EP1586220B1 - Method and device for controlling a reproduction unit using a multi-channel signal - Google Patents

Description

The present invention relates to a method and a device for controlling a set of restitution of an acoustic field comprising a plurality of rendering elements, from a plurality of acoustic or audiophonic signals each associated with a general direction of restitution. predetermined, defined with respect to a point of the given space.

Such a set of signals is commonly referred to as "multichannel signal" and corresponds to a plurality of signals, called channels, transmitted in parallel or multiplexed with each other, each intended for an element or a group of elements of restitution, arranged in a predefined general direction with respect to a given point.

For example, a conventional multichannel system known as "5.1 ITU-R BF 775-1" and comprises five channels for rendition elements placed in five predetermined general directions with respect to a listening center, defined by angles 0 °, + 30 °, -30 °, + 110 ° and -110 °.

Such an arrangement therefore corresponds to the arrangement of a loudspeaker or group of speakers in front of the center, one on each side in front of right and left and one on each side behind to the right and left.

The control signals being each associated with a determined direction, the application of these signals to a restitution assembly whose elements do not respond to the predetermined spatial configuration, causes significant deformations of the acoustic field restored.

There are systems that incorporate delay means on the channels, to compensate at least partially, the distance of the playback elements from the listening center. These systems, however, do not allow to take into account the spatial arrangement of the restitution set.

It therefore appears that no existing method or system allows a good quality rendering from a multichannel type signal with a restitution set of any spatial configuration.

The object of the present invention is to remedy this problem by defining a method and a system for controlling the reproduction assembly, the spatial configuration of which is arbitrary.

• une étape de détermination de caractéristiques au moins spatiales dudit ensemble de restitution, permettant la détermination de paramètres représentatifs pour au moins un élément dudit ensemble de restitution de sa position dans les trois dimensions de l'espace par rapport audit point donné ;
• une étape de détermination de filtres d'adaptation à partir desdites caractéristiques au moins spatiales dudit ensemble de restitution et desdites directions générales de restitution prédéterminée associées à ladite pluralité de signaux d'entrée d'informations acoustiques ;
• une étape de détermination d'au moins un signal de pilotage desdits éléments dudit ensemble de restitution par l'application desdits filtres d'adaptation à ladite pluralité de signaux d'entrée d'informations acoustiques; et
• une étape de délivrance dudit au moins un signal de pilotage en vue d'une application auxdits éléments de restitution.

The subject of the invention is a method of controlling a set of restitution of an acoustic field comprising a plurality of restitution elements each associated with a predetermined general restitution direction relative to a given point, to obtain a field acoustics restored with specific characteristics substantially independent of the intrinsic characteristics of restitution of said assembly, characterized in that it comprises:

• a step of determining at least spatial characteristics of said restitution set, allowing the determination of representative parameters for at least one element of said set of restitution of its position in the three dimensions of the space with respect to said given point;
• a step of determining matching filters from said at least spatial characteristics of said restitution set and said predetermined restitution general directions associated with said plurality of acoustic information input signals;
• a step of determining at least one control signal of said elements of said restitution set by applying said matching filters to said plurality of acoustic information input signals; and
• a step of delivering said at least one control signal for application to said rendering elements.

• ladite étape de détermination de caractéristiques au moins spatiales dudit ensemble de restitution, comporte une sous-étape de saisie permettant de déterminer tout ou partie des caractéristiques dudit ensemble de restitution ;
• ladite étape de détermination de caractéristiques au moins spatiales dudit ensemble de restitution, comporte une étape de calibrage permettant de délivrer tout ou partie des caractéristiques dudit ensemble de restitution ;
• ladite sous-étape de calibrage comporte pour au moins un des éléments de restitution :
• une sous-étape d'émission d'un signal spécifique vers ledit au moins un élément dudit ensemble de restitution ;
• une sous-étape d'acquisition de l'onde sonore émise en réponse par ledit au moins un élément ;
• une sous-étape de transformation desdits signaux acquis en un nombre fini desdits coefficients représentatifs de l'onde sonore émise ; et
• une sous-étape de détermination de paramètres spatiaux et/ou acoustiques dudit élément à partir desdits coefficients représentatifs de l'onde sonore émise ;
• ladite sous-étape de calibrage comporte en outre une sous-étape de détermination de la position dans au moins l'une des trois dimensions de l'espace dudit au moins un élément dudit ensemble de restitution ;
• ladite étape de calibrage comporte une sous-étape de détermination de la réponse en fréquence dudit au moins un élément dudit ensemble de restitution ;
• ladite étape de détermination de filtres d'adaptation comprend :
• une sous-étape de détermination d'une matrice de décodage représentative de filtres permettant la compensation des altérations de restitution dues aux caractéristiques spatiales dudit ensemble de restitution ;
• une sous-étape de détermination d'une matrice de rayonnement multicanal idéale représentative des directions générales prédéterminées associes à chaque signal d'informations de la pluralité des signaux d'entrée ; et
• une sous-étape de détermination d'une matrice représentative desdits filtres d'adaptation à partir de ladite matrice de décodage et de ladite matrice de rayonnement multicanal ;
• ladite étape de détermination de filtres d'adaptation comporte une pluralité de sous-étapes de calcul permettant de délivrer un ordre limite de précision spatiale des filtres d'adaptation, une matrice correspondant à une fenêtre spatiale représentative de la répartition dans l'espace de la précision souhaitée lors de la reconstruction du champ acoustique et une matrice représentative du rayonnement de l'ensemble de restitution, ladite sous-étape de calcul de la matrice de décodage étant réalisée à partir des résultats de ces sous-étapes de calcul ;
• les matrices de décodage, de rayonnement multicanal idéal et d'adaptation sont indépendantes de la fréquence, l'étape de détermination d'au moins un signal de pilotage desdits éléments dudit ensemble de restitution par l'application desdits filtres d'adaptation correspondant à de simples combinaisons linéaires suivies de retard.
• ladite étape de détermination de caractéristiques dudit ensemble de restitution permet la détermination de caractéristiques acoustiques dudit ensemble de restitution et ledit procédé comporte une étape de détermination de filtres de compensation de ces caractéristiques acoustiques, ladite étape de détermination d'au moins un signal de pilotage comprenant alors une sous-étape d'application desdits filtres de compensation acoustique ;
• ladite étape de détermination de caractéristiques acoustiques est adaptée pour délivrer des paramètres représentatifs pour au moins un élément de sa réponse en fréquence ;
• ladite étape de détermination d'au moins un signal de pilotage comporte une sous-étape d'ajustement de gain et d'application de retards afin d'aligner temporellement le front d'onde des éléments de restitution en fonction de leur distance par rapport audit point donné.

According to other characteristics:

• said step of determining at least spatial characteristics of said restitution set, comprises an input sub-step for determining all or part of the characteristics of said restitution set;
• said step of determining at least spatial characteristics of said restitution set, comprises a calibration step for delivering all or part of the characteristics of said restitution set;
• said substep of calibration comprises for at least one of the restitution elements:
• a substep of transmitting a specific signal to said at least one element of said restitution set;
• a substep of acquisition of the sound wave emitted in response by said at least one element;
• a substep of transforming said acquired signals into a finite number of said coefficients representative of the emitted sound wave; and
• a sub-step of determining spatial and / or acoustic parameters of said element from said coefficients representative of the sound wave emitted;
• said calibration sub-step further comprises a substep of determining the position in at least one of the three dimensions of the space of said at least one element of said rendering assembly;
• said calibration step comprises a substep of determining the frequency response of said at least one element of said restitution set;
• said step of determining adaptation filters comprises:
• a sub-step of determining a decoding matrix representative of filters allowing the compensation of the restitution alterations due to the spatial characteristics of said restitution set;
• a substep of determining an ideal multi-channel radiation matrix representative of the predetermined general directions associated with each information signal of the plurality of input signals; and
• a substep of determining a representative matrix of said matching filters from said decoding matrix and said multichannel radiation matrix;
• said step of determining adaptation filters comprises a plurality of calculation sub-steps for delivering a limit order of spatial accuracy of the adaptation filters, a matrix corresponding to a spatial window representative of the spatial distribution of the adaptation filter; desired precision during the reconstruction of the acoustic field and a representative matrix of the radiation of the restitution assembly, said substep of calculating the decoding matrix being carried out on the basis of the results of these calculation sub-steps;
• the decoding, multichannel radiation and adaptation matrices are independent of the frequency, the step of determining at least one control signal of said elements of said restitution set by the application of said matching filters corresponding to simple linear combinations followed by delay.
• said step of determining characteristics of said restitution assembly makes it possible to determine acoustic characteristics of said set of restitution and said method comprises a step of determining compensation filters of these acoustic characteristics, said step of determining at least one control signal then comprising a substep of application of said acoustic compensation filters;
• said step of determining acoustic characteristics is adapted to deliver representative parameters for at least one element of its frequency response;
• said step of determining at least one pilot signal includes a gain and delay adjustment sub-step for temporally aligning the wavefront of the rendering elements according to their distance from said auditing point given.

The invention also relates to a computer program comprising program code instructions for executing the steps of the method when said program is executed by a computer.

The invention also also relates to a removable medium of the type comprising at least one processing processor and a non-volatile memory element, characterized in that said memory comprises a program comprising code instructions for executing the steps of the method when said processor executes said program.

• des moyens de détermination de caractéristiques au moins spatiales dudit ensemble de restitution, permettant la détermination de paramètres représentatifs pour au moins un élément dudit ensemble de restitution de sa position dans les trois dimensions de l'espace par rapport audit point donné ;
• des moyens de détermination de filtres d'adaptation à partir desdites caractéristiques au moins spatiales dudit ensemble de restitution et des directions générales de restitution prédéterminée associées à ladite pluralité des signaux d'entrée d'informations acoustiques ; et
• des moyens de détermination d'au moins un signal de pilotage desdits éléments dudit ensemble de restitution par l'application desdits filtres d'adaptation à ladite pluralité de signaux d'entrée d'informations acoustiques.

The subject of the invention is also a device for controlling a set of restitution of an acoustic field comprising a plurality of rendering elements, comprising means for inputting a plurality of acoustic information input signals. each associated with a predetermined general direction of restitution defined with respect to a given point, characterized in that it further comprises:

• means for determining at least spatial characteristics of said restitution set, enabling the determination of representative parameters for at least one element of said set of restitution of its position in the three dimensions of space with respect to said given point;
• means for determining adaptation filters from said at least spatial characteristics of said restitution assembly and predetermined restitution general directions associated with said plurality of acoustic information input signals; and
• means for determining at least one control signal of said elements of said restitution set by applying said matching filters to said plurality of acoustic information input signals.

• lesdits moyens de détermination des caractéristiques au moins spatiales dudit ensemble de restitution comportent des moyens de saisie directe desdites caractéristiques ;
• il est adapté pour être associé à des moyens de calibrage permettant la détermination des caractéristiques au moins spatiales dudit ensemble de restitution ;
• lesdits moyens de calibrage comprennent des moyens d'acquisition d'une onde sonore comportant quatre capteurs de pression disposés selon une forme générale de tétraèdre ;
• lesdits moyens de détermination de caractéristiques sont adaptés pour la détermination de caractéristiques acoustiques d'au moins un desdits éléments de restitution dudit ensemble de restitution, ledit dispositif comportant des moyens de détermination de filtres de compensation acoustique à partir desdites caractéristiques acoustiques et lesdits moyens de détermination d'au moins un signal de pilotage étant adaptés pour l'application desdits filtres de compensation acoustique ;
• lesdits moyens de détermination des caractéristiques acoustiques sont adaptés pour la détermination de la réponse en fréquence desdits éléments de l'ensemble de restitution.

According to other features of this device:

• said means for determining the at least spatial characteristics of said restitution assembly comprise means for directly inputting said characteristics;
• it is adapted to be associated with calibration means for determining the at least spatial characteristics of said restitution set;
• said calibration means comprise means for acquiring a sound wave comprising four pressure sensors arranged in a general shape of a tetrahedron;
• said characteristic determining means are adapted for the determination of acoustic characteristics of at least one of said rendering elements of said reproduction assembly, said device comprising means for determining acoustic compensation filters from said acoustic characteristics and said determining means at least one pilot signal being adapted for the application of said acoustic compensation filters;
• said means for determining the acoustic characteristics are suitable for determining the frequency response of said elements of the reproduction unit.

• lesdits moyens de détermination d'une pluralité de signaux d'entrée sont formés d'une unité de lecture et de décodage des disques audio et/ou vidéo numériques.

The invention also relates to an audio and video data processing apparatus comprising means for determining a plurality of acoustic information input signals each associated with a predetermined general restitution direction defined by a given point, characterized in that it further comprises a device for controlling a reproduction unit;

• said means for determining a plurality of input signals are formed by a unit for reading and decoding digital audio and / or video discs.

• la Fig.1 est une représentation d'un repère sphérique ;
• la Fig.2 est un schéma d'un système de restitution selon l'invention ;
• la Fig.3 est un organigramme du procédé de l'invention ;
• la Fig.4 est un schéma de moyens de calibrage mis en oeuvre dans le procédé de l'invention ;
• la Fig.5 est un organigramme détaillé de l'étape de calibrage ;
• la Fig.6 est une représentation simplifiée d'un capteur utilisé pour la mise en oeuvre de l'étape de calibrage ;
• la Fig.7 est un organigramme détaillé de l'étape de détermination de filtres d'adaptation ; et
• les Figs.8 et 9 sont des schémas de moyens de détermination de signaux de pilotage ; et
• la Fig.10 est un schéma d'un mode de réalisation d'un dispositif mettant en oeuvre le procédé de l'invention.

The invention will be better understood on reading the description which follows, given solely by way of example and with reference to the appended drawings, in which:

• the Fig.1 is a representation of a spherical landmark;
• the Fig.2 is a diagram of a rendering system according to the invention;
• the Fig.3 is a flowchart of the method of the invention;
• the Fig.4 is a scheme of calibration means implemented in the method of the invention;
• the Fig.5 is a detailed flowchart of the calibration step;
• the Fig.6 is a simplified representation of a sensor used for the implementation of the calibration step;
• the Fig.7 is a detailed flowchart of the step of determining adaptation filters; and
• the Figs.8 and 9 are diagrams of means for determining driving signals; and
• the Fig.10 is a diagram of an embodiment of a device implementing the method of the invention.

On the figure 1 a conventional spherical landmark has been shown to specify the coordinate system referred to in the text.

This reference is an orthonormal reference, of origin O and having three axes ( OX ), ( OY ) and ( OZ ).

In this reference, a noted position x is described by means of its spherical coordinates ( r , θ, φ,), where r denotes the distance from the origin O , θ the orientation in the vertical plane and φ the orientation in the horizontal plane.

In such a reference, an acoustic field is known if one defines at every point at each instant t the acoustic pressure noted p ( r , θ, φ, t ), whose time Fourier transform is noted P ( r , θ , φ, f ) where f is the frequency.

The invention is based on the use of a family of space-time functions for describing the characteristics of any acoustic field.

In the embodiment described, these functions are so-called spherical Fourier-Bessel functions of the first kind, hereinafter referred to as Fourier-Bessel functions.

In an empty zone of sound sources and empty of obstacles, the Fourier-Bessel functions are solutions of the wave equation and constitute a base that generates all acoustic fields produced by sound sources located outside this zone. .

Any three-dimensional acoustic field is thus expressed by a linear combination of the Fourier-Bessel functions, according to the expression of the inverse Fourier-Bessel transform which expresses: $$P\left(r,\theta ,\phi ,f\right)=4\pi {\displaystyle \underset{l=0}{\overset{\infty }{\Sigma }}}{\displaystyle \underset{m=-l}{\overset{l}{\Sigma }}}{P}_{l,m}\left(f\right)j^l{j}_l\left(\mathit{kr}\right){\mathrm{there}}_l^m\left(\theta ,\phi \right)$$

c est la célérité du son dans l'air (340 ms^-1), jr(kr) est la fonction de Bessel sphérique de première espèce d'ordre l définie par $j_l\left(x\right)=\sqrt{\frac{\pi }{2x}}{J}_{l+1/2}\left(x\right)$

où J_v (x) est la fonction de Bessel de première espèce d'ordre v, et ${y_l}^m\left(\theta ,\phi \right)$

est l'harmonique sphérique réelle d'ordre l et de terme m, avec m allant de -l à l, définie par : $$y_l^m\left(\theta ,\phi \right)=\{\begin{array}{ll}\frac{1}{\sqrt{\pi }}{P}_l^{\left|m\right|}\left(\cos \theta \right)\cos \left(m\phi \right)& \mathrm{pour}m>0\\ \frac{1}{\sqrt{2\pi }}{P}_l^0\left(\cos \theta \right)& \mathrm{pour}m=0\\ \frac{1}{\sqrt{\pi }}{P}_l^{\left|m\right|}\left(\cos \theta \right)\sin \left(m\phi \right)& \mathrm{pour}m<0\end{array}$$

In this equation, the terms P _{l, m} ( f ) are, by definition, the Fourier-Bessel coefficients of the field p ( r , θ, φ, t ), $k=\frac{2\mathit{\pi f}}{\mathrm{vs}}$

it is the celerity of the sound in the air (340 ms ^-1 ), jr ( kr ) is the spherical Bessel function of first kind of order l defined by $j_l\left(x\right)=\sqrt{\frac{\mathrm{<figure-callout\; id="2"\; label="\pi "\; filenames="imgf0002.png,imgf0005.png"\; state="\{\{state\}\}">\pi </figure-callout>}}{2x}}{J}_{l+1/2}\left(x\right)$

where J _v ( x ) is the Bessel function of the first kind of order v , and ${{\mathrm{there}}_l}^m\left(\theta ,\phi \right)$

is the real spherical harmonic of order l and of term m , with m ranging from - l to l , defined by: $${\mathrm{there}}_l^m\left(\theta ,\phi \right)=\{\begin{array}{ll}\frac{1}{\sqrt{\pi }}{P}_l^{\left|m\right|}\left(\cos \theta \right)\cos \left(m\phi \right)& \mathrm{for}m>0\\ \frac{1}{\sqrt{2\pi }}{P}_l^0\left(\cos \theta \right)& \mathrm{for}m=0\\ \frac{1}{\sqrt{\pi }}{P}_l^{\left|m\right|}\left(\cos \theta \right)\sin \left(m\phi \right)& \mathrm{for}m<0\end{array}$$

sont les fonctions de Legendre associées définies par : $$P_l^m\left(x\right)=\sqrt{\frac{2l+1}{2}}\sqrt{\frac{\left(l-m\right)!}{\left(l+m\right)!}}{\left(1-x^2\right)}^{m/2}\frac{{\mathrm{d}}^m}{\mathrm{d}{x}^m}{P}_l\left(x\right)$$

avec P_l (x) les polynômes de Legendre, définis par : $$P_l\left(x\right)=\frac{1}{2^{l}l!}\frac{{\mathrm{d}}^l}{\mathrm{d}{x}^l}{\left(x^2-1\right)}^l$$

In this equation, the ${P_l}^m\left(x\right)$

are the associated Legendre functions defined by: $$P_l^m\left(x\right)=\sqrt{\frac{2l+1}{2}}\sqrt{\frac{\left(l-m\right)!}{\left(l+m\right)!}}{\left(1-x^2\right)}^{m/2}\frac{{\mathrm{d}}^m}{\mathrm{d}{x}^m}{P}_l\left(x\right)$$

with P _l ( x ) the Legendre polynomials, defined by: $$P_l\left(x\right)=\frac{1}{2^{l}l!}\frac{{\mathrm{d}}^l}{\mathrm{d}{x}^l}{\left(x^2-1\right)}^l$$

The Fourier-Bessel coefficients are also expressed in the time domain by the coefficients p _{l, m} ( t ) corresponding to the inverse time Fourier transform of the coefficients P _{l, m} ( f ).

In a variant, the method of the invention uses function bases expressing themselves as linear combinations, possibly infinite, of Fourier-Bessel functions.

On the figure 2 schematically shows a restitution system in which the method of the invention is implemented.

This system comprises a decoder or adapter 1 driving a reproduction assembly 2 which comprises a plurality of elements 3 ₁ to 3 _N , such that loudspeakers, loudspeakers or any other sound source or group of sound sources, arranged in any manner in a listening place 4. The origin O of the reference mark is placed arbitrarily in listening area 4 called center 5 of the restitution set.

The set of spatial, acoustic and electrodynamic characteristics is considered as the intrinsic characteristics of the restitution ensemble 2.

The adapter 1 receives as input a signal SI of multichannel type comprising acoustic information to be reproduced and a definition signal SL comprising information representative of at least spatial characteristics of the reproduction unit 2 and in particular enabling the determination of representative parameters for at least one element 3 _n of the reproduction unit 2 to its position in three dimensions of space in relation to the given point 5.

At the end of the treatment corresponding to the method of the invention, the adapter 1 transmits to the attention of each of the elements or groups of elements 3 ₁ to 3 _N of the reproduction assembly 2, a signal sc ₁ to sc _N specific steering.

On the figure 3 schematically shows the main steps of the method according to the invention implemented with a restitution system such as that described with reference to the figure 2 .

This method comprises a step 10 of determining operating parameters, adapted to allow at least the determination of the spatial characteristics of the reproduction assembly 2.

Step 10 comprises a step 20 for entering the parameters and / or a calibration step 30 making it possible to determine and / or measure characteristics of the reproduction assembly 2.

In the embodiment described, step 10 also comprises a step 40 of determining description parameters of the predetermined general directions associated with the different channels of the multichannel input signal SI.

At the end of step 10, information relating to at least the different predetermined general directions associated with each of the input channels as well as to the position in the three dimensions of the space of each of the elements or groups of elements 3 _n of the restitution assembly 2, are determined.

This information is used during a step 50 of determining the adaptation filters making it possible to take into account the spatial characteristics of the reproduction unit 2 in order to define adaptation filters of the multichannel input signal to the spatial configuration specific of the refund set 2.

Advantageously, step 10 also makes it possible to determine acoustic characteristics for all or part of the elements 3 ₁ to 3 _N of the reproduction assembly 2.

In this case, the method comprises a step 60 for determining acoustic compensation filters for compensating for the influence of the specific acoustic characteristics of the elements 3 ₁ to 3 _N.

The filters defined during the steps 50 and advantageously 60, can thus be stored, so that the steps 10, 50 and 60 must be repeated only if the spatial configuration of the reproduction assembly 2 and / or the nature of the multichannel input signal.

The method then comprises a step 70 for determining the control signals sc ₁ to sc _N intended for the elements of the reproduction assembly 2, comprising a sub-step 80 for applying the adaptation filters determined during step 50 to the different channels c ₁ ( t ) to c _Q ( t ) forming the multichannel input signal SI and advantageously, a sub-step 90 for applying the acoustic compensation filters determined in step 60.

The signals sc ₁ to sc _N thus delivered are applied to the elements 3 ₁ to 3 _N of the reproduction unit 2, in order to restore the acoustic field represented by the multichannel input signal SI with an optimum adaptation to the spatial characteristics and advantageously acoustic, of the restitution assembly 2.

It therefore appears that, thanks to the implementation of the method of the invention, the characteristics of the acoustic field restored are substantially independent of the intrinsic characteristics of restitution of the restitution assembly 2 and in particular of its spatial configuration.

The main steps of the process of the invention will now be described in greater detail.

• des paramètres x _n exprimés dans le repère sphérique au moyen des coordonnées r_n , θ _n , et φ _n , et représentatifs de la position des éléments 3 _n par rapport au centre d'écoute 5 ; et/ou
• des paramètres H_n (f), représentatifs de la réponse en fréquence des éléments 3 _n .

During the step 20 of entering parameters an operator or a suitable memory system can specify all or part of the calculation parameters and in particular:

• parameters x _n expressed in the spherical coordinate system by means of the coordinates r _n , θ _n , and φ _n , and representative of the position of the elements 3 _n with respect to the listening center 5; and or
• parameters H _n ( f ), representative of the frequency response of the elements 3 _n .

This step 20 is implemented by means of an interface of conventional type such as a microcomputer or any other appropriate means.

The calibration step 30 and the means for implementing this step will now be described in more detail.

On the figure 4 the detail of calibration means is shown. They comprise a decomposition module 91, an impulse response determination module 92 and a calibration parameter determination module 93.

The calibration means are adapted to be connected to a sound acquisition device 100 such as a microphone or any other suitable device, and to be connected in turn to each element 3 _n of the reproduction assembly 2 in order to collect information about this element.

On the figure 5 the detail of an embodiment of the calibration step 30 implemented by the calibration means described above and making it possible to measure characteristics of the reproduction assembly 2 is shown.

In a sub-step 32, the calibration means emit a specific signal u _n ( t ) such as a pseudo-random sequence MLS (Maximum Length Sequence) to the attention of an element 3 _n . The acquisition device 100 receives, at a sub-step 34, the sound wave emitted by the element 3 _n in response to receiving the signal u _n (t) and transmits signals I ₁ cp (t) cp ₁ ( t ) representative of the wave received at the decomposition module 91.

In a substep 36, the decomposition module 91 decomposes the signals picked up by the acquisition device 100 into a finite number of Fourier-Bessel coefficients q _{l, m} ( t ).

$$Q_{1,-1}\left(f\right)=\frac{3}{8\sqrt{\pi }}\frac{c}{2\mathit{\pi jRf}}\left(C{P}_1\left(f\right)-C{P}_2\left(f\right)+C{P}_3\left(f\right)-C{P}_4\left(f\right)\right)$$

$$Q_{1,0}\left(f\right)=\frac{3}{8\sqrt{\pi }}\frac{c}{2\mathit{\pi jRf}}\left(C{P}_1\left(f\right)+C{P}_2\left(f\right)-C{P}_3\left(f\right)-C{P}_4\left(f\right)\right)$$

$$Q_{1,1}\left(f\right)=\frac{3}{8\sqrt{\pi }}\frac{c}{2\mathit{\pi jRf}}\left(C{P}_1\left(f\right)-C{P}_2\left(f\right)-C{P}_3\left(f\right)+C{P}_4\left(f\right)\right)$$

For example, the acquisition device 100 consists of 4 pressure sensors located at the 4 vertices of a tetrahedron of radius R as shown with reference to FIG. figure 6 . The signals of the 4 pressure sensors are then noted cp ₁ ( t ) to cp ₄ ( t ). The coefficients q _0.0 ( t ) to q _1.1 ( t ) representative of the sensed acoustic field are deduced from the signals cp ₁ ( t ) to cp ₄ ( t ) according to the following relations: $$Q_{0,0}\left(f\right)=\frac{1}{\sqrt{4\pi }}\frac{\mathrm{VS}{P}_1\left(f\right)+\mathrm{VS}{P}_2\left(f\right)+\mathrm{VS}{P}_3\left(f\right)+\mathrm{VS}{P}_4\left(f\right)}{4}$$

$${\mathrm{<figure-callout\; id="1"\; label="Q"\; filenames="imgf0005.png,imgf0006.png"\; state="\{\{state\}\}">Q</figure-callout>}}_{1,-1}\left(f\right)=\frac{3}{8\sqrt{\pi }}\frac{\mathrm{<figure-callout\; id="2"\; label="vs"\; filenames="imgf0002.png,imgf0005.png"\; state="\{\{state\}\}">vs</figure-callout>}}{2\mathit{\pi jRf}}\left(\mathrm{VS}{P}_1\left(f\right)-\mathrm{VS}{P}_2\left(f\right)+\mathrm{VS}{P}_3\left(f\right)-\mathrm{VS}{P}_4\left(\mathrm{<figure-callout\; id="1"\; label="f\; Q"\; filenames="imgf0005.png,imgf0006.png"\; state="\{\{state\}\}">f\; </figure-callout>},\right)\right)$$

$$Q_{}$$$${}_{1,0}\left(f\right)=\frac{3}{8\sqrt{\pi }}\frac{\mathrm{<figure-callout\; id="2"\; label="vs"\; filenames="imgf0002.png,imgf0005.png"\; state="\{\{state\}\}">vs</figure-callout>}}{2\mathit{\pi jRf}}\left(\mathrm{VS}{P}_1\left(f\right)+\mathrm{VS}{P}_2\left(f\right)-\mathrm{VS}{P}_3\left(f\right)-\mathrm{VS}{P}_4\left(\mathrm{<figure-callout\; id="1"\; label="f\; Q"\; filenames="imgf0005.png,imgf0006.png"\; state="\{\{state\}\}">f\; </figure-callout>},\right)\right)$$

$$Q_{}$$$${}_{1,1}\left(f\right)=\frac{3}{8\sqrt{\pi }}\frac{\mathrm{<figure-callout\; id="2"\; label="vs"\; filenames="imgf0002.png,imgf0005.png"\; state="\{\{state\}\}">vs</figure-callout>}}{2\mathit{\pi jRf}}\left(\mathrm{VS}{P}_1\left(f\right)-\mathrm{VS}{P}_2\left(f\right)-\mathrm{VS}{P}_3\left(f\right)+\mathrm{VS}{P}_4\left(f\right)\right)$$

In these relations CP ₁ ( f ) to CP ₄ ( f ) are the Fourier transforms from cp ₁ ( t ) to cp ₄ ( t ) and Q _0,0 ( f ) to Q _1,1 ( f ) are the transforms Fourier of q _0.0 ( t ) to q _1.1 ( t ).

When these coefficients are defined by the module 91, they are addressed to the response determination module 92.

In a substep 38, the response determination module 92 determines the impulse responses hp _{l, m} ( t ) which connect the Fourier-Bessel coefficients q _{l, m} ( t ) and the transmitted signal u _n ( t). ). The determination method depends on the specific signal emitted. The described embodiment uses a method adapted to MLS type signals, such as the correlation method.

The impulse response delivered by the response determination module 92 is addressed to the parameter determination module 93.

In a substep 39, the module 93 derives information on elements of the reproduction set.

In the embodiment described, the parameter determination module 93 determines the distance r _n between the element 3 _n and the center 5 from its response hp _0,0 ( t ) and the measurement of the time put by the it is propagated from the element 3 _n to the acquisition device 100, by delay estimation methods on the response hp _0,0 ( t ).

The direction ( θ _n , φ _n ) of the element 3 _n is deduced by calculating the maximum of the inverse spherical Fourier transform applied to the responses hp _0,0 ( t ) to hp _1,1 ( t ) taken at the time t where hp _0,0 (t) has a maximum. Advantageously, the coordinates θ _n and φ _n are estimated over several instants, chosen preferably around the moment when hp _0,0 ( t ) has a maximum. The final determination of the coordinates θ _n and φ _n is obtained by means of averaging techniques between the different estimations.

Thus, in the embodiment described, the acquisition device 100 is able to unambiguously encode the orientation of a source in space.

As a variant, the coordinates θ _n and φ _n are estimated from other responses among the hp _{l, m} ( t ) available or are estimated in the frequency domain from the responses HP _{/ , m} ( f ), corresponding to the transforms Fourier responses hp _{/ , m} ( t ).

Thus, step 30 makes it possible to determine the parameters r _n , θ _n and φ _n .

In the embodiment described, the module 93 also delivers the transfer function H _n ( f ) of each element 3 _n , from the responses hp _{/ , m} ( t ) from the response determination module 92.

A first solution consists in constructing the response hp ' _0,0 ( t ) corresponding to the selection of the part of the response hp _0,0 ( t ) which comprises a non-zero signal and devoid of the reflections introduced by the listening site. 4. The frequency response H _n ( f ) is derived by Fourier transform from the previously freened response hp ' _0,0 ( t ). The window can be chosen from conventional smoothing windows, such as for example rectangular, Hamming, Hanning, and Blackman.

A second more complex solution consists in applying a smoothing on the module and advantageously on the phase of the frequency response HP _0.0 ( f ) obtained by Fourier transform of the response hp _0.0 ( t ). For each frequency f , the smoothing is obtained by convolution of the response HP _0.0 ( f ) by a window centered on f . This convolution corresponds to an averaging of the response HP _0.0 ( f ) around the frequency f . The window can be chosen from conventional windows, for example rectangular, triangles and Hamming. Advantageously, the width of the window varies with the frequency. For example, the window width can be proportional to the frequency f which is applied to the smoothing. Compared to a fixed window, a variable window with the frequency makes it possible to at least partially eliminate the room effect in the high frequencies while avoiding a truncation effect of the response HP _0.0 ( f ) in the low frequencies .

Sub-steps 32 to 39 are repeated for all the elements 3 ₁ to 3 _N of the reproduction assembly 2.

As a variant, the calibration means comprise other means for acquiring information relating to the elements 3 ₁ to 3 _N , such as laser position measuring means, signal processing means using signal processing techniques. lane formation or any other appropriate means.

The means implementing the calibration step 30 consist for example of an electronic card or a computer program or any other appropriate means.

Step 40 thus makes it possible, as has been said above, to determine parameters describing the format of the multichannel input signal and in particular the general predetermined directions associated with each channel.

This step 40 may correspond to an operator selecting a format from a list of formats each associated with stored parameters, and may also correspond to an automatic format detection performed on the input multichannel signal. Alternatively, the method is adapted for a single given multichannel signal format. In yet another embodiment, step 40 allows a user to specify his own format by manually entering the parameters describing the directions associated with each channel.

It appears that the steps 20, 30 and 40 forming the parameter determination step 10 allow at least the determination of positioning parameters in the space of the elements 3 _n of the reproduction assembly 2 and the format of the multichannel signal. SI .

On the figure 7 a detailed flowchart of step 50 of determining the matching filters is shown.

This step comprises a plurality of sub-steps for calculating and determining matrices representative of the previously determined parameters.

• le plus petit angle α _min formé par une paire d'éléments de l'ensemble de restitution 2 est calculé automatiquement au moyen d'une relation trigonométrique, telle que par exemple : $$a_{n1*,n2*}=\mathrm{acos}\left(\sin {\theta }_{\mathrm{n}1}\sin {\theta }_{n2}\cos \left({\phi }_{n1}-{\phi }_{n2}\right)+\cos {\theta }_{n1}\cos {\theta }_{n2}\right)$$
  
  $$a_{\mathit{min}}=\min \left({\mathit{a}}_{\mathit{n}\mathit{1},\mathit{n}\mathit{2}}\right)$$
  
  parmi l'ensemble des couples (n1, n2) tels que n1≠n2; et
• ensuite, l'ordre maximum L est déterminé automatiquement comme étant le plus grand entier respectant la relation suivant : $$L<\mathrm{\pi }/a_{\mathit{min}}\mathrm{.}$$
  

Thus, during a substep 51, a parameter L , called limit order representative of the spatial accuracy desired during the step 50 of determining the adaptation filters, is determined for example as follows:

• the smallest angle α _min formed by a pair of elements of the restitution set 2 is automatically calculated by means of a trigonometric relation, such as for example: $${\mathrm{at}}_{\mathrm{not}1*,\mathrm{not}2*}=\mathrm{acos}\left(\sin {\theta }_{\mathrm{not}1}\sin {\theta }_{\mathrm{not}2}\cos \left({\phi }_{\mathrm{not}1}-{\phi }_{\mathrm{not}2}\right)+\cos {\theta }_{\mathrm{not}1}\cos {\theta }_{\mathrm{not}2}\right)$$
  
  $${\mathrm{at}}_{\mathit{min}}=\min \left({\mathit{at}}_{\mathit{not}\mathit{1},\mathit{not}\mathit{2}}\right)$$
  
  from the set of pairs ( n1 , n2 ) such that n1 ≠ n2 ; and
• then, the maximum order L is automatically determined as being the largest integer respecting the following relation: $$\mathrm{The}<\mathrm{\pi }/{\mathrm{at}}_{\mathit{min}}\mathrm{.}$$
  

The step 50 of determining adaptation filters then comprises a substep 52 of determining a matrix W of the acoustic field weighting. This matrix W corresponds to a spatial window W ( r , f ) representative of the distribution in space of the desired precision during the reconstruction of the field. Such a window makes it possible to specify the size and the shape of the zone where the field must be correctly reconstructed. For example, it may be a ball centered on the center 5 of the rendering assembly. In the embodiment described, the spatial window and the matrix W are independent of the frequency.

W is a diagonal matrix of size ( L +1) ² containing weighting coefficients W _l and in which each coefficient W _l is 2 1 + 1 times later on the diagonal. The matrix W thus has the following form: $$\mathit{W}=\left[\begin{array}{cccccccc}{W}_0& 0& \cdots & \cdots & \cdots & \cdots & \cdots & 0\\ 0& {\mathrm{<figure-callout\; id="1"\; label="W"\; filenames="imgf0005.png,imgf0006.png"\; state="\{\{state\}\}">W</figure-callout>}}_1& \ddots & & & & & ⋮\\ ⋮& \ddots & {\mathrm{<figure-callout\; id="1"\; label="W"\; filenames="imgf0005.png,imgf0006.png"\; state="\{\{state\}\}">W</figure-callout>}}_1& \ddots & & & & ⋮\\ ⋮& & \ddots & {\mathrm{<figure-callout\; id="1"\; label="W"\; filenames="imgf0005.png,imgf0006.png"\; state="\{\{state\}\}">W</figure-callout>}}_1& \ddots & & & ⋮\\ ⋮& & & \ddots & \ddots & \ddots & & ⋮\\ ⋮& & & & \ddots & W_{\mathrm{The}}& \ddots & ⋮\\ ⋮& & & & & \ddots & \ddots & 0\\ 0& \cdots & \cdots & \cdots & \cdots & \cdots & 0& W_{\mathrm{The}}\end{array}\right]$$

In the embodiment described, the values taken by the coefficients W ₁ are the values of a function such as a Hamming window of size of 2 L +1 evaluated at 1 , so that the parameter W ₁ is determined for l ranging from 0 to L.

Step 50 then comprises a substep 53 for determining a matrix M representative of the radiation of the reproduction assembly, in particular from the position parameters. x _n . The radiation matrix M makes it possible to deduce Fourier-Bessel coefficients representing the acoustic field emitted by each element 3 _n from the reproduction unit as a function of the signal it receives.

M is a matrix of size ( L +1) ² on N , consisting of elements M _{l, m, n} , the indices l , m denoting the line l ² + l + m and n denoting the column n . The matrix M thus has the following form: $$\left[\begin{array}{cccc}{M}_{0,0,1}& {\mathrm{<figure-callout\; id="2"\; label="M"\; filenames="imgf0002.png,imgf0005.png"\; state="\{\{state\}\}">M</figure-callout>}}_{0,0,2}& \cdots \cdots & M_{0,0,\mathrm{<figure-callout\; id="1"\; label="NOT\; M"\; filenames="imgf0005.png,imgf0006.png"\; state="\{\{state\}\}">NOT\; </figure-callout>}}& \\ M_{}{}_{1,-1,1}& {\mathrm{<figure-callout\; id="1"\; label="M"\; filenames="imgf0005.png,imgf0006.png"\; state="\{\{state\}\}">M</figure-callout>}}_{1,-1,2}& \cdots \cdots & {\mathrm{<figure-callout\; id="1"\; label="M"\; filenames="imgf0005.png,imgf0006.png"\; state="\{\{state\}\}">M</figure-callout>}}_{1,-1,\mathrm{<figure-callout\; id="1"\; label="NOT\; M"\; filenames="imgf0005.png,imgf0006.png"\; state="\{\{state\}\}">NOT\; </figure-callout>}}& \\ M_{}{}_{1,0,1}& {\mathrm{<figure-callout\; id="1"\; label="M"\; filenames="imgf0005.png,imgf0006.png"\; state="\{\{state\}\}"><figure-callout\; id="2"\; label="M"\; filenames="imgf0002.png,imgf0005.png"\; state="\{\{state\}\}">M</figure-callout></figure-callout>}}_{1,0,2}& \cdots \cdots & {\mathrm{<figure-callout\; id="1"\; label="M"\; filenames="imgf0005.png,imgf0006.png"\; state="\{\{state\}\}">M</figure-callout>}}_{1,0,\mathrm{<figure-callout\; id="1"\; label="NOT\; M"\; filenames="imgf0005.png,imgf0006.png"\; state="\{\{state\}\}"><figure-callout\; id="1"\; label="NOT\; M"\; filenames="imgf0005.png,imgf0006.png"\; state="\{\{state\}\}">NOT\; </figure-callout></figure-callout>}}& \\ M_{}{}_{}{}_{1,1,1}& {\mathrm{<figure-callout\; id="1"\; label="M"\; filenames="imgf0005.png,imgf0006.png"\; state="\{\{state\}\}"><figure-callout\; id="1"\; label="M"\; filenames="imgf0005.png,imgf0006.png"\; state="\{\{state\}\}"><figure-callout\; id="2"\; label="M"\; filenames="imgf0002.png,imgf0005.png"\; state="\{\{state\}\}">M</figure-callout></figure-callout></figure-callout>}}_{1,1,2}& \cdots \cdots & {\mathrm{<figure-callout\; id="1"\; label="M"\; filenames="imgf0005.png,imgf0006.png"\; state="\{\{state\}\}"><figure-callout\; id="1"\; label="M"\; filenames="imgf0005.png,imgf0006.png"\; state="\{\{state\}\}">M</figure-callout></figure-callout>}}_{1,1,\mathrm{NOT}}\\ ⋮& ⋮& & ⋮\\ M_{\mathrm{The},-\mathrm{The},1}& M_{\mathrm{The},-\mathrm{The},2}& \cdots \cdots & M_{\mathrm{The},-\mathrm{The},\mathrm{NOT}}\\ ⋮& ⋮& & ⋮\\ M_{\mathrm{The},0,1}& M_{\mathrm{The},0,2}& \cdots \cdots & M_{\mathrm{The},0,\mathrm{NOT}}\\ ⋮& ⋮& & ⋮\\ M_{\mathrm{The},\mathrm{The},1}& M_{\mathrm{The},\mathrm{The},2}& \cdots \cdots & M_{\mathrm{The},\mathrm{The},\mathrm{NOT}}\end{array}\right]$$

In the embodiment described, the elements M _{l, m, n are} obtained from a plane wave radiation model, so that: $$M_{l,m,\mathrm{not}}={\mathrm{there}}_l^m\left({\theta }_{\mathrm{not}},{\phi }_{\mathrm{not}}\right)$$

The matrix M thus defined is representative of the radiation of the reproduction unit. In particular, M is representative of the spatial configuration of the restitution set.

Sub-steps 51 to 53 may be executed sequentially or simultaneously.

The step 50 of determining adaptation filters then comprises a substep 54 of taking into account all the parameters of the rendering system 2 determined previously, in order to deliver a decoding matrix D representative of so-called reconstruction filters. .

Indeed, the elements D _{n, l, m} ( f ) of the matrix D correspond to reconstruction filters which, applied to the Fourrier-Bessel coefficients P _{l, m} ( f ) of a known acoustic field, make it possible to determine the control signals of a reproduction unit for reproducing this acoustic field.

The decoding matrix D is therefore the inverse of the radiation matrix M.

The matrix D is obtained from the matrix M by means of inversion methods under constraints involving additional optimization parameters.

In the embodiment described, step 50 is adapted to perform an optimization thanks to the weighting matrix of the acoustic field W which In particular, it makes it possible to reduce the spatial distortion in the reproduced acoustic field.

dans laquelle M ^T est la matrice transposée conjuguée de M .This matrix D is delivered in particular from the matrix M , according to the following expression: $$\mathit{D}={\left({\mathit{M}}^{\mathrm{T}}\mathit{WM}\right)}^{-1}{\mathit{M}}^{\mathrm{T}}\mathit{W}$$

where M ^T is the conjugated transposed matrix of M.

In the embodiment described, the matrices M and W are independent of the frequency, so that the matrix D is also independent of the frequency. It consists of elements denoted D _{n, l, m} organized as follows: $$\left[\begin{array}{cccccccccc}{\mathrm{<figure-callout\; id="1"\; label="D"\; filenames="imgf0005.png,imgf0006.png"\; state="\{\{state\}\}">D</figure-callout>}}_{1,0,0}& {\mathrm{<figure-callout\; id="1"\; label="D"\; filenames="imgf0005.png,imgf0006.png"\; state="\{\{state\}\}"><figure-callout\; id="1"\; label="D"\; filenames="imgf0005.png,imgf0006.png"\; state="\{\{state\}\}">D</figure-callout></figure-callout>}}_{1,1,-1}& {\mathrm{<figure-callout\; id="1"\; label="D"\; filenames="imgf0005.png,imgf0006.png"\; state="\{\{state\}\}"><figure-callout\; id="1"\; label="D"\; filenames="imgf0005.png,imgf0006.png"\; state="\{\{state\}\}">D</figure-callout></figure-callout>}}_{1,1,0}& {\mathrm{<figure-callout\; id="1"\; label="D"\; filenames="imgf0005.png,imgf0006.png"\; state="\{\{state\}\}"><figure-callout\; id="1"\; label="D"\; filenames="imgf0005.png,imgf0006.png"\; state="\{\{state\}\}"><figure-callout\; id="1"\; label="D"\; filenames="imgf0005.png,imgf0006.png"\; state="\{\{state\}\}">D</figure-callout></figure-callout></figure-callout>}}_{1,1,1}& \cdots & {\mathrm{<figure-callout\; id="1"\; label="D"\; filenames="imgf0005.png,imgf0006.png"\; state="\{\{state\}\}">D</figure-callout>}}_{1,\mathrm{The},-\mathrm{The}}& <figure-callout\; id="1"\; label="\cdots \; D"\; filenames="imgf0005.png,imgf0006.png"\; state="\{\{state\}\}">\cdots \; </figure-callout>& D_{}{}_{1,\mathrm{The},0}& \cdots & {\mathrm{<figure-callout\; id="1"\; label="D"\; filenames="imgf0005.png,imgf0006.png"\; state="\{\{state\}\}">D</figure-callout>}}_{1,\mathrm{The},\mathrm{The}}\\ {\mathrm{<figure-callout\; id="2"\; label="D"\; filenames="imgf0002.png,imgf0005.png"\; state="\{\{state\}\}">D</figure-callout>}}_{2,0,0}& {\mathrm{<figure-callout\; id="2"\; label="D"\; filenames="imgf0002.png,imgf0005.png"\; state="\{\{state\}\}"><figure-callout\; id="1"\; label="D"\; filenames="imgf0005.png,imgf0006.png"\; state="\{\{state\}\}">D</figure-callout></figure-callout>}}_{2,1,-1}& {\mathrm{<figure-callout\; id="2"\; label="D"\; filenames="imgf0002.png,imgf0005.png"\; state="\{\{state\}\}"><figure-callout\; id="1"\; label="D"\; filenames="imgf0005.png,imgf0006.png"\; state="\{\{state\}\}">D</figure-callout></figure-callout>}}_{2,1,0}& {\mathrm{<figure-callout\; id="2"\; label="D"\; filenames="imgf0002.png,imgf0005.png"\; state="\{\{state\}\}"><figure-callout\; id="1"\; label="D"\; filenames="imgf0005.png,imgf0006.png"\; state="\{\{state\}\}"><figure-callout\; id="1"\; label="D"\; filenames="imgf0005.png,imgf0006.png"\; state="\{\{state\}\}">D</figure-callout></figure-callout></figure-callout>}}_{2,1,1}& \cdots & {\mathrm{<figure-callout\; id="2"\; label="D"\; filenames="imgf0002.png,imgf0005.png"\; state="\{\{state\}\}">D</figure-callout>}}_{2,\mathrm{The},-\mathrm{The}}& <figure-callout\; id="2"\; label="\cdots \; D"\; filenames="imgf0002.png,imgf0005.png"\; state="\{\{state\}\}">\cdots \; </figure-callout>& D_{}{}_{2,\mathrm{The},0}& \cdots & {\mathrm{<figure-callout\; id="2"\; label="D"\; filenames="imgf0002.png,imgf0005.png"\; state="\{\{state\}\}">D</figure-callout>}}_{2,\mathrm{The},\mathrm{The}}\\ ⋮& ⋮& ⋮& ⋮& & ⋮& & ⋮& & ⋮\\ D_{\mathrm{NOT},0,0}& D_{\mathrm{NOT},1,-1}& D_{\mathrm{NOT},1,0}& D_{\mathrm{NOT},1,1}& \cdots & D_{\mathrm{NOT},\mathrm{The},-\mathrm{The}}& \cdots & D_{\mathrm{NOT},\mathrm{The},0}& \cdots & D_{\mathrm{NOT},\mathrm{The},\mathrm{The}}\end{array}\right]$$

Step 54 thus makes it possible to deliver the matrix D representative of so-called reconstruction filters and enabling the reconstruction of an acoustic field from any configuration of the reproduction assembly. Thanks to this matrix, the method of the invention makes it possible to take into account the configuration of the reproduction assembly 2 and in particular to compensate the alterations of the acoustic field due to its specific spatial configuration.

As a variant, the parameters relating to the reproduction assembly 2 may be variable depending on the frequency.

For example, in such an embodiment, each element D _{n, 1, m} ( f ) of the matrix D can be determined by associating with each of the N control signals a directivity function D _n ( θ , φ , f ) specifying at each frequency f amplitude, and advantageously the desired phase on the _n sc drive signal in the case of a plane wave in the direction (θ, φ).

By directivity function D _n (θ, φ, f ) is meant a function that associates a real or complex value, possibly depending on the frequency or a frequency range, with each direction of the space.

In the embodiment described, the directivity functions are independent of the frequency and denoted D _n (θ, φ).

avec

These directivity functions D _n (θ, φ) can be determined by specifying that certain physical quantities between an ideal field and the same field reproduced by the restitution set comply with predetermined laws. For example, these quantities may be the pressure at the center and the orientation of the velocity vector. In some cases, it is desired that only 3 driving signals be active to reproduce a plane wave. The active piloting signals, denoted sc _{n 1} to sc _{n 3} , are those that supply the restitution elements whose directions are closest to the direction (θ, φ) of the plane wave. The active rendering elements, denoted 3 _{n 1} to 3 _{n 3} , form a triangle containing the direction (θ, φ) of the plane wave. In this case, the values of the directivities D _n1 (θ, φ) to D _{n 3} (θ, φ) associated with the 3 active elements 3 _{n 1} to 3 _{n 3} are given by:

with

In this relation, α corresponds to the vector containing [ D _n1 (θ, φ) ... D _n3 (θ, φ)] and the directions ( _θn1 , _φn2 ), ( _θn2 , _φn2 ) and ( _θn3 , φ _n3 ) correspond respectively to the directions of the elements 3 _{n 1} , 3 _{n 2} and 3 _{n 3} .

It is considered that the values of the directivities D _n (θ, φ) corresponding to the non-active restitution elements are zero.

The above relationship is repeated for K directions (θ _k, φ _k) of different plane waves. Thus, each of the directivity functions D _n (θ, φ) is provided in the form of a list of K samples. Each sample is provided in the form of a pair {((θ _k , φ _k ), D _n (θ _k , φ _k ))} where (θ _k , φ _k ) is the direction of the sample k and where D _n (θ _k , φ _k ) is the value of the directivity function associated with the control signal sc _n for the direction ((θ _k , φ _k ).

For each frequency f , the coefficients D _{n , l , m} ( f ) of each directivity function are deduced from the samples {(((θ _k , φ _k ), D _n (θ _k , φ _k ))}. are obtained by inversion of the angular sampling process which makes it possible to deduce the samples from the list {((θ _k , φ _k ), D _n (θ _k , φ _k ))} from a directivity function provided under This inversion can take different forms to control the interpolation between samples.

In other embodiments, the directivity functions are directly provided in the form of Fourrier-Bessel type D _{n, / , m} ( f ) coefficients.

The coefficients D _{n , /, m} ( f ) thus determined are used to form the matrix D.

Step 50 then comprises a step 55 of determining an ideal multichannel radiation matrix S representative of the predetermined general directions associated with each channel of the multichannel input signal SI .

The S matrix is representative of the radiation a set of ideal restitution, i.e. full conformity with the predetermined branch of the multichannel format. Each element S _{l , m , q} ( f ) of the matrix S makes it possible to deduce the Fourier-Bessel coefficients P _{l , m} ( f ) from the acoustic field ideally restored by each channel c _q ( t ).

The matrix S is determined by associating with each input channel c _q ( t ) and advantageously for each frequency f , a directivity figure representative of a distribution of sources supposed to emit the signal of the channel c _q ( t ).

The distribution of sources is given in the form of spherical harmonics coefficients S _{l , m , q} ( f ). The coefficients S _{/, m , q} ( f ) are arranged in the matrix S of size ( L +1) ² on Q , where Q is the number of channels.

associée au canal c_q (t) dans le format multicanal d'entrée. Les coefficients S _l,m,q (f) sont alors indépendants de la fréquence. Ils sont notés S _/,m,q et s'obtiennent par la relation : $$S_{l,m,q}\left(f\right)=y_l^m\left({\theta }_q,{\phi }_q\right)$$

In the embodiment described, the shaping step associates with each channel c _q ( t ) a plane wave source oriented in the direction (θ _q , φ _q ) corresponding to the direction $\left({\theta }_q^{\mathrm{vs}},{\phi }_q^{\mathrm{vs}}\right)$

associated with the channel c _q ( t ) in the multichannel input format. The coefficients S _{l , m , q} ( f ) are then independent of the frequency. They are noted S _{/, m , q} and are obtained by the relation: $$S_{l,m,q}\left(f\right)={\mathrm{there}}_l^m\left({\theta }_q,{\phi }_q\right)$$

In other embodiments, the ideal radiation matrix S combines a discrete distribution of plane wave sources with certain channels to simulate the effect of a speaker belt. In this case, the coefficients S _{l , m , q} are obtained by summation of the contributions of each of the elementary sources.

In still other embodiments, the ideal radiation matrix S associates certain channels c _q ( t ) with a continuous distribution of plane wave sources described by a directivity function S _q (θ, φ). In this case, the coefficients S _{l , m , q} of the matrix S are obtained directly by Spherical Fourier transform of the directivity function S _q ( θ, φ) . In these embodiments, the matrix S is independent of frequency.

In other more complex embodiments the matrix S associates with certain channels, a distribution of sources producing a diffuse field. In this case, the matrix S varies with the frequency. These embodiments are adapted to multichannel formats which consider differently the front and rear channels. For example, in applications intended for rendering in cinema theaters, the rear channels are often intended to recreate a diffuse atmosphere.

In other embodiments, the matrix S associates sound sources whose response is not flat to certain channels. For example, in the case where the multichannel format associates with the channel c _q ( t ) a plane wave source of frequency response H ^{( q )} ( f ), the S _{/, m , q} ( f ) vary with the frequency and are obtained by the relation: $$S_{l,m,q}\left(f\right)={\mathrm{there}}_l^m\left({\theta }_q,{\phi }_q\right)H^{\left(q\right)}\left(f\right)$$

If the multichannel format associates with some channels a superposition of the aforementioned source distribution types, the coefficients S _{l , m , q} ( f ) of the radiation matrix are obtained by summation of the coefficients associated with each type of distribution of source.

Finally, step 50 comprises a substep 56 for determining a spatial adaptation matrix A corresponding to the adaptation filters to be applied to the multichannel input signal in order to obtain an optimum restitution taking into account the spatial configuration of the input signal. restitution set 2.

The spatial adaptation matrix A is obtained from the S- shaping and D- decoding matrices by means of the relation: $$\mathit{AT}=\mathit{DS}$$

The adaptation matrix A makes it possible to generate signals sa ₁ ( t ) to its _N ( t ) adapted to the spatial configuration of the reproduction set from the channels c ₁ ( t ) to c _Q ( t ). Each element A _{n, q} ( f ) is a filter specifying the contribution of the channel c _q ( t ) to the adapted signal sa _n ( t ). Thanks to the adaptation matrix A , the method of the invention allows the optimum restitution of the acoustic field described by the multichannel signal by a restitution set of any spatial configuration.

In the embodiment described, the matrices D and S are independent of the frequency and the matrix A also. In this case, the elements of the matrix A are constants denoted A _{n, q} and each of the adapted signals sa ₁ ( t ). its _N ( t ) is obtained by simple linear combinations of the input channels c ₁ ( t ) to c _Q ( t ), where appropriate followed by delay as will be described below.

The filters represented by the matrix A can be implemented in different forms of filters and / or filtering methods. In the case where the filters used are parameterized directly with frequency responses, the coefficients A _{n, q} ( f ) are directly delivered by step 50. Advantageously, the step 50 of determining adaptation filters comprises a sub-step. step 57 conversion to determine the filter parameters for other filtering methods.

• des réponses impulsionnelles finies a _n,q (t) calculées par transformée de Fourier temporelle inverse de A _n,q (f), chaque réponse impulsionnelle a _n,q (t) est échantillonnée puis tronquée à une longueur propre à chaque réponse ; ou
• des coefficients de filtres récursifs à réponses impulsionnelles infinies calculées à partir des A _n,q (f) avec des méthodes d'adaptation.

For example, the filter combinations A _{n , q} ( f ) are converted to:

• finite impulse responses a _{n , q} ( t ) computed by inverse time Fourier transform of A _{n , q} ( f ), each impulse response a _{n , q} ( t ) is sampled and then truncated to a length specific to each response; or
• recursive filter coefficients with infinite impulse responses computed from A _{n , q} ( f ) with adaptation methods.

At the end of step 50 the parameters of the adaptation filters A _{n , q} ( f ) are provided.

Step 60 thus makes it possible, as has been said above, to determine the filters for compensating the acoustic characteristics of the elements of the reproduction assembly 2 in the case where parameters relating to these acoustic characteristics such as the frequency responses H _n ( f ), are determined during step 10 of determining the parameters.

à partir des réponses en fréquence H_n (f), peut être réalisée de manière classique en appliquant des méthodes d'inversion de filtres, comme par exemple l'inversion directe, les méthodes de déconvolution, les méthodes Wiener ou d'autres.The determination of such filters, noted $H_{\mathrm{not}}^{\left(I\right)}\left(f\right),$

from the frequency responses H _n ( f ), can be carried out conventionally by applying filter inversion methods, such as direct inversion, deconvolution methods, Wiener or other methods.

Depending on the embodiments, the compensation relates only to the amplitude of the response or else to the amplitude and the phase.

This step 60 makes it possible to determine a compensation filter for each element 3 _n of the reproduction assembly 2 as a function of its specific acoustic characteristics.

sont directement appliquées. Avantageusement, l'étape 60 de détermination de filtres de compensation comprend une sous-étape de conversion afin de déterminer les paramètres des filtres pour d'autres méthodes de filtrage.As before, these filters can be implemented in different forms of filters and / or filtering methods. In case the used filters are parameterized directly with frequency responses, the responses $H_{\mathrm{not}}^{\left(I\right)}\left(f\right)$

are directly applied. Advantageously, the step 60 of determining compensation filters comprises a conversion sub-step in order to determine the parameters of the filters for other filtering methods.

sont converties en :

• des réponses impulsionnelles finies $h_n^{\left(I\right)}\left(t\right)$
  
  calculées par transformée de Fourier temporelle inverse de $H_n^{\left(I\right)}\left(f\right),$
  
  chaque réponse impulsionnelle $h_n^{\left(I\right)}\left(t\right)$
  
  est échantillonnée puis tronquée à une longueur propre à chaque réponse ; ou
• des coefficients de filtres récursifs à réponses impulsionnelles infinies calculées à partir des $H_n^{\left(I\right)}\left(f\right)$
  
  avec des méthodes d'adaptation.

For example, filtering combinations $H_{\mathrm{not}}^{\left(I\right)}\left(f\right)$

are converted to:

• finite impulse responses $h_{\mathrm{not}}^{\left(I\right)}\left(t\right)$
  
  calculated by inverse time Fourier transform of $H_{\mathrm{not}}^{\left(I\right)}\left(f\right),$
  
  each impulse response $h_{\mathrm{not}}^{\left(I\right)}\left(t\right)$
  
  is sampled and truncated to a specific length for each response; or
• infinite impulse response recursive filter coefficients calculated from the $H_{\mathrm{not}}^{\left(I\right)}\left(f\right)$
  
  with methods of adaptation.

sont fournis.At the end of step 60, the parameters of the compensation filters $H_{\mathrm{not}}^{\left(I\right)}\left(f\right)$

are provided.

We will now describe in more detail step 70 of determining driving signals.

This step 70 comprises a sub-step 80 for applying the adaptation filters represented by the matrix A to the multichannel input signal SI corresponding to the acoustic field to be restored. As has been said previously, the adaptation filters A _{n , q} ( f ) integrate the characteristic parameters of the reproduction set 2.

At substep 80, appropriate signals its ₁ (t) at its _N (t) are obtained by the application of adaptive filters A _{n, q} (f) to the channels c ₁ (t) _Q c ( t ) the signal SI .

In the embodiment described, the adaptation matrix A is independent of the frequency and the adaptation coefficients A _{n, q} are applied as follows: $$v_{\mathrm{not}}\left(f\right)={\displaystyle \underset{q=1}{\overset{Q}{\Sigma }}}{\mathrm{vs}}_q\left(t\right){\mathrm{AT}}_{\mathrm{not},q}$$

The adaptation is continued by an adjustment of the gains and the application of delays in order to align the wave fronts of the elements 3 ₁ to 3 _N of the reproduction assembly 2 temporally with respect to the element furthest away. The signals adapted its ₁ ( t ) to its _N ( t ) are deduced from the signals v ₁ ( t ) to v _N ( t ) according to the expression: $$s{\mathrm{at}}_{\mathrm{not}}\left(t\right)=r_{\mathrm{not}}{v}_{\mathrm{not}}\left(t-\frac{\max \left(r_{\mathrm{not}}\right)-r_{\mathrm{not}}}{\mathrm{vs}}\right)$$

avec C_q (f) la transformée de Fourier temporelle du canal c_q (t) et V_n (f) défini par: $$V_n\left(f\right)=\frac{{\mathit{SA}}_n\left(f\right)}{r_n}{e}^{-2{\mathit{\pi jr}}_{n}f/c}$$

où SA_n (f) est la transformée de Fourier temporelle de sa_n (t).In other embodiments, the adaptation matrix A varies with the frequency and the adaptation filters A _{n , q} ( f ) are applied as follows: $$V_{\mathrm{not}}\left(f\right)={\displaystyle \underset{q=1}{\overset{Q}{\Sigma }}}{\mathrm{VS}}_q\left(f\right){\mathrm{AT}}_{\mathrm{not},q}\left(f\right)$$

with C _q ( f ) the time Fourier transform of the channel c _q ( t ) and V _n ( f ) defined by: $$V_{\mathrm{not}}\left(f\right)=\frac{{\mathit{HER}}_{\mathrm{not}}\left(f\right)}{r_{\mathrm{not}}}{e}^{-2{\mathit{\pi jr}}_{\mathrm{not}}f/\mathrm{vs}}$$

where SA _n ( f ) is the temporal Fourier transform of its _n ( t ).

• les paramètres sont directement les réponses en fréquence A _n,q (f), et le filtrage est effectué dans le domaine fréquentiel, par exemple, à l'aide des techniques usuelles de convolution par blocs ;
• les paramètres sont directement les réponses impulsionnelles finies a _n,q (t), et le filtrage est effectué dans le domaine temporel par convolution ; ou
• les paramètres sont les coefficients de filtres récursifs à réponses impulsionnelles infinies, et le filtrage est effectué dans le domaine temporel au moyen des relations de récurrence.

According to the form of the parameters of the adaptation filters A _{n , q} ( f ), each filtering of the channels c _q ( t ) by the adaptation filters A _{n , q} ( f ) can be carried out according to conventional filtering methods, such as for example:

• the parameters are directly the frequency responses A _{n , q} ( f ), and the filtering is performed in the frequency domain, for example, using standard block convolution techniques;
• the parameters are directly the finite impulse responses to _{n , q} ( t ), and the filtering is done in the time domain by convolution; or
• the parameters are the recursive filter coefficients with infinite impulse responses, and the filtering is done in the time domain by means of the recurrence relations.

The substep 80 ends with a gain adjustment and the application of delays in order to temporally align the wave fronts of the elements 3 ₁ to 3 _N of the restitution assembly 2 with respect to the element furthest away. . The signals adapted its ₁ ( t ) to its _N ( t ) are deduced from the signals v ₁ ( t ) to v _N ( t ) according to the expression: $$s{\mathrm{vs}}_{\mathrm{not}}\left(t\right)=r_{\mathrm{not}}{v}_{\mathrm{not}}\left(t-\frac{\max \left(r_{\mathrm{not}}\right)-r_{\mathrm{not}}}{\mathrm{vs}}\right)$$

On the figure 8 the filtering structure corresponding to the sub-step 80 for applying the spatial adaptation filters as described above is represented.

est appliqué au signal adapté sa_n (t) correspondant afin d'obtenir le signal de pilotage sc_n (t) de l'élément 3_n , selon la relation : $${\mathit{SC}}_n\left(f\right)={\mathit{SA}}_n\left(f\right)H_n^{\left(I\right)}\left(f\right)$$

où SC_n (f) est la transformée de Fourier temporelle de sc_n (t) et où SA_n (f) est la transformée de Fourier temporelle de sa_n (t).Advantageously, step 70 comprises a sub-step 90 for compensating for the acoustic characteristics of the reproduction assembly. Each compensation filter $H_{\mathrm{not}}^{\left(I\right)}\left(f\right)$

is applied to the corresponding signal its corresponding _n ( t ) in order to obtain the control signal sc _n ( t ) of the element 3 _n , according to the relation: $${\mathit{SC}}_{\mathrm{not}}\left(f\right)={\mathit{HER}}_{\mathrm{not}}\left(f\right)H_{\mathrm{not}}^{\left(I\right)}\left(f\right)$$

where SC _n ( f ) is the time Fourier transform of sc _n ( t ) and where SA _n ( f ) is the time Fourier transform of its _n ( t ).

des caractéristiques acoustiques est décrite en référence à la figure 9.The application of compensation filters $H_{\mathrm{not}}^{\left(I\right)}\left(f\right)$

acoustic characteristics is described with reference to the figure 9 .

• dans le cas où les paramètres de filtrage sont des réponses en fréquence $H_n^{\left(I\right)}\left(f\right),$
  
  le filtrage peut être effectué au moyen de méthodes de filtrage dans le domaine fréquentiel, comme par exemple des techniques de convolution par bloc ;
• dans le cas où les paramètres de filtrage sont des réponses impulsionnelles $h_n^{\left(I\right)}\left(t\right),$
  
  le filtrage peut être effectué dans le domaine temporel par convolution temporelle ;
• dans le cas où les paramètres de filtrage sont des coefficients de relations de récurrence, le filtrage peut être réalisé dans le domaine temporel au moyen de filtres récursifs à réponse impulsionnelle infinie.

According to the form of the parameters of these filters, each filtering of the signals sa _n ( t ) can be carried out according to conventional filtering methods, such as for example:

• in case the filtering parameters are frequency responses $H_{\mathrm{not}}^{\left(I\right)}\left(f\right),$
  
  the filtering can be carried out by means of filtering methods in the frequency domain, for example block convolution techniques;
• in the case where the filtering parameters are impulse responses $h_{\mathrm{not}}^{\left(I\right)}\left(t\right),$
  
  the filtering can be done in the time domain by time convolution;
• in the case where the filtering parameters are recurrence relation coefficients, the filtering can be performed in the time domain by means of infinite impulse response recursive filters.

In some simplified embodiments, the method of the invention does not compensate for the specific acoustic characteristics of the elements of the rendering assembly. In this case, step 60 as well as substep 90 are not performed and the appropriate signals sa ₁ ( t ) to its _N ( t ) correspond directly to the control signals sc ₁ to sc _N.

By applying the method of the invention, each element 3 ₁ to 3 _N therefore receives a specific driving signal sc ₁ to sc _N and emits an acoustic field which contributes to the optimal reconstruction of the acoustic field to be restored. Indeed, the simultaneous control of the set of elements 3 ₁ to 3 _N allows an optimal reconstruction of the acoustic field corresponding to the multichannel input signal by the restitution set 2 whose spatial configuration is arbitrary, or else does not correspond to to a fixed configuration.

Moreover, other embodiments of the method of the invention may be envisaged, and in particular embodiments inspired by the techniques described in the French patent application filed on February 28, 2002, under No. 02 02 585 .

• G_n (f), représentatif du gabarit de l'élément 3 _n de l'ensemble de restitution spécifiant la bande de fréquence de fonctionnement de cet élément ;
• N _l,m,n (f), représentatif de la réponse spatio-temporelle de l'élément 3 _n correspondant au champ acoustique produit dans le lieu d'écoute 4 par l'élément 3 _n , lorsque celui-ci reçoit en entrée un signal impulsionnel ;
• W(r,f), décrivant pour chaque fréquence f considérée une fenêtre spatiale représentative de la répartition dans l'espace de contraintes de reconstruction du champ acoustique, ces contraintes permettant de spécifier la répartition dans l'espace de l'effort de reconstruction du champ acoustique ;
• W_l (f), décrivant directement sous forme de pondération des coefficients de Fourier-Bessel et pour chaque fréquence f considérée, une fenêtre spatiale représentative de la répartition dans l'espace de contraintes de reconstruction du champ acoustique ;
• R(f), représentatif, pour chaque fréquence f considérée, du rayon de la fenêtre spatiale lorsque celle-ci est une boule ;
• µ(f), représentatif, pour chaque fréquence f considérée, de la capacité d'adaptation locale souhaitée à l'irrégularité spatiale de la configuration de l'ensemble de restitution ;
• {(l_k , m_k )}(f), constituant pour chaque fréquence f considérée, une liste de fonctions spatio-temporelles dont la reconstruction est imposée ;
• L(f), imposant, pour chaque fréquence f considérée, l'ordre limite de détermination de filtres ;
• RM(f), définissant, pour chaque fréquence f considérée, le modèle de rayonnement des éléments 3₁ à 3 _N de l'ensemble de restitution 2.

In particular, the step 50 of determining the spatial adaptation filters can take into account numerous optimization parameters such as:

• G _n ( f ), representative of the template of the element 3 _n of the reproduction unit specifying the operating frequency band of this element;
• N _{l , m , n} ( f ), representative of the spatio-temporal response of the element 3 _n corresponding to the acoustic field produced in the listening location 4 by the element 3 _n , when the latter receives as input a pulse signal;
• W ( r , f ), describing for each frequency f considered a spatial window representative of the distribution in the space of reconstruction constraints of the acoustic field, these constraints making it possible to specify the spatial distribution of the reconstruction effort of the acoustic field;
• W _l ( f ), describing directly in the form of weighting of the Fourier-Bessel coefficients and for each frequency f considered, a spatial window representative of the spatial distribution of reconstruction constraints of the acoustic field;
• R ( f ), representative, for each frequency f considered, of the radius of the spatial window when the latter is a ball;
• μ ( f ), representative, for each frequency f considered, of the desired local adaptation capacity to the spatial irregularity of the configuration of the reproduction unit;
• {( l _k , m _k )} ( f ), constituting for each frequency f considered, a list of spatio-temporal functions whose reconstruction is imposed;
• L ( f ), imposing, for each frequency f considered, the limit order of determination of filters;
• RM ( f ), defining, for each frequency f considered, the radiation pattern of the elements 3 ₁ to 3 _N of the reproduction assembly 2.

All or part of these optimization parameters can intervene during the sub-step 54 of determining the decoding matrix D. Thus, as described in the patent application filed in France under the number 02 02 585 , the parameters N _{l , m , n} ( f ) and RM ( f ) occur in the sub-step 53 of determining the radiation matrix M, the parameters W (r, f), W _l (f) R (f) are involved in the substep 52 of determining the matrix W, the parameters {(l _k, m _k )} ( f ) intervene in an additional substep in the determination of a matrix F. The decoding matrix D is then determined during the sub-step 54, for each frequency f , as a function of the matrices M , W and F and the parameters G _n ( f ) and μ ( f ).

Still, according to the patent application 02 02 585 , the calculation of the matrix D can be done frequency by frequency by considering only the active elements for each frequency considered. This method of determining the matrix D uses the parameter G _n ( f ) and makes it possible to make the most of a restitution set whose elements have different operating frequency bands.

It appears that the implementation of the method of the invention described here is more efficient and therefore faster than existing methods and in particular that the method described in the French patent application filed under the number 02 02 585 .

Indeed, to adapt a multichannel signal comprising Q channels to a restitution set comprising N elements with a spatial precision of order L , it appears that the method of the invention requires Q × N adaptation filters instead of Q ( L +1 ) ² + ( L +1) ² N filters necessary for the implementation of the process described in the French patent application filed under No. 02 02 585 .

For example, the adaptation of a "5.1 ITU-R BF 775-1" signal to a 5-speaker reproduction set with 5-fold precision requires 25 filters instead of 360 filters.

On the figure 10 , there is shown a diagram of an embodiment of an apparatus implementing the method as described above.

This apparatus comprises the adapter 1 which is formed of a unit 110 delivering a multichannel signal such as an audio-video disk reading unit called DVD player 112. The multichannel signal delivered by the unit 110 is intended for the elements of 2. The format of this signal SI is automatically recognized by the adapter 1 which is adapted to match parameters describing the predetermined general direction associated with each channel of the signal SI.

According to the invention, this adapter 1 also integrates an additional calculation unit 114 as well as information acquisition means 116.

For example, the input means 116 are formed of an infrared interface with a remote control or with a computer and allow a user to determine the parameters defining the positions in the space of the restitution elements 3 ₁ to 3 _N.

These different parameters are used by the computer 114 to determine the matrix A defining the adaptation filters.

Subsequently, the computer 114 applies the adaptive filters multichannel signal SI to output the control signals sc sc ₁ to _N to the reproduction unit 2.

Of course, the device embodying the invention can take other forms, such as software implemented on a computer or a complete device incorporating calibration means and means for capturing and determining characteristics. of the restitution set more complete.

Thus, the method can also be implemented in the form of a device dedicated to the optimization of multichannel rendering systems, outside an audio-video decoder and associated therewith. In this case, the device is adapted to receive a multichannel signal as input and to output control signals of elements of a reproduction set.

Advantageously, the device is adapted to be connected to the acquisition device 100 necessary for the calibration step and / or is provided with an interface for entering parameters, in particular the position of the elements of the reproduction set and possibly the multichannel input format.

Such an acquisition device 100 can be connected wired or wireless (radio, infra-red) and can be integrated with an accessory, such as a remote control, or be independent.

The method may be implemented by a device integrated into an element of an audio-video system responsible for the processing of multichannel signals, for example a "surround" processor or decoder, an audio-video amplifier integrating decoding functions. multichannel or a fully integrated audio-video system.

The method of the invention can also be implemented in an electronic card or in a dedicated chip. Advantageously, it can be integrated as a program in a signal processing processor (DSP).

The method may take the form of a computer program to be executed by a computer. The program receives as input a multichannel signal and delivers the control signals of a reproduction set that may be integrated into this computer.

Furthermore, the calibration means can be made by implementing a method different from that described above, such as, for example, a method inspired by the techniques described in the French patent application filed May 7, 2002 under the number 02 05 741 .

Claims (22)

1. A method for controlling a reproduction unit (2) for an acoustic field including a plurality of reproduction elements (3_n) from a plurality of acoustic information input signals (SI) each associated with a predetermined general reproduction direction defined relative to a given point (5) of the space, to obtain a reproduced acoustic field with specific characteristics substantially independent from the intrinsic reproduction characteristics of said unit (2), characterized in that it includes:

   - a step (10) for determining at least spatial characteristics of said reproduction unit (2), making it possible to determine representative parameters for at least one element (3_n) of said reproduction unit (2) from its position in all three spatial dimensions relative to said given point (5);

   - a step (50) for determining adaptation filters (A) from said at least spatial characteristics of said reproduction unit (2) and said general predetermined reproduction directions associated with said plurality of acoustic information input signals (SI);

   - a step (70) for determining at least one control signal for said elements of said reproduction unit by applying said adaptation filters to said plurality of acoustic information input signals (SI); and

   - a step for delivering said at least one control signal for application to said reproduction elements (3_n).
2. The method according to claim 1, characterized in that said step (10) for determining at least spatial characteristics of said reproduction unit (2) includes a capture sub-step (20) making it possible to determine all or some of the characteristics of said reproduction unit (2).
3. The method according to any one of claims 1 and 2, characterized in that said step (10) for determining at least spatial characteristics of said reproduction unit (2) includes a calibration step (30) making it possible to deliver all or some of the characteristics of said reproduction unit (2).
4. The method according to claim 3, characterized in that said calibration sub-step (30) includes, for at least one of the reproduction elements (3_n):

   - a sub-step (32) for emitting a specific signal (u_n(t)) toward said at least one element (3_n) of said reproduction unit (2);

   - a sub-step (34) for acquisition of the sound wave emitted in response by said at least one element (3_n);

   - a sub-step (36) for converting said acquired signals into a finite number of said coefficients representative of the emitted sound wave; and

   - a sub-step (39) for determining spatial and/or acoustic parameters of said element (3_n) from said coefficients representative of the emitted sound wave.
5. The method according to any one of claims 3 and 4, characterized in that said calibration sub-step (30) further includes a sub-step for determining the position in at least one of the three spatial dimensions of said at least one element (3_n) of said reproduction unit (2).
6. The method according to any one of claims 3 to 5, characterized in that said calibration step (30) includes a sub-step for determining the frequency response (H_n(f)) of said at least one element (3_n) of said reproduction unit (2).
7. The method according to any one of claims 1 to 6, characterized in that said step (50) for determining adaptation filters comprises:

   - a sub-step (54) for determining a decoding matrix (D) representative of filters making it possible to compensate reproduction alterations due to the spatial characteristics of said reproduction unit (2);

   - a sub-sub (55) for determining an ideal multi-channel radiation matrix (S) representative of the predetermined general directions associated with each information signal of the plurality of input signals (SI); and

   - a sub-step (56) for determining a matrix (A) representative of said adaptation filters from said decoding matrix (D) and said multi-channel radiation matrix (S).
8. The method according to claim 7, characterized in that said step (50) for determining adaptation filters includes a plurality of calculation sub-steps (51, 52, 53) making it possible to deliver a limiting order (L) for the spatial precision of the adaptation filters, a matrix (W) corresponding to a spatial window representative of the distribution in space of the desired precision during the reconstruction of the acoustic field, and a matrix (M) representative of the radiation of the reproduction unit (2), said sub-step (54) for calculating the decoding (D) matrix (2) being carried out from the results of said calculation sub-steps.
9. The method according to one of claims 7 or 8, characterized in that the decoding (D), ideal multi-channel radiation (S) and adaptation (A) matrices are independent of the frequency, the step (70) for determining at least one control signal of said elements of said reproduction unit by applying said adaptation filters corresponding to simple linear combinations followed by delay.
10. The method according to any one of claims 1 to 9, characterized in that said step (10) for determining characteristics of said reproduction unit (2) makes it possible to determine acoustic characteristics of said reproduction unit (2) and in that said method includes a step (60) for determining compensation filters of these acoustic characteristics, said step (70) for determining at least one control signal then comprising a sub-step (90) for applying said acoustic compensation filters.
11. The method according to claim 10, characterized in that said step (10) for determining acoustic characteristics is suitable for delivering representative parameters for at least one element (3_n) of its frequency response (H_n(f)).
12. The method according to any one of claims 1 to 11, characterized in that said step (70) for determining at least one control signal includes a sub-step for adjusting the gain and applying delays so as to temporally align the wave front of the reproduction elements (3_n) based on their distance relative to said given point (5).
13. A computer program comprising program code instructions for carrying out the steps of the method according to any one of claims 1 to 12 when said program is running on a computer.
14. A removable support of the type comprising at least one processor and at least one non-volatile memory, characterized in that said memory comprises a program comprising code instructions for carrying out the steps of the method according to any one of claims 1 to 12, when said processor runs said program.
15. A control device of a reproduction unit (2) of an acoustic field including a plurality of reproduction elements (3_n), including input means (112) for a plurality of acoustic information input signals (SI) each associated with a predetermined general reproduction direction defined relative to a given point (5), characterized in that it further includes:

    - means (116) for determining at least spatial characteristics of said reproduction unit (2), making it possible to determine representative parameters for at least one element (3_n) of said reproduction unit (2) from its position in the three spatial dimensions relative to said given point (5);

    - means (114) for determining adaptation filters (A) from said at least spatial characteristics of said reproduction unit (2) and predetermined general reproduction directions associated with said plurality of acoustic information input signals (SI); and

    - means (114) for determining at least one control signal (sc_n) for said elements (3_n) of said reproduction unit (2) by applying said adaptation filters (A) to said plurality of acoustic information input signals (SI).
16. The device according to claim 15, characterized in that said means for determining at least spatial characteristics of said reproduction unit (2) include direct input means (116) for said characteristics.
17. The device according to any one of claims 15 and 16, characterized in that it is suitable for being associated with calibration means (91, 92, 93, 100) making it possible to determine at least spatial characteristics of said preproduction unit (2).
18. The device according to claim 17, characterized in that said calibration means comprise means for acquiring a sound wave (100) including four pressure sensors positioned generally in the shape of a tetrahedron.
19. The device according to any one of claims 15 to 18, characterized in that said means for determining characteristics are suitable for determining acoustic characteristics of at least one of said elements (3_n) of said reproduction unit (2), said device including means for determining acoustic compensation filters from said acoustic characteristics and said means for determining at least one control signal being suitable for applying said acoustic compensation filters.
20. The device according to claim 19, characterized in that said means for determining acoustic characteristics are suitable for determining the frequency response (H_n(f)) of said elements (3_n) of the reproduction unit (2).
21. An audio and video data processing apparatus including means (112) for determining a plurality of acoustic information input signals (SI) each associated with a predetermined general reproduction direction defined by a given point (5), characterized in that it further includes a control device for a reproduction unit (2) according to any one of claims 1 to 19.
22. The apparatus according to claim 21, characterized in that said means for determining a plurality of input signals are made up of a unit (112) for reading and decoding digital audio and/or video discs.

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