EP2571290B1 - Local sound field synthesis with a virtual scattering body - Google Patents
Local sound field synthesis with a virtual scattering body Download PDFInfo
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- EP2571290B1 EP2571290B1 EP20110181445 EP11181445A EP2571290B1 EP 2571290 B1 EP2571290 B1 EP 2571290B1 EP 20110181445 EP20110181445 EP 20110181445 EP 11181445 A EP11181445 A EP 11181445A EP 2571290 B1 EP2571290 B1 EP 2571290B1
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04S—STEREOPHONIC SYSTEMS
- H04S7/00—Indicating arrangements; Control arrangements, e.g. balance control
- H04S7/30—Control circuits for electronic adaptation of the sound field
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04S—STEREOPHONIC SYSTEMS
- H04S2420/00—Techniques used stereophonic systems covered by H04S but not provided for in its groups
- H04S2420/13—Application of wave-field synthesis in stereophonic audio systems
Definitions
- the present invention relates to the reproduction or synthesis of a sound field in a limited audience area, in particular the sound field synthesis by scattering on a virtual scattering body and subsequent time reversal.
- stereophonic techniques of audio reproduction with the help of two or more speakers by level differences or differences in transit time creates a spatial sound impression in natural hearing.
- the desired spatial hearing impression arises only within a limited range of the so-called "sweet spot".
- a number of methods have been presented which deal with the tracking or enlargement of the sweet spot in stereophonic (illusory) playback. Exemplary here on the pamphlets DE-A-102005052904 . DE-A-10125229 or US-B-6633648 directed.
- stereophonic sound can only convey the impression of a sound source that is at least as far away from the nearest speakers as possible.
- no physical synthesis of a desired complex sound field can be achieved.
- Wave field synthesis allows the physical synthesis of a sound field over a broad range.
- WFS Wave field synthesis
- a description of the wave field syn thesis can be found in the documents AJ Berkhout, D. de Vries, and P. Vogel. Acoustic control by wave field synthesis. Journal of the Acoustical Society of America, Volume 93 (5): 2764-2778, May 1993 or S. Spors, R. Rabenstein, and J. Ahrens. The Theory of Wave Field Synthesis Revisited. In proceedings of 124th Convention of the Audio Engineering Society, May 17-20, Amsterdam, The Netherlands, 2008 be removed. It can be used arbitrarily shaped convex or straight speaker arrangements, which need not necessarily be closed.
- the loudspeaker drive signals can be calculated analytically.
- Ambisonics Another family of methods for sound field reconstruction in which the drive signal can be analytically calculated is called Ambisonics.
- the traditional formulation of Ambisonics (see eg J. Daniel, Representation of champs acoustics, application à la transmission and reproduction of scenes sonores complexes dans un contexte multimedia, PhD thesis, liable Paris 6, 2001 ) requires circular or spherical arrangements of loudspeakers. With the help of numerical algorithms, the loudspeaker signals are generated, which lead to the reproduction of the desired sound field.
- the limitation of the spatial bandwidth of the drive function necessary in the calculation path has the effect that the reconstruction of the desired sound field in the center of the loudspeaker arrangement is most accurate (“sweet spot"). The further the considered place is from the center, the larger the deviations become.
- the formulation of the underlying physical problem in the form of the synthesis equation provides insight into the required mechanisms for the synthesis of a sound field.
- the acoustic boundary conditions for the solution of the synthesis equation correspond to those of a scattering body with homogeneous Dirichlet boundary conditions.
- the external sound field of a system for sound field synthesis corresponds to the scattering of the desired sound field at the contour of the system.
- the boundary conditions at the scattering body then correspond to homogeneous Dirichlet boundary conditions, ie the system for sound field synthesis behaves like a soft-sound scattering body.
- the required difference in the sound velocity in the normal direction can be obtained from the scattering of the virtual sound field at a scattering body with the equivalent geometry as the synthesis system.
- the outer sound field then corresponds again to the scattering of the virtual sound field at the equivalent scattering body.
- the in the EP-A-2182744 proposed invention allows the free placement of the sweet spot or the sweet area within a closed speaker assembly at Ambisonics.
- the loudspeaker drive signals can be calculated analytically.
- the method is significantly more efficient than other approaches, but limited to closed (eg, circular and spherical) arrangements.
- the DE-A-10 2007 032 272 and DE-A-10 2005 003 431 describe the technical realization of a virtual headphone.
- one or more virtual sound sources are generated in the vicinity of the ears of the listener to simulate a headphone.
- These virtual sound sources are realized by acoustic focusing.
- These Virtual sound sources are operated by means of a so-called crosstalk compensation, which compensates for the crosstalk of the signals to the opposite ears out. This is a common technique when playing binaural signals through speakers.
- the virtual sources are tracked the head movement, thereby the crosstalk compensation can be kept constant during head movements. This is a significant advantage of this invention.
- the synthesis of outer ear transfer functions to realize other properties than exist in the database is not considered.
- the sound field synthesis in the method is only used for generating the sources for the virtual headphone and not for the synthesis of a sound field in a local area.
- the lossless acoustic wave equation contains only temporal and spatial derivatives of second degree (see eg Didier Cassereau and Mathias Fink, Time-Reversal of Ultrasonic Fields Part III: Theory of the Closed-Time Reversal Cavitv, IEEE TRANSACTIONS ON ULTRASONICS, FERROELECTRICS, AND FREQUENCY CONTROL, VOL. 39, NO. SEPTEMBER 1992 ). From this, the interesting property of the wave equation implies that in a known solution of the wave equation, this solution also represents a solution of the wave equation in a reversal of time. Practically, this principle is used to focus sound energy on a point or an object.
- a sound source is placed at the desired focus point in a first step and the sound pressure is recorded at the later source positions by means of microphones.
- the microphones are replaced by sound sources that are driven by the time-reversed pre-recorded signal.
- the sound source in the desired focus point and the microphones can also be virtual.
- the present invention is intended to provide an improved and, in particular, a simplified method for reconstructing a sound field in a locally limited listening area.
- the present invention is based on the basic idea to combine the findings about the external sound field of a system for sound field synthesis with the time-reversal acoustics for the local synthesis of a sound field.
- the listener area is surrounded by a virtual scattering body.
- This scattering body can be up to the maximum Range speakers and / or be arbitrarily small.
- the external sound field is now given by the scattering of the desired virtual sound field at a diffuser whose geometry is equivalent to the geometry of the audience area.
- the principles of time-reversal acoustics are used for this purpose.
- the field outside the local listener area can be interpreted as the time-reversed field created by a virtual scatterer at the position of the listener area.
- This external field can be synthesized by applying time reversal through loudspeakers outside the local listener area. This creates the field of the desired virtual source within the local listener area.
- the present invention provides a method for determining driving signals for reproducing a desired sound field within a local listening area by means of a plurality of loudspeakers at positions outside the local listener area, comprising the steps of: first, determining a virtual sound field outside the local listener area; Scattering of the desired sound field is created on a virtual diffuser with a geometry that corresponds to the geometry of the local listener area, and the signals of this virtual sound field at the positions of the speakers are determined.
- the driving signals for the loudspeakers are determined by time-reversing the signals of the virtual sound field at the corresponding loudspeaker positions.
- the loudspeakers to be used are preferably selected from among the plurality of loudspeakers and these are driven by the time-reversed signals.
- the field within the scattered body corresponds to the incident field. It is further believed that this field can propagate outward from the scatterer. However, these portions of the sound field should preferably not be taken into account in the control of the speakers. Furthermore, the theory of time-reversal acoustics does not take into account the propagation direction of the wave fronts. However, this is crucial for a listener, for example, in the localization of sound sources. Both can be done by a spatial fenestration (selection) in the selection of the used, ie the active speakers.
- the loudspeakers are preferably arranged in a circular or linear or rectangular or oval or spherical form.
- amplitudes of the loudspeaker signals are corrected, as will also be briefly explained below.
- the virtual scattering body can have sound-soft or reverberant or mixed boundary conditions.
- the virtual sound field is described as generated by a virtual source.
- the virtual source is a point source or a plane wave.
- the virtual source is a complex directional source.
- the method comprises the step of selecting speakers to be used from the plurality of speakers. It can be selected speakers that are not in the propagation direction of the virtual sound field. It is also possible, when selecting the loudspeakers, to select loudspeakers whose propagation direction with respect to the local listener zone coincides with the propagation direction of the virtual sound field.
- the virtual sound field is determined with the 2.5-dimensional wave field synthesis.
- the listener area be placed dynamically within the speaker assembly.
- the listener area can be adapted to the position of a moving listener.
- the virtual sound field is preferably a sound field measured by means of microphones outside the audience area.
- impulse responses can also be calculated.
- the signal of the virtual source can then be folded to produce the desired virtual sound field within the local zones.
- the incident sound field of the virtual source is calculated as a source signal for a temporal (Dirac) pulse. That is, in this case, the space-time impulse response from the virtual scatterer to the loudspeaker positions is then calculated. This must be taken into account when applying the time reversal and possibly also when selecting the loudspeakers.
- the method according to the invention can also be applied to measured sound fields.
- the sound field must be measured with a microphone array, which is located outside the virtual scattering body. From the analysis of the sound field, the incident sound field on the virtual scattering body and thus the scattered field at the loudspeaker positions can be calculated.
- the boundary conditions for the virtual scattering body can be set as sound-soft according to the above statements, or alternatively as reverberant.
- the 2.5-dimensional synthesis uses secondary sources at the boundary of the (planar) listening area. If point sound sources are used as secondary sources, this is referred to as a 2.5-dimensional synthesis.
- the 2.5-dimensional synthesis suffers from the occurrence of artifacts, in particular amplitude deviations between the desired virtual sources and the synthesized sound field. This is taken into account by correcting the amplitudes of the loudspeaker signals.
- the virtual source can also be modeled as a source with complex directionality.
- the combination with the local sound field synthesis according to the invention provides a significant advantage, since the desired directional characteristic is not distorted by the artifacts of spatial sampling.
- the inventive method also allows the synthesis of quiet zones within a system for sound field synthesis by the superposition of a synthesized throughout the field sound field and a local sound field. If the sound field within the local listener area has a reversed phase with respect to the global sound field, there is cancellation of the global sound field within the local listener area, and a quiet zone within the local listener area is formed.
- the invention provides a method of creating a quiet zone or zone of reduced sound pressure within a sound field, comprising the steps of: a) determining first drive signals for reproducing the desired sound field within the loudspeaker listening range according to the method of the invention; b) determining second drive signals for reproducing the desired sound field within the area covered by the speakers; c) driving the speakers with the time-reversed signals; and d) phase-reversed superimposition of the drive signals according to step c) with drive signals for the loudspeakers according to step b).
- step b) is performed by wave field synthesis or near-field compensated higher-order ambisonics.
- the method according to the invention is independent of the technique used for the calculation of the scattered sound field of the virtual scattering body.
- the scattering of the virtual sound field to a body can, for example, by means of in NA Gumerov and R. Duraiswami, Fast Multipole Methods for the Helmholtz Equation in Three Dimensions, Elsevier, 2004 or by means of numerical methods such as, for example, the 'boundary element method (BEM)' or 'finite element method' (FEM).
- the method according to the present invention enables the synthesis of a sound field in a local listener zone, wherein within the local zone with a given number of loudspeakers a higher accuracy is achieved.
- the desired local playback area can be placed dynamically and freely in front of the loudspeaker arrangement and so e.g. be adapted dynamically to the listener position, in particular by a suitable choice of the position and the geometry of the virtual scattering body.
- the method can also be used as a substitute for another method of local synthesis in the extrapolation or synthesis of outer ear transfer functions. Furthermore, the generation of quiet zones or zones with reduced sound pressure or reduced energy within the synthesized sound field is possible.
- the local synthesis is considered within a 3 meter diameter circular array consisting of 60 loudspeakers.
- the local listener zone is circular with a diameter of 60 cm and is located in the center of the speaker assembly.
- FIG. 2 (a) shows the sound field in the synthesis of a monofrequency plane wave with a frequency of 1 kHz by means of traditional wave field synthesis.
- FIG. 2 (b) shows the same scenario, for a frequency of 5 kHz. Due to the higher frequency and the finite loudspeaker spacing, significant artifacts of the spatial sampling in the synthesized sound field can be observed.
- FIG. 3 shows the application of the described method to local synthesis. As a virtual scattering body, a sphere with sound-soft boundary conditions was assumed. The ball is also shown in the figures.
- FIG. 3 clearly shows that at a frequency of the plane wave of 5 kHz an accurate synthesis within the local listener range is possible. Outside the local listening area, artifacts are created.
- FIG. 4 (a) shows the synthesis of a monofrequency plane wave with a frequency of 1 kHz.
- FIG. 4 (b) the same scenario with a frequency of 4 kHz. Again, there are clear artifacts of spatial sampling within the entire listening area.
- FIG. 5 shows the application of the described method for local synthesis for the synthesis of a plane wave with a frequency of 4 kHz. The improvement in the local listener area, as opposed to FIG. 4 (b) , is clearly visible.
- the synthesis of a sound field is considered, within which forms a quiet zone.
- the geometry corresponds to the first example.
- FIG. 6 shows the synthesis of a monofrequency plane wave with a frequency of 1 kHz using traditional wave field synthesis.
- FIG. 7 shows the formation of a quiet zone in the center of the loudspeaker arrangement. This was realized by phase-reversed superimposition of the control signals of the traditional wave field synthesis and the proposed local synthesis.
- 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.
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Description
Die vorliegende Erfindung betrifft die Wiedergabe bzw. Synthese eines Schallfeldes in einem begrenzten Zuhörerbereich, insbesondere die Schallfeldsynthese durch Streuung an einem virtuellen Streukörper und anschließende Zeitumkehr.The present invention relates to the reproduction or synthesis of a sound field in a limited audience area, in particular the sound field synthesis by scattering on a virtual scattering body and subsequent time reversal.
Es sind zahlreiche Verfahren zur Audiowiedergabe oder zur physikalischen Synthese eines Schallfeldes bekannt.Numerous methods for audio reproduction or physical synthesis of a sound field are known.
So wird bei stereophonischen Techniken der Audiowiedergabe mit Hilfe von zwei oder mehr Lautsprechern durch Pegeldifferenzen oder Laufzeitdifferenzen ein räumlicher Schalleindruck beim natürlichen Hören erzeugt. Der gewünschte räumliche Höreindruck entsteht dabei nur innerhalb eines begrenzten Bereichs dem sogenannten "sweet spot". Es wurden in der Vergangenheit eine Reihe von Verfahren vorgestellt, welche sich mit der Nachführung bzw. Vergrößerung des Sweet Spot bei stereophonischer (illusatorischer) Wiedergabe befassen. Beispielhaft wird hier auf die Druckschriften
Mit der Stereophonie kann im Allgemeinen nur der Eindruck einer Schallquelle, die mindestens den Abstand zu den nächst gelegenen Lautsprechern hat, vermittelt werden. Es kann aber keine physikalische Synthese eines gewünschten komplexen Schallfeldes erzielt werden.In general, stereophonic sound can only convey the impression of a sound source that is at least as far away from the nearest speakers as possible. However, no physical synthesis of a desired complex sound field can be achieved.
Dagegen ermöglicht die Wellenfeldsynthese (WFS) die physikalische Synthese eines Schallfeldes über einen ausgedehnten Bereich. Eine Beschreibung der Wellenfeldsynsthese kann beispielsweise den Dokumenten
Eine weitere Familie von Verfahren zur Schallfeldrekonstruktion, bei denen das Ansteuerungssignal analytisch berechnet werden kann, wird mit Ambisonics bezeichnet. Die traditionelle Formulierung von Ambisonics (siehe z.B.
Erweiterungen der traditionellen Formulierung von Ambisonics (siehe z.B.
Neben diesen etablierten Verfahren wurde in den letzten Jahren eine Reihe von verallgemeinerten Verfahren zur Synthese eines Schallfeldes entwickelt. Diese basieren auf der expliziten Lösung der Synthesegleichung. Diese beschreibt den mathematischen Zusammenhang zwischen dem synthetisierten Schallfeld in einem Zielbeschallungsbereich und den Ansteuerungssignalen einer kontinuierlichen Verteilung von Schallquellen durch eine Integralgleichung. Diese kann durch Anwendung von Operatortheorie gelöst werden, wie in
Weiterhin wird in
Beide Verfahren, die Wellenfeldsynthese und erweitertes Ambisonics, streben die physikalisch akkurate Wiedergabe in einem möglichst großen Zuhörerbereich an. In der praktischen Realisierung beider Verfahren sind der erreichbaren Genauigkeit allerdings Grenzen gesetzt. Die endliche Anzahl von Lautsprechern führt zu einer Reihe von Artefakten, die zum Teil im gesamten Zuhörerbereich auftreten. Dies hat zu der Entwicklung einer Reihe von Ansätzen geführt, die eine höhere Genauigkeit in einem begrenzten Zuhörerbereich ermöglichen als Wellenfeldsynthese oder Ambisonics.Both methods, wavefield synthesis and advanced ambisonics, aim for physically accurate playback in the widest possible audience. In the practical implementation of both methods, the achievable accuracy, however, limits. The finite number of speakers results in a number of artifacts, some of which occur throughout the listening area. This has led to the development of a number of approaches that allow for higher accuracy in a limited audience than wavefield synthesis or ambisonics.
Die in der
Der in
Der in
Die
Ein weiteres Verfahren ist die sogenannte Zeitumkehr-Akustik. Die verlustlose akustische Wellengleichung enthält nur zeitliche und räumliche Ableitungen zweiten Grades (siehe z.B.
Die vorliegende Erfindung soll ein verbessertes und insbesondere ein vereinfachtes Verfahren zu Rekonstruktion eines Schallfelds in einem lokal begrenzten Zuhörerbereich bereitstellen.The present invention is intended to provide an improved and, in particular, a simplified method for reconstructing a sound field in a locally limited listening area.
Die vorliegende Erfindung beruht auf der Grundidee, zur lokalen Synthese eines Schallfelds die Erkenntnisse über das äußere Schallfeld eines Systems zur Schallfeldsynthese mit der Zeitumkehr-Akustik zu kombinieren. Hierzu wird angenommen, dass der Zuhörerbereich von einem virtuellen Streukörper umhüllt ist. Dieser Streukörper kann maximal bis zu den Lautsprechern reichen und/oder beliebig klein sein. Das externe Schallfeld ist nun durch die Streuung des gewünschten virtuellen Schallfeldes an einem Streukörper gegeben, dessen Geometrie zu der Geometrie des Zuhörerbereichs äquivalent ist.The present invention is based on the basic idea to combine the findings about the external sound field of a system for sound field synthesis with the time-reversal acoustics for the local synthesis of a sound field. For this purpose it is assumed that the listener area is surrounded by a virtual scattering body. This scattering body can be up to the maximum Range speakers and / or be arbitrarily small. The external sound field is now given by the scattering of the desired virtual sound field at a diffuser whose geometry is equivalent to the geometry of the audience area.
Die entsprechenden akustischen Randbedingungen müssen nun am Rand des lokalen Zuhörerbereiches synthetisiert werden. Dies könnte zum Beispiel - ähnlich dem Verfahren aus der oben bereits angesprochenen Veröffentlichung von F.M. Fazi et al. - durch eine explizite Lösung der zugrundeliegenden Integralgleichungen erfolgen. Hierfür sind aber komplexe mathematische Berechnungen nötig.The corresponding acoustic boundary conditions must now be synthesized at the edge of the local listening area. For example, similar to the method of the F.M. Fazi et al. - by an explicit solution of the underlying integral equations. But this requires complex mathematical calculations.
Gemäß der vorliegenden Erfindung werden hierzu die Prinzipien aus der Zeitumkehr-Akustik angewendet. Das Feld außerhalb des lokalen Zuhörerbereichs kann als das zeitumgekehrte Feld interpretiert werden, welches durch einen virtuellen Streukörper an der Position des Zuhörerbereichs entstanden ist. Dieses äußere Feld kann durch die Anwendung der Zeitumkehr durch Lautsprecher außerhalb des lokalen Zuhörerbereichs synthetisiert werden. Dadurch entsteht innerhalb des lokalen Zuhörerbereichs das Feld der gewünschten virtuellen Quelle.According to the present invention, the principles of time-reversal acoustics are used for this purpose. The field outside the local listener area can be interpreted as the time-reversed field created by a virtual scatterer at the position of the listener area. This external field can be synthesized by applying time reversal through loudspeakers outside the local listener area. This creates the field of the desired virtual source within the local listener area.
Dementsprechend stellt die vorliegende Erfindung ein Verfahren zur Bestimmung von Ansteuerungssignalen zur Wiedergabe eines gewünschten Schallfelds innerhalb eines lokalen Zuhörerbereichs mittels mehrerer Lautsprecher an Positionen außerhalb des lokalen Zuhörerbereichs bereit, das die folgenden Schritte aufweist: Zunächst wird ein virtuelles Schallfeld außerhalb des lokalen Zuhörerbereichs bestimmt, das durch Streuung des gewünschten Schallfelds an einem virtuellen Streukörper mit einer Geometrie entsteht, die der Geometrie des lokalen Zuhörerbereichs entspricht, und die Signale dieses virtuellen Schallfeldes an den Positionen der Lautsprecher werden bestimmt. Die Ansteuerungssignale für die Lautsprecher werden durch Zeitumkehren der Signale des virtuellen Schallfelds an den entsprechenden Lautsprecherpositionen bestimmt. Zur Wiedergabe des gewünschten Schallfelds innerhalb des lokalen Zuhörerbereichs werden nach Bestimmen der Ansteuerungssignalen für die Lautsprecher vorzugsweise die zu verwendenden Lautsprecher unter den mehreren Lautsprecher ausgewählt und diese werden mit den zeitumgekehrten Signalen angesteuert.Accordingly, the present invention provides a method for determining driving signals for reproducing a desired sound field within a local listening area by means of a plurality of loudspeakers at positions outside the local listener area, comprising the steps of: first, determining a virtual sound field outside the local listener area; Scattering of the desired sound field is created on a virtual diffuser with a geometry that corresponds to the geometry of the local listener area, and the signals of this virtual sound field at the positions of the speakers are determined. The driving signals for the loudspeakers are determined by time-reversing the signals of the virtual sound field at the corresponding loudspeaker positions. For reproducing the desired sound field within the local listener area, after determining the drive signals for the loudspeakers, the loudspeakers to be used are preferably selected from among the plurality of loudspeakers and these are driven by the time-reversed signals.
Bei der Berechnung des gestreuten Feldes wird in der Regel davon ausgegangen, dass das Feld innerhalb des Streukörpers dem einfallenden Feld entspricht. Weiterhin wird angenommen, dass dieses Feld aus dem Streukörper nach außen propagieren kann. Diese Anteile des Schallfelds sollen aber vorzugsweise bei der Ansteuerung der Lautsprecher nicht berücksichtigt werden. Weiterhin wird bei der Theorie der Zeitumkehr-Akustik nicht die Ausbreitungsrichtung der Wellenfronten berücksichtigt. Diese ist aber für einen Zuhörer zum Beispiel bei der Lokalisation von Schallquellen ausschlaggebend. Beides kann durch eine räumliche Fensterung (Selektion) bei der Auswahl der zu verwendenden, also der aktiven Lautsprecher erfolgen.In the calculation of the scattered field, it is generally assumed that the field within the scattered body corresponds to the incident field. It is further believed that this field can propagate outward from the scatterer. However, these portions of the sound field should preferably not be taken into account in the control of the speakers. Furthermore, the theory of time-reversal acoustics does not take into account the propagation direction of the wave fronts. However, this is crucial for a listener, for example, in the localization of sound sources. Both can be done by a spatial fenestration (selection) in the selection of the used, ie the active speakers.
Bei dem erfindungsgemäßen Verfahren sind die Lautsprecher vorzugsweise kreisförmig oder linear oder rechteckig oder oval oder kugelförmig angeordnet.In the method according to the invention, the loudspeakers are preferably arranged in a circular or linear or rectangular or oval or spherical form.
Es ist ferner bevorzugt, dass die Amplituden der Lautsprechersignale korrigiert werden, wie auch im Folgenden noch kurz erläutert wird.It is further preferred that the amplitudes of the loudspeaker signals are corrected, as will also be briefly explained below.
Der virtuelle Streukörper kann schallweiche oder schallharte oder auch gemischte Randbedingungen haben.The virtual scattering body can have sound-soft or reverberant or mixed boundary conditions.
Gemäß einer weiter bevorzugten Ausführungsform wird das virtuelle Schallfeld als durch eine virtuelle Quelle erzeugt beschrieben. Vorzugsweise ist die virtuelle Quelle eine Punktquelle oder eine ebene Welle. Gemäß einer anderen Ausführungsform ist die virtuelle Quelle eine Quelle mit komplexer Richtcharakteristik.According to a further preferred embodiment, the virtual sound field is described as generated by a virtual source. Preferably, the virtual source is a point source or a plane wave. In another embodiment, the virtual source is a complex directional source.
Weiter bevorzugt weist das Verfahren den Schritt des Auswählens von zu benutzenden Lautsprechern aus den mehreren Lautsprechern auf. Dabei können Lautsprecher ausgewählt werden, die sich nicht in der Ausbreitungsrichtung des virtuellen Schallfelds befinden. Es ist auch möglich, bei der Auswahl der Lautsprecher Lautsprecher auszuwählen, deren Ausbreitungsrichtung bezogen auf die lokale Zuhörerzone mit der Ausbreitungsrichtung des virtuellen Schallfelds übereinstimmen.More preferably, the method comprises the step of selecting speakers to be used from the plurality of speakers. It can be selected speakers that are not in the propagation direction of the virtual sound field. It is also possible, when selecting the loudspeakers, to select loudspeakers whose propagation direction with respect to the local listener zone coincides with the propagation direction of the virtual sound field.
Bevorzugt wird das virtuelle Schallfeld mit der 2,5-dimensionalen Wellenfeldsynthese bestimmt.Preferably, the virtual sound field is determined with the 2.5-dimensional wave field synthesis.
Es ist ferner bevorzugt, dass der Zuhörerbereich dynamisch innerhalb der Lautsprecheranordnung platziert wird. Dabei kann der Zuhörerbereich an die Position eines bewegten Zuhörers angepasst werden.It is further preferred that the listener area be placed dynamically within the speaker assembly. In this case, the listener area can be adapted to the position of a moving listener.
Das virtuelle Schallfeld ist vorzugsweise ein mittels Mikrophonen außerhalb des Zuhörerbereichs gemessenes Schallfeld.The virtual sound field is preferably a sound field measured by means of microphones outside the audience area.
Mit dem Berechnungsverfahren gemäß der Erfindung für die Ansteuerungssignale können auch Impulsantworten berechnet werden. Mit diesen kann dann das Signal der virtuellen Quelle gefaltet werden, um das gewünschte virtuelle Schallfeld innerhalb der lokalen Zonen zu erzeugen. Dazu muss bei der Berechnung des Schallfeldes, welches vom virtuellen Streukörper gestreut wird, angenommen werden, dass das einfallende Schallfeld der virtuellen Quelle für einen zeitlichen (Dirac) Impuls als Quellensignal berechnet wird. Das heißt, in diesem Fall wird dann die raum-zeitliche Impulsantwort vom virtuellen Streukörper zu den Lautsprecherpositionen berechnet. Diese muss bei der Anwendung der Zeitumkehr und gegebenenfalls auch bei der Auswahl der Lautsprecher berücksichtigt werden.With the calculation method according to the invention for the drive signals, impulse responses can also be calculated. With these, the signal of the virtual source can then be folded to produce the desired virtual sound field within the local zones. For this purpose, when calculating the sound field which is scattered by the virtual scattering body, it must be assumed that the incident sound field of the virtual source is calculated as a source signal for a temporal (Dirac) pulse. That is, in this case, the space-time impulse response from the virtual scatterer to the loudspeaker positions is then calculated. This must be taken into account when applying the time reversal and possibly also when selecting the loudspeakers.
Das erfindungsgemäße Verfahren kann auch auf gemessene Schallfelder angewendet werden. Hierzu muss das Schallfeld mit einem Mikrophonarray vermessen werden, welches sich außerhalb des virtuellen Streukörpers befindet. Aus der Analyse des Schallfeldes kann das einfallende Schallfeld auf dem virtuellen Streukörper und damit das gestreute Feld an den Lautsprecherpositionen berechnet werden.The method according to the invention can also be applied to measured sound fields. For this purpose, the sound field must be measured with a microphone array, which is located outside the virtual scattering body. From the analysis of the sound field, the incident sound field on the virtual scattering body and thus the scattered field at the loudspeaker positions can be calculated.
Die Randbedingungen für den virtuellen Streukörper können gemäß den obigen Ausführungen als schallweich angesetzt werden, oder alternativ auch als schallhart.The boundary conditions for the virtual scattering body can be set as sound-soft according to the above statements, or alternatively as reverberant.
Bei einer 2.5-dimensionalen Synthese mittels Wellenfeldsynthese kann eine Korrektur der Amplituden der Lautsprechersignale nötig werden. Im Vergleich zu einer dreidimensionalen Wellenfeldsynthese verwendet die 2,5-dimensionale Synthese Sekundärquellen an der Umgrenzung des (planaren) Hörbereichs. Werden dazu Punktschallquellen als Sekundärquellen verwendet, wird von einer 2,5-dimensionale Synthese gesprochen. Die 2,5-dimensionale Synthese leidet jedoch unter dem Auftreten von Artefakten, insbesondere Amplitudenabweichungen zwischen den gewünschten virtuelen Quellen und dem synthetisierten Schallfeld. Dies wird durch eine Korrektur der Amplituden der Lautsprechersignale berücksichtigt.In a 2.5-dimensional synthesis using wave field synthesis, it may be necessary to correct the amplitudes of the loudspeaker signals. Compared to a three-dimensional wave field synthesis, the 2.5-dimensional synthesis uses secondary sources at the boundary of the (planar) listening area. If point sound sources are used as secondary sources, this is referred to as a 2.5-dimensional synthesis. However, the 2.5-dimensional synthesis suffers from the occurrence of artifacts, in particular amplitude deviations between the desired virtual sources and the synthesized sound field. This is taken into account by correcting the amplitudes of the loudspeaker signals.
Aufgrund des typischerweise klein gewählten Zuhörerbereichs und der somit kleinen Apertur ist es oft nicht sinnvoll, das beschriebenen Verfahren zur lokalen Schallfeldsynthese bei tiefen Frequenzen zu nutzen. Für tiefe Frequenzen können die normalen Verfahren zur Schallfeldsynthese genutzt werden, da hier die typische physikalische Genauigkeit der herkömmlichen Verfahren ausreichend ist. Das Überblenden zwischen den beiden Verfahren kann durch eine Fensterfunktion im Frequenzbereich geschehen.Due to the typically small selected listening area and thus small aperture, it is often not useful to use the described method for local sound field synthesis at low frequencies. For low frequencies, the normal methods for sound field synthesis can be used, since the typical physical accuracy of conventional methods is sufficient here. The crossfading between the two methods can be done by a window function in the frequency domain.
Die virtuelle Quelle kann neben dem typischen Punktquellenmodell auch als Quelle mit komplexer Richtcharateristik modelliert werden. Hierzu kann beispielsweise das in
Das erfindungsgemäße Verfahren erlaubt auch die Synthese von Ruhezonen innerhalb eines Systems zur Schallfeldsynthese durch die Überlagerung eines im gesamten Bereich synthetisierten Schallfeldes und eines lokalen Schallfeldes. Falls das Schallfeld innerhalb des lokalen Zuhörerbereichs gegenüber dem globalen Schallfeld eine umgekehrte Phase aufweist, gibt es innerhalb des lokalen Zuhörerbereiches Auslöschung bzw. Dämpfung des globalen Schallfeldes, und es bildet sich eine Ruhezone innerhalb des lokalen Zuhörerbereiches aus.The inventive method also allows the synthesis of quiet zones within a system for sound field synthesis by the superposition of a synthesized throughout the field sound field and a local sound field. If the sound field within the local listener area has a reversed phase with respect to the global sound field, there is cancellation of the global sound field within the local listener area, and a quiet zone within the local listener area is formed.
Gemäß diesem Aspekt stellt die Erfindung ein Verfahren zur Erzeugung einer Ruhezone oder einer Zone mit vermindertem Schalldruck innerhalb eines Schallfeldes bereit, mit den Schritten: a) Bestimmen von ersten Ansteuerungssignalen zur Wiedergabe des gewünschten Schallfeldes innerhalb des Zuhörerbereichs für die Lautsprecher gemäß dem erfindungsgemäßen Verfahren; b) Bestimmen von zweiten Ansteuerungssignalen zur Wiedergabe des gewünschten Schallfeldes innerhalb des durch die Lautsprecher umfassten Bereiches; c) Ansteuern der Lautsprecher mit den zeitumgekehrten Signalen; und d) phasenumgekehrtes Überlagern der Ansteuerungssignale gemäß Schritt c) mit Ansteuersignalen für die Lautsprecher gemäß Schritt b).In accordance with this aspect, the invention provides a method of creating a quiet zone or zone of reduced sound pressure within a sound field, comprising the steps of: a) determining first drive signals for reproducing the desired sound field within the loudspeaker listening range according to the method of the invention; b) determining second drive signals for reproducing the desired sound field within the area covered by the speakers; c) driving the speakers with the time-reversed signals; and d) phase-reversed superimposition of the drive signals according to step c) with drive signals for the loudspeakers according to step b).
Vorzugsweise erfolgt Schritt b) durch Wellenfeldsynthese oder near-field compensated higher-order Ambisonics.Preferably, step b) is performed by wave field synthesis or near-field compensated higher-order ambisonics.
Prinzipiell ist das erfindungsgemäße Verfahren unabhängig von der Technik, die für die Berechnung des gestreuten Schallfeldes des virtuellen Streukörpers verwendet wird. Die Streuung des virtuellen Schallfeldes an einen Körper kann zum Beispiel mittels der in
Das Verfahren gemäß der vorliegenden ermöglicht die Synthese eines Schallfeldes in einer lokalen Zuhörerzone, wobei innerhalb der lokalen Zone mit einer gegebenen Anzahl von Lautsprechern eine höhere Genauigkeit erzielt wird. Der gewünschte lokale Wiedergabebereich kann dynamisch und frei innerhalb bzw. vor der Lautsprecheranordung platziert werden und so z.B. dynamisch an die Hörerposition angepasst werden, insbesondere durch eine geeignete Wahl der Position und der Geometrie des virtuellen Streukörpers. Das Verfahren kann auch als Ersatz für ein anderes Verfahren der lokalen Synthese bei der Extrapolation bzw. Synthese von Außenohrübertragungsfunktionen verwendet werden. Weiterhin ist auch die Erzeugung von Ruhezonen oder Zonen mit vermindertem Schalldruck bzw. verminderter Energie innerhalb des synthetisierten Schallfeldes möglich.The method according to the present invention enables the synthesis of a sound field in a local listener zone, wherein within the local zone with a given number of loudspeakers a higher accuracy is achieved. The desired local playback area can be placed dynamically and freely in front of the loudspeaker arrangement and so e.g. be adapted dynamically to the listener position, in particular by a suitable choice of the position and the geometry of the virtual scattering body. The method can also be used as a substitute for another method of local synthesis in the extrapolation or synthesis of outer ear transfer functions. Furthermore, the generation of quiet zones or zones with reduced sound pressure or reduced energy within the synthesized sound field is possible.
Die Erfindung wird im Folgenden anhand von Ausführungsbeispielen unter Verweis auf die beigefügten Figuren näher beschrieben.
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Fig. 1 zeigt ein Beispiel eines von einem kugelförmigen Streukörper mit schallweichen Randbedingungen gestreuten Felds für eine ebene Welle als einfallendes Schallfeld; -
Fig. 2 zeigt das Schallfeld bei der Synthese einer monofrequenten ebenen Welle mit einer Frequenz (a)von 1 kHz und (b) von 5 kHz mittels traditioneller Wellenfeldsynthese durch eine kreisförmige Lautsprecheranordnung; -
Fig. 3 zeigt die Anwendung des erfindungsgemäßen Verfahrens auf das Szenario ausFig. 2(b) ; -
Fig. 4 zeigt das Schallfeld bei der Synthese einer monofrequenten ebenen Welle mit einer Frequenz (a)von 1 kHz und (b) von 4 kHz mittels traditioneller Wellenfeldsynthese durch eine lineare Lautsprecheranordnung; -
Fig. 5 zeigt die Anwendung des beschriebenen Verfahrens zur lokalen Synthese für die Synthese einer ebenen Welle mit einer Frequenz von 4 kHz entsprechend dem inFig. 4(b) gezeigten Aufbau; -
Fig. 6 zeigt die Ausbildung einer Ruhezone in dem Aufbau gemäßFig. 2 mittels traditioneller Wellenfeldsynthese und -
Fig. 7 zeigt die Ausbildung einer Ruhezone im Aufbau nachFig. 6 mittels der vorliegenden Erfindung.
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Fig. 1 Fig. 12 shows an example of a plane wave field scattered by a spherical diffuser with soft-sound boundary conditions as an incident sound field; -
Fig. 2 shows the sound field in the synthesis of a monofrequency plane wave with a frequency (a) of 1 kHz and (b) of 5 kHz by means of traditional wavefield synthesis through a circular loudspeaker arrangement; -
Fig. 3 shows the application of the method according to the invention to the scenarioFig. 2 (b) ; -
Fig. 4 shows the sound field in the synthesis of a monofrequency plane wave with a frequency (a) of 1 kHz and (b) of 4 kHz by means of traditional wave field synthesis through a linear loudspeaker arrangement; -
Fig. 5 shows the application of the described method for local synthesis for the synthesis of a plane wave with a frequency of 4 kHz according to the inFig. 4 (b) shown construction; -
Fig. 6 shows the formation of a quiet zone in the structure according toFig. 2 using traditional wave field synthesis and -
Fig. 7 shows the formation of a quiet zone in the structureFig. 6 by means of the present invention.
Bei einem ersten Beispiel wird die lokale Synthese innerhalb einer kreisförmigen Anordnung mit einem Durchmesser von 3 m bestehend aus 60 Lautsprechern betrachtet. Die lokale Zuhörerzone ist kreisförmig mit einem Durchmesser von 60 cm und befindet sich im Zentrum der Lautsprecheranordnung.
Im zweiten Ausführungsbeispiel wird eine lineare Anordnung von insgesamt 60 Lautsprechern betrachtet, wobei der Abstand zwischen den Lautsprechern 15 cm beträgt.
Im dritten Ausführungsbeispiel wird die Synthese eines Schallfeldes betrachtet, innerhalb welchem sich eine Ruhezone ausbildet. Die Geometrie entspricht dem ersten Beispiel.
Obwohl die Erfindung mittels der Figuren und der zugehörigen Beschreibung dargestellt und detailliert beschrieben ist, sind diese Darstellung und diese detaillierte Beschreibung illustrativ und beispielhaft zu verstehen und nicht als die Erfindung einschränkend. Es versteht sich, dass Fachleute Änderungen und Abwandlungen machen können, ohne den Umfang der folgenden Ansprüche zu verlassen. Insbesondere umfasst die Erfindung ebenfalls Ausführungsformen mit jeglicher Kombination von Merkmalen, die vorstehend zu verschiedenen Aspekten und/oder Ausführungsformen genannt oder gezeigt sind.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 those skilled in the art can make changes and modifications without departing from the scope of the following 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.
Die Erfindung umfasst ebenfalls einzelne Merkmale in den Figuren auch wenn sie dort im Zusammenhang mit anderen Merkmalen gezeigt sind und/oder vorstehend nicht genannt sind.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.
Im Weiteren schließt der Ausdruck "umfassen" und Ableitungen davon andere Elemente oder Schritte nicht aus. Ebenfalls schließt der unbestimmte Artikel "ein" bzw. "eine" und Ableitungen davon eine Vielzahl nicht aus. Die Funktionen mehrerer in den Ansprüchen aufgeführter Merkmale können durch eine Einheit erfüllt sein. Die Begriffe "im Wesentlichen", "etwa", "ungefähr" und dergleichen in Verbindung mit einer Eigenschaft beziehungsweise einem Wert definieren insbesondere auch genau die Eigenschaft beziehungsweise genau den Wert. Alle Bezugszeichen in den Ansprüchen sind nicht als den Umfang der Ansprüche einschränkend zu verstehen.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 (14)
- A method for determining control signals for reproducing a desired sound field within a local audience area by means of a plurality of loudspeakers at positions outside the audience area, comprising the steps of:- determining a scattered virtual sound field outside the audience area, which is generated by scattering the desired sound field at a virtual scattering body having a geometry that is equivalent to the geometry of the audience area, wherein the virtual scattering body has acoustically soft, acoustically hard or mixed edge conditions,- determining the signals of the scattered virtual sound field at the positions of the loudspeakers and- determining the control signals for the loudspeakers by time-reversing the signals of the scattered virtual sound field.
- The method according to claim 1, wherein the loudspeakers are arranged in a circular or linear or rectangular or oval or spherical manner.
- The method according to claim 1 or 2, wherein the amplitudes of the loudspeaker signals are corrected.
- The method according to any one of the preceding claims, wherein the scattered virtual sound field is described as being generated by a virtual source.
- The method according to claim 4, wherein the virtual source is a point source or a plane wave.
- The method according to any one of the preceding claims, further comprising the step of selecting loudspeakers to be used from the plurality of loudspeakers.
- The method according to claim 6, wherein loudspeakers are selected which are not located in the propagation direction of the scattered virtual sound field.
- The method according to claim 6, wherein when selecting loudspeakers, loudspeakers are selected whose propagation direction relative to the local audience zone corresponds to the propagation direction of the scattered virtual sound field.
- The method according to any one of the preceding claims, wherein the scattered virtual sound field is determined by means of a 2.5-dimensional wave field synthesis.
- The method according to any one of the preceding claims, wherein the audience area is placed dynamically within the loudspeaker arrangement.
- The method according to claim 10, wherein the audience area is adapted to the position of a moved auditor.
- A method for reproducing a desired sound field within a local audience area by means of a plurality of loudspeakers at positions outside the audience area, comprising the steps of:- determining control signals for reproducing the desired sound field within the audience area for the loudspeakers in accordance with the method according to any one of claims 1 to 11, and- controlling the loudspeakers by means of the time-reversed signals.
- A method for generating a quiet zone or a zone with reduced sound pressure within a sound field, comprising the steps of:(a) determining first control signals for reproducing the desired sound field within the audience area for the loudspeakers in accordance with the method according to any one of claims 1 to 11;(b) determining second control signals for reproducing the desired sound field within the area covered by the loudspeakers;(c) controlling the loudspeakers by means of the time-reversed signals; and(d) phase-reversed superposition of the control signals according to step (c) with the control signals for the loudspeakers according to step (b).
- The method according to claim 13, wherein step (b) is performed by wave field synthesis or near-field compensated higher-order ambisonics.
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