WO2007048815A2

WO2007048815A2 - Method for the reduction of an interference signal in a room, and application of said method

Info

Publication number: WO2007048815A2
Application number: PCT/EP2006/067785
Authority: WO
Inventors: Harry Bachmann
Original assignee: Anocsys Ag
Priority date: 2005-10-26
Filing date: 2006-10-26
Publication date: 2007-05-03
Also published as: EP1941490A2; WO2007048815A3

Abstract

Disclosed is a method for reducing an interference signal (x) in a room by means of an adaptive noise reduction system. According to said method, the interference signal (x) is detected using at least one sensor unit, a transmission path (1) of the room is estimated using an adaptive process by minimizing an error signal (e) which is determined from an actual output signal in the room and a signal (y) estimated with the aid of the transmission path (1), and the error signal (e) is fed to the adaptive process to continuously optimize the same. The invention is characterized in that the error signal (e) is fed to an additional filter unit (4) to generate an output signal (y2), a transmission function of the additional filter unit (4) is adjusted in accordance with the error signal (e) by means of another adaptive process, and the output signal (y2) is subtracted from the actual output signal along with the estimated signal (y).

Description

Method for reducing a noise signal in a room and an application of the method

The present invention relates to a method for reducing a noise signal in a room according to the preamble of claim 1, an application of the method, a device according to the preamble of claim 9 and a use of the device.

Noise sources are increasingly perceived as an environmental impact and are considered to reduce the quality of life. However, as noise sources are often unavoidable, noise reduction methods based on the principle of wave cancellation have already been proposed.

The principle of Active Noise Canceling (ANC) is based on the cancellation of sound waves due to interference. These interferences are generated by one or more electro-acoustic transducers, such as loudspeakers. The signal radiated by the electro-acoustic transducers is calculated by means of a suitable algorithm and continuously corrected. The basis for the calculation of the signal to be radiated by the electro-acoustic transducers is the information supplied by one or more sensors. These are on the one hand information about the nature of the signal to be minimized. For example, a microphone can be used for this purpose which detects the noise to be minimized. On the other hand, information about the remaining residual signal is needed. Again, microphones can be used.

The basic principle applied with active noise reduction was Paul Lueg in a patent document from the year 1935 and the disclosure number AT-141 998 B described. This document discloses how noise in a tube can be extinguished by means of

Generation of a signal with opposite phase position.

An algorithm for active noise reduction requires information from at least one sensor (for example a microphone), which determines the residual error, which is also referred to below as the error signal. Depending on the application and the algorithm used, another sensor is provided which provides information about the nature of the signal to be minimized, which is referred to below as the interference signal. Furthermore, an adaptive

Noise reduction system one or more actuators (usually electro-acoustic transducers are used in the form of speakers, it being expressly mentioned that other suitable for the particular application actuators or transducers can be used) for reproducing the determined correction signal.

The information from the sensors must be converted by an analog / digital converter into a suitable format. After processing by the Algorithm, the signal is converted back from a digital / analog converter and transmitted to the actuators.

One problem associated with active noise reduction through adaptive processes is the fact that the adaptive process takes some time to process the signals. All signals to be processed are thus subject to a time delay caused by the adaptive process. This time delay represents a limit and is a decisive factor in whether a signal can even be processed by the adaptive process at all.

Whether an interference signal can thus be adapted by an adaptive algorithm for the purpose of determining a correction signal suitable for minimizing the interference signal also depends, inter alia, on the adaptive process being able to calculate the correction signal faster than the interference signal arriving in the region to be reassured, taking into account in that the actuators and transducers are also subject to a time delay.

If the interference signal arrives in time before the correction signal (from the adaptive algorithm for reducing the interference signal) in the area to be processed, the signal can no longer be minimized.

Interference signals are often acoustic signals that do not transmit by air, but via solid structures such as floors, steel girders or heating pipes and these materials have a greater speed of sound compared to acoustic signals transmitted by air. However, since these signals are detected not only by the sensor responsible for detecting the noise, but also by the sensor detecting the error signal, this can cause instability of the entire system.

The present invention is therefore based on the object of specifying a method in which the aforementioned disadvantages or problems do not occur.

This object is achieved by the features stated in the characterizing part of claim 1. Further

Embodiments of the present invention, an application, a device and a use of the device are specified in further claims.

It is expressly mentioned that the number of sensors and actuators mentioned in the following description may differ from the number actually used, and that the sensors and actuators used need not necessarily be microphones and loudspeakers, even if, for the following reasons

Intelligibility in each case from microphones or loudspeakers is assumed.

The present invention initially relates to a method for reducing a noise signal in a room by means of a adaptive noise reduction system. The procedure is

that the interference signal is detected by means of at least one sensor unit, that a transmission distance of the space is estimated by means of an adaptive process by minimizing an error signal, the error signal being a superposition of an actual output signal in space and a signal estimated using the transmission link, and

- That the error signal is fed to the adaptive process for ongoing optimization.

The inventive method is characterized by

- That the error signal is fed to a further filter unit for generating an output signal,

- That a transfer function of the further filter unit is adjusted by means of a further adaptive process in response to the error signal and - that the output signal is subtracted together with the estimated signal from the actual output signal.

As one of the advantages of the method according to the invention, the increase in efficiency is due to the fact that in particular signals can be processed very efficiently, which have different transit times, ie which propagate at different speeds. Another feature of the present invention is the stability enhancing effect in systems where adaptive processes process signals having different transit times, or where some of the signals are faster than the existing control structure, and therefore from the existing adaptive process without them favorable extension can not or only insufficiently processed and accordingly could have a destabilizing effect. The present invention thus has possibilities of how certain signal components can be detected such that the stability of the adaptive process is not affected by signals having a high speed, and signals which are not processed correctly by the adaptive process in order to minimize a spurious signal due to the transmission speed can be taken into account during processing.

An embodiment of the present invention is that the noise signal is detected outside the room.

Another embodiment of the present invention is that the actual interference signal is supplied to the adaptive process for ongoing optimization.

A still further embodiment of the present invention is that included in the noise signal Signal components are excluded from the noise reduction.

A further embodiment of the present invention consists in that the excluded signal components are specified in regions.

Another embodiment of the present invention is that the output signal is passed through a filter in which the excluded signal components are attenuated. Thus, an adaptive control structure is specified, in which by means of an additional filter certain frequency ranges are excluded from processing by the adaptive process.

Finally, another embodiment of the present invention is that a signal desired in space is subtracted from the error signal.

In particular, the present invention is useful for active noise reduction in a vehicle, it being expressly stated that this invention can not only be used in active noise reduction systems, but can also be used in other applications related to adaptive processes.

Furthermore, a device according to the invention for reducing an interfering signal in a room by means of an adaptive noise reduction system is specified. The device comprises: - At least one sensor unit for detecting the interference signal and

an adaptive process unit for estimating a transmission distance of the space by minimizing an error signal, wherein the error signal is a

Superposition of an actual output signal in space and a signal estimated using the transmission link and the adaptive processing unit is acted upon. According to the invention, the device is characterized by

a further filter unit, which is supplied with the error signal for generating an output signal,

a further adaptive process unit which is operatively connected to the further filter unit for setting its transfer function, the error signal being supplied to the further adaptive process unit, and

- means for subtracting the output signal and the estimated signal from the actual output signal.

An embodiment of the present invention is that at least one sensor unit is arranged outside the room.

Another embodiment of the present invention is that the actual existing interference signal of the adaptive process unit is applied. A still further embodiment of the present invention is that a filter is provided, through which the output signal is guided, wherein in the filter level of auszuschliessenden signal components are at least reduced.

Finally, one embodiment of the present invention is that means are provided for subtracting a signal desired in space from the error signal.

The inventive device is particularly suitable for active noise reduction in a vehicle.

The present invention will now be explained in more detail by means of embodiments with reference to drawings. Show it:

1 is a simplified block diagram of a method according to the invention,

2 shows a simplified block diagram of a further method according to the invention,

3 is a simplified block diagram of an embodiment of a known method,

4 shows a simplified block diagram of a further embodiment of a method according to the invention, Fig. 5 is a simplified block diagram of yet another embodiment of a method according to the invention and

Fig. 6 shows an application of a method according to the invention (in a motor vehicle) in a schematic representation.

Fig. 3 shows a block diagram of a known active noise reduction system. A disturbance signal x to be minimized is applied to a transmission path 1 (for example a room) with a transfer function H. In space, the interfering signal x travels a certain distance. The interference signal x is usually changed by the transfer function H, wherein by the

Transfer function H the interference signal x is delayed in particular. In the space forming the transmission path 1 contains, for example, air and one or more of the space completely or partially separating wall. If the interfering signal x is noise that arises outside of the room and is loud enough to be perceived within this room and thus detected by a sensor unit (for example a microphone) contained in the room, then this noise is generated in the context of the noise Characteristic of the transmission path 1 changed.

According to FIG. 3, the interference signal x present outside the space is also applied to a filter unit 2 and an adaptive process unit 3, wherein the adaptive process unit 3 is operatively connected to the filter unit 2. To form an error signal e, an actual output signal of the transmission path 1 and a correction signal y estimated by the filter unit are counted together in an addition unit 6, wherein the estimated correction signal y is inverted in advance. The error signal e is applied in the sequence of the adaptive process unit 3.

The algorithm used in the adaptive process unit 3 is only stable and therefore can only be operated in an active noise reduction system if the delay of the interference signal x through the transmission link 1 is greater than the delay caused by the filter unit 2 and the adaptive process unit 3.

Thus, the adaptive process unit 3 must compulsorily calculate the correction signal y necessary for minimizing the interference signal x in a shorter time than the time required by the interference signal x to traverse the transmission path 1.

If, for example, two sensor units are used in the room for detecting signals, one of the sensor units detects the interference signal x which is fed to the adaptive process unit 3 and the filter unit 2 and the other sensor unit detects the error signal e which is fed to the adaptive process unit 3, then the correction signal y compellingly must be calculated faster than the time required by the disturbance signal x, the Backtracking the distance between the two sensor units is needed.

FIG. 1 shows a block diagram of an embodiment variant of the present invention in which the error signal e is applied not only to the adaptive processing unit 3 controlling the filter unit 2 but additionally to another filter unit 4 and to another adaptive process unit 5, in which a further adaptive process for setting an adjustable in the further filter unit 4 transfer function is applied. A signal generated in the further filter unit 4 is referred to below as y2. In a further addition unit 7, a sum is formed from the two signals y and y2, which is counted together after previous inversion in a known manner in the addition unit 6 with the actual output signal of the transmission path 1. In the adaptive process units 3 and 5, adjustments are made in the respective filter units 2 and 4, respectively, such that the error signal e is minimal.

The further adaptive process unit 5, which is operatively connected to the further filter unit 4, operates in a feedback method, ie without prior knowledge of the interference signal x. The further adaptive process unit 5 only adapts the remaining error signal e, ie it is not subject to the time delays caused by the adaptive process unit 3. Fig. 2 shows a block diagram of another embodiment of the present invention. The signal y2 is filtered in addition to the variant indicated in FIG. 1 by a filter 13 for generating a signal y2 '. This filtering is necessary because the further adaptive process unit 5 without the filter 13 would minimize the total error signal e, which is usually undesirable. The reasons can be, for example, safety-related nature - for example, a car horn - or the need verbal communication, if people are in the calming area, ie in space. So always, if within the calming certain signals should not be minimized respectively allowed. Signals that are excluded from the processing are the signals that can not pass through the filter 13 and accordingly the further adaptive process unit 5 are not acted upon. This variant thus advantageously makes it possible to preclude signals with specific properties from being processed by the further adaptive process unit 5 operatively connected to the further filter unit 4.

In accordance with the above explanations with respect to an exclusion of certain signals which should not be eliminated in space, the characteristic of the filter 13 should be chosen.

Fig. 4 shows a block diagram of another embodiment of the present invention. In In addition to the embodiment variant indicated in FIG. 2, a desired signal 14 is fed into the room 1 to be calm. The desired signal 14 is subtracted in the addition units 15 and 16 from the error signal e respectively in the addition unit 29 from the interference signal x to be minimized, thus ensuring that the adaptive process units 3 and 5 do not consider the desired signal 14. Thus, the desired signal 14 is not minimized.

Fig. 5 shows a block diagram of a still further improved variant of the present invention. Either for stability reasons or with insufficient computing power in the adaptive process units 3 and 5 and in the filter units 2 and 4, the desired signal 14 can also be subtracted directly after the addition unit 6 in the addition unit 17 from the residual error e.

Fig. 6 shows a practical application of the inventive method in a motor vehicle 20 in a schematic representation. The application will be described in detail below only in relation to the engine noise, it being expressly understood that other sounds, such as rolling noise of the wheels on the driving surface, may also be taken into account.

The interference signal to be reduced 8 is, for example, the engine noise generated at the engine 18 and the area to be calmed is a contained in the motor vehicle 20 passenger compartment 19. The caused by the engine 18 and by a microphone 22 detected in the engine compartment noise x - the engine noise - spreads in various ways and accordingly passes in different ways in the passenger compartment 19. On the one hand, the interference signal x spreads through the air, so passes for example through holes between the passenger compartment and the engine compartment In this case, the engine noise moves with the propagation speed known for air from the engine compartment into the passenger compartment 19. On the other hand, the engine noise also moves over solid structures, such as the body of the motor vehicle 20 at a much higher speed ( as by air) from the engine 18 into the passenger compartment 19.

As a further favorable feature of the present invention in the rear region 24 by the rolling resistance of the motor vehicle resulting noise propagating in the direction of travel 25, ie in the opposite direction to the first-mentioned application, by suitable means of processing, as in the former Application - engine noise - described, kept away.

It should be expressly mentioned here that the described application is the example of a motor vehicle with front-wheel drive, the invention being analogously applicable to other types of drive, such as in a rear-wheel drive vehicle. Further, it should be mentioned here that the presented invention can also be used for still other sounds occurring in a vehicle, that this description, for reasons of clarity, but refers to the engine noise of a motor vehicle, which is equipped with front-wheel drive. Furthermore, the applicability of the invention is not limited to motor vehicles.

The airborne portion of engine noise generated at engine 18 is detected in passenger compartment 19 by the portion of the algorithm shown in FIGS. 1 and 2, consisting of adaptive process unit 3 and filter unit 2, to minimize engine noise in passenger compartment 19 adapted. The portion of the engine noise generated at the engine 18 that propagates at a greater speed than in the case of air over the body and enters the passenger compartment 19 is determined by means of the part of the engine unit 18 consisting of the further adaptive process unit 5 and the further filter unit 4 2 for the purpose of minimizing engine noise in the passenger compartment 19.

Music, voice or other signal detected by one of the microphones 23 and radiated from the speakers 21 into the passenger compartment 19 can be processed by the further adaptive process unit by means of the measures shown in FIG. 4 and FIG 5 and the further filter unit 4 existing part, respectively from the adaptive process unit 3 and the filter unit 2 of the algorithms shown in FIG. 1 and FIG. 2.

Claims

claims

A method of reducing an interfering signal (x) in a room by means of an adaptive noise reduction system, the method being

- That the interference signal (x) by means of at least one sensor unit (22) is detected,

- That a transmission distance (1) of the space is estimated by means of an adaptive process by a

Error signal (e) is minimized, wherein the error signal (e) is a superposition of an actual output signal in space and a signal (y) estimated by means of the transmission link (1), and

that the error signal (e) is supplied to the adaptive process for ongoing optimization, characterized

- That the error signal (e) of a further filter unit (4) for generating an output signal (y2) is supplied,

- That a transfer function of the further filter unit (4) by means of a further adaptive process in response to the error signal (e) is set and

- That the output signal (y2) together with the estimated signal (y) is subtracted from the actual output signal.

2. The method according to claim 1, characterized in that the interference signal (x) is detected outside the room.

3. The method according to claim 1 or 2, characterized in that the interference signal actually present (x) is supplied to the adaptive process for ongoing optimization.

4. The method according to any one of claims 1 to 3, characterized in that in the interference signal (x) contained

Signal components are excluded from the noise reduction.

5. The method according to claim 4, characterized in that the excluded signal components are given in regions.

6. The method according to claim 4 or 5, characterized in that the output signal (y2) via a filter (13) is guided, in which the excluded signal components are attenuated.

7. The method according to any one of claims 1 to 6, characterized in that a signal desired in space signal (14) from the error signal (e) is subtracted.

8. Application of the method according to one of claims 1 to 7 for active noise reduction in a vehicle.

9. An apparatus for reducing a noise signal (x) in a room by means of an adaptive noise reduction system, the apparatus comprising:

- At least one sensor unit (22) for detecting the interference signal (x) and

- an adaptive process unit (3) for estimating a transmission link (1) of the space by minimizing an error signal (e), the error signal (e) superimposing an actual output signal in space and an estimated signal (y ) and the adaptive process unit (3) is acted upon, characterized by

- Another filter unit (4), which is the error signal (e) applied to generate an output signal (y2),

- Another adaptive processing unit (5), which is operatively connected to the further filter unit (4) for setting the transfer function, wherein the error signal (e) of the further adaptive process unit (5) is supplied, and

- means for subtracting the output signal (y2) and the estimated signal (y) from the actual output signal.

10. The device according to claim 9, characterized in that at least one sensor unit (22) is arranged outside the room.

11. The device according to claim 9 or 10, characterized in that the actually existing interference signal (x) of the adaptive process unit (3) is acted upon.

12. Device according to one of claims 9 to 11, characterized in that a filter (13) is provided, through which the output signal (y2) is guided, wherein in the filter (13) levels of auszuschliessenden signal components are at least reduced.

13. Device according to one of claims 9 to 12, characterized in that means for subtracting a signal desired in space (14) from the error signal (e) are provided.

14. Use of the device according to one of claims 9 to 13 for active noise reduction in a vehicle.