EP1943640A1

EP1943640A1 - Method for determining a transmission function, and device for carrying out said method

Info

Publication number: EP1943640A1
Application number: EP06793953A
Authority: EP
Inventors: Harry Bachmann
Original assignee: Anocsys AG
Current assignee: Anocsys AG
Priority date: 2005-10-25
Filing date: 2006-10-03
Publication date: 2008-07-16
Also published as: US20090225998A1; WO2007048682A1

Abstract

An unknown transmission function comprising an input signal (x) and an actual output signal (y) is estimated. According to the invention, an estimated output signal (y) is generated by means of an adaptive process (2) using the input signal (x), an error signal (e) is generated from the actual output signal (y) and the estimated output signal (y), and the adaptive process (2) is improved based on the error signal (e), at least one signal path, i.e. a signal path conducting the error signal or a signal path conducting the estimated output signal (y), being impinged upon by a predefined signal in accordance with at least one condition. The invention makes it possible to substantially optimize adaptive processes or algorithms. Also disclosed are an application of said method, a device, and a use of said device.

Description

Method for determining a transfer function and a device for carrying out the method

The present invention relates to a method for optimizing an adaptive algorithm according to the preamble of claim 1, an application of the method, a device for carrying out the method 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. By this document is disclosed how noise in a tube can be extinguished by generating a signal with opposite phase.

Further developments led to a number of specific algorithms, such as the LMS (Least Mean Square) and related algorithms such as the FxLMS or the NLMS.

An algorithm for active noise reduction requires information from at least one sensor (for example a microphone), which determines the residual error - also referred to below as an error signal. Depending on the application and algorithm used, another sensor is provided that provides information about the nature of the signal to be minimized. Further, an adaptive noise reduction system requires one or more actuators (for example in the form of loudspeakers) to output the correction signal. The information from the sensors must be converted by an analog / digital converter into a suitable format. After being processed by the algorithm, the signal is reconverted from a digital to analogue converter and sent to the Actuators transmitted. These converters are subject to limitations in both resolution and dynamics.

Many algorithms, in particular the known gradient methods, have some instabilities with uncorrelated input signals. Together with the limitations of the converters, this can lead to uncontrolled behavior of the algorithm with small input signals or with rapid signal changes. This can be expressed in the form of low-frequency noises or as generally unstable behavior of the overall system.

The present invention is therefore based on the object of specifying a method for determining a transfer function, which does not have the above disadvantages.

This object is achieved by the features stated in the characterizing part of claim 1. Advantageous embodiments of the invention, an application of the method, a device for carrying out the method and a use of the device are specified in further claims.

A method for optimizing an adaptive algorithm by which an unknown transfer function is estimated, comprising an input signal and an actual output signal, is indicated, the method being that an estimated output signal is generated using the input signal through an adaptive process, that an error signal is generated from the actual output signal and the estimated output signal, and that the adaptive process is enhanced due to the error signal. According to the invention, depending on at least one condition, at least one signal is modified in one of the following signal paths:

a signal path carrying the error signal;

a signal path carrying the estimated output signal.

Thus, for the first time, a method is provided which is particularly suitable for optimizing adaptive algorithms, since unwanted signals can be kept away from the adaptive process during a defined period of time with the method according to the invention, in particular during the start-up phase and the phase-out phase of an active noise reduction system the system becomes more stable and robust overall. The triggering time or the mentioned condition is set by switching the entire system on or off.

Another embodiment of the present invention is that a weighting function of the one acting on the error signal and the estimated output signal Processing unit is selectable from a number of predefined functions.

In yet another embodiment of the present invention, it is contemplated that the condition for

Changing a signal path of the guided in this signal path signal is dependent.

Even if the method according to the invention is particularly suitable for active noise reduction, others are possible

Applications are not excluded. On the contrary: the method according to the invention is particularly suitable for improving the stability and the robustness of all adaptive systems.

Furthermore, the subject of the present invention is a device which comprises the following features:

an adaptive processor unit for determining an estimated output signal, wherein the processor unit is supplied with an input signal,

Means for determining an error signal from an actual output signal and the estimated output signal, the error signal being supplied to the adaptive processor unit, and a processing unit in at least one of the following signal paths:

a signal path carrying the error signal;

a signal path carrying the estimated output signal. A further embodiment variant comprises means for determining the weighting function of the processing unit from a number of predefined weighting functions for the error signal and for the estimated output signal.

In yet another embodiment of the present invention, the processing unit has an adjustable weighting function.

The present invention is based on

Embodiments with reference to drawings further explained below. Show it:

1 shows a variant of an inventive device in a schematic representation,

2 is a simplified block diagram of the embodiment variant shown in FIG. 1, also in a schematic representation,

FIG. 3 is a simplified block diagram of a processing unit used in FIG. 2; FIG.

Fig. 4 is a waveform for illustrating a possible operation of a

Processing unit according to FIG. 3 and

5 shows a further signal curve for illustrating a possible mode of operation of a processing unit according to FIG. 3. Fig. 1 shows an embodiment of an inventive device for the reduction of noise. It is a so-called Adaptive Noise Canceller (ANC) system that eliminates or at least reduces noise in a room R using the principle of signal cancellation.

Central unit of such an adaptive

Noise reduction system is an adaptive processor unit 2 connected to an external microphone unit

1 operatively connected, wherein the addition "externally" indicates a arranged outside the space R microphone unit. Thus, a noise source which is usually present outside the room R can be better detected. Furthermore, two internal microphone units 3 and two loudspeaker units 4 are provided in the room R, all of which are operatively connected to the adaptive processor unit 2. As can be seen from Fig. 1, in each case between one of

Microphone units 1, 3 and the adaptive processor unit

2 or between each of the speaker units 4 and the adaptive processor unit 2, a processing unit 5, 6 is provided, which makes it possible to modify the respective signal path.

In the adaptive processor unit 2, a reduction signal is now fed via the loudspeakers 4 into the room R on the basis of the signal recorded with the microphone unit 1, so that a signal passing through the walls or windows in FIG the space R reaching noise signal is cleared or reduced by signal cancellation or signal reduction in the space R. So that this can be achieved under changing conditions with success, with the help of the microphone units 3 an error signal is recorded and sent to the adaptive

Processor unit 2 is returned, so that in the adaptive processor unit 2, the calculations of the reduction signal can be improved and in the sequence a signal cancellation or signal reduction can be achieved.

It is expressly understood that any number of microphone units 1, 3 and 4 speaker units is conceivable without the inventive principle is abandoned. Also, instead of the microphone units 1, 3 and / or the

Speaker units 4 other converter units conceivable.

2 shows a block diagram of a simplified embodiment of the invention according to FIG. 1. According to the invention, signals can be modified in single or multiple signal paths. For this purpose - as shown in Fig. 2 - a processing unit 5, 6 is provided, which acts on both the estimated output signal y and the error signal e via multiplier units 12 and 16. It is conceivable in a further embodiment that a processing unit 5, 6 is provided for each signal to be modified, ie for each signal path, wherein the weighting functions which are applied to the signals in the signal paths may be different. A weighting function, which in the

Processing unit 5, 6 is applied to a signal of the signal path, for example, modifies the signal during the time interval of the initialization of the entire system (i.e., at or immediately after switching on) or during the time interval after the interruption or shutdown according to a predefined function. The output of the adaptive processor unit 2 is thus modified in the multiplier unit 12 according to the weighting function. The modified signal is transmitted to a loudspeaker unit - as can be seen again from FIG. 1.

In the same way, in a further embodiment of the invention, the signal path of a microphone unit is modified and subsequently modified in a processing unit having a corresponding weighting function. The result is - again with regard to the embodiment variant according to FIG. 1 - passed on to the adaptive processor unit 2. As a consequence, the adaptive processor unit 2 receives an error signal e modified according to the predetermined weighting functions. This embodiment makes sense, in particular, when a noise in accordance with a predetermined weighting function must be actively minimized in a timed interval in order to avoid abrupt signal changes. This also results in an often desired smoothing effect with rapid signal changes. The mentioned embodiment also contributes significantly to the stability of the overall system, since these rapid transitions are otherwise detected by the sensors - ie the microphone units 3 - for detecting the residual noise. In this way, the adaptive noise reduction system can optimally adapt to the current situation, in particular in the case of input signals which are difficult to process.

Thus any shortcomings of the analog / digital and digital / analog converters or other components required in digital systems lose their influence.

The processing unit 5, 6 shown in FIG. 2 is subjected to an input signal which is fed via a switching unit 18. The switching unit 18 is, for example, a main switch, via which the power supply to the overall system can be switched on or off. A switching state change of the switching unit 18 serves as a triggering time for a weighting function. Thus, from the time of a switching state change, the weighting is changed as a function of time according to a predefined function. Various weighting functions and their application will be explained in more detail with reference to FIGS. 3 to 5.

FIG. 3 shows one of the processing units 5, β, to which an input signal 13 is supplied, which is dependent on a change in state triggers a predetermined change in a weighting function. In the processing unit 5, 6, an output signal 14 is generated, which results, for example, from the profile of the weighting function according to FIG. 4 or FIG. 5. In this case, any weighting function can be used, in particular an ascending ramp function 19 according to FIG. 4 or a falling ramp function 15 according to FIG. 5, a constant value, an exponential increase / decrease or a combination thereof. In the graph shown in Fig. 4, the time on the abscissa and the output signal 14 on the ordinate is shown. In particular, the following can be derived from the illustrated profile: The output signal 14 reaches the value normalized to the value 1 (100%) in accordance with the predetermined ramp function 15 after a time T.

5 shows a falling ramp function, the function having the value 0 (0%) in the interval 17, which also has a favorable stability behavior.

While the weighting function according to FIG. 4 is suitable for the initialization process, the weighting function according to FIG. 5 can be used excellently during the switch-off process.

Claims

claims

1. A method for determining an unknown transfer function (H) of a space (R), the one

Input signal (x) and an actual output signal (y), the method being

that an estimated output signal (y) is generated using the input signal (x) by means of an adaptive process (2),

- That an error signal (e) from the actual output signal (y) and the estimated output signal

(y) is generated and

in that the adaptive process (2) is improved on the basis of the error signal (e), characterized in that, depending on at least one condition, at least one signal is modified in one of the following signal paths:

a signal path carrying the error signal (e); one leading the estimated output (y)

Signal path.

2. The method according to claim 1, characterized in that the condition for changing a signal path of the guided in this signal path signal (x, e, y) is dependent.

3. The method according to any one of claims 1 to 2, characterized in that signals from several signal paths are modified simultaneously.

4. The method according to any one of claims 1 to 3, characterized in that the modification of a signal takes place according to a predetermined weighting function.

5. Application of the method according to one of claims 1 to 4 for active noise reduction in a room (R).

6. An apparatus for performing the method according to one of claims 1 to 4, characterized by - an adaptive processor unit (2) for determining an estimated output signal (y), wherein the processor unit (2) an input signal (x) is applied,

- means (11) for determining an error signal (e) from an actual output signal (y) and the estimated output signal (y), the error signal (e) being supplied to the adaptive processor unit (2), and

a processing unit (5, 6) in at least one of the following signal paths:

a signal path carrying the error signal (e);

one leading the estimated output (y)

Signal path.

7. Device according to claim 6, characterized in that means are provided for determining a level or an average power of a signal (x, e, y), said means being operatively connected to at least one processing unit (5, 6).

8. The device according to claim 7, characterized in that the means for determining a level or an average power of a signal (x, e, y) in a signal path with the switching unit (5, 6) are operatively connected in the same signal path.

9. Device according to one of claims 6 to 8, characterized in that a plurality of switching units (5, 6) are activated simultaneously.

10. Device according to one of claims 6 to 9, characterized in that the processing unit (5, 6) has a predefined weighting function.

11. Device according to one of claims 6 to 10, characterized in that the processing units (5, 6) are operatively connected to each other.

12. Use of the device according to one of claims 6 to 11 for active noise reduction in a space (R).