Abstract:
A device for operating voice-controlled systems, such as communication and/or intercommunication systems in motor vehicles, includes a plurality of microphones and at least one loudspeaker. Voice signals received by the microphones are transmitted to the at least one loudspeaker. The voice signals are subjected to a low-value frequency shift before being transmitted to the loudspeaker(s) or to the input of a voice-controlled device to thereby suppress feedback.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a method and a device, for operating voice-controlled systems, such as communication and/or one-way/two-way intercom devices in motor vehicles, where voice signals are picked up by a multiple microphone system and transmitted to at least one loudspeaker. 
   BACKGROUND INFORMATION 
   On the one hand, methods of this type are used in motor vehicles for voice- controlled intercom operation, but they are also used for supporting voice-input controlled electronic or electric modules. In this case, the fundamental problem is that, depending on the operating state, corresponding background noise is present in the motor vehicle. This background noise masks the voice commands. One- and two-way intercom systems in motor vehicles are advantageous in large vehicles, minibusses, and the like. However, they can also be used in normal passenger cars. Suppressing background noise or filtering out the voice command is still very important in the use of voice-controlled input units for electric components in the vehicle. 
   A voice-recognition device for a motor vehicle is described, for example in European Patent No. 0 078 014, where sensors signal or feed into the amplifier system of the voice- recognition device, whether or not the engine is running and/or the vehicle is moving. This device guides a level control, by which it is attempted to isolate the voice command from the background noise. 
   German Patent No. 37 42 929 describes a system having two microphones, one of the microphones being disposed at the mouth of the operator, and another in proximity, which is, however, for picking up the structure-borne noise. Both microphone signals are triggered so, that structure-borne noise can be subtracted from the total noise. 
   German Published Patent Application No. 197 05 471 describes a voice-recognition system using transverse filtering. In this case, a frequency analysis is performed, which is only used for the purpose of recognizing speech commands. No ambient-noise compensation is performed. 
   Filtering is described in International Patent Publication No. WO 97/34290, in which periodic interference signals are filtered out by ascertaining their periods and canceling them out by interference, using a generator, so that the voice signal remains. 
   German Patent No. 41 06 405 describes a method in which noise is subtracted from the voice signal, a plurality of microphones being used. 
   The use of a multiple microphone array is known from described in German Published Patent Application No. 39 25 589. When using the array in the motor vehicle, one of the microphones is disposed in the engine compartment and another microphone is disposed in the passenger compartment. Both signals are then subtracted. A disadvantage in this case, is that only the engine noise i.e. the actual operational noise of the vehicle itself, is subtracted from the total signal in the passenger compartment. Specific ambient noises are not, however, considered. The lack of feedback suppression presents a special problem. Wherever microphones and loudspeakers are arranged in acoustically coupleable proximity, the acoustic signal decoupled at the loudspeaker is fed back into the microphone. This results in so-called feedback and a subsequent overload. 
   German Published Patent Application No. 39 25 589 also describes a method, in which a composite signal is formed. The composite signal includes a voice signal and an external noise signal. A detection of the external noise is performed separately. The external noise and voice signals are filtered and subtracted from the composite signal. The results is used to control the filter. This method, however, cannot effectively prevent the occurrence of an echo and/or feedback. 
   A similar method is known from DE 39 25 589 A1, where a composite signal made of a voice signal and an external signal is formed. The additional picking-up of external noise takes place separately. The external-noise and voice signals are lead over a filter and are subtracted from the composite signal. Then, the result of the comparison controls the filter. A method of this type cannot effectively prevent the 
   Therefore, it is an object of the present invention to provide a method and device for operating voice-controlled systems in motor vehicles so that instances of feedback and 
   SUMMARY 
   Regarding a device of the species, the stated object of the present invention is achieved by the characterizing features of claim  5 . Advantageous further refinements of the device according to the present invention are specified in the remaining claims. 
   With regard to both the method and the device, the present invention is based on a communication and/or one-way/two-way intercom device in motor vehicles. A multiple microphone system is provided to pick up both voice and noise signals. Noise signals are subtracted from the total signal, so that the filtered voice signal remains. 
   The present invention includes initially shifting the frequency of the specific microphone signal by a small amount Δ F, and only then transmitting the microphone signal to the loudspeaker(s) or to the input of a voice-controlled device. The frequency shift of the present invention, which is performed at a defined position and is not arbitrary, supports the filtering on the one hand, and decouples feedback, and therefore the echo signal, on the other hand. This result is achieved by subtracting the composite signal shifted by Δ F of another, i.e., a second, microphone from the composite signal of a first microphone, the frequency of which has not yet been shifted, and vice versa. 
   Since, without the aforesaid frequency shift of the present invention, feedback is nothing more than the, fed-back, amplified voice signal, such feedback cannot be eliminated by conventional systems and procedures. This is therefore the case, because devices conventional only separate the voice signal from the noise signal, and identify the fed-back signal as a voice signal, and not as a noise signal. For this reason, the aforesaid instances of feedback cannot be controlled by the conventional systems and methods and cannot be controlled simultaneously. 
   In contrast, the method and the device of the present invention, the latter of which relates to the connection of the individual elements to one another, eliminate feedback effects in simple and efficient manner. 
   Since feedback, always occurs when the microphone and loudspeaker locations are close together, a generally occurs in motor vehicles, the elimination of this feedback is very important. This is not only valid in the case of intercom operation, where electroacoustical feedback is uncomfortable for the passengers, but it also has special significance in the use of voice-controlled input interfaces of electrical or electronic components on the vehicle. This only applies when the entire system in the vehicle includes both microphones and loudspeakers, and in this case, also when the input to electrical devices is voice-controlled. Feedback and resulting overloads can cause considerable malfunctions and misinterpretations of the voice command, even in the case of intelligent input interfaces. Depending on the application, this also constitutes a safety hazard. As an option, noise reduction can also be implemented at the same time, i.e., simultaneously. 
   The present invention is represented in the drawing, and subsequently described in detail. 

   
     BRIEF DESCRIPTION OF THE DRAWING 
     The FIGURE is a schematic view of a device for operating voice-controlled systems in motor vehicles according to the present invention. 
   

   DETAILED DESCRIPTION 
   In the illustrated exemplary embodiment of the present-invention, the vehicle interior is subdivided into two subspaces, namely front and rear. 
   A microphone M  1  and a loudspeaker L  2  are located in the front section. Microphone M  1  picks up the voice signal, and possibly picks up noise signals as well. In this case, the noise signal is made up of the background noise in the passenger compartment, which occurs while operating the vehicle. This background noise may include engine noises, wind noises, rolling noises, but also acoustical echo signals from the other subspace, and the like. The composite signal (total signal) (total signal) detected at M  1 , which may include of background speech and background noise, is fed to a first summation point S  1 . Then, a correspondingly conditioned signal from an acoustic model AM  1  in front is also fed to this summation point. In this exemplary embodiment, the subtraction signal generated in acoustic model AM  1  originates from the signal, which is obtained in the rear section of the vehicle, and is already shifted in frequency. Because this signal, which comes from M  2 , is frequency-shifted in F  2 , and originates from the rear subspace of the passenger compartment, is also taken into account in front on a signal basis, by AM  1 , the signal, which is generated in the rear subspace of the vehicle, is acoustically transported up front, into the front subspace of the passenger compartment, and is also registered by M  1 , is subtracted again at summation point S  1 . Thus, the rear subspace of the passenger compartment is acoustically separated from the front subspace of the passenger compartment by device AM  1 . That is, the total detectable acoustical signal is initially fed into M  1 , and the echo from the rear subspace of the passenger compartment is initially subtracted at summation point S  1 . The original signal from the front subspace of the passenger compartment, which is obtained from M  1  in this manner, is then supplied to a frequency-shifting device F  1 , and shifted by an amount A F, e.g. 5 Hz. The F  1  output signal obtained in this manner is then supplied to loudspeaker L  1  of the rear passenger-compartment subspace and, on the other hand, is simultaneously fed into device AM  2  in the same manner. In this case, AM  2  again represents the acoustic model for the rear subspace of the passenger compartment. A voice message is transmitted in an analogous manner from the rear subspace of the passenger compartment, via M  2 , to the front subspace of the passenger compartment, via L  2 . That is, microphone M  2  registers the voice message together with the background noise in the rear subspace of the passenger compartment, and transmits them to summation point S  2 , which the total acoustical signal picked up by M  1 , i.e., the echo as well as ambient noises, is subtracted. In turn, the echo-free signal from microphone M  2 , which is generated in this manner, is then supplied to a frequency-shifting device F  2 , as well, which again shifts the frequency by an amount Δ F. At the output of this frequency-shifting device F  2 , the result, i.e., the signal conditioned in this manner, is again supplied to the front subspace of the passenger compartment, namely to loudspeaker L  2  positioned there. The frequency shift for the transmission from the front to the rear can also be different from the frequency shift from the rear to the front. 
   All in all, the result is a closed, feedback-free system. The shifting of the frequency is an important feature here, and the echo from the front to the rear subspace, and vice versa, is eliminated by the interaction with the connection via acoustic models AM  1  and AM  2 . 
   However, it is also possible to add a noise-signal subtraction to the echo suppression and feedback elimination. This can also be appropriately taken into consideration in the specific acoustic model AM  1  and AM  2 . The additional components necessary for this purpose, such as noise-signal microphones, are not shown here in further detail. 
   Therefore the total background noise signal, which may include an echo and/or other noises, is subtracted from every from every acoustical input signal from M  1  and M  2 , before it is processed further and fed to loudspeakers L  2  and L  1 , respectively. So not only does an acoustic decoupling occur between the front and rear subspaces of the passenger compartment, but also the remaining noise signals are quasi compensated for, or subtracted, in the same step.