In-car communication system for multiple acoustic zones

An In-Car Communication (ICC) system supports the communication paths within a car by receiving the speech signals of a speaking passenger and playing it back for one or more listening passengers. Signal processing tasks are split into a microphone related part and into a loudspeaker related part. A sound processing system suitable for use in a vehicle having multiple acoustic zones includes a plurality of microphone In-Car Communication (Mic-ICC) instances coupled and a plurality of loudspeaker In-Car Communication (Ls-ICC) instances. The system further includes a dynamic audio routing matrix with a controller and coupled to the Mic-ICC instances, a mixer coupled to the plurality of Mic-ICC instances and a distributor coupled to the Ls-ICC instances.

FIELD OF INVENTION

The present invention relates generally to a sound processing system and, more particularly, to a sound processing system including several microphones and loudspeakers in multiple acoustic zones for use in receiving and reproducing audio signals within a vehicle to provide increased intelligibility.

BACKGROUND OF THE INVENTION

Due to a large amount of background noise, the communication within a car driving at high or even moderate speeds is often difficult. This is especially true if one of the communication partners is the driver and the other is one of the backseat passengers. As a result of the high noise level, the backseat passengers often lean towards the driver or other front passengers. Furthermore, speakers sometime attempt to overcome the noise levels by speaking louder. Even if both of these responses to the noise enhance the quality of the “communication channel” it is exhausting and uncomfortable for the backseat passengers to continue to lean forward and speak louder for extended periods of time. The situation can be improved by using in-car communication (ICC) systems. These systems receive the speech of each passenger by means of a single microphone or with an array of microphones. The received signals of the speaking passenger are processed by the system and played back via loudspeakers which are located close to the non-speaking passengers. Comparable to public address systems, in-car communication systems operate within a closed electro-acoustic loop. Thus, signal processing is used to guarantee stable operation so as to avoid acoustic feedback which results in artifacts such as howling or whistling.

In-Car Communication systems are implemented to support the communication between passengers in adverse automotive environments. The communication between driver and passengers in the rear seats may be strongly disturbed by background noises caused by the tires of the car, the sound of the engine, wind noises or passing cars. Furthermore, the driver has to concentrate on road traffic and therefore cannot turn toward the listener in the rear seat. Since the driver generally speaks towards the windshield, the sound perceived by passengers in the rear of the car is significantly attenuated. Speech intelligibility is additionally degraded by background noise. Therefore, conventional approaches for In-Car Communication systems use microphones to receive the driver's speech signal perform speech enhancement to reduce background noises and amplify the speech signal before the signal is played back in the rear of the car. The reverse communication channel may be supported as well by using microphones close to the passenger in the rear seat and additional loudspeakers in the front of the car. The first case may be viewed as a unidirectional and the second one as a bidirectional ICC system. Bidirectional systems are conventionally implemented using two ICC instances operated in parallel to avoid unstable amplification within the closed loop of both ICC instances. An “instance” generally means a set of executable processor instructions (e.g., signal processing chain instructions), a software thread, firmware or hardware.

FIG. 1shows a conventional implementation of a bidirectional ICC system using two ICC signal processing chains. Signal processing includes processing tasks such as noise reduction, equalization and notch filtering (for suppressing feedback). Details of these signal processing tasks can be found in “Signal Processing for In-Car Communication Systems” by Gerhard Schmidt and Tim Haulick, Chapter from “Topics in Acoustic Echo and Noise Control, 2006, Springer Berlin Heidelberg pp 547-598, (referred to herein as “Schmidt and Haulick”) and incorporated by reference in its entirety.

Up to now conventional ICC systems have been successfully implemented only for two acoustic zones, (e.g. for supporting the communication between the front passengers (front zone) and the passengers on the backseat (rear zone)). During operation, sound reinforcement in such a system bears the risk of going unstable due to signal echo coupling back into the microphones. Each ICC processing chain contains two mechanisms to avoid howling artifacts resulting from such instability: a notch filter that suppresses howling artifacts in the signal (e.g., feedback suppression in Schmidt and Haulick, pp. 571-573) and a loss control mechanism to guarantee that both directions are not open at the same time to avoid unstable operation in a closed loop (e.g., see Attenuation Control in Schmidt and Haulick, p. 578). However, when there are multiple acoustic zones, in general the signals that come from one acoustic zone are played back into all other acoustic zones (except for the zone with the active speaker). With M input channels and N output channels there are for each of the M input channels N−1 output channels that have to be supported. This results in M×(N−1) paths that have to be considered and processed. Computations are needed for each acoustic path from each microphone to each loudspeaker to provide specific equalizer settings. In conventional systems this results in M×(N−1) equalizers that have to be computed where M is the number of microphones and N is the number of loudspeakers. In conventional systems, the notch filter is calculated for each signal processing chain. These computations are expensive in terms of processor resources. Therefore the cost to support multiple acoustic zones would be prohibitive for most mass market vehicles.

BRIEF DESCRIPTION OF INVENTION

An In-Car Communication (ICC) system supports the communication paths within a car by receiving the speech signals of a speaking passenger and playing it back for one or more listening passengers. Signal processing such as noise reduction, equalization and notch filtering (for suppressing feedback) is necessary to achieve improved speech intelligibility in the car while ensuring a stable operation without howling. Embodiments disclosed herein, describe ICC sound processing systems where two or more acoustic zones are supported in an efficient manner. Signal processing tasks are split into a microphone related part (Mic-ICC) and into a loudspeaker related part (Ls-ICC). In contrast to conventional systems loss control is not realized in each signal processing chain (referred to as an “instance”) but in a global module. In one embodiment, N acoustic zones can be supported with M Mic-ICC instances and N Ls-ICC instances. In the processing chain there is a dynamic audio routing matrix that passes the active speaker channels to the appropriate loudspeakers. The system obtains information from the individual Mic-ICC instances and adjusts a set of matrix weights dynamically.

In one embodiment, a sound processing system suitable for use in a vehicle having a plurality of microphones and a plurality of loudspeakers distributed in multiple acoustic zones includes a plurality of microphone In-Car Communication (Mic-ICC) instances coupled to corresponding ones of the plurality of microphones, a plurality of loudspeaker In-Car Communication (Ls-ICC) instances coupled to corresponding ones of the plurality of loudspeakers and a dynamic audio routing matrix. The dynamic audio routing matrix includes a controller and coupled to the plurality of Mic-ICC instances, a mixer coupled to the plurality of Mic-ICC instances and a distributor coupled to the plurality of Ls-ICC instances. Such a system has several advantages over conventional systems. The interaction of the different ICC instances is controlled in a single module by the dynamic audio routing matrix making the system more manageable. The split ICC instances (Mic and Ls) allow for further optimizations to substantially reduce the computational power required to process the signals in real time. In this embodiment the dynamic audio routing matrix replaces the multiple loss controls tasks (sometime referred to as gain control tasks or attenuation control tasks) in each of the multiple conventional ICC instances. Here, the dynamic audio routing matrix and mixer act as multiple loss controllers.

For each acoustic path from each microphone to each loudspeaker a specific equalizer setting is necessary. In conventional systems this results in:M*(N−1) equalizers that have to be computed;where M is the number of Mic-ICC instances; andN is the number of number of Ls-ICC instances.

A technique for providing speech intelligibility in a vehicle having a plurality of microphones and a plurality of loudspeakers distributed in multiple acoustic zones includes the steps of processing speech from the plurality of microphones using a corresponding plurality of microphone In-Car Communication (Mic-ICC) instances, analyzing signals from the plurality of Mic-ICC instances, detecting speech and determining active acoustic path, calculating weights for the plurality of Mic-ICC instances based on speech and active acoustic paths, applying the calculated weights to provide weighted audio signals and distributing the weighted audio signals to a plurality of loudspeaker ICC (Ls-ICC) instances coupled to corresponding ones of the plurality of loudspeakers. With such a technique, only those equalizers which correspond to the acoustic path that is active at any given time need be calculated. The system requires only N−1 equalizers to be processed instead of M*(N−1) in conventional systems.

In another aspect of the invention, a technique includes mapping a plurality of input channels formed by the plurality of microphones and corresponding Mic-ICC instances to at least one selected channel and distributing the at least one selected channel signal from the at least one selected channel to the plurality of loud speakers through the corresponding plurality of Ls-ICC instances. Such a technique allows for a single notch filter to be calculated instead of a notch filter for each ICC instance. This optimization in embodiments according to aspects of the invention provides efficient integration of a notch filter into the dynamic audio routing matrix. The notch filter is, in general, the most expensive algorithm in terms of CPU and memory. In these embodiments, the audio routing matrix is split into two vectors: an input weighting vector (mixer) that maps M input channels to one single channel and an output distributing vector (distributor) that distributes one single signal to multiple output channels. In between, a single notch filter can be integrated. In other words, the notch filter has to be calculated only once instead of N times. In these embodiments, the dynamic audio routing matrix further includes a controller coupled to the input mixer and to the output distributor. The Mic-ICC instances are each coupled to the input mixer and the plurality of Ls-ICC instances are coupled to the output distributor. In one embodiment, the optimized sound processing system can efficiently support two, three, four, five, six or more acoustic zones.

Alternate configurations of the invention include a multiprogramming or multiprocessing computerized device such as a vehicle on board computer or dedicated computing signal processing device or the like configured with software and/or circuitry (e.g., a processor as summarized above) to process any or all of the method operations disclosed herein as embodiments of the invention. Still other embodiments of the invention include software programs such as a Java Virtual Machine and/or an operating system that can operate alone or in conjunction with each other with a multiprocessing computerized device to perform the method embodiment steps and operations summarized above and disclosed in detail below. One such embodiment comprises a computer program product that has a non-transitory computer-readable storage medium including computer program logic encoded as instructions thereon that, when performed in a multiprocessing computerized device having a coupling of a memory and a processor, programs the processor to perform the operations disclosed herein as embodiments of the invention to carry out data access requests. Such arrangements of the invention are typically provided as software, code and/or other data (e.g., data structures) arranged or encoded on a computer readable medium such as an optical medium (e.g., CD-ROM), floppy or hard disk or other medium such as firmware or microcode in one or more ROM, RAM or PROM chips, field programmable gate arrays (FPGAs) or as an Application Specific Integrated Circuit (ASIC). The software or firmware or other such configurations can be installed onto the computerized device (e.g., during operating system execution or during environment installation) to cause the computerized device to perform the techniques explained herein as embodiments of the invention.

DETAILED DESCRIPTION

An In-Car Communication (ICC) sound processing system supports communication paths within a vehicle by receiving speech from a speaker through microphones, processing the speech and reproducing the speech using loudspeakers for listeners in the vehicle. Signal processing tasks such as noise reduction, equalization and notch filtering (for suppressing feedback) are necessary to achieve improved speech intelligibility in the car while ensuring a stable operation without howling and other artifacts. Up to now, conventional ICC systems have only been successfully implemented for two acoustic zones (e.g., supporting communication between the front passengers and driver (in a front acoustic zone) and the passengers in the backseat (in a rear acoustic zone). Such conventional bidirectional systems have been implemented with two separate ICC instances operating in both directions: from front to rear and from rear to front. Such operation is computationally intensive and is difficult to apply to more than two acoustic zones. Embodiments of the present invention split the ICC instances into a microphone portion and loudspeaker portion resulting in a sound processing system which is more efficient than a conventional system and which can support multiple acoustic zones.

Now referring toFIG. 2, a sound processing system100suitable for use in a vehicle102having a plurality of microphones114FD-114RP(collectively referred to as microphones114) and a plurality of loudspeakers112FD-112BP(collectively referred to as loudspeakers112) distributed in multiple acoustic zones104FD-104RP(collectively referred to as acoustic zones104) receives signals from the microphones114, processes the microphone signals (here116FD) and outputs digitally processed signals through loudspeakers112to passengers110FP,110RDand110RP. For the microphones114, loudspeakers112and multiple acoustic zones104inFIG. 2, the subscript references refer to the following positions within the vehicle102:D driver side;P passenger side;F front seats;R rear seats; andB behind rear seats.

In one embodiment, the sound processing system100further includes an on-board computer interface107which can communicate over the car area network (CAN bus)108with the vehicle's102on-board computer106.

FIG. 2depicts a scenario where the driver110FDis speaking. It is noted that the some sound may be output through loudspeaker112FD, but this will generally be at a much reduced level. In this example, the driver110FDis speaking (as indicated by signals116FD) into microphone114FD. The sound processing system100receives the signals from microphone114FD, processes the signals and sends the signals to loudspeakers in the three other acoustic zones104FP, RP and RDto produce sound for the passengers.

Additional information, for example, about passengers, vehicle speed and other information which might affect communication within the vehicle can be obtained by the sound processing system100by means of the on-board computer interface107which can communicate over the car area network (CAN bus)108with the vehicle's102on-board computer106.

Now referring toFIG. 3, the sound processing system100ofFIG. 2includes a plurality of microphone In-Car Communication (Mic-ICC) instances124(or simply Mic-ICC124) coupled to microphones and a plurality of loudspeaker ICC (Ls-ICC) instances122(or simply Ls-ICC122) coupled to corresponding ones of the plurality of loudspeakers112. The sound processing system100further includes a dynamic audio routing matrix120having a mixer126(also referred to as a weighting module126) coupled to the plurality of microphone ICC (Mic-ICC) instances124, a controller128coupled to mixer126and a distributor130coupled to the plurality of Ls-ICC instances122. The controller128includes an adaptive gain controller129.

Here, ICC instances are split into a microphone related part (Mic-ICC)124and into a loudspeaker related part (Ls-ICC)122. In contrast to conventional systems the controller is not realized in each instance but in a global module, the dynamic audio routing matrix120. In a system having N acoustic zones, the signal processing can be supported with M Mic-ICC124instances and N Ls-ICC122instances. The dynamic audio routing matrix120separates the microphones114and Mic-ICC124instances from the loudspeakers112and the Ls-ICC122instances. The dynamic audio routing matrix120replaces several loss controllers in what would have been several combined ICC instances.

In operation, controller128obtains signal information from the individual Mic-ICC instances124and determines and dynamically adjusts matrix weights in the mixer126and thereby effectively determines the active Mic-ICC instance124. The matrix weights are then applied by the weighting module126to pass signals from the active Mic-ICC instance124through the distributor130to the Ls-ICC instances122to operate the loudspeakers112which provide sound in the corresponding acoustic zone. The adaptive gain controller129adjusts playback level to compensate for current noise levels in the vehicle by adjusting a playback level for each Ls-ICC122individually to compensate for current noise levels in the corresponding acoustic zone. Alternatively, gain compensation can be performed within the individual Ls-ICC instances122instead of the dynamic routing matrix120.

By separating ICC processing for incoming microphone signals and enhanced speech signals to be played back via the vehicles loudspeakers, the sound processing system100efficiently supports several communication paths. The Mic-ICC124instances receive the microphone signals from microphones in corresponding acoustic zone and may perform high pass filtering, beam forming, noise reduction and gain control to compensate for varying speech levels. Each Mic-ICC124instance provides an enhanced single-channel speech signal. The controller128within the dynamic audio routing matrix120identifies which acoustic zone is active in order to pass through the corresponding input signal. The signals originating from inactive acoustic zones are suppressed by the mixer126. Control of the input signals may be realized either by binary decisions or by a soft weighting of the signals. The Ls-ICC122instances receive the signals from the distributor130and may perform equalizer, signal limiter and gain control operations to scale the play back level depending on the level of the background noise. Each Ls-ICC122instance provides the output signal for one or more loudspeakers112. The controller128within the dynamic audio routing matrix120sets the weights for the distributor130to provide sufficient gain for speech communication in all acoustic zones104. This may be realized either by binary decisions (e.g., on or off) or by a soft weighting of the signals. In particular, for the different acoustic zones104the distributor130uses different weighting factors in order to adjust the gain level for each specific acoustic zones.

In one embodiment, the delay to reproduce speech from microphones114to speakers112is limited to be a maximum of 10 ms to reduce echo artifacts. In another embodiment, the number of Mic-ICCs124is equal to the number of Ls-ICCs122. It is understood that each acoustic zone may contain more than one microphone generating signals to be processed by the corresponding Mic-ICC and that more than one loudspeaker may be addressed by an Ls-ICC (e.g., loudspeakers112RDand112BDin acoustic zone104RD). In embodiments have multiple microphones or microphone arrays, the resulting signals can be processed by one of many beam forming techniques as is known in the art.

For each acoustic zone104which is supported by a Mic-ICC124, a subset of Ls-ICC122instances can be assigned. It is possible to pass the signal of the corresponding Mic-ICC124to N−1 Ls-ICC instances122(all other acoustic zones except for the zone of the active speaker). However, it is also possible to assign a subset of Ls-ICC122instances. For example inFIG. 2, speech from the driver110Ein acoustic zone104FDis passed to the back seats (zones104RD and104RP) but not to the front passenger110FPin zone104FP. The dynamic audio routing matrix120is configurable. Specific subsets of the N Ls-ICC122instances can be assigned to each single Mic-ICC124. This configuration is usually made before operation when initializing the system. In one embodiment, the initialization and configuration of the sound processing system100is performed when the vehicle is started (with ignition). Certain predetermined settings of the configuration are loaded from a separate configuration file or from a parameter file.

The sound processing system100has several advantages over conventional systems. The interaction of the different ICC instances is controlled in a single module, the dynamic audio routing matrix120, making the system more manageable. For each acoustic path from each microphone to each loudspeaker a specific equalizer setting is necessary. Computational requirements are substantially reduced because the dynamic routing matrix120only calculates those equalizers which correspond to an active acoustic path at any given time. Thus only N−1 equalizers are calculated instead of M*(N−1) equalizers (where N equals the number of loudspeaker and M equals the number of microphones) in conventional systems. In one embodiment, the dynamic audio routing matrix120uses predetermined equalization parameters corresponding to the multiple acoustic zones and vehicle audio system including the vehicle cabin configuration.

FIG. 4shows the sound processing system ofFIG. 2implemented for a roadster with rear speakers. For roadsters, communication between driver and co-driver may be supported by assigning one ICC instance to the driver and a second one to the co-driver as shown inFIG. 4. Within each acoustic zone104several microphones may be used to capture the speech of the speaker. The loudspeaker or loudspeakers of the other zone are employed to play back the enhanced speech signal. Both instances have to communicate with each other to ensure that only one instance is active. Both scenarios may be realized by two split ICC instances (i.e., Mic-ICC124instances and Ls-ICC122instances).

In convertibles (not shown) additional acoustic zones are supported due to strong background noises. Microphones and loudspeakers are located as close as possible to the corresponding speaker and listener. Therefore it is advantageous to apply additional split ICC instances (Mic-ICC124and Ls-ICC122) for each passenger separately.

Now referring toFIG. 5a sound processing system100′ includes an alternate dynamic audio routing matrix120′ according to another aspect of the invention. The alternate dynamic audio routing matrix120′ includes an input selector134, and output selector136and a notch filter138.

In operation, the weights of the input selector134and output selector136are set depending on detected signal activity. In one embodiment, the notch filter138is realized as an adaptive filter. The notch filter138is designed to suppress sinusoidal components in signals from the plurality of Mic-ICCs114selected by input selector134. Howling artifacts, that might occur in closed electro-acoustic loops, are characterized by sinusoidal components. These sinusoidal components can be suppressed effectively with the notch filter138.

Another advantage of this architecture is the fact that only one notch filter138is needed for feedback suppression. The notch filter138ensures stability of the closed-loop of loudspeaker, microphone and ICC system. Conventionally, one notch filter is needed for each instance, and the one to one requirement is computationally expensive. The components in the alternate dynamic audio routing matrix120′ split the Mic-ICC124from the Ls-ICC122and perform the audio signal routing connecting the active speaker with the listeners. For each loudspeaker, the processed speech signal is pre-equalized and limited in volume. Separating the processing for microphone arrays and loudspeakers avoids the conventional computational overhead. The efficiency of sound processing100′ allows utilization, in some embodiments, of a more complex notch filter compared to conventional systems with replicated instances of ICC systems.

As only one notch filter is needed, the length of the adaptive filter can be chosen larger as more CPU and memory are available. As a result a better frequency resolution can be achieved. Sinusoidal components can be suppressed more effectively with less distortion of the residual signal. A further optimization is the efficient integration of the notch filter138into the dynamic audio routing matrix120′. The notch filter is in general the most expensive algorithm in terms of CPU and memory. Conventionally, the notch filter was calculated in each single ICC instance. In sound processing system100′ the audio routing matrix120′ is split into two vectors: an input selection vector mapped by the input selector134from N input channels to one single channel and an output selection vector distributed by the output selector136from one single signal to multiple output channels. The notch filter138is integrated between the input selector134and the output selector136. In operation, the notch filter is calculated only once instead of N times where N is the number of ICC instances in a conventional system. Instead of a hard selection of input and output within the dynamic routing matrix also smooth weighting factors can be applied (as described above inFIG. 2).

Incorporation of loss control into controller128is important to realize a computationally efficient system. In contrast to conventional approaches (e.g. in telephony where the participants of the communication system are spatially separated), here the participants of the communication system are not spatially separated by more than a few meters at most. Therefore, the problem of cross-talk has to be addressed. To separate each participant, time delay and differences in volume may be used to distinguish the microphone signals of the active speaker and to control cross-talk. Here, one acoustic zone is considered to be active using the result of the last signal frame processed. The remaining N−1 zones are assumed to be inactive.

For each zone the power of the processed Mic-ICC signal is calculated by recursive smoothing, in one embodiment. The resulting speech levels are compared within the controller for a threshold decision. The decision is used to increase or decrease the weighting factors which are applied in the output selection. In detail, the speech level of the currently active zone is compared with the speech level of the inactive zone with the second highest score whereas the scores of the inactive zones are compared with the one of the active zone.

Furthermore, the gain of each loudspeaker may be controlled depending on the position of the speaker. When the driver is speaking, the attenuation of the direct sound signal is higher for passenger on the rear seats compared to the co-driver. Therefore, in this case the loudspeakers of the rear passengers require a processing chain with higher gain. The latter may be realized by different settings of the equalizer filters or by different weights of the output distributor.

In other embodiments, the sound processing system is extended to vehicles with more than two seat rows such as vans. InFIGS. 6A-6Cthe problem of speech communication across three seat rows is shown. Communication with passengers behind the speaker is complicated due to the head orientation of the speaker. Furthermore, communication between the last row and the driver is degraded due to the distance between both seat rows and due to the attenuation of the sound signal caused by the second row.FIG. 6Ashows a driver communicating with passengers in the second and third rows of a vehicle, for example a van.FIG. 6Bshows the sound processing system ofFIG. 2implemented for a van in which passengers in the second row communicate with passengers in the third row.FIG. 6Cshows the sound processing system ofFIG. 2implemented for a van in which passengers in the third row communicate with the driver or co-driver.

The scenarios shown inFIGS. 6A-6Care challenging with respect to computational complexity and audio signal routing. Using several unidirectional ICC instances as in a conventional solution may be too complex since memory consumption and computational overhead is multiplied by the number of instances (N). Each microphone signal is processed separately and equalizing is calculated for N*(N−1) communication channels irrespective whether the speech signal is passed through or blocked by the loss control function.

Now referring toFIG. 7, a flow diagram700details the operation of system for providing improved speech intelligibility in a vehicle having a plurality of microphones and a plurality of loudspeakers distributed in multiple acoustic zones. In step702, speech from the plurality of microphones is processed using a corresponding plurality of microphone In-Car Communication (Mic-ICC) instances. In step704, signals from the plurality of Mic-ICC instances are analyzed in the mixer126and controller128. Speech is detected and active acoustic paths are determined by the controller in step706.

In step708, the controller calculates weights for the plurality of Mic-ICC instances based on speech and active acoustic paths, and the calculated weights are applied, in step710, to provide weighted audio signals. The weighted audio signals are distributed to a plurality of loudspeaker ICC (Ls-ICC) instances coupled to the corresponding plurality of loudspeakers in step712.

In another embodiment, signal activity is detected on the basis of the input signals, and the weights are changed dynamically depending on signal activity. Using the weights, the active acoustic paths are determined and equalizers need only be calculated for the active acoustic paths. In order to reduce echo artifacts, the signal delay from the plurality of microphones to the plurality of loudspeakers distributed in multiple acoustic zones is kept to less than about 10 ms.

In yet another embodiment, speaker activity is detected in order to determine active acoustic paths. The sound processing system100can interface with an on-board computer via a CAN bus or other equivalent systems to obtain further information about passengers in the vehicle. For example, it is possible to determine whether there are passengers in various seats in the vehicle and to determine vehicle speed and then adjust the playback level for each Ls-ICC122instance as a function of vehicle speed.

In another aspect of the invention, the sound processing system estimates the background noise level for each of the multiple acoustic zones and adjusts the playback level in the distributor for each Ls-ICC122instance as a function of estimated background noise level in corresponding ones of the multiple acoustic zones.

In a conventional unidirectional ICC the level of the background noise is typically estimated on the basis of a microphone signal and the output signal is amplified by a gain factor that depends on this estimated noise level. For example, for high noise levels the amplification gain of the ICC is higher than for low noise level environments. However, in conventional systems, the noise estimate is not based on the listener's position but instead to the speaker's position (as it is estimated from the microphone signal).

In bidirectional systems or in multi-zone systems as implemented in embodiments described herein, the noise levels at the listeners' positions are measured where the acoustic zones of the listeners are equipped with microphones (in general, there is a Mic-ICC and a LS-ICC for each acoustic zone). In these cases the controller128in conjunction with the mixer126receives the noise estimates from the Mic-ICCs or it determines a noise estimate on the basis of the Mic-ICC output signals. Based on these noise estimates, amplification factors for the loudspeaker signals of the corresponding acoustic zone are determined. These amplification factors are applied within the distributor, for example, by multiplying with the original weighting factors to get final weighting factors.

The controller128receives signals and additional information, from all Mic-ICC124instances. The additional information includes but is not limited to estimates of the background noise level that are based on the unprocessed microphone signals and signals that are preprocessed in a special way (e.g., using spectral estimates available from noise reduction processing to calculate a signal-to-noise ratio which can be used for speech activity detection). Weights of the mixer126and the distributor130are set depending on detected signal activity.

Alternative methods for speech activity detection are possible in conjunction with the system. For example, visual information from a camera can be used to detect speech activity. Furthermore, sensors (pressure, optical, belt buckle sensors) may provide information about which seats in the vehicle are occupied. This information may be considered in the speech activity detection. Some of this information can be obtained through the interface on board computer via the CAN bus to determine whether there are passengers in various seats and to receive a determination or vehicle speed

Now referring toFIG. 8, a flow diagram800illustrates further details of the sound processing system100′ ofFIG. 5. In step802, the input selector in conjunction with the mixer maps the input channels formed by the plurality of microphones and corresponding Mic-ICC instances to a selected channel. In step804, the controller selects at least one selected channel based on the calculated weights determined by the mixer.

In step806, the controller calculates a notch filter to reduce feedback. The controller calculates N−1 sets of equalizer coefficients where N equals the total number of Ls-ICC instances in the system in step808. The notch filter is applied to at least one selected channel in step810. The equalized signals are distributed to the plurality of loud speakers through the corresponding plurality of Ls-ICC instances in step812. In one embodiment, the filtered input from at least one selected channel is distributed to the the corresponding plurality of Ls-ICC instances in step814. In one embodiment, the input selector selects a single channel.

Depending on the vehicle type and the intended application different requirements have to be fulfilled by a speech communication system. For sedans, for example, it may be sufficient to support the communication between driver/co-driver and passengers on the rear seats. In this case the automobile may be divided into four acoustic zones as shown inFIG. 2. In other embodiments the automobile may be divided into two acoustic zones.

While the system and method for processing sound signals in an ICC system has been particularly shown and described with references to embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.