Acoustic characterization of audio equipment with radio wave localization

Abstract

Audio playback equipment (2), arranged to implement multichannel audio playback in an audio system (1) from initial audio signals (Sa1), and to: acquire the position of the audio playback equipment (3), obtained by a localization method using radio frequency waves; acquire at least one audio parameter representative of an acoustic response of the audio playback equipment (3); adapt at least one of the initial audio signals (Sa1) according to the position of the audio playback equipment (3), and at least one audio parameter, to obtain second audio signals (Sa2); implement multichannel audio playback using the second audio signals (Sa2). ABRIDGED FIGURE: Fig. 1

Description

Title of the invention: Acoustic characterization of audio equipment with radio wave localization

[0001] The invention relates to the field of audio systems comprising audio broadcasting equipment (for example a decoder box) and one or more audio playback devices (for example a television).

[0002] BACKGROUND

[0003] A set-top box, or STB, is an audio-video broadcasting device whose primary function is to acquire an audio-video stream, decode this stream, and broadcast the video stream through a television and the audio stream through the television speakers and / or possibly through other audio playback equipment (soundbar, connected speakers, etc.).

[0004] Some recent set-top boxes incorporate one or more speakers. The speaker(s) can be used in a voice assistant function, but also to contribute to implementing a multichannel audio system that reproduces the audio stream of the audio-video stream. Multichannel reproduction makes it possible to obtain optimal and immersive sound rendering.

[0005] The multichannel audio system then includes audio channels comprising the speakers of the decoder box, as well as possibly the speakers of the television, and / or the speakers of other audio playback equipment connected to the decoder box (e.g. soundbar, connected speakers, etc.).

[0006] It is envisaged to integrate, into an audio system comprising a decoder box, new audio playback equipment, for example a new television. To implement multichannel playback, it is necessary to synchronize and homogenize the sound playback of the different audio playback devices in the system.

[0007] Methods are known, implemented by an audio-video amplifier connected to speakers, which allow for the synchronization and homogenization of sound reproduction between different audio playback devices. However, in these prior art methods, the speakers must be known to the amplifier, which represents a significant constraint for the user.

[0008] OBJECT

[0009] The invention aims to integrate an "unknown" audio playback device into an audio system comprising an audio playback device that implements multichannel playback.

[0010] SUMMARY

[0011] To achieve this goal, an audio playback device is proposed, arranged to implement, from initial audio signals, multichannel audio playback in an audio system comprising a plurality of audio devices, at least one of the audio devices being integrated into an audio playback device separate from the audio playback device,

[0012] the audio broadcasting equipment comprising a processing unit arranged to: - acquire a position of the audio playback equipment, obtained by a localization method using radio frequency waves; - acquire at least one audio parameter representative of an acoustic response of the audio playback equipment; - adapt at least one of the first audio signals according to the position of the audio playback equipment, and at least one audio parameter, to obtain second audio signals; - implement multichannel audio playback using second audio signals.

[0013] The processing unit of the audio playback equipment (e.g., a set-top box) thus acquires the position of the audio playback equipment (e.g., a television), as well as the audio parameter(s) representative of the acoustic response of the audio playback equipment. The processing unit uses this information to precisely configure the audio system in order to synchronize and homogenize the sound between the different components of the audio system.

[0014] Thus, an "unknown" audio reproduction device, i.e. whose position and acoustic performance are unknown, can be acoustically integrated optimally into a controlled audio system to ensure optimal audio rendering.

[0015] We further propose an audio playback equipment as previously described, in which the processing unit is also arranged to acquire an orientation of the audio playback equipment, and to adapt at least one of the first audio signals also according to the orientation of the audio playback equipment.

[0016] An audio broadcasting equipment as previously described is further proposed, comprising a first primary localization module arranged to implement a time-of-flight measurement method to measure a distance between the audio broadcasting equipment and the audio playback equipment, and an angle measurement method to measure at least one angle between the audio broadcasting equipment and the audio playback equipment.

[0017] An audio playback equipment as previously described is further proposed, in which the first primary location module comprises a primary UWB module arranged to communicate with a secondary UWB module of the audio playback equipment.

[0018] An audio broadcasting device as previously described is also proposed, the primary UWB module comprising two first pairs of antennas positioned orthogonally with respect to each other, the first two pairs of antennas being arranged to cooperate with at least one second pair of antennas integrated into the secondary UWB module.

[0019] An audio playback device as previously described is further proposed, wherein the first primary location module is arranged to implement a radar technique, preferably Doppler, and includes a radar source arranged to cooperate with at least one radio frequency tag positioned on the audio playback device.

[0020] Further, an audio playback device as previously described is proposed, wherein said at least one audio parameter is selected from:

[0021] - an acoustic delay due to a transmission chain between the equipment of audio broadcasting and audio playback equipment, and / or processing performed by the audio playback equipment, and

[0022] - a function for transferring audio playback equipment.

[0023] An audio playback device as previously described is further proposed, wherein at least one audio parameter includes an indicator of a change in sound volume resulting from a volume command issued by a user to the audio playback device, the processing unit being arranged to adapt, according to said indicator, at least a first audio signal transmitted to the audio playback device so as to compensate for said change in sound volume.

[0024] An audio broadcasting device as previously described is also proposed, the audio broadcasting device being a decoder box integrating an audio device comprising at least one loudspeaker.

[0025] An audio broadcasting equipment as previously described is also proposed, the audio broadcasting equipment being arranged to determine a user's position, the processing unit being arranged to adapt at least a first audio signal also according to the user's position.

[0026] Further, an audio broadcasting equipment as previously described is proposed, the audio broadcasting equipment being connected to an accessory equipment separate from the audio broadcasting equipment and the audio playback equipment, and being arranged to receive from said accessory equipment the position of the audio playback equipment, as well as said at least one audio parameter.

[0027] An audio broadcasting method is further proposed, implemented in the processing unit of an audio broadcasting device as previously described, comprising the steps of: - acquire a position of the audio playback equipment, obtained by a localization method using radio frequency waves; - acquire at least one audio parameter representative of an acoustic response of the audio playback equipment; - adapt at least one of the first audio signals according to the position of the audio playback equipment, and at least one audio parameter, to obtain second audio signals; - use the second audio signals to implement multichannel audio playback.

[0028] A computer program is further proposed comprising instructions which lead the processing unit of the audio broadcasting equipment as previously described to execute the steps of the audio broadcasting process as previously described.

[0029] A computer-readable recording medium is also proposed, on which the computer program as previously described is recorded.

[0030] An accessory device is also proposed, arranged to be connected to an audio playback device as previously described, the accessory device comprising:

[0031] - a second primary localization module arranged to evaluate the position of the audio playback equipment, the second primary localization module being arranged to implement the localization method using radio frequency waves; - an audio capture module, including at least one microphone, and arranged to produce at least one audio parameter representative of the acoustic response of the audio playback equipment; - a first communication module, arranged to transmit to the audio broadcasting equipment the position of the audio playback equipment, as well as at least one audio parameter.

[0032] An accessory equipment as previously described is also proposed, the first communication module being arranged to receive the second audio signals transmitted by the audio broadcasting equipment, the accessory equipment further comprising a second communication module arranged to transmit the second audio signals to the audio devices of the audio system to implement multichannel audio playback.

[0033] A system is further proposed comprising the audio playback equipment as previously described, and a secondary localization module arranged to be positioned on the audio playback equipment and used to implement the localization method.

[0034] A system as previously described is further proposed, comprising audio broadcasting equipment as previously described, the radio frequency location module comprising said at least one radio frequency tag which is a passive tag comprising an array of dielectric resonators and a Van Atta reflector.

[0035] A system as previously described is further proposed, comprising an audio broadcasting equipment as previously described, the radio frequency location module comprising at least one radio frequency tag which is an active tag comprising a Van Atta reflector, a microwave switch, and a processor arranged to activate and deactivate the Van Atta reflector, according to a determined frequency, by driving the microwave switch(s).

[0036] A system as previously described is also proposed, comprising audio broadcasting equipment as previously described, the system further comprising accessory equipment as previously described.

[0037] The invention will be better understood in the light of the following description of particular, non-limiting embodiments of the invention. Brief description of the drawings

[0038] Reference will be made to the attached drawings, among which:

[0039] [Fig-1] [Fig. 1] represents a decoder box and a television;

[0040] [Fig.2] [Fig.2] represents steps in an implemented audio broadcasting process in the decoder box;

[0041] [Fig.3] [Fig.3] illustrates the TWR technique;

[0042] [Fig.4] [Fig.4] illustrates the PDoA technique;

[0043] [Fig.5] [Fig.5] represents the primary UWB module;

[0044] [Fig.6] [Fig.6] represents the different angles of the decoder box and the television;

[0045] [Fig.7] [Fig.7] represents a decoder box and a television;

[0046] [Fig.8] [Fig.8] represents the television in its reference position, and the television oriented at an angle [3;

[0047] [Fig.9] [Fig.9] represents a Van Atta reflector;

[0048] [Fig. 10] the [Fig. 10] illustrates the principle of determining the orientation angle [3] that forms the normal to the surface of the label with respect to the normal to the reference surface of the decoder box;

[0049] [Fig. 11] the [Fig. 11] represents an active label;

[0050] [Fig. 12] [Fig. 12] represents a decoder box and a television;

[0051] [Fig. 13] [Fig. 13] is a graph comprising the curves of the signal of synchronization signal emitted and synchronization signal received;

[0052] [Fig. 14] [Fig. 14] is a graph representing the cross-correlation between the emitted synchronization signal and the received synchronization signal;

[0053] [Fig. 15] [Fig. 15] represents a graph comprising the curve of the emitted test signal, a graph comprising the curve of the received test signal, and a graph representing the transfer function of the television;

[0054] [Fig. 16] [Fig. 16] represents a decoder box, a television and a user;

[0055] [Fig. 17] [Fig. 17] represents a set-top box, a television, speakers and a accessory equipment. DETAILED DESCRIPTION

[0056] With reference to [Fig.1], the audio system 1 comprises an audio broadcasting device 2 and an audio playback device 3, which are two separate devices connected to each other.

[0057] By "audio playback equipment" is meant equipment which acquires (from outside or internally) an audio stream comprising one or more audio signals, and which transmits the audio signal(s) to one or more audio playback equipment for playback.

[0058] By "audio playback equipment" is meant equipment which includes an audio device comprising at least one loudspeaker, which receives at least one audio signal and reproduces it by producing a sound signal through its loudspeaker(s).

[0059] Here, the audio broadcasting equipment 2 is a set-top box (also called a TV decoder, or audiovisual decoder, or Set-Top Box). The set-top box 2 is an "advanced" set-top box which incorporates an audio device 4 comprising several speakers 5.

[0060] The audio playback equipment 3 is here a television which also integrates an audio device comprising several speakers 7, in this case a right speaker 7a and a left speaker 7b.

[0061] The audio system 1 may also possibly include other audio playback equipment, such as "satellite" speakers placed around the television 3, but these are not mentioned at this time.

[0062] The decoder box 2 and the television 3 are connected here by an HDMI 9 link (for High Definition Multimedia Interface).

[0063] The primary functions of the decoder box 2 consist of receiving an audio-video stream, processing it, separating the audio stream and the video stream, transmitting the video stream to the television 3, and transmitting all or part of the audio stream to the audio devices of the audio system 1.

[0064] The audio-video stream can originate from any source, which is for example a broadcast network (satellite television network, Internet connection, network of digital terrestrial television (DTT), cable television network, etc.), other equipment connected to the set-top box (a CD, DVD or BluRay player, a smartphone, a tablet, etc.), or even a storage medium (for example a USB key or a memory card connected to the set-top box).

[0065] The decoder box 2 also plays the role of audio playback equipment in the audio system 1: its speakers 5 reproduce part of the audio stream.

[0066] The audio device 4 of the decoder box 2 also includes an audio chain 10, comprising components (in particular one or more audio amplifiers) which shape the audio signals reproduced by the speakers 5 of the decoder box 2.

[0067] The decoder box 2 further includes a processing unit 11. The processing unit 11 is an electronic and software unit. The processing unit 11 includes at least one processing component 12, which is, for example, a "general-purpose" processor, a processor specializing in signal processing (or DSP, for Digital Signal Processor), a processor specializing in artificial intelligence algorithms (of the NPU type, for Neural Processing Unit), a microcontroller, or a programmable logic circuit such as an FPGA (for Field Programmable Gate Arrays) or an ASIC (for Application Specified Integrated Circuit).

[0068] The processing unit 11 also includes one or more memories 14, connected to or integrated into the processing component(s) 12. At least one of these memories 14 forms a computer-readable recording medium, on which is recorded at least one computer program comprising instructions which lead the processing unit 11 to execute the steps of the audio broadcasting process which will be described.

[0069] The audio stream includes initial Sal audio signals.

[0070] The processing unit 11 of the decoder box 2 implements, from the first audio signals Sal of the audio stream, a multichannel audio reproduction in the audio system 1.

[0071] The decoder box 2 further includes a first primary localization module 15. The first primary localization module 15 implements a localization method using radio frequency waves to determine the position of the television 3, and therefore of the speakers 7 of the television 3. Advantageously, the localization method also makes it possible to determine the orientation of the television 3, and therefore of the speakers 7 of the television 3.

[0072] In the context of the present invention, the term "radio frequency" should be understood broadly as potentially including: - a radio wave whose spectrum belongs to the frequency range extending from 8.3 kHz to 3000 GHz, in particular from 3.1 to 10.6 GHz; or - an optical wave, in particular in the infrared range.

[0073] The decoder box 2 further includes one or more microphones 16, and an acquisition chain 17 connected to the microphones 16 for processing the audio signals produced by the microphones 16 from the capture of sound signals. The decoder box 2 uses these microphones 16 in particular to acquire at least one audio parameter representative of an acoustic response of the television 3.

[0074] With reference to [Fig. 2], the processing unit 11 of the decoder box 2 is arranged to: - acquire a position of the television 3, obtained by a localization method using radio frequency waves: step El; - acquire at least one audio parameter representative of an acoustic response of the television 3: step E2; - adapt at least one of the first audio signals Sal according to the position of the TV 3, and at least one audio parameter, to obtain second audio signals Sa2, and implement multichannel audio playback using the second audio signals Sa2: step E3.

[0075] Advantageously, in step E1, the processing unit 11 also acquires the orientation of the TV 3, and in step E3, the processing unit 11 adapts at least one of the first audio signals Sal also according to the orientation of the TV 3.

[0076] The adaptation of each first Sal audio signal includes, for example, an optimization of the level of said first Sal audio signal according to the frequency.

[0077] The processing unit 11 therefore acquires the audio stream, produces the second audio signals Sa2 from the first audio signals Sal, and implements multichannel audio playback using the second audio signals Sa2 which are transmitted to the audio devices of the audio system 1 (here integrated into the TV 3 and the decoder box 2).

[0078] It is understood that each second audio signal Sa2, which is associated with a first audio signal Sal which does not undergo the adaptation just mentioned, is equal to the first audio signal Sal itself.

[0079] As will be seen below, the audio settings may include an indicator of a change in the TV volume. The processing unit 11 checks the volume and adapts one or more first audio Sal signals to compensate for this change: step E4.

[0080] The decoder box 2 can thus, without knowing the television 3, acoustically characterize it within the user's environment, and thereby take into account its acoustic performance, which includes, for example, frequency response and efficiency, also considering reverberations and reflections of sound depending on the position of the television 3 relative to the walls of the room and objects. This ensures immersive sound reproduction including the speakers 7 of the television 3.

[0081] The treatment illustrated in [Fig.2] is carried out for example at each calibration of the audio system 1, or at regular intervals (for example every day).

[0082] We are interested first of all in the localization method which makes it possible to determine the position of the television 3 and, optionally, its orientation.

[0083] The first primary location module 15 is arranged to implement a time-of-flight measurement method to measure a distance between the decoder box 2 and the television 3, and an angle measurement method to measure at least one angle between the decoder box 2 and the television 3.

[0084] The localization method preferably uses UWB technology (for Ultra Wide Band).

[0085] In a first embodiment, the localization method uses a TWR (Two Ways Ranging) technique and a PDOA (Phase Direction Of Arrival) technique. The combined implementation of these two techniques makes it possible to obtain 3D localization (which corresponds to the case of an audio system installed in a house).

[0086] As illustrated in [Fig.1], the first primary location module 15 of the decoder box 2 includes a primary UWB module 20.

[0087] A secondary location module (radio frequency), which in this case is a secondary UWB module 21, is installed on the television 3. This is, for example, a label (a self-adhesive label, for example) or "tag," which can be permanently or temporarily attached. The secondary UWB module 21 is equipped with a battery 22 for its power supply.

[0088] Of course, the position of the secondary UWB module 21 in the figures does not correspond to the actual position. The module 21 is preferably positioned in the middle of the upper part of the frame of the TV 3 to locate the speakers of the TV 3.

[0089] The primary UWB module 20 communicates with the secondary UWB module 21. The localization method therefore uses the TWR technique to calculate a time of flight of UWB signals to measure a distance between the primary UWB module 20 and the secondary UWB module 21, and the PDoA technique to measure at least one angle between the decoder box 2 and the television 3.

[0090] The principle of UWB is based on wave trains containing information and also a timestamp, the system being temporally synchronized. The wave train is sent by a transmitter, received by a receiver which decodes it and then sends it back to the transmitter. The radio time of flight is thus determined by measuring the travel time in one direction and in the other and subtracting the travel time in the electronics as well as the software processing time in each of the transmitters and receiver. The time of flight (or ToF for Time of Flight) is determined by the TWR technique.

[0091] With reference to Figure 3, in this method, an initiating device sends a first message "POLL", and a receiving device responds, a precise time after transmission, by sending a second message "RESP". The initiating device then subtracts, from the TRound time between the transmission of the first message and the reception of the second message, the TReply (known) response time of the receiving device.

[0092] The initiating equipment thus obtains the propagation time of two waves. The initiating equipment then calculates:

[0093] -pv {TRound-TReply) 1 Gold — 2

[0094] The distance between the initiating equipment and the receiving equipment is obtained using the formula:

[0095] Distance = ToF xc (where c is the radio frequency in air).

[0096] The TWR also allows the angle of arrival to be measured in receive mode. by measuring the difference in arrival time and / or phase of the signal on a pair of antennas, as will be described.

[0097] With reference to [Fig.4], the classic PDoA technique works as follows with two UWB communication modules each comprising two antennas.

[0098] Each UWB communication module is capable of measuring the angle of arrival (AoAy), which is the angle between: - the line D connecting said UWB communication module and another UWB communication module of another piece of equipment; - the normal line N to the UWB communication module, that is to say an imaginary line orthogonal to the plane in which the two UWB antennas Ant1, Ant2 of the said UWB communication module extend.

[0099] This AoA angle is calculated by measuring the phase shift of the carrier of the received signal between the two antennas Antl, Ant2, or PDoA (for Phase Difference of Arrival). This phase shift corresponds to a small difference in distance between the distance measurement obtained via one antenna Antl and the distance measurement obtained via the other antenna Ant2.

[0100] The PDoA is related to the angle of arrival (AoA) by this equation: [01011 A>A = «rcsin(^^)

[0102] where: - X is the wavelength of the UWB signal carrier; - d is the distance between the Antl, Ant2 antennas.

[0103] Here, the system is improved in the following way.

[0104] With reference to Figures 5 and 6, the primary UWB module 20 of the decoder box 2 here comprises two first pairs of antennas 23a, 23b and 24a, 24b, positioned orthogonally with respect to each other, an antenna switch 25, and a processing module 26 possibly integrated into the processing unit 11).

[0105] The secondary UWB module 21 of the TV 3 includes at least one second pair of antennas, here two second pairs of antennas 27a, 27b and 28a, 28b, positioned orthogonally with respect to each other, an antenna switch 29 and a processing component 30.

[0106] The processing module 26 of the primary UWB module 20 therefore drives the antenna switch 25 to measure the angle q> 1, then drives the antenna switch 25 to measure the angle 01. The primary UWB module 20 generates two consecutive measurements to produce the measurement of the two angles q> 1 and 01.

[0107] The primary UWB module 20 also implements the time-of-flight method to measure the distance between the primary UWB module 20 and the secondary UWB module 21, and therefore between the decoder box 2 and the television 3.

[0108] The decoder box 2 therefore obtains a measurement in polar coordinates in space with on the one hand the flight distance and on the other hand the two angles.

[0109] The decoder box 2 can thus measure the exact position of the secondary UWB module 21 in space relative to the decoder box 2.

[0110] Similarly, the secondary UWB module 21 measures the angles q>2 and 02, and can measure the exact position of the decoder box 2 in space relative to the television 3.

[0111] The secondary UWB module 21 transmits its measurements to the primary UWB module 20 (via UWB communication), and the processing unit 11 of the decoder box 2 can then determine: - the different orientation angles of the decoder box 2; - the different orientation angles of the television 3; - the distance between the two devices.

[0112] The frequency of the UWB signal carrier used is, for example, 6.5 GHz. The separation distance of the Antl, Ant2 antennas of a pair of antennas of a UWB module, which is fixed at X / 2 (see [Fig.4]), is therefore approximately 26 mm, which makes it easy to integrate the UWB modules 20, 21 into the decoder box 2 and into the television 3 due to their small size.

[0113] It should be noted that it is possible to provide only one pair of antennas in the secondary UWB module 21 of the television 3. In this case, the orientation of the television 3 and the decoder box 2 is no longer accessible at either angle, but it is then possible to consider that the television 3 is correctly positioned in its nominal position. vertical and the decoder box 2 in its nominal horizontal position (or vertical if decoder box is designed that way).

[0114] In a second embodiment, the first primary localization module is arranged to implement a radar-type technique, preferably Doppler.

[0115] As is known, a radar device allows angles and distances to be measured. Depending on the nature of the radar source, several embodiments can be considered.

[0116] With reference to Figures 7 and 8, the first primary location module 34 of the decoder box 2 comprises a primary radar module 35 including a radar source 31, a processing module 32 (possibly integrated into the processing unit 11) and a receiving module 33.

[0117] Television 3 is equipped with a secondary location module (radio frequency), here a secondary radar module comprising at least one radio frequency tag 36, which can be passive or active.

[0118] The radar source 31 is here an FMCW (Frequency Modulated Continuum Wave) source. The source 31 emits a continuous wave. The source 31 is configured to emit a radar signal with a scanning frequency, preferably in the millimeter wave range, for example in the 57-64 GHz frequency band.

[0119] This frequency band has the following advantage in particular. In the case where the audio system 1 includes a number of audio playback devices in addition to the television 3 (for example several speakers), and therefore a number of tags, this frequency band is wide enough to cause a large set of RF tags to react in turn, in order to distinguish them without risk of confusion.

[0120] The label 36 of the television 3 is configured to emit a signal at a natural resonant frequency in response to the radar signal.

[0121] The receiving module 33 of the decoder box 2 is configured to receive signals emitted by the tag 36 in response to the radar signal.

[0122] The processing module 32 of the decoder box 2 is configured to analyze the signals received by the receiving module 33 and to deduce position parameters of the television 3 relative to the decoder box 2, these parameters including a distance and at least one angle.

[0123] Advantageously, the radar source 31, the receiving module 32 and the processing module 33 are implemented in the same component, and for example in one of the following 60 GHz radar components: Texas Instruments IWRL6432; Infineon BGT60TR13C (registered trademarks).

[0124] The RF tag 36 can be either passive or active (by responding to a specific frequency or by relying on a different response over time so as to discriminate and serve for localization).

[0125] To allow for easy and minimal bulky attachment to the television 3, the RF label 36 is preferably flexible. The label 36 is made, for example, of a polyamide film (e.g., Kapton, a registered trademark) and copper, or of polycarbonate with a printed silver layer. The label 36 may include patterns that resonate at one or more specific frequencies, each resonant frequency being determined, in particular, by the geometry and size of the patterns.

[0126] Thus, this type of circuit makes it possible to define a radar signature characterized by one or more specific resonance frequency(ies) and associated respectively with each audio playback equipment, which advantageously makes it possible to identify each audio playback equipment in a unique way, during the probing by the radar source 31.

[0127] For each value of the frequency and the scanning angle of the radar source 31, the receiving module 33 measures the frequency response, i.e. the amplitude (or power) as a function of the frequency of the signals emitted by the tag 36. On the basis of these amplitudes (respectively powers), the processing module 32 determines the position coordinates, i.e. the distance d and the azimuth angle 0 and possibly the elevation angle cp of the television 3 with respect to the radar source 31, according to known radar processing techniques.

[0128] Advantageously, the processing module 32 also determines the orientation [3 of the television 3 with respect to its reference position.

[0129] In most cases, it is assumed that the television 3 is positioned at the same height as the decoder box 2 and therefore as the radar source 31 (q> fixed at 90°), so that it is sufficient to measure the azimuth angle 0. It is also possible to determine all the parameters d, q>, 0, [3.

[0130] For this purpose, during a preliminary calibration step (for example, factory characterization), the amplitude (or power) responses of different RF tags are pre-recorded as a function of distances dr and reference orientations [3r] of each RF tag relative to the radar source.

[0131] It has indeed been observed that RF tags exhibit sufficiently characteristic amplitude (or power) responses to reliably distinguish their respective positions d, 0 and orientation [3 (i.e. the value of the relative angle of the TV 3 with the radar source which serves as a reference).

[0132] The RF label 36 of the television 3 can therefore be a passive label.

[0133] The passive label may include a resonant surface comprising a network of Dielectric Resonators 37 (DR).

[0134] The resonators can be made from beads made of zirconium dioxide (ZrO2). The frequency response of each bead shows a maximum absorption at 79 GHz and a resonance peak at 86 GHz for a bead with a diameter of 0.6 mm.

[0135] These beads can be arranged in a network, for example according to a 9X5 matrix.

[0136] Advantageously, to have a frequency response of the label that depends less on the inclination, i.e. on the angle of incidence of the radar signal on the label, a reflector can be used.

[0137] The use of a tetrahedral reflector has been considered.

[0138] The angular response can then be used to deduce the angular position of the label relative to the radar source, taking into account the re-emitted power as a function of the angle of incidence of the radar signal.

[0139] However, the tetrahedral reflector is bulky and not particularly suitable for being fixed to the surface of an audio playback device such as a television.

[0140] Therefore, instead of the tetrahedral reflector, a planar reflector of the Van Atta 38 type is used.

[0141] The RF label of the television therefore includes a Van Atta reflector and an array of dielectric resonators, for example a matrix of ZrO2 beads.

[0142] With reference to [Fig.9], the Van Atta reflector 38 is a planar antenna array 39 (patch array). This reflector emits a radiated signal in response to the incident radar signal.

[0143] The incident signal has an angle θ1 with the imaginary line orthogonal to the plane in which the two antennas extend. The radiated signal has an angle θ2. The resonator creates an angular offset:

[0144] 03 = 02- 01.

[0145] ô is a phase gradient.

[0146] For example, this reflector is a single-sided circuit, and for example a flexible film (made of Kapton for example) that can be produced by inkjet printing.

[0147] The flexibility of the label is particularly advantageous because it allows it to be affixed to a curved surface, for example, in the case of a television 3 with a curved external surface. It is possible to produce a very small label (between 1 and 5 cm in length).

[0148] To estimate the orientation of the television 3 relative to the radar source 31, the processing unit 11 of the decoder box 2 acquires and uses the angular response of the Van Atta reflector 38.

[0149] The response of the Van Atta reflector depends on the angle of incidence of the radar signal. Indeed, this response is maximum for an angle of incidence of zero (01 = 0°, i.e. when the incident radar signal is perpendicular to the surface of the RF tag) and decreases on either side, forming a main lobe followed by two secondary lobes (one on each side of the main lobe) as the angle of incidence increases.

[0150] The power reflected by the reflector can be measured as a function of the angle of incidence and compared to the power at normal incidence, i.e. to the reference power which would be obtained for a zero angle (01 = 0°), according to a predefined measurement template (measured in the factory or determined by calculation).

[0151] For example, in the case of the passive label, this measurement will be made outside the resonances of the dielectric network.

[0152] Depending on the power reflected by the label outside the resonance, by measuring the reflected power for a given angle of incidence, the processing unit 11 of the decoder box 2 can advantageously deduce, taking into account the distance to the target obtained elsewhere, an estimate of the orientation of the television 3 with respect to the decoder box 2.

[0153] With reference to [Fig. 10], the way in which the orientation angle [3] formed by the normal to the surface of the label 36 with respect to the normal to the reference surface of the decoder box 2 is measured is explained.

[0154] For a given scanning direction 0 of the radar source 31, the reflected power PI by the label 36 is measured in the scanning direction and the angle corresponding to the angle

[31] is determined according to a predetermined template. This template is obtained in a reference position, corresponding for example to the case where the television 3 is positioned directly opposite the decoder box 2 (i.e. with 0 = 0° and [3 = 0°).

[0155] RF tags can also be active tags.

[0156] With reference to [Fig. 11], each RF tag 40 comprises a reflector 41, one or more microwave switches 42, and a relatively basic, low-power processor 43. The processor is, for example, powered by a button cell battery 44.

[0157] The reflector 41 is active for a predetermined period of time. It is the processor 43 that activates and deactivates the reflector 41, according to a predetermined frequency, by controlling the microwave switch(s) 42.

[0158] The reflector 41 is again a Van Atta reflector, which includes a planar antenna array 59.

[0159] Processor 43 activates or deactivates the Van Atta network.

[0160] When reflector 41 is activated, it is "visible" to the radar source. When it is When deactivated, it disappears from the radar source.

[0161] The active label 40 therefore forms a "blinking" radar target at the frequency determined by the processor.

[0162] During the activation of the reflector, the decoder box measures the reception level to estimate the angle of inclination of the label, as previously described.

[0163] Another label, positioned orthogonally to the first, activated with the same processor but on disjoint time intervals, would allow, as described above, the angle to be measured in an orthogonal axis, thus accessing a 3D measurement.

[0164] It is noted that RF tags can also be implemented using multi-frequency resonant circuits printed on PCBs, similar to existing passive UWB RFID tags. Such circuits consist of three resonators (for example, two spiral-shaped resonators connected by a transmission line resonator), each resonator being configurable in active or passive mode corresponding to two binary states, for a total of 2³ = 8 states, i.e., 8 possible codes). Thus, these circuits can be configured to exhibit different frequency responses, thereby enabling the encoding of different binary sequences.

[0165] We are now interested in acquiring at least one audio parameter representative of the acoustic response of the television 3.

[0166] At least one audio parameter is selected from: - an acoustic delay linked to a transmission chain between the decoder box 2 and the television 3, and to a processing carried out by the television, and - a transfer function of the television 3.

[0167] With reference to Figures 12 to 14, to determine the acoustic delay, the decoder box 2 sends an emitted synchronization signal Se (audio signal) to the TV 3 via the HDMI link.

[0168] When the TV 3 receives the transmitted synchronization signal Se, the TV 3 applies the transmitted synchronization signal to its speakers 7, which generate an audio synchronization signal Ss. Speaker 7a generates the Ssl signal and speaker 7b generates the Ss2 signal:

[0169] Ss = Ssl+Ss2.

[0170] The microphones 16 of the decoder box 2 capture the audio synchronization signal Ss and produce a received synchronization signal Sr. Then, the decoder box 2 estimates the acoustic delay in real time. For this, the processing unit 11 calculates The cross-correlation between the transmitted synchronization signal Se sent to the television and the received synchronization signal Sr. The cross-correlation signal is, for example, similar to the signal in [Fig. 14]. The time at which peak P occurs corresponds to the delay Re.

[0171] With reference to [Fig. 15], to obtain the transfer function Ft, the decoder box 2 transmits an emitted test signal Ste to the TV, then captures, using microphones, the audio test signal produced by the TV speakers from the audio test signal. The microphones produce a received test signal Str. The processing unit deduces the transfer function from the emitted test signal Ste and the received test signal Str.

[0172] The transfer function Ft in dB is such that:

[0173] Ft = Str-Ste,

[0174] where Str is the sound response, i.e. the received test signal produced by the microphones 16 of the decoder box 2, and Ste is the excitation, i.e. the emitted test signal sent to the television 3.

[0175] In the example in [Fig. 15], the test signal emitted Ste is a pink noise signal over a frequency band between 10 and 18000 Hz. Other examples of test signals may be used, such as a white noise signal.

[0176] Advantageously, at least one audio parameter includes an indicator of a change in the sound volume of the TV 3, resulting from a volume command issued by a user to the TV 3, the processing unit 11 of the decoder box 2 being arranged to detect the change in volume and adapt the first audio signal(s) Sal transmitted to the TV 3 to compensate for said change in sound volume.

[0177] Preferably, the change in sound volume is detected by the processing unit 11 by comparing the transfer function obtained at two different times. If the sound volume of the television 3 increases or decreases, the level of the transfer function (in dB) is globally increased or decreased respectively by a given amount over the entire frequency response range of the television 3. For example, this amount is obtained by subtracting the transfer function obtained at a first time from the transfer function obtained at a second time. The indicator of the change in volume of the television 3 is therefore, for example, equal to this amount.

[0178] In a first embodiment, the audio system 1 is configured so that the overall sound volume is intended to be controlled by the user solely through volume commands sent to the set-top box 2 (i.e., via the set-top box 2's remote control). The volume commands sent by The user via the TV remote control 3 should therefore have no effect on the overall perceived sound volume.

[0179] In this case, when the user sends a volume command to the TV 3 (via the TV 3 remote control), this command will modify the TV's configuration and therefore its transfer function. The processing unit 11 of the set-top box 2 will then modify the first audio signal Sal from the TV 3 to compensate for this volume change. For example, if the user lowers the volume of the TV 3 by 5 dB, the transfer function will be lowered by 5 dB. Through a feedback control system based on comparing the real-time level to a reference level defined when the set-top box 2 is switched on, the level of the second audio signal Sa2 sent to the TV 3 will be increased to compensate for the change in the TV 3's configuration and ensure the overall sound balance of the audio system 1.

[0180] In a second embodiment, the audio system 1 is configured so that the overall sound volume can also be managed by the user through volume commands sent to the TV 3 (i.e., via the TV remote control).

[0181] In this case, when the user sends a volume command to TV 3, for example a volume decrease, this command will modify the configuration of TV 3 and therefore the transfer function of TV 3.

[0182] This volume control is taken into account by the television 3, but it is the decoder box 2 which continues to manage the overall sound volume.

[0183] The decoder box 2 will therefore lower the overall sound volume in the system by the equivalent level but increase the level sent to the television 3 so that it does not suffer twice from the reduction in sound level.

[0184] The invention therefore makes it possible to acoustically characterize the TV 3 in the user's environment (acoustic performance including frequency response and efficiency taking into account reverberations and reflections of sound depending on the position of the TV 3 relative to the walls of the room and objects) and to ensure immersive sound reproduction including the speakers 7 of the TV 3. The processing unit 11 configures the audio system 1 in real time, using the location data and the audio parameters.

[0185] The processing unit 11 of the decoder box 2 is also arranged to adapt the first audio signal Sal transmitted to the TV 3 according to the orientation of the TV 3 and its transfer function Ft.

[0186] Thanks to the distance and orientation information gathered by radio wave localization, the decoder box 2 will add to the previous processing an acoustic compensation based on the orientation of the TV speakers, taking into account the standard directivity of a TV speaker. In fact, it is generally known for speaker dimensions of a few centimeters, compatible with use in a television (3 to 8 cm usually).

[0187] A transfer function exhibiting significant attenuation in the high frequencies may be due to a loudspeaker that is inefficient in this frequency band, or to a television 3 oriented at a significant angle relative to the set-top box (70 to 90°), or to a considerable distance between the television 3 and the set-top box 2 in a listening room heavily filled with high-frequency absorbing materials. The distance and angle information previously determined using the localization means 15 will eliminate the last two uncertainties mentioned above, and thus allow for amplification of the high frequencies in the signal sent to the television 3 to compensate for the speaker's weakness. The processing unit 11 therefore modifies the levels of the first audio signal Sal sent to the television 3 according to the acoustic frequency, depending on the orientation and / or position of the television 3.

[0188] As already stated, the processing unit 11 of the decoder box 2 acquires the position (and optionally) the orientation of the television 3, acquires the audio parameter(s), and adapts at least one of the first audio signals Sal of the audio stream according to this / these information to obtain the second audio signals Sa2. The processing unit 11 then transmits the second audio signals Sa2 to the various audio devices to implement this "optimized" multichannel playback.

[0189] As we have seen, the audio system 1 can include other audio playback equipment, such as loudspeakers. These loudspeakers are therefore equipped with RF tags as previously described.

[0190] The processing unit 11 therefore knows the position of the speakers and the television 3, and can adapt certain first audio signals Sal to produce second audio signals Sa2 intended for these devices, which are adapted to give them specific functionalities depending on their position, for example their elevation (up-firing), their acoustic performance, particular functionalities (subwoofer), etc.

[0191] This configuration is used to feed the real-time "mapping" of the immersive sound provider. Thus, a configuration specific to the presence of the TV 3 can be provided in the case where the TV 3 contributes with its integrated speakers 7 to the sound reproduction, which makes it possible to improve the sound rendering in the user's listening space.

[0192] The application of the invention is not limited to rear channels but more generally to an audio system comprising other audio reproduction channels, such as subwoofers and side speakers.

[0193] Advantageously, with reference to [Fig.16], the decoder box 2 also determines the position (A, a) of the user 45. The processing unit 11 adapts the first audio Sal signals also according to the position of the user.

[0194] Indeed, to optimally configure an audio system comprising several audio devices, and therefore to obtain an immersive rendering, determining the angular position (distance, angle) but also the orientation of each of the speakers relative to the user 45 is essential since the acoustic diagram 46 and therefore the relative power of the speaker at a given point depends on the power of the speaker and the acoustic directivity diagram, the latter being linked to the orientation of the speaker.

[0195] Once the user's position and the positions and orientations of all audio playback devices are obtained, the processing unit 11 uses this information to configure these devices in order to optimize the sound rendering according to the user's position.

[0196] Since the distances (d, A) and angles (0, |3) are determined at regular (configurable) time intervals, the configuration can be adjusted in real time according to the user's position.

[0197] It is noted that the invention can also be implemented in the case where the decoder box does not include means for locating the television, nor means for capturing the audio parameters of the television.

[0198] With reference to [Fig. 17], the audio system 1 comprises the TV speakers 3 and the speakers 47.

[0199] This time, the decoder box 2 is a "classic" decoder box, which does not include a speaker and does not include any means of localization.

[0200] An accessory device 48 is integrated into the audio system 1. The accessory device 48 is, for example, a dongle.

[0201] Accessory equipment 48 is here connected to the TV 3, for example via an HDMI link 49.

[0202] Accessory equipment 48 includes a processing unit 50 (comprising, like processing unit 11, at least one processing component and at least one memory), a second primary localization module 51, an audio capture module 52, and a first communication module 53.

[0203] Accessory equipment 48 is connected to the set-top box 2 via the first communication module 53. The first communication module 53 implements either a wired or a wireless connection 54. The wired connection is, for example, an HDMI connection. For example, accessory equipment 48 is configured in "pass-through" mode, i.e., allowing the entire audio / video signal from the set-top box 2 to pass through.

[0204] The first communication module 53 may also include a wired communication interface of another type (e.g. Ethernet) for communicating with the decoder box 2.

[0205] The second primary localization module 51 of the accessory equipment 48 evaluates the position (and advantageously the orientation) of the television 3. The second primary localization module 51 implements a localization method using radio frequency waves. Preferably, the localization method is the same as that described above when implemented by the set-top box 2.

[0206] The second primary localization module 51 includes, for example, the primary UWB module, or the radar source, the receiving module and the processing module which have been previously described.

[0207] The audio capture module 52 includes at least one microphone 56, and is arranged to produce at least one audio parameter representative of the acoustic response of the TV 3.

[0208] Here, for reasons of compactness, accessory equipment 48 does not have speakers.

[0209] The television 3 and the speakers 47 each include a radio frequency location module 55, for example a tag.

[0210] It is therefore the accessory equipment 48 that determines the position and orientation of the television and the audio speakers 47 using a localization method employing radio frequency waves. It is also the accessory equipment 48 that evaluates the audio parameter(s) representative of the acoustic responses of the television 3 and the speakers 47.

[0211] This data is transmitted to the processing unit 11 of the decoder box 2. The processing unit 11 acquires the data, adapts the first audio signals Sal according to this data, produces the second audio signals Sa2, and implements multichannel audio playback using the second audio signals Sa2.

[0212] In one embodiment, it is the decoder box 2 that transmits the second audio signals Sa2 to the audio devices of the audio system 1.

[0213] In another embodiment, the accessory equipment 48 further includes a second communication module 57 arranged to transmit the second audio signals to the audio devices of the audio system 1 to implement multichannel audio playback.

[0214] The first communication module 53 of the accessory equipment 48 then receives the second audio signals Sa2 produced by the decoder box 2 and transmitted by the decoder box 2 to the accessory equipment 48. It is then the accessory equipment 48 which transmits the second audio signals Sa2 to the audio devices to implement multichannel audio playback.

[0215] The second communication module 57 includes, for example, a wireless communication interface, for example according to the IEEE 802.11 (Wi-Fi) protocol.

[0216] Thus, accessory equipment 48 is configured to send via Wi-Fi one or more audio data streams to a plurality of wireless audio playback devices.

[0217] In the example of [Fig. 17], accessory equipment 48 is configured to send two separate audio streams to two wireless speakers 47 (Wi-Fi).

[0218] Obviously, accessory equipment 48 can be configured according to any other wireless communication protocol compatible with the wireless audio playback devices considered.

[0219] Thus, the accessory equipment 48, equipped with its wireless communication interface, can be advantageously combined with an audio-visual decoder lacking wireless communication capabilities. In this case, the accessory equipment 48 allows the use of wireless speakers for greater ease of installation.

[0220] The use of accessory equipment 48 is particularly advantageous when the subscriber's set-top box 2 does not also have built-in speakers. In this case, the subscriber can enjoy an immersive system, particularly with 360° sound reproduction, using known wireless rear speakers and the speakers of the unknown television 3.

[0221] According to one embodiment, the accessory equipment 48 is configured to retrieve information from the TV 3 relating to the TV 33 (for example the TV model, model number, number and distribution of speakers on the TV), for example via the HDMI link by accessing the EDID (for Extended Display Identification Data) of the TV, so as to be able to precisely position the TV speakers in the sound space, once the RF label associated with the TV has been located.

[0222] Of course, the invention is not limited to the embodiments described but encompasses any variant falling within the scope of the invention as defined by the claims.

[0223] As we have seen, the audio playback equipment whose position (and possibly orientation) is used to adapt the audio signals of the multichannel playback is not necessarily a television.

[0224] Similarly, the audio broadcasting equipment is not necessarily a set-top box; it may be a different piece of equipment, for example a HiFi amplifier connected to speakers.

[0225] It would be possible, in order to determine the position (and possibly the orientation) of the audio playback equipment(s), to use antennas from the audio broadcasting equipment (and other RF components) that are already used for other functions. For example, in the case of the set-top box, the antennas used for communication in a Wi-Fi network can be used. Similarly, the microphones used can be microphones originally intended for other functions (for example, the voice assistant function). The implementation of the invention is therefore very inexpensive since it does not require dedicated hardware, with the exception of the RF label placed on the audio playback equipment.

[0226] The localization modules can implement technologies different from those described here. For example, it is possible to use LIDAR (i.e., Light Detection and Ranging) or Wi-Fi signals (or signals from any other radio communication method) to implement the time-of-flight measurement method. The use of FMCW mode for the localization method using Doppler radar has been described. Another possible embodiment uses Pulsed Doppler radar, which is based on wave trains and is compatible with the UWB standard (which also has a Pulsed Doppler radar mode, since it is message-based and therefore pulsed in nature).

Claims

Demands

1. Audio playback equipment (2), arranged to implement multichannel audio playback from first audio signals (Sal) in an audio system (1) comprising a plurality of audio devices (3, 47), at least one of the audio devices being integrated into an audio playback equipment (3) separate from the audio playback equipment (2), the audio playback equipment comprising a processing unit (11) arranged to: - acquire a position (q>, d) of the audio playback equipment (3), obtained by a localization method using radio frequency waves; - acquire at least one audio parameter (Ft, Re) representative of an acoustic response of the audio playback equipment (3); - adapt at least one of the first audio signals (Sal) according to the position of the audio playback equipment (3), and at least one audio parameter (Ft, Re), to obtain second audio signals (Sa2);- implement multichannel audio playback using second audio signals (Sa2).;

2. Audio playback equipment according to claim 1, wherein the processing unit (11) is also arranged to acquire an orientation (|3) of the audio playback equipment (3), and to adapt at least one of the first audio signals (Sal) also according to the orientation of the audio playback equipment (3).

3. Audio broadcasting equipment according to any one of the preceding claims, comprising a first primary localization module (15; 34) arranged to implement a time-of-flight measurement method for measuring a distance (d) between the audio broadcasting equipment (2) and the audio playback equipment (3), and an angle measurement method (q>, 0, |3) for measuring at least one angle between the audio broadcasting equipment (2) and the audio playback equipment (3).

4. Audio broadcasting equipment according to claim 3, wherein the first primary location module (15) comprises a module primary UWB (20) arranged to communicate with a secondary UWB module (21) of the audio playback equipment (3).

5. Audio broadcasting equipment according to claim 4, the primary UWB module (20) comprising two first pairs of antennas (23a, 23b, 24a, 24b) positioned orthogonally with respect to each other, the first two pairs of antennas being arranged to cooperate with at least one second pair of antennas (27a, 27b, 28a, 28b) integrated in the secondary UWB module (21).

6. Audio broadcasting equipment according to claim 3, wherein the first primary location module (34) is arranged to implement a radar technique, preferably Doppler, and comprises a radar source (31) arranged to cooperate with at least one radio frequency tag (36; 40) positioned on the audio playback equipment (3).

7. Audio broadcasting equipment according to any one of the preceding claims, wherein said at least one audio parameter is selected from: - an acoustic delay (Re) due to a transmission chain between the audio broadcasting equipment (2) and the audio playback equipment (3), and / or to processing carried out by the audio playback equipment (3), and - a transfer function (Ft) of the audio playback equipment (3).

8. Audio playback equipment according to any one of the preceding claims, wherein at least one audio parameter includes an indicator of a change in sound volume resulting from a volume command issued by a user (45) to the audio playback equipment (2), the processing unit (11) being arranged to adapt, according to said indicator, at least a first audio signal transmitted to the audio playback equipment (3) so as to compensate for said change in sound volume.

9. Audio broadcasting equipment according to any one of the preceding claims, the audio broadcasting equipment (2) being a decoder box (2) incorporating an audio device (4) comprising at least one loudspeaker (5).

10. Audio broadcasting equipment according to any one of the preceding claims, the audio broadcasting equipment (2) being arranged to determine a position (A, a) of a user (45), the unit of processing (11) being arranged to adapt at least a first audio signal (Sal) also according to the position of the user (45).

11. Audio broadcasting equipment according to claim 1, the audio broadcasting equipment (2) being connected to an accessory equipment (48) separate from the audio broadcasting equipment (2) and the audio playback equipment (3), and being arranged to receive said accessory equipment (48) the position (q>, d) of the audio playback equipment (3), as well as said at least one audio parameter (Ft, Re).

12. An audio playback method, implemented in the processing unit (11) of an audio playback device (2) according to any one of the preceding claims, comprising the steps of: - acquiring a position (q>, d) of the audio playback device (3), obtained by a localization method using radio frequency waves; - acquiring at least one audio parameter (Ft, Re) representative of an acoustic response of the audio playback device (3); - adapting at least one of the first audio signals (Sal) according to the position of the audio playback device (3), and at least one audio parameter (Ft, Re), to obtain second audio signals (Sa2); - using the second audio signals (Sa2) to implement multichannel audio playback.

13. Computer program comprising instructions that cause the processing unit (11) of the audio broadcasting equipment (2) according to any one of claims 1 to 11 to perform the steps of the audio broadcasting process according to claim 12.

14. Computer-readable recording medium on which the computer program according to claim 13 is recorded.

15. Accessory equipment (48), arranged to be connected to audio broadcasting equipment according to claim 11, the accessory equipment comprising: - a second primary location module (51) arranged to evaluate the position ( <p, d) de l’équipement de restitution audio (3), le deuxième module de localisation primaire (51) étant agencé to implement the localization method using radio frequency waves; - an audio capture module (52), comprising at least one microphone (56), and arranged to produce at least one audio parameter (Ft, Re) representative of the acoustic response of the audio playback equipment (3); - a first communication module (53), arranged to transmit to the audio broadcasting equipment (2) the position (q>, d) of the audio playback equipment (3), as well as at least one audio parameter (Ft, Re).

16. Accessory equipment according to claim 15, the first communication module (53) being arranged to receive the second audio signals (Sa2) transmitted by the audio broadcasting equipment (2), the accessory equipment (48) further comprising a second communication module (57) arranged to transmit the second audio signals to the audio devices (47) of the audio system (1) to implement multichannel audio playback.

17. System comprising the audio playback equipment (2) according to any one of claims 1 to 11, and a secondary localization module (21; 36; 40) arranged to be positioned on the audio playback equipment (3) and used to implement the localization method.

18. System according to claim 17, comprising an audio broadcasting equipment (2) according to claim 6, the radio frequency location module comprising said at least one radio frequency tag (36) which is a passive tag comprising an array of dielectric resonators (37) and a Van Atta reflector (38).

19. System according to claim 17, comprising audio broadcasting equipment according to claim 6, the radio frequency location module comprising at least one radio frequency tag (40) which is an active tag comprising a Van Atta reflector (41), a microwave switch (42), and a processor (43) arranged to activate and deactivate the Van Atta reflector, according to a determined frequency, by driving the microwave switch(s).

20. The system according to claim 17, comprising audio broadcasting equipment according to claim 11, the system further comprising accessory equipment (48) according to claim 15.

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