EP1649719B1 - Device and method for operating voice-assisted systems in motor vehicles - Google Patents

Description

The invention relates to a method and a device for operating voice-assisted systems, such as communication and / or voice / intercom devices in motor vehicles, in which recorded via a microphone arrangement speech signals and transmitted to at least one speaker.

Methods of this type are used in motor vehicles for voice-assisted intercom operation or to support voice input controlled electronic or electrical assemblies. The fundamental problem here is that in the motor vehicle depending on the operating condition, a corresponding background noise is present. This covers the voice commands. Speech and intercom systems in motor vehicles are mainly advantageous for large vehicles, minibuses and the like. However, they can also be used in normal passenger cars. When using voice-controlled input units for electrical components in the vehicle, the suppression of the noise or the filtering of the voice command is still of particular importance.

So is out of the EP 0078014 B1 a speech recognition device for a motor vehicle, in which in the amplifier system of the speech recognition device is reported or fed via sensors, whether the engine is in operation and / or the vehicle is moving. Thereafter, a level control is aimed at trying to filter out the voice command from the background noise.

From the WO 97/34290 Filtering is known in which periodic interference signals are filtered out by determining their period and interpreting them by means of a generator so that the speech signal is left over.

From the DE 197 05 471 A1 It is known to support speech recognition using transversal filtering.

From the DE 41 06 405 C2 For example, a method is known in which a noise subtraction is performed from the speech signal using a plurality of microphones. An intercom with multiple microphones also discloses the DE 199 58 836 A1 ,

From the DE 39 25 589 A1 the use of a multiple microphone arrangement is known, wherein when used in the motor vehicle one of the microphones in the engine compartment and another is arranged in the passenger compartment. Then there is a subtraction of both signals. The disadvantage here is that only the engine noise or the actual operating noise of the vehicle itself is subtracted from the total signal in the passenger compartment. Specific noise is ignored. Likewise, a feedback suppression is missing. Wherever microphones and loudspeakers are arranged in acoustically coupled proximity, it happens that the acoustic signal coupled out at the loudspeaker feeds back into the microphone. It comes to a so-called feedback and a subsequent overload. Solutions for avoiding such overload are from the EP 1 077 013 B1 , of the WO 02/069487 A1 as well as the WO 02/21817 A2 known.

From the US-B1 6,353,609 is a generic method for operating a voice-assisted system, such as a communication and / or voice / intercom in a motor vehicle, known, with at least one microphone and at least one speaker for reproducing a signal generated by means of the microphone and with a between the microphone and the notch filter arranged in the loudspeaker, whereby a power dependent on a frequency of the signal is determined.

The invention is therefore the object of developing a method and a device of the generic type such that the verbal communication of the occupants of a vehicle is improved.

This object is achieved by operating a voice-assisted system, such as a communication and / or voice / intercom device in a motor vehicle, having at least one microphone and at least one loudspeaker for reproducing a signal generated by means of the microphone and one between the microphone and the speaker arranged bandpass filter one of a Frequency-dependent power of the signal is determined and the band-pass filter is set in response to at least a local maximum of the power of the signal over the frequency.

Of course, a local maximum of the power of the signal over the frequency may include the global maximum of the power of the signal over the frequency.

In this case, by means of the first derivative of the power of the signal after the frequency, an edge signal is formed, which assumes a first binary value, if the first derivative of the power of the signal after the frequency is greater than zero, and which assumes a second binary value, if the first derivative the power of the signal after the frequency is less than zero, wherein the local maximum of the power of the signal is determined as a function of the first derivative of the edge signal.

In the invention, the bandpass filter is a notch filter or a filterbank having at least one notch filter. The filter bank may e.g. Include 10 notch filters.

In a further advantageous embodiment of the invention, a presence of a local maximum of the power of the signal is assumed only if the first derivative of the edge signal is less than zero.

In a further advantageous embodiment of the invention, the bandpass filter is set as a function of at least two local maxima of the power of the signal over the frequency.

In a further advantageous embodiment of the invention, all local maxima are determined in a frequency range. In a further advantageous embodiment of the invention, the global maximum is determined in the frequency range.

• zumindest der Leistung des mittels des Mikrofons erzeugten Signals bei der Frequenz, bei der die Leistung des mittels des Mikrofons erzeugten Signals maximal ist,

zu

• dem Mittelwert der Leistung des mittels des Mikrofons erzeugten Signals bei weiteren Frequenzen des mittels des Mikrofons erzeugten Signals

größer ist als ein Rückopplungs-Leistungsgrenzwert (RatioThreshold, OutGrdRatioThreshold).In a further advantageous embodiment of the invention, the bandpass filter is set such that it blocks the proportion of the signal generated by the microphone at a blocking frequency only when the ratio

• at least the power of the signal generated by the microphone at the frequency at which the power of the signal generated by the microphone is at a maximum,

to

• the average of the power of the signal generated by the microphone at other frequencies of the signal generated by the microphone

is greater than a rebound power limit (RatioThreshold, OutGrdRatioThreshold).

• zumindest der Leistung des mittels des Mikrofons erzeugten Signals bei der Frequenz, bei der die Leistung des mittels des Mikrofons erzeugten Signals maximal ist,

zu

• dem Mittelwert der Leistung des mittels des Mikrofons erzeugten Signals bei weiteren Frequenzen des mittels des Mikrofons erzeugten Signals

länger als ein Zeit-Verhältnis-Grenzwert (BinRatioTimeThreshold) größer ist als ein Rückopplungs-Leistungsgrenzwert (RatioThreshold, OutGrdRatioThreshold).In a further advantageous embodiment of the invention, the bandpass filter is set such that it blocks the proportion of the signal generated by the microphone at a blocking frequency only when the ratio

• at least the power of the signal generated by the microphone at the frequency at which the power of the signal generated by the microphone is at a maximum,

to

• the average of the power of the signal generated by the microphone at other frequencies of the signal generated by the microphone

greater than a Time Ratio Limit (BinRatioTimeThreshold) is greater than a Feedback Power Limit (RatioThreshold, OutGrdRatioThreshold).

• der Leistung des mittels des Mikrofons erzeugten Signals bei der Frequenz, bei der die Leistung des mittels des Mikrofons erzeugten Signals maximal ist, plus/oder der Leistung des mittels des Mikrofons erzeugten Signals bei einer der mehr Frequenzen des mittels des Mikrofons erzeugten Signals, die der Frequenz, bei der die Leistung des mittels des Mikrofons erzeugten Signals maximal ist, benachbart sind,

zu

• dem Mittelwert der Leistung des mittels des Mikrofons erzeugten Signals bei weiteren Frequenzen des mittels des Mikrofons erzeugten Signals

größer ist als ein Rückopplungs-Leistungsgrenzwert (RatioThreshold, OutGrdRatioThreshold).In a further advantageous embodiment of the invention, the bandpass filter is set such that it blocks the proportion of the signal generated by the microphone at a blocking frequency only when the ratio

• the power of the signal produced by means of the microphone at the frequency at which the power of the signal generated by the microphone is at its maximum, plus the power of the signal generated by the microphone at one of the more frequencies of the signal generated by the microphone; Frequency at which the power of the signal generated by means of the microphone is maximum, adjacent,

to

• the average of the power of the signal generated by the microphone at other frequencies of the signal generated by the microphone

is greater than a rebound power limit (RatioThreshold, OutGrdRatioThreshold).

• der Leistung des mittels des Mikrofons erzeugten Signals bei der Frequenz, bei der die Leistung des mittels des Mikrofons erzeugten Signals maximal ist, plus/oder der Leistung des mittels des Mikrofons erzeugten Signals bei einer der mehr Frequenzen des mittels des Mikrofons erzeugten Signals, die der Frequenz, bei der die Leistung des mittels des Mikrofons erzeugten Signals maximal ist, benachbart sind,

zu

• dem Mittelwert der Leistung des mittels des Mikrofons erzeugten Signals bei weiteren Frequenzen des mittels des Mikrofons erzeugten Signals

länger als ein Zeit-Verhältnis-Grenzwert (BinRatioTimeThreshold) größer ist als ein Rückopplungs-Leistungsgrenzwert (RatioThreshold, OutGrdRatioThreshold).In a further advantageous embodiment of the invention, the bandpass filter is set such that it blocks the proportion of the signal generated by the microphone at a blocking frequency only when the ratio

• the power of the signal produced by means of the microphone at the frequency at which the power of the signal generated by the microphone is at its maximum, plus the power of the signal generated by the microphone at one of the more frequencies of the signal generated by the microphone; Frequency at which the power of the signal generated by means of the microphone is maximum, adjacent,

to

• the average of the power of the signal generated by the microphone at other frequencies of the signal generated by the microphone

greater than a Time Ratio Limit (BinRatioTimeThreshold) is greater than a Feedback Power Limit (RatioThreshold, OutGrdRatioThreshold).

• der Leistung des mittels des Mikrofons erzeugten Signals bei der Frequenz, bei der die Leistung des mittels des Mikrofons erzeugten Signals maximal ist, plus/oder der Leistung des mittels des Mikrofons erzeugten Signals bei der Frequenz des mittels des Mikrofons erzeugten Signals,
  • die der Frequenz, bei der die Leistung des mittels des Mikrofons erzeugten Signals maximal ist, unmittelbar benachbart ist, und
  • bei der die Leistung größer ist als bei einer Frequenz, die der Frequenz, bei der die Leistung des mittels des Mikrofons erzeugten Signals maximal ist, ebenfalls unmittelbar benachbart ist,

zu

• dem Mittelwert der Leistung des mittels des Mikrofons erzeugten Signals bei weiteren Frequenzen des mittels des Mikrofons erzeugten Signals

größer ist als ein Rückopplungs-Leistungsgrenzwert (RatioThreshold, OutGrdRatioThreshold).In a further advantageous embodiment of the invention, the bandpass filter is set such that it blocks the proportion of the signal generated by the microphone at a blocking frequency only when the ratio

• the power of the signal generated by the microphone at the frequency at which the power of the signal generated by the microphone is at a maximum, plus / or the power of the signal generated by the microphone at the frequency of the signal generated by the microphone,
  • which is immediately adjacent to the frequency at which the power of the signal generated by the microphone is maximum, and
  • in which the power is greater than at a frequency which is also immediately adjacent to the frequency at which the power of the signal generated by the microphone is maximal,

to

• the average of the power of the signal generated by the microphone at other frequencies of the signal generated by the microphone

is greater than a rebound power limit (RatioThreshold, OutGrdRatioThreshold).

• der Leistung des mittels des Mikrofons erzeugten Signals bei der Frequenz, bei der die Leistung des mittels des Mikrofons erzeugten Signals maximal ist, plus/oder der Leistung des mittels des Mikrofons erzeugten Signals bei der Frequenz des mittels des Mikrofons erzeugten Signals,
  • die der Frequenz, bei der die Leistung des mittels des Mikrofons erzeugten Signals maximal ist, unmittelbar benachbart ist, und
  • bei der die Leistung größer ist als bei einer Frequenz, die der Frequenz, bei der die Leistung des mittels des Mikrofons erzeugten Signals maximal ist, ebenfalls unmittelbar benachbart ist,

zu

• dem Mittelwert der Leistung des mittels des Mikrofons erzeugten Signals bei weiteren Frequenzen des mittels des Mikrofons erzeugten Signals

länger als ein Zeit-Verhältnis-Grenzwert (BinRatioTimeThreshold) größer ist als ein Rückopplungs-Leistungsgrenzwert (RatioThreshold, OutGrdRatioThreshold).In a further advantageous embodiment of the invention, the bandpass filter is set such that it blocks the proportion of the signal generated by the microphone at a blocking frequency only when the ratio

• the power of the signal generated by the microphone at the frequency at which the power of the signal generated by the microphone is at its maximum, plus the power of the signal generated by the microphone at the frequency of the signal generated by the microphone,
  • which is immediately adjacent to the frequency at which the power of the signal generated by the microphone is maximum, and
  • in which the power is greater than at a frequency which is also immediately adjacent to the frequency at which the power of the signal generated by the microphone is maximal,

to

• the average of the power of the signal generated by the microphone at other frequencies of the signal generated by the microphone

greater than a Time Ratio Limit (BinRatioTimeThreshold) is greater than a Feedback Power Limit (RatioThreshold, OutGrdRatioThreshold).

• der Leistung des mittels des Mikrofons erzeugten Signals bei der Frequenz, bei der die Leistung des mittels des Mikrofons erzeugten Signals maximal ist, plus der Leistung des mittels des Mikrofons erzeugten Signals bei der Frequenz des mittels des Mikrofons erzeugten Signals,
  • die der Frequenz, bei der die Leistung des mittels des Mikrofons erzeugten Signals maximal ist, unmittelbar benachbart ist, und
  • bei der die Leistung größer ist als bei einer Frequenz, die der Frequenz, bei der die Leistung des mittels des Mikrofons erzeugten Signals maximal ist, ebenfalls unmittelbar benachbart ist,

zu

• dem Mittelwert der Leistung des mittels des Mikrofons erzeugten Signals aller, zumindest wesentlichen, weiteren (untersuchten) Frequenzen des mittels des Mikrofons erzeugten Signals

größer ist als ein Rückopplungs-Leistungsgrenzwert (RatioThreshold, OutGrdRatioThreshold).In a further advantageous embodiment of the invention, the bandpass filter is set such that it blocks the proportion of the signal generated by the microphone at a blocking frequency only when the ratio

• the power of the signal generated by the microphone at the frequency at which the power of the signal generated by the microphone is at its maximum, plus the power of the signal generated by the microphone at the frequency of the signal generated by the microphone,
  • which is immediately adjacent to the frequency at which the power of the signal generated by the microphone is maximum, and
  • in which the power is greater than at a frequency which is also immediately adjacent to the frequency at which the power of the signal generated by the microphone is maximal,

to

• the average of the power of the signal generated by the microphone of all, at least substantially, further (examined) frequencies of the signal generated by the microphone

is greater than a rebound power limit (RatioThreshold, OutGrdRatioThreshold).

• der Leistung des mittels des Mikrofons erzeugten Signals bei der Frequenz, bei der die Leistung des mittels des Mikrofons erzeugten Signals maximal ist, plus der Leistung des mittels des Mikrofons erzeugten Signals bei der Frequenz des mittels des Mikrofons erzeugten Signals,
  • die der Frequenz, bei der die Leistung des mittels des Mikrofons erzeugten Signals maximal ist, unmittelbar benachbart ist, und
  • bei der die Leistung größer ist als bei einer Frequenz, die der Frequenz, bei der die Leistung des mittels des Mikrofons erzeugten Signals maximal ist, ebenfalls unmittelbar benachbart ist,

zu

• dem Mittelwert der Leistung des mittels des Mikrofons erzeugten Signals aller, zumindest wesentlichen, weiteren (untersuchten) Frequenzen des mittels des Mikrofons erzeugten Signals

länger als ein Zeit-Verhältnis-Grenzwert (BinRatioTimeThreshold) größer ist als ein Rückopplungs-Leistungsgrenzwert (RatioThreshold, OutGrdRatioThreshold).In a further advantageous embodiment of the invention, the bandpass filter is set such that it blocks the proportion of the signal generated by the microphone at a blocking frequency only when the ratio

• the power of the signal generated by the microphone at the frequency at which the power of the signal generated by the microphone is at its maximum, plus the power of the signal generated by the microphone at the frequency of the signal generated by the microphone,
  • which is immediately adjacent to the frequency at which the power of the signal generated by the microphone is maximum, and
  • in which the power is greater than at a frequency which is also immediately adjacent to the frequency at which the power of the signal generated by the microphone is maximal,

to

• the average of the power of the signal generated by the microphone of all, at least substantially, further (examined) frequencies of the signal generated by the microphone

greater than a Time Ratio Limit (BinRatioTimeThreshold) is greater than a Feedback Power Limit (RatioThreshold, OutGrdRatioThreshold).

In a further advantageous embodiment of the invention, the Rückopplungs Leistungsgrenzwert (RatioThreshold, OutGrdRatioThreshold) is determined in response to an output signal of the bandpass filter.

In a further advantageous embodiment of the invention, the Rückopplungs Leistungsgrenzwert (RatioThreshold, OutGrdRatioThreshold) is between 20 and 50.

• der Leistung des mittels des Mikrofons erzeugten Signals bei der Frequenz, bei der die Leistung des mittels des Mikrofons erzeugten Signals maximal ist,

zu

• dem Mittelwert der Leistung des mittels des Mikrofons erzeugten Signals bei weiteren Frequenzen, bei denen die Leistung des mittels des Mikrofons erzeugten Signals ein lokales Maximum aufweist,

größer ist als ein Zusatz-Leistungsgrenzwert (RichContentThreshold).In a further advantageous embodiment of the invention, the bandpass filter is set such that it blocks the proportion of the signal generated by the microphone at a blocking frequency only when the ratio

• the power of the signal generated by the microphone at the frequency at which the power of the signal generated by the microphone is at a maximum,

to

• the mean value of the power of the signal generated by the microphone at other frequencies at which the power of the signal generated by the microphone has a local maximum,

is greater than an additional performance limit (RichContentThreshold).

• der Leistung des mittels des Mikrofons erzeugten Signals bei der Frequenz, bei der die Leistung des mittels des Mikrofons erzeugten Signals maximal ist,

zu

• dem Mittelwert der Leistung des mittels des Mikrofons erzeugten Signals bei allen weiteren (untersuchten) Frequenzen, bei denen die Leistung des

mittels des Mikrofons erzeugten Signals ein lokales Maximum aufweist,
größer ist als ein Zusatz-Leistungsgrenzwert (RichContentThreshold).In a further advantageous embodiment of the invention, the bandpass filter is set such that it blocks the proportion of the signal generated by the microphone at a blocking frequency only when the ratio

• the power of the signal generated by the microphone at the frequency at which the power of the signal generated by the microphone is at a maximum,

to

• the mean value of the power of the signal generated by the microphone at all other (tested) frequencies at which the power of the

signal generated by the microphone has a local maximum,
is greater than an additional performance limit (RichContentThreshold).

Power of the signal generated by the microphone at the frequency at which the power of the signal generated by the microphone is maximum, and / or power of the signal generated by the microphone at a frequency at which the power of the signal generated by the microphone is a local Maximum, in the sense of the aforementioned invention should alternatively or additionally include the power that has the signal at a closely adjacent frequency of the aforementioned frequency and which (still) has a similar high performance as the respective maximum.

In a further advantageous embodiment of the invention, the additional power limit (RichContentThreshold) is between 20 and 50, in a particularly advantageous embodiment of the invention between 30 and 40.

In a further advantageous embodiment of the invention, the bandpass filter is set depending on its output signal.

Fig. 1

ein Kraftfahrzeug,

Fig. 2

ein Ausführungsbeispiel für eine erfindungsgemäße Einrichtung,

Fig. 3

ein Notchfilter,

Fig. 4

eine Filterbank,

Fig. 5

ein Ausführungsbeispiel für einen in einer Entscheidungslogik implementierten Ablaufplan,

Fig. 6

ein Leistung-Frequenz-Diagramm,

Fig. 7

ein Ausführungsbeispiel für Abfrage 41 in Fig. 5,

Fig. 8

ein Leistung-Frequenz-Diagramm und

Fig. 9

ein Leistung-Frequenz-Diagramm.

Further advantages and details emerge from the following description of exemplary embodiments. Showing:

Fig. 1

a motor vehicle,

Fig. 2

an embodiment of an inventive device,

Fig. 3

a notch filter,

Fig. 4

a filter bank,

Fig. 5

an embodiment of a flowchart implemented in a decision logic,

Fig. 6

a power-frequency diagram,

Fig. 7

an embodiment for query 41 in Fig. 5 .

Fig. 8

a power-frequency diagram and

Fig. 9

a power-frequency diagram.

Fig. 1 shows the interior view of a motor vehicle 1 from above. Here, reference numerals 2 and 3, the front seats and reference numerals 4, 5 and 6, the rear seats of the motor vehicle. Reference numerals 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 and 20 denote speakers. Reference numerals 21, 22, 23 and 24 denote microphones. The loudspeakers 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 and 20 partly belong to a music system and partly to a communication / speech / intercom device. They can also be used by both systems.

In the present exemplary embodiment, the loudspeakers 9, 17, 18, 19, 20 give a signal generated by the microphone 21, the loudspeakers 7, 17, 18, 19, 20 a signal generated by the microphone 22, the loudspeakers 7, 9, 19, 20 a signal generated by the microphone 23 and the speakers 7, 9, 17, 18 a signal generated by the microphone 24 from. In this way, the possibility of verbal communication in a motor vehicle is supported. In principle, the better the communication between one of the microphones 21, 22, 23, 24 and one of the loudspeakers 7, 9, 17, 18, 19, 20, the better the communication. However, the possibility of such a gain is limited by possible feedback effects due to sound emitted by a loudspeaker 7, 9, 17, 18, 19, 20 which is received by a microphone 21, 22, 23, 24 and then amplified and transmitted through the loudspeaker 7 , 9, 17, 18, 19, 20 is broadcast.

To reduce such feedback is according to Fig. 2 between a microphone 30, which may be one of the microphones 21, 22, 23, 24, and a loudspeaker 31, which may be one of the loudspeakers 7, 9, 17, 18, 19, 20, a bandpass filter 32 is provided. This filters a signal S generated by the microphone 30 and provides a filtered signal S 'in which certain frequency ranges are filtered out, for which a decision logic 33 has recognized the risk of feedback. For this purpose, the decision logic 33 determines filter parameters f _c and Q by means of which the bandpass filter 32 is set.

To amplify the signal S and / or the signal S 'amplifiers, not shown, may be provided. However, the amplifier function can also be taken over by the bandpass filter.

Fig. 3 shows the characteristic of a designed as a notch filter bandpass filter, the gain V of the bandpass filter is plotted against the frequency f. Here f _c denotes the center frequency of the bandpass filter and Q its quality. For filtering a plurality of frequency ranges, the bandpass filter 32 is advantageously a filter bank, as in FIG Fig. 4 shown executed. The filter bank advantageously comprises up to 10 notch filters.

Fig. 5 shows an exemplary embodiment of a flowchart implemented in a decision logic 33. Initially, in a step 40, the frequency f of Signal S is analyzed and, as exemplified in Fig. 6 shown, the power P of the signal S an, for example 192, different examination frequencies f _n , f _{n + 1} , f _{n + 2} , f _{n + 3} , f _{n + 4} , f _{n + 5} , f _{n + 6} , f _{n +7} , f _{n + 8} determined, which are eg 40Hz apart.

It has proved to be advantageous to determine the power at the examination frequencies _fn , fn _{+ 1} , fn _{+ 2} , fn _{+ 3} , fn _{+ 4} , fn _{+ 5} , fn _{+ 6} , fn _{+ 7} , f _{n + 8} , ie to form an average value over time, and this time average of the power instead of the actual power of the signal S at the examination frequencies f _n , f _{n + 1} , f _{n + 2} , f _{n + 3} to investigate f _{n + 4} , f _{n + 5} , f _{n + 6} , f _{n + 7} , f _{n + 8} . If the power of the signal S is mentioned in the description and the claims, this can thus also include the average value of the power formed over a certain period of time. Furthermore, the term of the power according to the invention may include the amplitude or its time average. In the sense of the invention, other variations of the power, the amplitude or their time averages should also be included, such as normalized quantities. For example, under the power of the signal S at an examination frequency f _n in the sense of the invention, the value of the power of the signal S at this examination frequency f _{n can be} divided by the sum of the power of the signal S at all examination frequencies f _n , f _{n + 1} , f _{n + 2} , f _{n + 3} , f _{n + 4} , f _{n + 5} , f _{n + 6} , f _{n + 7} , f _{n + 8} .

Step 40 is followed by a query 41 as to whether, for an examination frequency f _n , f _{n + 1} , f _{n + 2} , f _{n + 3} , f _{n + 4} , f _{n + 5} , f _{n + 6} , f _{n + 7} , f _{+ 8} the risk of feedback exists. Details of this query are with respect to Fig. 7 executed. If there is no risk of feedback for any examination frequency f _n , f _{n + 1} , f _{n + 2} , f _{n + 3} , f _{n + 4} , f _{n + 5} , f _{n + 6} , f _{n + 7} , f _{n + 8} , the query 41 is followed by step 40. However, if for an examination frequency f _n , f _{n + 1} , f _{n + 2} , f _{n + 3} , f _{n + 4} , f _{n + 5} , f _{n + 6} , f _{n + 7} , f _{n + 8 there is} the risk of feedback, query 41 is followed by a query 42 as to whether the signal S generated by the microphone 30 has already been reduced by signal components around this examination frequency by means of the bandpass filter.

If the signal S generated by the microphone 30 is not already reduced by signal components around the examination frequency by means of the bandpass filter, the query 42 is followed by a query 43 as to whether a bandpass filter is available. If a bandpass filter is available, query 43 is followed by a step 47, in which a bandpass filter is selected and the filter parameters, ie the center frequency f _c and the quality Q of the bandpass filter, are generated. The center frequency f _c is an example of the blocking frequency in the sense of the claims. The blocking frequency in the sense of However, claims can also be in particular the frequency range around the center frequency f _c , which the bandpass filter actually filters out of the signal S generated by the microphone 30.

gebildet werden, wobei

• fkorr    die Korrekturfrequenz,
• fdist    der Abstand zwischen der Untersuchungsfrequenz, bei der die Leistung des mittels des Mikrofons erzeugten Signals maximal ist, und einer die größte Leistung aufweisenden Untersuchungsfrequenz unmittelbar neben der Untersuchungsfrequenz, bei der die Leistung des mittels des Mikrofons erzeugten Signals maximal ist,
• Pmax    die Leistung des mittels des Mikrofons erzeugten Signals bei der Untersuchungsfrequenz, bei der die Leistung des mittels des Mikrofons erzeugten Signals maximal ist,
• Pmaxneigh    die Leistung des mittels des Mikrofons erzeugten Signals bei der die größte Leistung aufweisenden Untersuchungsfrequenz unmittelbar neben der Untersuchungsfrequenz, bei der die Leistung des mittels des Mikrofons erzeugten Signals maximal ist, und
• sign ein Vorzeichen

ist, wobei sign positiv ist, wenn die die größte Leistung aufweisende Untersuchungsfrequenz unmittelbar neben der Untersuchungsfrequenz, bei der die Leistung des mittels des Mikrofons erzeugten Signals maximal ist, größer ist als die Untersuchungsfrequenz, bei der die Leistung des mittels des Mikrofons erzeugten Signals maximal ist, und wobei sign sonst negativ ist.The center frequency f _c can be set, for example, equal to the examination frequency for which feedback has been determined. In an alternative embodiment of the invention, however, the center frequency f _c may also be the examination frequency added with a correction frequency. This correction frequency is formed, for example, as a function of the power of the signal generated by the microphone at the examination frequency at which the power of the signal generated by the microphone is maximum, and the power of the signal generated by the microphone at at least one lying next to this examination frequency examination frequency. Thus, the correction frequency, for example, according to $$\mathrm{Fcorr}=\mathrm{sign}*\mathrm{FDIST}*\mathrm{Pmaxneigh}/\left(\mathrm{Pmax}+\mathrm{Pmaxneigh}\right)$$

be formed, where

• fkorr the correction frequency,
• fd is the distance between the examination frequency at which the power of the signal generated by the microphone is maximum, and a test power having the highest performance immediately adjacent to the examination frequency at which the power of the signal generated by the microphone is maximum,
• Pmax the power of the signal generated by the microphone at the examination frequency at which the power of the signal generated by means of the microphone is maximum,
• Pmaxneigh the power of the signal generated by the microphone at the highest power examination frequency immediately adjacent to the examination frequency at which the power of the signal generated by the microphone is maximum, and
• sign a sign

, where sign is positive, if the examination power having the highest power immediately adjacent to the examination frequency at which the power of the signal generated by the microphone is maximum is larger than that Examination frequency at which the power of the signal generated by the microphone is maximum, and where sign is otherwise negative.

• Es werden 192 Untersuchungsfrequenzen f₁, f₂, .... f₁₉₂ angenommen. f₁ ist gleich 40Hz. fdist ist für alle Untersuchungsfrequenzen 40Hz. Zudem gilt für die Leistungen des mittels des Mikrofons erzeugten Signals bei den Untersuchungsfrequenzen f₁, f₂, .... f₁₉₂: $$\mathrm{<figure-callout\; id="1"\; label="P\; f"\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">P</figure-callout>}\left({\mathrm{f}}_{}\right)\left({\mathrm{}}_{\mathrm{1}}\mathrm{,}{\mathrm{<figure-callout\; id="2"\; label="f"\; filenames="imgf0005.png"\; state="\{\{state\}\}">f</figure-callout>}}_{\mathrm{2}}\mathrm{,}\mathrm{....}{\mathrm{f}}_{\mathrm{94}}\right)\mathrm{=}\mathrm{1}$$
  
  $$\mathrm{P}\left({\mathrm{f}}_{\mathrm{95}}\right)\mathrm{=}\mathrm{4}$$
  
  $$\mathrm{P}\left({\mathrm{f}}_{\mathrm{96}}\right)\mathrm{=}\mathrm{16}$$
  
  $$\mathrm{P}\left({\mathrm{f}}_{\mathrm{97}}\right)\mathrm{=}\mathrm{2}$$
  
  $$\mathrm{P}\left({\mathrm{f}}_{\mathrm{98}}\mathrm{,}{\mathrm{f}}_{99}\mathrm{,}\mathrm{....}{\mathrm{f}}_{192}\right)\mathrm{=}\mathrm{1}$$
  

This is explained in more detail with reference to the following example:

• 192 examination frequencies f ₁ , f ₂ , .... f _{192 are} assumed. f ₁ is equal to 40Hz. fdist is 40Hz for all exam frequencies. In addition, for the powers of the signal generated by the microphone at the examination frequencies f ₁ , f ₂ , .... f ₁₉₂ : $$\mathrm{<figure-callout\; id="1"\; label="P\; f"\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">P\; </figure-callout>}\left({\mathrm{f}}_{}\right)\left({\mathrm{}}_{\mathrm{1}}\mathrm{.}{\mathrm{<figure-callout\; id="2"\; label="f"\; filenames="imgf0005.png"\; state="\{\{state\}\}">f</figure-callout>}}_{\mathrm{2}}\mathrm{.}\mathrm{....}{\mathrm{f}}_{\mathrm{94}}\right)\mathrm{=}\mathrm{1}$$
  
  $$\mathrm{P}\left({\mathrm{f}}_{\mathrm{95}}\right)\mathrm{=}\mathrm{4}$$
  
  $$\mathrm{P}\left({\mathrm{f}}_{\mathrm{96}}\right)\mathrm{=}\mathrm{16}$$
  
  $$\mathrm{P}\left({\mathrm{f}}_{\mathrm{97}}\right)\mathrm{=}\mathrm{2}$$
  
  $$\mathrm{P}\left({\mathrm{f}}_{\mathrm{98}}\mathrm{.}{\mathrm{f}}_{99}\mathrm{.}\mathrm{....}{\mathrm{f}}_{192}\right)\mathrm{=}\mathrm{1}$$
  

Then: $$\mathrm{Fcorr}\mathrm{=}\left(\mathrm{-}\right)\mathrm{*}\mathrm{40}\mathrm{Hz}\mathrm{*}\mathrm{4}\mathrm{/}\left(\mathrm{16}\mathrm{+}\mathrm{2}\right)\mathrm{=}\mathrm{-}\mathrm{8th}\mathrm{Hz}$$

The examination frequency at which the power of the signal generated by the microphone is maximum is thus 3840 Hz and the blocking frequency 3832 Hz.

gebildet werden, wobei

• fkorr    die Korrekturfrequenz,
• Δf    der Abstand zwischen zwei Untersuchungsfrequenzen,
• Pmax    die Leistung des mittels des Mikrofons erzeugten Signals bei der Untersuchungsfrequenz, bei der die Leistung des mittels des Mikrofons erzeugten Signals maximal ist,
• Pneighright    die Leistung des mittels des Mikrofons erzeugten Signals bei der Untersuchungsfrequenz unmittelbar oberhalb der Untersuchungsfrequenz, bei der die Leistung des mittels des Mikrofons erzeugten Signals maximal ist, und
• Pneighleft    die Leistung des mittels des Mikrofons erzeugten Signals bei der Untersuchungsfrequenz unmittelbar unterhalb der Untersuchungsfrequenz, bei der die Leistung des mittels des Mikrofons erzeugten Signals maximal ist,

ist.The correction frequency may also be according to $$\mathrm{Fcorr}=\mathrm{.delta.f}*\left(\mathrm{Pneighright}-\mathrm{Pneighleft}\right)/\left(\mathrm{Pmax}+\left|\mathrm{Pneighright}-\mathrm{Pneighleft}\right|\right)$$

be formed, where

• fkorr the correction frequency,
• Δf the distance between two examination frequencies,
• Pmax the power of the signal generated by the microphone at the examination frequency at which the power of the signal generated by means of the microphone is maximum,
• Pneighright the power of the signal generated by the microphone at the examination frequency immediately above the examination frequency at which the power of the signal generated by the microphone is maximum, and
• Pneighleft the power of the signal generated by the microphone at the examination frequency immediately below the examination frequency at which the power of the signal generated by the microphone is maximum,

is.

Die Untersuchungsfrequenz, bei der die Leistung des mittels des Mikrofons erzeugten Signals maximal ist, ist somit 3840Hz und die Sperrfrequenz 3835,56Hz.On the basis of the above numerical example, in this case: $$\mathrm{Fcorr}\mathrm{=}\mathrm{40}\mathrm{Hz}\mathrm{*}\left(\mathrm{2}\mathrm{-}\mathrm{4}\right)\mathrm{/}\left(\mathrm{16}\mathrm{+}\left|\mathrm{4}\mathrm{-}\mathrm{2}\right|\right)\mathrm{=}\mathrm{-}\mathrm{4}\mathrm{.}\mathrm{44}\mathrm{Hz}$$

The examination frequency at which the power of the signal generated by the microphone is maximum is thus 3840 Hz and the blocking frequency 3835.56 Hz.

The quality Q is set to a predetermined value of e.g. 1 / 40Hz set.

If query 43 indicates that no bandpass filter is available, query 43 is followed by a step 48 in which the power of signal S is reduced by a reduction factor which is advantageously between 2 dB and 5 dB, in particular at substantially 3dB becomes.

If the query 42 shows that the signal S generated by the microphone 30 is already reduced by signal components around the examination frequency by means of the bandpass filter, then the query 42 is followed by a query 44. The query 44 queries whether by further widening the frequency range in which locks the bandpass filter, ie by further reduction of the quality Q, a predetermined minimum quality would be exceeded.

If a further minimum widening of the frequency range would fall below a predetermined minimum quality, the query 44 is followed by a step 45, otherwise a step 46. In step 45, which corresponds to step 48, the power of the signal S is reduced by a reduction factor, which is advantageously between 2dB and 5dB, especially at substantially 3dB. In step 46, the Q is reduced, i. expanded the bandpass filter.

Steps 45, 46, 47 and 48 are followed by a step 49, in which a time between 0.1s and 3s is awaited.

• der Leistung MaxBinPwrPlusNeighbor des mittels des Mikrofons 30 erzeugten Signals S bei der Untersuchungsfrequenz, bei der die Leistung des mittels des Mikrofons 30 erzeugten Signals S maximal ist, plus der Leistung des mittels des Mikrofons 30 erzeugten Signals S bei der Untersuchungsfrequenz des mittels des Mikrofons 30 erzeugten Signals S,
  • die der Untersuchungsfrequenz, bei der die Leistung des mittels des Mikrofons 30 erzeugten Signals S maximal ist, unmittelbar benachbart ist, und
  • bei der die Leistung größer ist als bei einer Untersuchungsfrequenz, die der Untersuchungsfrequenz, bei der die Leistung des mittels des Mikrofons 30 erzeugten Signals S maximal ist, ebenfalls unmittelbar benachbart ist,

zu

• dem Mittelwert MeanBinPwrRemainder der Leistung des mittels des Mikrofons 30 erzeugten Signals S aller weiteren Untersuchungsfrequenzen des mittels des Mikrofons 30 erzeugten Signals S

größer ist als ein Rückopplungs-Leistungsgrenzwert OutGrdRatioThreshold. Fig. 7 shows an embodiment for the query 41. In this case, first a query 61 is provided, whether the power of the output signal S 'of the bandpass filter 32 exceeds an output limit. Exceeds the power of the output signal S 'of the bandpass filter 32, the output limit, the query 61 follows a query 62, for example, if the ratio PowerRatio3

• the power MaxBinPwrPlusNeighbor of the signal S generated by the microphone 30 at the examination frequency at which the power of the signal S generated by the microphone 30 is maximum, plus the power of the signal S generated by the microphone 30 at the examination frequency of the microphone 30 generated by the microphone Signal S,
  • which is immediately adjacent to the examination frequency at which the power of the signal S generated by the microphone 30 is maximum, and
  • in which the power is greater than at an examination frequency which is also immediately adjacent to the examination frequency at which the power of the signal S generated by means of the microphone 30 is maximal,

to

• the mean value MeanBinPwrRema of the power of the signal S generated by the microphone 30 of all other examination frequencies of the signal S generated by means of the microphone 30

is greater than a feedback output limit OutGrdRatioThreshold.

• der Leistung MaxBinPwrPlusNeighbor des mittels des Mikrofons 30 erzeugten Signals S bei der Frequenz, bei der die Leistung des mittels des Mikrofons 30 erzeugten Signals S maximal ist, plus der Leistung des mittels des Mikrofons 30 erzeugten Signals S bei der Untersuchungsfrequenz des mittels des Mikrofons 30 erzeugten Signals S,
  • die der Untersuchungsfrequenz, bei der die Leistung des mittels des Mikrofons 30 erzeugten Signals S maximal ist, unmittelbar benachbart ist, und
  • bei der die Leistung größer ist als bei einer Untersuchungsfrequenz, die der Untersuchungsfrequenz, bei der die Leistung des mittels des Mikrofons 30 erzeugten Signals S maximal ist, ebenfalls unmittelbar benachbart ist,

zu

• dem Mittelwert MeanBinPwrRemainder der Leistung des mittels des Mikrofons 30 erzeugten Signals S aller weiteren Untersuchungsfrequenzen des mittels des Mikrofons 30 erzeugten Signals S

länger als ein Zeit-Verhältnis-Grenzwert OutBinRatioTimeThreshold größer ist als ein Rückopplungs-Leistungsgrenzwert OutGrdRatioThreshold. Der Rückopplungs-Leistungsgrenzwert OutGrdRatioThreshold liegt zwischen 30 und 40.Means of the query 62 is advantageously - as provided in this embodiment - queried whether the ratio PowerRatio3

• the power MaxBinPwrPlusNeighbor of the signal S generated by the microphone 30 at the frequency at which the power of the signal S generated by the microphone 30 is maximum, plus the power of the signal S generated by the microphone 30 at the examination frequency of the microphone 30 generated by the microphone Signal S,
  • which is immediately adjacent to the examination frequency at which the power of the signal S generated by the microphone 30 is maximum, and
  • in which the power is greater than at an examination frequency which is also immediately adjacent to the examination frequency at which the power of the signal S generated by means of the microphone 30 is maximal,

to

• the mean value MeanBinPwrRema of the power of the signal S generated by the microphone 30 of all other examination frequencies of the signal S generated by means of the microphone 30

OutBinRatioTimeThreshold is greater than a time-out limit value greater than a OutGrdRatioThreshold feedback power limit. The feedback power limit OutGrdRatioThreshold is between 30 and 40.

It may be advantageously further provided that the query 62 is answered only positive if the global maximum is longer than a time limit OutGrdMaxBinTimeThreshold at an examination frequency.

To carry out the query 62, first the local maxima are determined. For this purpose, the first derivative of the power of the signal S after the frequency f is first determined (for the examination frequencies). From the first derivative of the power of the signal S after the frequency f, an edge signal is then taken, which assumes a first binary value, when the first derivative of the power of the signal S after the frequency f is greater than zero, and assumes a second binary value, if the first derivative of the power of the signal S after the frequency f is less than zero. Subsequently, the first derivative of the edge signal is determined. In this case, in an advantageous embodiment of the invention, a presence of a local maximum of the power of the signal S on the frequency f is assumed only if the first derivative of the edge signal is smaller than a limit value. Table 1 function idx_vec = FinfInfletions (x, flec_thresh) dtdx = diff (x); dtdx = dtdx>0; dt2dx = diff (dtdx); idx_vec = find (dt2dx <flec_thresh); idx_vec = idx_vec + 1;

Table 1 shows an embodiment of a program programmed in the language Matlab ™, which contains the indices idx_vec of the examination frequencies determined where local maxima exist according to the aforementioned criteria. Here x denotes a vector with the powers at the individual examination frequencies and flec_thresh a value between 0 and -1.

The local maximum with the highest power is considered the global maximum.

If query 62 is answered in the affirmative, query 62 is followed by a query 63, otherwise step 64 follows.

• der Leistung des mittels des Mikrofons 30 erzeugten Signals S bei der Untersuchungsfrequenz, bei der die Leistung des mittels des Mikrofons 30 erzeugten Signals S maximal ist,

zu

• dem Mittelwert der Leistung des mittels des Mikrofons 30 erzeugten Signals S bei allen weiteren Untersuchungsfrequenzen, bei denen die Leistung des mittels des Mikrofons 30 erzeugten Signals S ein lokales Maximum aufweist,

kleiner gleich einem Zusatz-Leistungsgrenzwert RichContentThreshold ist.The query 63 queries whether the signal S has a strong harmonic component. For this purpose, an exemplary advantageous embodiment queries whether the ratio

• the power of the signal S generated by means of the microphone 30 at the examination frequency at which the power of the signal S generated by means of the microphone 30 is maximal,

to

• the mean value of the power of the signal S generated by means of the microphone 30 at all other examination frequencies at which the power of the signal S generated by means of the microphone 30 has a local maximum,

is less than or equal to an additional performance limit RichContentThreshold.

• der Leistung des mittels des Mikrofons 30 erzeugten Signals S bei der Untersuchungsfrequenz, bei der die Leistung des mittels des Mikrofons 30 erzeugten Signals S maximal ist,

zu

• dem Mittelwert der Leistung des mittels des Mikrofons 30 erzeugten Signals S bei allen weiteren Untersuchungsfrequenzen, bei denen die Leistung des mittels des Mikrofons 30 erzeugten Signals S ein lokales Maximum aufweist,

kleiner gleich einem Zusatz-Leistungsgrenzwert RichContentThreshold ist, dann folgt der Abfrage 63 der Schritt 64. Andernfalls wird eine Rückkopplung angenommen.Returns the query 63 that the ratio

• the power of the signal S generated by means of the microphone 30 at the examination frequency at which the power of the signal S generated by means of the microphone 30 is maximal,

to

• the mean value of the power of the signal S generated by means of the microphone 30 at all other examination frequencies at which the power of the signal S generated by means of the microphone 30 has a local maximum,

is less than an additional power limit RichContentThreshold, then query 63 is followed by step 64. Otherwise, feedback is assumed.

In step 64, the process is stopped for a predetermined hold time, eg 3s. After the holding time has elapsed, a feedback is denied.

If the query 61 shows that the power of the output signal S 'of the band-pass filter 32 does not exceed the output limit, the query 61 follows a query 65 corresponding essentially to the query 62. However, a different feedback power limit RatioThreshold and not OutGrdRatioThreshold is used , However, the RatioThreshold rebound power limit is also advantageously between 30 and 40.

If query 65 is answered in the affirmative, query 65 is followed by query 66 corresponding to query 63. Otherwise, the presence of feedback is denied.

• der Leistung des mittels des Mikrofons 30 erzeugten Signals S bei der Untersuchungsfrequenz, bei der die Leistung des mittels des Mikrofons 30 erzeugten Signals S maximal ist,

zu

• dem Mittelwert der Leistung des mittels des Mikrofons 30 erzeugten Signals S bei allen weiteren Untersuchungsfrequenzen, bei denen die Leistung des mittels des Mikrofons 30 erzeugten Signals S ein lokales Maximum aufweist,

kleiner gleich einem Zusatz-Leistungsgrenzwert RichContentThreshold ist, dann wird das Vorliegen einer Rückkopplung verneint. Andernfalls wird eine Rückkopplung angenommen.Returns the query 66 that the ratio

• the power of the signal S generated by means of the microphone 30 at the examination frequency at which the power of the signal S generated by means of the microphone 30 is maximal,

to

• the mean value of the power of the signal S generated by means of the microphone 30 at all other examination frequencies at which the power of the signal S generated by means of the microphone 30 has a local maximum,

is less than an additional power limit RichContentThreshold, then the presence of a feedback is negated. Otherwise, feedback is assumed.

The feedback detection according to the invention is not limited to the above-described embodiment. The feedback detection can for example be configured such that only the query 65 is provided. The feedback detection can also be configured in such a way, the embodiment according to Fig. 7 with their binary decision logic by a fuzzy decision logic, so fuzzy logic or neural networks to replace.

The query 63 according to Fig. 7 is described below with reference to two in FIGS. 8 and 9 illustrated in a power-frequency diagram signals 80 and 90. The power P of the signals 80 and 90 is plotted in dB over the index idx_vec of the examination frequencies. It is assumed that the query 61 for both signals 80 and 90 shows that the power of the output signal S 'of the band-pass filter 32 exceeds the output limit and that therefore the Query 61 follows query 62. It is further assumed that the query 62 is answered in the affirmative. The + signs in FIGS. 8 and 9 designates all examination frequencies that have been recognized as local / global maxima by means of the program according to Table 1.

In Fig. 8 reference numeral 81 denotes the global maximum of the signal 80. In Fig. 9 reference numeral 91 denotes the global maximum of the signal 90. The examination frequencies are spaced apart by 40 Hz. The additional performance limit RichContentThreshold is 37.

• der Leistung des Signals 80 bei der Untersuchungsfrequenz, bei der die Leistung des Signals 80 maximal ist,

zu

• dem Mittelwert der Leistung des Signals 80 bei allen weiteren Untersuchungsfrequenzen, bei denen die Leistung des Signals 80 ein lokales Maximum aufweist,

beträgt in etwa 16 und ist damit deutlich kleiner als 37. Die Abfrage 63 würde somit positiv beantwortet und somit das Vorliegen von Rückkopplung verneint.The relationship

• the power of the signal 80 at the examination frequency at which the power of the signal 80 is maximum,

to

• the average of the power of the signal 80 at all other test frequencies at which the power of the signal 80 has a local maximum,

is approximately 16 and is thus significantly smaller than 37. The query 63 would thus respond positively and thus denies the presence of feedback.

• der Leistung des Signals 90 bei der Untersuchungsfrequenz, bei der die Leistung des Signals 90 maximal ist,

zu

• dem Mittelwert der Leistung des Signals 90 bei allen weiteren Untersuchungsfrequenzen, bei denen die Leistung des Signals 90 ein lokales Maximum aufweist,

beträgt in etwa 73 und ist damit deutlich größer als 37. Die Abfrage 63 würde somit verneint und daher Rückkopplung angenommen.The relationship

• the power of the signal 90 at the examination frequency at which the power of the signal 90 is maximum,

to

• the average of the power of the signal 90 at all other examination frequencies at which the power of the signal 90 has a local maximum,

is approximately 73 and is thus significantly larger than 37. The query 63 would thus be negative and therefore assumed feedback.

LIST OF REFERENCE NUMBERS

1 motor vehicle 2, 3 front seats 4, 5, 6 rear seats 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 31 speaker 21, 22, 23, 24, 30 Microphones 32 Bandpass filter 33 decision logic 40, 45, 46, 47, 48, 49, 64 steps 41, 42, 43, 44, 61, 62, 63, 65, 66 Interrogate 80, 90 signal 81, 91 global maximum BinRatioTimeThreshold Time ratio limit f frequency f _n , f _{n + 1} , f _{n + 2} , f _{n + 3} , f _{n + 4} , f _{n + 5} , f _{n + 6} , f _{n + 7} , f _{n + 8} , f ₁ , f ₂ , f ₄₄ , f ₈₈ , f ₉₄ , f ₉₅ , f ₉₇ , f ₉₈ , f ₁₂₂ , f ₁₉₂ frequency points f _c center frequency FDIST The distance between the examination frequency at which the power of the signal generated by the microphone is maximum and the highest performance examination frequency immediately adjacent to the examination frequency at which the power of the signal generated by the microphone is maximum Fcorr correction frequency MaxBinPwrPlusNeighbor Power of the signal generated by the microphone at the frequency at which the power of the signal generated by the microphone is maximum, plus the power of the signal generated by the microphone at the frequency of the signal generated by the microphone, that at which the frequency Power of the signal generated by the microphone is maximum, is immediately adjacent, and in which the power is greater than at a frequency of the frequency at which the power of the signal generated by the microphone is maximum, is also immediately adjacent MeanBinPwrRemainder Average power of the signal generated by the microphone of all other (examined) frequencies Q quality OutGrdRatioThreshold, RatioThreshold Rückopplungs-power limit P power Pmax Power of the signal generated by the microphone at the examination frequency at which the power of the signal generated by the microphone is maximum Pmaxneigh Power of the signal generated by the microphone at the highest power examination frequency immediately adjacent to the examination frequency at which the power of the signal generated by the microphone is maximum Pneighleft Power of the signal generated by the microphone at the examination frequency immediately below the examination frequency at which the power of the signal generated by the microphone is maximum Pneighright Power of the signal generated by the microphone at the examination frequency immediately above the examination frequency at which the power of the signal generated by the microphone is maximum PowerRatio3 performance ratio RichContentThreshold Auxiliary power limit S signal S ' filtered signal sign sign V reinforcement .delta.f Distance between two examination frequencies

Claims (19)

1. Method for operating a voice-assisted system, such as a communication and/or voice/intercom device in a motor vehicle (1), having at least one microphone (30) and at least one loudspeaker (31) for reproducing a signal produced by means of the microphone (30) and also having a notch filter arranged between the microphone (30) and the loudspeaker (31), wherein a frequency-dependent power of the signal (S) is ascertained, characterized in that the notch filter is set on the basis of at least one local maximum for the power of the signal (S) over the frequency (f), wherein a first derivation for the power of the signal (S) on the basis of the frequency (f) is used to form an edge signal which assumes a first binary value when the first derivation of the power of the signal (S) on the basis of the frequency (f) is greater than or equal to zero, and which assumes a second binary value when the first derivation of the power of the signal (S) on the basis of the frequency (f) is less than zero, the local maximum of the power of the signal (S) being ascertained on the basis of the first derivation of the edge signal.
2. Method according to the preceding claim, characterized in that all the local maxima in a frequency range are determined.
3. Method according to Claim 2, characterized in that the global maximum in the frequency range is determined.
4. Method according to one of the preceding claims, characterized in that the notch filter is set such that it rejects the proportion of the signal (S) produced by means of the microphone (30) at a stop frequency only if the ratio

   - of at least the power of the signal (S) produced by means of the microphone (30) at the frequency at which the power of the signal (S) produced by means of the microphone (30) is at a maximum

   to

   - the average of the power of the signal (S) produced by means of the microphone (30) at further frequencies of the signal (S) produced by means of the microphone (30)

   is greater than a feedback power limit value (RatioThreshold, OutGrdRatioThreshold).
5. Method according to one of the preceding claims, characterized in that the notch filter is set such that it rejects the proportion of the signal (S) produced by means of the microphone (30) at a stop frequency only if the ratio

   - of at least the power of the signal (S) produced by means of the microphone (30) at the frequency at which the power of the signal (S) produced by means of the microphone (30) is at a maximum

   to

   - the average of the power of the signal (S) produced by means of the microphone (30) at further frequencies of the signal (S) produced by means of the microphone (30)

   is greater than a feedback power limit value (RatioThreshold, OutGrdRatioThreshold) for longer than a time ratio limit value (BinRatioTimeThreshold).
6. Method according to one of the preceding claims, characterized in that the notch filter is set such that it rejects the proportion of the signal (S) produced by means of the microphone (30) at a stop frequency only if the ratio

   - of the power of the signal (S) produced by means of the microphone (30) at the frequency at which the power of the signal (S) produced by means of the microphone (30) is at a maximum plus the power of the signal (S) produced by means of the microphone (30) at frequencies of the signal (S) produced by means of the microphone (30) which are adjacent to the frequency at which the power of the signal (S) produced by means of the microphone (30) is at a maximum

   to

   - the average of the power of the signal (S) produced by means of the microphone (30) at further frequencies of the signal (S) produced by means of the microphone (30)

   is greater than a feedback power limit value (RatioThreshold, OutGrdRatioThreshold).
7. Method according to one of the preceding claims, characterized in that the notch filter is set such that it rejects the proportion of the signal (S) produced by means of the microphone (30) at a stop frequency only if the ratio

   - of the power of the signal (S) produced by means of the microphone (30) at the frequency at which the power of the signal (S) produced by means of the microphone (30) is at a maximum plus the power of the signal (S) produced by means of the microphone (30) at frequencies of the signal (S) produced by means of the microphone (30) which are adjacent to the frequency at which the power of the signal (S) produced by means of the microphone (30) is at a maximum

   to

   - the average of the power of the signal (S) produced by means of the microphone (30) at further frequencies of the signal (S) produced by means of the microphone (30)

   is greater than a feedback power limit value (RatioThreshold, OutGrdRatioThreshold) for longer than a time ratio limit value (BinRatioTimeThreshold).
8. Method according to one of the preceding claims, characterized in that the notch filter is set such that it rejects the proportion of the signal (S) produced by means of the microphone (30) at a stop frequency only if the ratio

   - of the power of the signal (S) produced by means of the microphone (30) at the frequency at which the power of the signal (S) produced by means of the microphone (30) is at a maximum plus the power of the signal (S) produced by means of the microphone (30) at the frequency of the signal (S) produced by means of the microphone (30)

   - which is immediately adjacent to the frequency at which the power of the signal (S) produced by means of the microphone (30) is at a maximum and

   - at which the power is greater than at a frequency which is likewise immediately adjacent to the frequency at which the power of the signal (S) produced by means of the microphone (30) is at a maximum

   to

   - the average of the power of the signal (S) produced by means of the microphone (30) at further frequencies of the signal (S) produced by means of the microphone (30)

   is greater than a feedback power limit value (RatioThreshold, OutGrdRatioThreshold).
9. Method according to one of the preceding claims, characterized in that the notch filter is set such that it rejects the proportion of the signal (S) produced by means of the microphone (30) at a stop frequency only if the ratio

   - of the power of the signal (S) produced by means of the microphone (30) at the frequency at which the power of the signal (S) produced by means of the microphone (30) is at a maximum plus the power of the signal (S) produced by means of the microphone (30) at the frequency of the signal (S) produced by means of the microphone (30)

   - which is immediately adjacent to the frequency at which the power of the signal (S) produced by means of the microphone (30) is at a maximum and

   - at which the power is greater than at a frequency which is likewise immediately adjacent to the frequency at which the power of the signal (S) produced by means of the microphone (30) is at a maximum

   to

   - the average of the power of the signal (S) produced by means of the microphone (30) at further frequencies of the signal (S) produced by means of the microphone (30)

   is greater than a feedback power limit value (RatioThreshold, OutGrdRatioThreshold) for longer than a time ratio limit value (BinRatioTimeThreshold).
10. Method according to one of the preceding claims, characterized in that the notch filter is set such that it rejects the proportion of the signal (S) produced by means of the microphone (30) at a stop frequency only if the ratio

    - of the power of the signal (S) produced by means of the microphone (30) at the frequency at which the power of the signal (S) produced by means of the microphone (30) is at a maximum plus the power of the signal (S) produced by means of the microphone (30) at the frequency of the signal (S) produced by means of the microphone (30)

    - which is immediately adjacent to the frequency at which the power of the signal (S) produced by means of the microphone (30) is at a maximum and

    - at which the power is greater than at a frequency which is likewise immediately adjacent to the frequency at which the power of the signal (S) produced by means of the microphone (30) is at a maximum

    to

    - the average of the power of the signal (S) produced by means of the microphone (30) at all further frequencies of the signal (S) produced by means of the microphone (30)

    is greater than a feedback power limit value (RatioThreshold, OutGrdRatioThreshold).
11. Method according to one of the preceding claims, characterized in that the notch filter is set such that it rejects the proportion of the signal (S) produced by means of the microphone (30) at a stop frequency only if the ratio

    - of the power of the signal (S) produced by means of the microphone (30) at the frequency at which the power of the signal (S) produced by means of the microphone (30) is at a maximum plus the power of the signal (S) produced by means of the microphone (30) at the frequency of the signal (S) produced by means of the microphone (30)

    - which is immediately adjacent to the frequency at which the power of the signal (S) produced by means of the microphone (30) is at a maximum and

    - at which the power is greater than at a frequency which is likewise immediately adjacent to the frequency at which the power of the signal (S) produced by means of the microphone (30) is at a maximum

    to

    - the average of the power of the signal (S) produced by means of the microphone (30) at all further frequencies of the signal (S) produced by means of the microphone (30)

    is greater than a feedback power limit value (RatioThreshold, OutGrdRatioThreshold) for longer than a time ratio limit value (BinRatioTimeThreshold).
12. Method according to one of Claims 5 to 11, characterized in that the feedback power limit value (RatioThreshold, OutGrdRatioThreshold) is stipulated on the basis of an output signal (S') from the notch filter.
13. Method according to one of Claims 5 to 12, characterized in that the feedback power limit value (RatioThreshold, OutGrdRatioThreshold) is between 20 and 50.
14. Method according to one of the preceding claims, characterized in that the notch filter is set such that it rejects the proportion of the signal (S) produced by means of the microphone (30) at a stop frequency only if the ratio

    - of the power of the signal (S) produced by means of the microphone (30) at the frequency at which the power of the signal (S) produced by means of the microphone (30) is at a maximum

    to

    - the average of the power of the signal (S) produced by means of the microphone (30) at further frequencies at which the power of the signal (S) produced by means of the microphone (30) has a local maximum

    is greater than a supplementary power limit value (RichContentThreshold).
15. Method according to one of the preceding claims, characterized in that the notch filter is set such that it rejects the proportion of the signal (S) produced by means of the microphone (30) at a stop frequency only if the ratio

    - of the power of the signal (S) produced by means of the microphone (30) at the frequency at which the power of the signal (S) produced by means of the microphone (30) is at a maximum

    to

    - the average of the power of the signal (S) produced by means of the microphone (30) at all further frequencies at which the power of the signal (S) produced by means of the microphone (30) has a local maximum

    is greater than a supplementary power limit value (RichContentThreshold).
16. Method according to one of Claims 14 to 15, characterized in that the supplementary power limit value (RichContentThreshold) is between 20 and 50.
17. Method according to Claim 16, characterized in that the supplementary power limit value (RichContentThreshold) is between 30 and 40.
18. Method according to one of the preceding claims, characterized in that the notch filter is set on the basis of its output signal (S').
19. Device for operating voice-assisted systems, wherein the device has

    - at least one microphone (30),

    - at least one loudspeaker (31) for reproducing a signal (S) produced by means of the microphone (30), and

    - a notch filter arranged between the microphone (30) and the loudspeaker,

    characterized in that the device has a decision logic unit for setting the notch filter on the basis of a method according to one of the preceding claims.

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