (3) changing abruptly from a third value to a fourth value, preferably from 1 to 0, when the output signal from the threshold-value decision maker (2) changes from the first to the second state, while the output of the edge controller (3) changes from the fourth to the third value on the basis of a prescribed time function when the output signal from the threshold-value decision maker (2) changes from the second to the first state.
10. Radio receiver according to one of Claims 5 to 9, characterized in that the first signal path (1 to 3) comprises a weighting circuit (1) in which, preferably a plurality of, signals indicating interference are individually weighted and combined to form a common interference signal.
11. Radio receiver according to one of Claims 6 to 10, characterized in that the [lacuna] the reception field strength of the received radio signal is evaluated in the first evaluation circuit (4) and in the third evaluation circuit (5), in each case using a monotonously rising characteristic curve, preferably implemented in the form of a staircase function, the first auxiliary field-strength signal (x) and the second auxiliary field-strength signal (PFST) being limited for large values of the reception field strength.
12. Radio receiver according to one of Claims 5 to 11, characterized in that, in order to form the second auxiliary interference signal (PINTERF), the auxiliary interference signal (s) is supplied to a second evaluation circuit (6), in which a counter (61) is incremented by a prescribed fifth value if interference indicated by the auxiliary interference signal (s) appears, while the counter (61) is decremented by a prescribed sixth value if there is no interference, and in which the counter reading of the counter (61) is evaluated using a monotonously falling characteristic curve (62), preferably implemented in the form of a staircase function.

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