EP2469892A1 - Reproduction of a sound field in a target sound area - Google Patents

Abstract

The method involves analytically determining a drive signal for electro-acoustic transducer corresponding to sound field which is to be reproduced in a target acoustic region below spatial aliasing frequency of sound. The drive signal is changed by spatial band-limiting, so that the sound is reproduced within a range of optimization with higher accuracy and the modified drive signal to the electro-acoustic transducer. An independent claim is included for apparatus for reproducing sound in target acoustic region.

Description

The present invention relates to the reproduction or reconstruction of a sound field in a target sound area with the aid of a plurality of electroacoustic transducers.

For the authentic physical reconstruction of a sound field over a wide range, the technique of wave field synthesis can be used. This technique uses a large number of loudspeakers and thereby avoids the problem that in an area within the loudspeaker arrangement, the so-called "sweet spot", the reconstruction of the desired sound field is significantly more accurate than in the rest of the audible range, as is the case for example with the stereo. Technique occurs. In this context, it should be noted that in stereo methods, not a sound field is physically reconstructed. Instead, two speakers create an illusion that sounds very similar to the natural model, but has completely different physical properties. In stereo, there is a sweet spot in that the illusion sounds most authentic at this point.

The loudspeaker drive signals for the individual loudspeakers in the wave field synthesis are calculated analytically. In the practical implementation, however, there are large deviations from the desired sound field over the entire potential listening area. The technique of wave field synthesis is for example in the publication by S. Spors, R. Rabenstein, and J. Ahrens, "The Theory of Wave Field Synthesis Revisited," Proceedings of the 124th Convention of the Audio Engineering Society, May 17-20, Amsterdam, The Netherlands, 2008 described.

Another known technique for reconstruction of a sound field is called Ambisonics and is for example in the WO 2005/0195954 A2 described. This technique requires circular or spherical arrangements of loudspeakers, where the loudspeaker signals are generated using numerical algorithms. The limitation of the spatial bandwidth of the drive signals necessary in the calculation path causes the reconstruction of the desired sound field in the center of the loudspeaker arrangement to be most accurate. In the center of the loudspeaker arrangement is therefore a sweet spot. With increasing Distance from the center of the speaker assembly, the deviations in the reconstructed sound field are larger. In the publication by J. Hannemann and KD Donohue, "Virtual Sound Source Rendering Using a Multipole Expansion and Method-of-Moments Approach," J. Audio Eng. Soc., Vol. 56, No. 6, June 2008 describes a method related to the Ambisonics method, which makes it possible to choose relatively freely the arrangement of the loudspeakers and the location of the sweet spot. Again, the loudspeaker signals are calculated using numerical and thus very computationally intensive algorithms.

M. Kolundija, C. Faller und M. Vetterli, "Sound Field Reconstruction: An Improved Approach For Wave Field Synthesis", in: 126th Convention of the AES, München, Deutschland, 7. bis 10. Mai 2009 wird ein numerisches Verfahren beschrieben, welches lineare Lautsprecheranordnungen verwendet und die Wiedergabe auf einer Kontur parallel zur Lautsprecheranordnung optimiert. Dabei entsteht ein Vorzugsabstrahlsektor, der die Optimierungskontur beinhaltet, in dem die Genauigkeit der Wiedergabe erhöht ist. Auch in diesem Verfahren werden die Lautsprechersignale mit numerischen und somit sehr rechenintensiven Algorithmen berechnet.With enhancements by Ambisonics, such as the technique called Higher Order Ambisonics, a more efficient method can be provided in conjunction with analytic calculation of the speaker drive signals. Such a method is for example in the publication by J. Ahrens and S. Spors, "Analytical driving functions for higher order Ambisonics", in: IEEE International Conference on Acoustics, Speech, and Signal Processing, Las Vegas, Nevada, March 30 to April 4, 2008 described. However, according to the method described there, the resulting reproduced sound field agrees even worse with the desired sound field, the further one moves away from the center of the arrangement. So again there is a sweet spot in the center of the loudspeaker arrangement. In the patent EP08167919 there is described a method related to the Higher Order Ambisonics that allows a sweet spot to be placed arbitrarily within the given array of electroacoustic transducers. However, this method requires that the arrangement of the electro-acoustic transducers surround or approximately surround the target sound area, as is the case, for example, with spherical or circular arrangements. In the publication of

M. Kolundija, C. Faller and M. Vetterli, "Sound Field Reconstruction: An Improved Approach to Wave Field Synthesis", in: 126th Convention of the AES, Munich, Germany, May 7 to 10, 2009 For example, a numerical method is described which uses linear speaker assemblies and optimizes playback on a contour parallel to the speaker assembly. This results in a preferred emission sector that includes the optimization contour in which the accuracy of the reproduction is increased. Also in this method, the loudspeaker signals are calculated using numerical and thus very computationally intensive algorithms.

It is therefore an object of the present invention to provide an efficient method and apparatus for reproducing a sound field, which produces a sweet spot or area with significantly increased physical accuracy. The arrangement of the speakers should be subject to as few restrictions as possible. In particular, it is desirable that the arrangement of the electroacoustic transducers used need not enclose the target PA range.

This object is achieved with the features of the claims.

The present invention provides a method and a device for reproducing a sound field in a target sound area. For this purpose, electroacoustic transducers, so speakers are arranged on a contour. First, a drive signal for the electroacoustic transducer is determined analytically. In this analytical determination results in a resulting sound field, which exactly corresponds to the sound field to be reproduced below a certain frequency, also called aliasing frequency. Above this aliasing frequency, deviations from the target sound field occur depending on the location, and there is no area in which significantly fewer deviations occur than elsewhere. This is inherent in the analytical determination. The analytical determination can be achieved according to a known method by analytically solving an integral equation describing the sound field to be reproduced. Such a method is for example in the publication J. Ahrens and S. Spors, "Reproduction of a plane-wave sound field using planar and linear arrays of loudspeakers", IEEE Int. Symposium on Communications Control and Signal Processing, St Julian's, Malta, 12-14. March 2008 described. To solve this integral equation, which is a surface or line integral via the drive signal of the electroacoustic transducer and the transfer function of the electroacoustic transducer, the components of the integral equation can be converted into a transformed region, for example by means of a Fourier transformation.

Starting from an integral equation, the desired sound field is thus described in a spatial frequency range. In this case, it is possible according to the invention to obtain the loudspeaker activation signals via the explicit solution of the integral equation, which is described in more detail below. Alternatively, the loudspeaker drive signals can be obtained via the relationships of the Kirchhoff-Helmholtz integral (as in wave field synthesis).

The determined drive signal is changed in such a way that an optimization range arises in which the resulting sound field corresponds to the sound field to be reproduced significantly more accurately, as this would be the case without the change of the drive signal. This change is made by spatial band limitation. The band limitation does not have to be performed symmetrically around the frequency 0, but can be configured as desired. The target sonic range with increased accuracy may be fixed, but it may also be changed depending on the position of a receiver. In the latter case, the change of the drive signal then preferably takes place in real time. For example, this method can then be used to determine a position of a receiver within the target sounding area and then to change the control signal in such a way that the desired position is adjusted accordingly.

The changed drive signal is supplied to the electroacoustic transducers. The converters convert the input electrical signals into sound signals, and emit them into the target PA range.

Furthermore, the present invention also provides an apparatus for reproducing a sound field in a target sound area. The device has a plurality of arranged on a contour electro-acoustic transducer and a processing module. The processing module is able to analytically determine from signals about the desired position and audio input signals a drive signal for the electroacoustic transducers and to change the drive signal such that an optimization range is created in which the resulting sound field corresponds more closely to the sound field to be reproduced than without the change would be the case. The range in which the resulting sound field is to most accurately correspond to the sound field to be reproduced may be shifted to a predetermined position. The drive signals may further be amplified by means of an amplifier unit and supplied to the electroacoustic transducers.

With the present invention, an optimization range can be generated, from which the reproduced sound field corresponds as closely as possible to the desired sound field. The optimization area, in which the reconstruction of the desired sound field is most accurate, can then be shifted to a desired position. Thus, the playback can be optimized to any location within the Zielbeschallungsbereichs. This change in the preferred emission direction can be performed in real time so that the reproduction can be tracked, for example, to a moving receiver. The determination of the location of the receiver can be carried out here by means of sensors, for example a camera.

The invention can be used to reproduce audio signals, in particular multi-channel audio signals. The audio signals can be provided by a variety of devices, such as CD, DVD or Blu-ray Disc devices, MP3 devices, computers or the like. The reproduced audio signals may be MPEG2 or MPEG4 signals, for example, or be in a Dolby format.

Fig. 1

schematisch eine Vorrichtung gemäß der vorliegenden Erfindung zeigt und

Fig. 2

ein erzeugtes Schallfeld zeigt, wobei in Fig. (a) das gewünschte Schallfeld gezeigt wird, in Fig. (b) das Resultat herkömmlicher Methoden wie der Wellenfeldsynthese und Fig. (c) das Ergebnis der vorgeschlagenen Erfindung.

The invention will be described in more detail below with reference to the accompanying figures, wherein

Fig. 1

schematically shows an apparatus according to the present invention and

Fig. 2

Fig. (a) shows the desired sound field, Fig. (b) shows the result of conventional methods such as wave field synthesis, and Fig. (c) shows the result of the proposed invention.

In Fig. 1 schematically a device according to an embodiment of the present invention is shown. On a contour 11 at the edge of the Zielbeschallungsbereichs 10 or in several speakers 20 are arranged. The drive signals for the loudspeakers 20 are determined in a processing module 30 and supplied to the loudspeakers 20 via an amplifier unit 31. For this purpose, the processing module 30 is fed with information 1 about the current location for which the sound reconstruction is to be optimized and audio input signals 2. In addition, the processing module 30 receives a third input signal 3 which carries information about the desired sound field (eg position of the virtual sound source).

To calculate the drive signals for the loudspeakers 20, the drive signal is first analytically, for example according to the publication already mentioned above Ahrens and S. Spors, "Reproduction of a plane-wave sound field using planar and linear arrays of loudspeakers", IEEE Int. Symposium on Communications Control and Signal Processing, St Julian's, Malta, 12-14. March 2008 performed procedures, calculated.

In the method described there, which is described here merely as an example, is described by a description of the sound field P to be reproduced by an integral on the drive signal D of the speakers, which are located on a contour outside the Zielbeschallungsbereichs, and the spatial transfer function G of the speakers, shown: $$P=\mathrm{\int }D\cdot \mathit{Gd}\mathrm{\Omega }$$

The integral here is a surface or line integral, depending on whether the calculation is to take place in three dimensions or only in one plane.

This integral equation is transformed into a spatial frequency domain by a suitable transformation such that the spatial spectra of P, D, and G (indicated by a tilde) are related by product: $$\tilde{P}=\tilde{D}\cdot \tilde{G}$$

This can be done for example by a Fourier transformation. The loudspeaker drive signal D can thus be calculated in the spatial frequency range as follows: $$\tilde{D}=\frac{\tilde{P}}{\tilde{G}}$$

e bezeichnet die Basis der Transformation. Für das Beispiel der Fouriertransformation ist e durch die komplexe Exponentialfunktion gegeben.The back transformation from D to D is typically represented by an integral: $$D=\mathrm{\int }\tilde{D}\cdot e$$

e denotes the basis of the transformation. For the example of Fourier transformation, e is given by the complex exponential function.

In order to shift the location where the reconstruction of the desired sound field is most accurate to a desired location, a function W representing the optimization is introduced according to the invention. This weighting function is generally dependent on the spatial frequency and can be applied to different steps in the above description. For example, it can be used multiplicatively in the inverse transformation of D : $$D=\mathrm{\int }W\cdot \tilde{D}\cdot e$$

If the loudspeaker drive signal D is not calculated in the spatial frequency range, then D can be subsequently transformed into a suitable spatial frequency range with a suitable transformation in order to apply the function W as described above.

Thus, the playback can be optimized to any location.

For example, based on the analytical calculation described above, a sweet spot may be generated by restricting the spatial bandwidth of the driving function D.

Such a spatial bandwidth limitation can be carried out in real time, so that the reproduction can be tracked, for example, to a moving receiver. In such a system, for example, a camera can be used to determine the position of the receiver and then optimize the playback to that position. The determination of the position of the receiver can also be done by a sensor that the listener carries, for example, in his pocket with it.

In Fig. 2 (b), (c) is shown the sound field generated by the speakers. The loudspeakers are located on the dashed lines indicated linear contour at the edge of the Zielbeschallungsbereichs. In Fig. 2 (a) is the desired sound field shown in Fig. 2 (b) the result if no optimization function W is applied. The deviations of the reconstruction from the desired sound field can be clearly seen.

However, the application of the optimization function W according to the present invention allows the accuracy of the reconstruction to be optimized in any range as in FIG Fig. 2 (c) shown. The center of the optimization area is indicated by a cross. If a listener moves beyond this optimization range, the system can track the optimization so that the sound field playback is optimal for the selected receiver.

While the invention has been illustrated and described in detail by the figures and the accompanying description, this description and detailed description are to be considered illustrative and exemplary and not limiting as to the invention. It is understood that professionals can make changes and modifications without the scope of the following To leave claims. In particular, the invention also includes embodiments with any combination of features that are mentioned or shown above in various aspects and / or embodiments.

The invention also includes individual features in the figures, even if they are shown there in connection with other features and / or not mentioned above.

Furthermore, the term "comprising" and derivatives thereof does not exclude other elements or steps. Also, the indefinite article "a" and "derivatives" and derivatives thereof do not exclude a variety. The functions of several features listed in the claims may be fulfilled by one unit. The terms "substantially", "approximately", "approximately" and the like in connection with a property or a value in particular also define precisely the property or exactly the value. All reference signs in the claims are not to be understood as limiting the scope of the claims.

Claims (13)

Method for reproducing a sound field in a target sound area by means of a plurality of electroacoustic transducers arranged along a contour, comprising the steps of: analytically determining a drive signal for the electroacoustic transducers, such that the resulting sound field in the target PA range below the spatial aliasing frequency corresponds to the sound field to be reproduced; Changing the drive signal by spatial band limiting so that the resulting sound field corresponds to the sound field to be reproduced within an optimization range with higher accuracy than would be the case without the change; and - Supplying the changed drive signal to the electroacoustic transducer. The method of claim 1, wherein the drive signal is determined by analytically solving an integral equation describing the sound field to be reproduced. The method of claim 2, wherein the integral equation is a surface or line integral over the drive signal of the electro-acoustic transducers and the spatial transfer function. The method of claim 3, wherein the solution of the integral equation occurs in a transformed region. The method of claim 1, wherein the drive signal is determined by the relationships of the Kirchhoff-Helmholtz integral. Method according to one of the preceding claims, wherein the changing of the Anstuenmgssignals by means of a weighting function. The method of any one of the preceding claims, further comprising the step - Moving the optimization area to a predetermined position within the Zielbeschallungsbereichs. Method according to one of the preceding claims, wherein the shift of the optimization range takes place in real time. The method of claim 7, wherein the predetermined position corresponds to the position of a moving receiver, wherein the predetermined position tracks the position of the receiver. Apparatus for reproducing a sound field in a target sound area (10), in particular by a method according to one of the preceding claims, with - Several electroacoustic transducers (20) and a processing module (30) for supplying a drive signal to the electro-acoustic transducers (20),
wherein the processing module (30) is capable of analytically determining the drive signal such that the resulting sound field in the target PA region (10) below the spatial aliasing frequency corresponds to the sound field to be rendered, and changing the drive signal by spatial bandlimiting such that an optimization range arises, in which the resulting sound field corresponds to the sound field to be reproduced more exactly than would be the case without the change. The apparatus of claim 10, wherein the optimization area is shifted to a predetermined position within the target sound area (10). An apparatus according to claim 10 or 11, further comprising an amplifier unit (31) for amplifying the changed drive signal determined by the processing module (30) and supplying the amplified signal to the electro-acoustic transducers (20). Apparatus according to claim 10, 11 or 12, further comprising an audio display device for providing an audio signal describing the sound field.

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