EP0781070B1 - Acoustic antenna for computer workstation - Google Patents

Description

The invention relates to an acoustic antenna for computer workstation.

At present, the use of radio stations IT work is set to grow, both in with regard to single-station workstations, which multi-user workstations, networked.

In all cases, the workstation tends to become a communication interface between the user and the machine, or the workstation, or even between each user, when the workstations are networked. In particular, in the latter case, a particularly interesting application of these workstations related to videoconferencing, application during which several workstations and well heard their users can communicate through messages conveyed by audio and video links.

In order to minimize disruption to the environment work of each workstation user above, it is essential that each workstation allows the user to communicate by video and audio messages regardless, in particular, of the position of the user, speaker, with respect to the station of work considered, or even, more generally, when several workstations are combined in the same meeting room, as part of a videoconference meeting multiple, regardless of the environmental context thus created, as well as noises generated by the fans of these workstations, external noise from air conditioning or other, as well as acoustic echo generated by the speakers of these workstations.

Classic computer workstations currently commercially available, even if these stations are equipped with so-called "multimedia" processing means such as in particular microphones and speakers, standard audio and video cards MPEG, cannot claim to carry out such functions.

More recent work has been carried out in order to implement computer workstations equipped with high-performance acoustic antennas, making it possible to perform the aforementioned functions. The solutions adopted, for example according to French patent application No. 94 08809, filed on July 15, 1994 in the name of the same inventors and which constitutes prior art according to Article 54 (3) EPC, have enabled the implementation work of computer workstations equipped with a "cylindrical" type acoustic antenna. This type of acoustic antenna actually comprises an aerial consisting of a plurality of microphones distributed over a concave surface. It presents good performances with regard to the selectivity and the directivity of the sound recording of the speaker, independently of the context of the environment of the latter, and of the coupling with the speaker (s).
However, the aerial thus formed, having the shape of a concave strip placed above the upper face of the video display monitor of the workstation, was considered unattractive by users or potential users. In addition, the concave strip constituting the aforementioned aerial cannot be easily integrated into the terminal of the computer workstation, in particular into the housing of the video display monitor thereof, unless significant modifications of the latter are provided, these modifications being moreover likely to modify the generally satisfactory conditions of sound recording.

From document WO-A-9 531 805 there are also known acoustic antennas rectilinear according to the preamble of independent claims 1 and 3.

The object of the present invention is to remedy the aforementioned drawbacks of art acoustic antennas more specifically intended for computer work.

An object of the present invention is in particular the implementation of an acoustic antenna for computer work preserving properties of conditions sound recording, likely to be integrated without major difficulty to the video display monitor of the workstation for which it is intended.

Another object of the present invention is also the implementation of an acoustic antenna for station workstation presenting, in addition to the properties of aforementioned sound condition, which, although not easily integrated, presents a very discreet appearance and therefore easily acceptable aesthetically for users.

These objectives are achieved by the devices according to the claims independent 1 and 3. Advantageous achievements are given in dependent claims 2 and 4-8.

The acoustic antenna, object of the present invention, finds application in the implementation of computer work, more particularly intended for videoconferencing applications.

• la figure 2a représente un schéma de principe d'une antenne acoustique conforme à l'objet de la présente invention, de type "broadside" en vocable anglo-saxon ;
• la figure 2b représente un schéma de principe d'une antenne acoustique conforme à l'objet de la présente invention, de type "end-fire" en vocable anglo-saxon ;
• la figure 3a représente un mode de réalisation préférentiel d'une antenne acoustique de type "broadside" telle que représentée en figure 2a ;
• la figure 3b représente un détail de réalisation de l'antenne acoustique de type "broadside" de la figure 3a ;
• la figure 4a représente un mode de réalisation non limitatif d'une antenne acoustique de type "end-fire" telle que représentée en figure 2b ;
• la figure 4b représente un mode de réalisation structurel de l'antenne acoustique telle que représentée en figure 4a ;
• la figure 4c représente une vue en coupe selon un plan de symétrie longitudinale de l'antenne acoustique représentée en figure 4b ;
• la figure 4d représente une antenne acoustique de type "end-fire" placée sur le bord supérieur du moniteur d'affichage d'une station de travail ;
• les figures 5a à 5d représentent différents diagrammes de directivité en réception pour différentes antennes acoustiques, objets de la présente invention.

It will be better understood on reading the description and on observing the drawings below, in which, in addition to FIG. 1 relating to the prior art,

• FIG. 2a represents a block diagram of an acoustic antenna conforming to the object of the present invention, of the "broadside" type in Anglo-Saxon term;
• FIG. 2b represents a block diagram of an acoustic antenna conforming to the object of the present invention, of the "end-fire" type in Anglo-Saxon term;
• FIG. 3a represents a preferred embodiment of an acoustic antenna of the "broadside" type as shown in FIG. 2a;
• FIG. 3b represents a detail of the acoustic antenna of the "broadside" type of FIG. 3a;
• FIG. 4a represents a nonlimiting embodiment of an acoustic antenna of the "end-fire" type as shown in FIG. 2b;
• Figure 4b shows a structural embodiment of the acoustic antenna as shown in Figure 4a;
• Figure 4c shows a sectional view along a longitudinal plane of symmetry of the acoustic antenna shown in Figure 4b;
• FIG. 4d represents an end-fire type acoustic antenna placed on the upper edge of the display monitor of a workstation;
• Figures 5a to 5d show different directivity patterns in reception for different acoustic antennas, objects of the present invention.

A more detailed description of the acoustic antenna for computer workstation conforming to the object of the present invention will now be given in conjunction with Figures 2a and 2b.

In general, it is indicated that the computer work includes a display monitor or display screen enabling the function of support of the acoustic antenna object of this invention.

In addition, it is indicated that the latter comprises a plurality of microphones, denoted M _i , connected to a summing circuit intended, from an incident sound wave OSI, to deliver a corresponding sound signal. In FIGS. 2a and 2b, the summing circuit is not shown so as not to overload the drawing. The microphones M _i are distributed in an arrangement to form at least one substantially rectilinear line, the line x'x in FIG. 2a. The microphones M _i are each spaced relative to a reference microphone, denoted M _ir , placed in the vicinity of the vertical axis of symmetry of the screen according to a determined distribution law. It is thus understood that the reference microphone M _ir allows, for a symmetrical configuration of the distribution of the microphones on the substantially rectilinear line x'x, to achieve a configuration symmetrical with respect to the average position of the user speaker. The arrangement of aforementioned microphones then presents a substantially cylindrical directivity diagram whose axis of revolution is formed by the rectilinear line previously mentioned.

In the case of FIG. 2a, it is indicated that the acoustic antenna for computer workstation, object of the present invention, corresponds to an embodiment of the "broadside" type. In such a case, it is indicated that the incident sound wave OSI, coming from the speaker, is then perpendicular to the above-mentioned rectilinear line x'x on which the microphones M _i are distributed. The arrangement of microphones then presents a directivity diagram in reception which is constituted by a substantially vertical disk of width D in the azimuth plane P, that is to say in the plane comprising the azimuth angle for the reference microphone M _ir .

In the case of the embodiment of FIG. 2a, it is indicated that the thickness of the disc thus formed in fact corresponds to the width of the main lobe of the directivity diagram on reception of the antenna thus formed. In such a case, it is indicated that the thickness D of the aforementioned disc is, at a given frequency, inversely proportional to the length of the antenna, that is to say ultimately to the number of microphones M _i and their spacing compared to the reference microphone M _ir .

In the case of the embodiment of FIG. 2b, this embodiment corresponding to an acoustic antenna of the "end-fire" type, the substantially straight line bears the reference y'y, this line being substantially parallel to the mean direction of propagation of the OSI incident sound wave. In such a case, the arrangement of microphones has, with respect to the reference microphone M _ir , a directivity diagram in reception also substantially cylindrical, the axis of revolution being formed by the above-mentioned straight line. In this case, however, the OSI incident sound wave parallel to the direction of the substantially rectilinear line y'y, on the contrary sees a more directivity pattern in reception insofar as the dimension D relative to the opening of the directivity in reception corresponds substantially to the diameter of the substantially cylindrical directivity diagram, the opening angle  of the main lobe being of the order of 80 °. In this case also, the reference microphone M _ir is of course placed in the vicinity of the vertical axis of symmetry of the screen and the successive microphones M _i are placed on the line y'y substantially in the vertical plane of symmetry of the aforementioned screen of the corresponding computer workstation.

A more detailed description of the embodiment relating to FIG. 2a corresponding to an antenna "broadside", will now be given in conjunction with Figure 3a.

In the embodiment of FIG. 3a, it is indicated that the acoustic antenna according to the invention comprises, to make the arrangement of microphones, a plurality of microphones M _i distributed on a first substantially horizontal line, placed in the upper part of the screen and at least one microphone placed on a second and a third line x ₁ x ' ₁ and x ₂ x' ₂ respectively, the second and the third line being placed perpendicular to the ends of the first line x'x. In accordance with a particularly advantageous aspect of the acoustic antenna, object of the present invention, the microphones of the first, second and third lines are arranged on a plane.

Preferably, as also shown in FIG. 3a, the microphones M _i are arranged on an antenna support, made for example of plastic material, this antenna support and the corresponding microphones M _i being arranged at the top of the filter. of the display screen, as shown in Figure 3a. The antenna support and the microphones can also be placed on the screen itself or on the video monitor comprising this screen. More particularly, it is indicated that the microphone support can be produced by a plastic strip whose height is of the order of a few centimeters, 4 to 5 cm, in the direction orthogonal to the direction of propagation of the OSI incident sound wave. The microphones M _i are thus embedded in the support strip and are thus placed 2 or 3 cm in front of the screen itself. Such an arrangement has been found satisfactory from the acoustic point of view insofar as such placement of the microphones does not disturb the sound pickup of the incident sound wave OSI. It is indicated that, in a conventional manner, the microphones M _i and the reference microphone M _ir are grouped by interconnection into elementary sub-antennas.

In Figure 3b, there is shown a detail of the antenna type "broadside" of Figure 3a, including the subdivision thereof into sub-antennas. The microphones, denoted M _i0 to M _i8 , are by way of nonlimiting example of unidirectional type. They are distributed symmetrically with respect to the central microphone M _i0 constituting in fact the reference microphone M _ir . The symmetrical distribution is heard on the support in the direction x'x orthogonal to the direction of the incident sound wave OSI. Each microphone is connected to a common summator Σ by means of filters, denoted H ₁ to H ₄ , by means of elementary summers, denoted S ₁ to S ₄ , each elementary summer S ₁ and S ₄ in fact defining a sub-antenna.

• le microphone de référence M_i0 est connecté aux quatre sommateurs élémentaires S₁ à S₄ ;
• les microphones M_i3, M_i4, respectivement adjacents aux microphones précédents M_i1, M_i2, aux sommateurs élémentaires S₄, S₃ ;
• les microphones successifs M_i5, M_i6 respectivement adjacents aux microphones précédents M_i3, M_i4, aux sommateurs élémentaires S₃, S₂ ;
• les microphones successifs M_i7, M_i8 respectivement adjacents aux microphones précédents M_i5, M_i6, aux sommateurs élémentaires S₁ et S₂.

In the embodiment of FIG. 3b,

• the reference microphone M _i0 is connected to the four elementary _summers S ₁ to S ₄ ;
• microphones M _i3 , M _i4 , respectively adjacent to the preceding microphones M _i1 , M _i2 , with elementary summers S ₄ , S ₃ ;
• the successive microphones M _i5 , M _i6 respectively adjacent to the preceding microphones M _i3 , M _i4 , with the elementary summers S ₃ , S ₂ ;
• the successive microphones M _i7 , M _i8 respectively adjacent to the preceding microphones M _i5 , M _i6 , at the elementary summers S ₁ and S ₂ .

The connection of each microphone to the aforementioned elementary summers can advantageously be carried out by means of corresponding switches, denoted I ₀ to I ₈ , and each elementary summator S ₁ to S ₄ can be connected to the common summator Σ via a filter H ₁ to H ₄ and a switch in series IS ₁ to IS ₄ . The law of spatial distribution of the microphones symmetrically with respect to the reference microphone M _i0 , along the direction x'x is of the form: x = kd In this relation, k is a relative integer, d represents an arbitrary distance linked to the cutoff frequency of the filters H ₁ to H ₄ , x represents the algebraic value of the abscissa of each microphone with respect to the reference microphone M _ir , the microphone M _i0 .

In a preferred embodiment, d = 2.13 cm, the abscissa of the 9 microphones installed on the support S were as follows: E7 E5 Mi3 e1 Mi0 Mi2 E4 E6 mi8 -8d -4d -2d -d 0 d 2d 4d 8d -17,04cm - 8.52 cm - 4.26 cm - 2.13 cm 0 2.13 cm 4.26 cm 8.52 cm 17.04 cm

It is then indicated that the value of the distance d is chosen as a function of the value of the cutoff frequency of the filters H ₁ to H ₄ .

The "broadside" antenna embodiment according to Figures 2a and 3a, 3b appears particularly interesting insofar as, while it allows conditions of completely satisfactory sound intake, the integration of the corresponding acoustic antenna does not pose any difficulty major.

Of course, and in order to increase the rate of rejection of environmental noise and the room effect, this in particular for application to videoconferencing workstations, in the case of the embodiment according to the figure 2a of the acoustic antenna, object of the present invention, this embodiment corresponding to a "broadside" type antenna, the only solution which can be practically envisaged for increasing the aforementioned rejection rate, is to reduce the thickness D of the disc, that is to say the opening dimension of the main lobe of the directivity diagram in reception, by the increase in the number of microphones M _i and in the dimensions of the antenna thus produced.

However, increasing the dimensions and the number of microphones cannot be envisaged beyond a certain limit, in particular because of the difficulties of integrating an antenna which would have dimensions which are too large compared to the dimensions of the monitor. display. In addition, when the thickness D of the disc, the opening dimension of the main lobe, decreases beyond a certain value, the slightest displacement of the speaker relative to the plane of symmetry of the reference microphone M _ir and ultimately of the plane of symmetry of the display screen, has the effect of causing a very strong reduction in the transmitted speech signal because the speaker is then outside the zone of maximum sensitivity of the main lobe of the directivity diagram in reception.

For this reason, and in accordance with the same aspect of the acoustic antenna, object of the present invention, a second embodiment, of the "end-fire" type, was developed, this embodiment corresponding to the antenna acoustics as described in connection with FIG. 2b.

In general, it is indicated that the acoustic antenna shown in FIG. 2b is similar to the microphones known by the name of micro guns. In addition, by the correct set of delays applied to the elementary speech signals delivered by each microphone M _i and by the reference microphone M _ir , the sound waves emitted by the speaker, the incident sound wave OSI being in the extension of the 'alignment of microphones in the above case, are in fact preferred.

Given the configuration of the microphones and delays, the directivity diagram in reception is, as shown in Figure 2b, formed by substantially a cylinder whose base is oriented towards the speaker.

Rejection of environmental noise and effect of room is substantially identical in number of microphones equal to that obtained with the type acoustic antenna "Broadside". However, the opening angle of the main lobe is much higher, around 80 ° instead of 25 ° in the case of the "broadside" type antenna. Consequently, the embodiment of FIG. 2b makes it possible to maintain sufficient speech quality when traveling speaker's sides with respect to the plane of symmetry vertical view screen.

A more detailed description of an embodiment preferential of the end-fire type acoustic antenna shown in Figure 2b will now be given in conjunction with Figure 4a.

In general, it is indicated that the acoustic antenna according to the invention is subdivided into sub-antennas. In the embodiment of FIG. 4a, the acoustic antenna, of the "end-fire" type, is deemed to consist of 9 successive microphones, aligned on a support from the reference microphone M _ir designated by M _i0 , noted S The other successive microphones, in the direction of propagation of the incident sound wave OSI, are noted successively M _i1 to M _i8 . As will be seen in FIG. 4a, the acoustic antenna according to the invention is subdivided into sub-antennas, each sub-antenna comprising microphones spaced on the rectilinear support by a determined distance. Thus, a first sub-antenna is formed by the microphones M _i8 to M _{i6 as} well as by the microphones M _i4 and by the reference microphone M _ir , these microphones being connected to the same elementary adder S ₁ , a second elementary antenna formed by microphones M _i6 to M _{i4 as} well as by microphones M _i2 and M _ir connected to the same elementary adder S ₂ , and a third elementary antenna is finally formed by microphones M _i4 to M _i1 and by the reference microphone M _ir linked to the same third elementary summator S ₃ . Of course, the elementary summers S ₁ , S ₂ , S ₃ are connected to a common summator, denoted Σ, delivering the speech signal via, for example, filters, denoted H ₁ , H ₂ and H ₃ .

According to a particularly advantageous characteristic of the acoustic antenna, object of the present invention, this antenna comprising means for analog-digital conversion of the sound signal delivered by each microphone M _i by sampling at a given sampling frequency Fe, each microphone is distant of the reference microphone M _ir according to a distance law such that the delays in reception by each microphone of an incident sound wave OSI are multiple of the sampling period T = 1 / Fe.

Of course, the sound signal delivered by each microphone is then subjected to a corresponding delay via a delay circuit, denoted D ₀ to D ₇ in FIG. 4a, the microphone M _i8 not being of course subject to no delay due to the maximum delay in receiving the sound signal from the speaker received by the latter microphone.

As shown in FIG. 4a, it is understood that the maximum delay is thus provided by the delay circuit D ₀ on the sound signal delivered by the reference microphone M _ir or M _i0 , the value of this delay being successively decreasing for the delays brought by the delay circuits D ₁ to D ₇ on the sound signals delivered successively by the corresponding microphones M _i1 to M _i7 .

The distribution law of microphones, reference microphones M _ir and successive microphones M _i1 to M _i8 , on the support S, this distribution law of course making it possible to generate successive delays on the signal of the incident sound wave OSI according to a determined delay law, and the corresponding delays brought by each delay circuit D ₀ to D ₇ , allow, at the level of each elementary summator S ₁ to S ₃ , and finally at the level of the global summator ateur, to ensure a summation in phase of the speech signals delivered by each microphone constituting the acoustic antenna according to the invention, and thus to favor the incident sound wave OSI originating from the speaker in the reception radiation lobe previously mentioned in the description.

More particularly, it is indicated that the microphones M _ir to M _i1 , M _i8 are successively spaced on the rectilinear support S by a distance in arithmetic progression of multiple reason of the smallest distance d separating the neighboring microphone from the microphone of reference. Thus, the distance separating two successive microphones is of the form: x = kd = k vs Fe .

In the previous relation, we indicate that k is a positive integer, c represents the propagation speed of the incident sound wave in the ambient environment and Fe represents the sampling frequency.

In the embodiment as represented in FIG. 4a, and taking into account the preceding indications, it is indicated that the microphone M _i1 is distant from the microphone M _ir , reference microphone, by the distance d, the microphones M _i2 to M _i4 are each at the same distance d. The microphones M _i5 and M _i6 are distant from the front microphone M _i4 respectively M _i5 by a distance 2d, and finally, the microphones M _i7 and M _i8 are distant from the front microphone, respectively M _i6 , M _i7 by a distance 4d . Consequently, and in order to ensure a suitable delay of the sound signal delivered by each microphone, the delay circuit D ₀ makes it possible to apply a delay equal to the sum of the delays introduced by the maximum spacing between the reference microphone M _ir and the extreme microphone M _i8 , ie a delay corresponding to 16 sampling periods since in fact, the minimum elementary distance d separating two successive microphones corresponds to a time delay in propagation of the incident sound wave equal to a sampling period.

In the same way, the delay circuits D ₁ to D ₇ make it possible successively to generate a delay equal to 15T, 14T, 13T, 12T, 10T, 8T and 4T where T represents the value of the sampling period of the sound signal delivered by each microphone.

It is indicated that developments have been made for an acoustic antenna of the "end-fire" type as described above and for a sampling frequency Fe = 16 kHz. Under these conditions, the minimum distance between microphones is given by the relation: d = vs Fe = 2.13 cm.

The abscissa of the 9 microphones installed on the support S were then as follows: 0 d 2d 3d 4d 6d 8d 12d 16d 0 cm 2.13 cm 4.26 cm 6.39 cm 8.52 cm 12.78 cm 17.04 cm 25.56 cm 34,08cm

The value of d can arbitrarily not limitative be chosen identical in the case of the antenna "broadside" and in the case of the "end-fire" antenna.

As regards a practical embodiment of the delay circuits D ₀ to D ₇ , it is indicated that these delay circuits can be produced, either by analog circuits when the delay is applied directly at the output of each microphone concerned, or, on the contrary, from digital circuits when the delay is applied while the analog-to-digital conversion previously mentioned in the description has already been carried out. The analog or digital embodiment of the delay circuits poses no problem because the analog to digital conversion of the speech signals delivered by each microphone can be carried out in a conventional manner from analog digital converters Δ, Σ. Corresponding embodiments will not be described in detail in the present description because they correspond to techniques known to those skilled in the art. These analog digital converters can be associated with the delay circuits or preferably at the output of the microphones, as mentioned in FIG. 4a by the reference + CAN.

The practical realization at the mechanical level of the acoustic antenna, object of the present invention, such as represented in FIG. 2b or 4a, on the other hand presents specific features allowing implementation developed of the acoustic antenna according to the invention.

In general, we indicate that the support S is made from a rigid support, acoustically not disturbing.

In a more particular way, as represented in FIG. 4b, the support S can consist of a rigid rod forming the rectilinear support and by a multiple microphone stands, each microphone stand microphone being formed by a double mechanical part substantially symmetrical structural element.

In FIG. 4b, the microphone supports carry, without limitation, the reference P ₀ to P ₄ for example. Each microphone support P ₀ to P ₄ is formed by a mechanical part with a double element of substantially symmetrical structure, a first element of which is intended to ensure the positioning of the corresponding microphone support on the rigid rod S, while a second element is intended to receive and maintain a corresponding microphone. In FIG. 4b, the mechanical part with a double element of substantially symmetrical structure has the shape of an eight, one of the rings of which is threaded on the support S in order to ensure the positioning of the microphone support on the rigid rod S above, and the second ring constituting the second element is intended to receive and maintain a microphone. The mechanical resistance of the microphones on the supports is guaranteed by a forced mounting, for example, or by a locking needle screw, any risk of shifting in position of the microphones being then eliminated.

In Figure 4c, there is shown a sectional view according to the longitudinal section plane Q of FIG. 4b.

As shown in FIG. 4c above, we indicates that the rod forming the support S is hollow and has a central core. The support rod S is in additionally provided on one of the generating lines of the surface side thereof, a plurality of through holes connecting the central soul and the part outside of the rod, this to allow the passage of fc connection wires of each microphone in the core Central. Finally, it is indicated that the mechanical parts to double structural element constituting the supports of microphones advantageously have a dimension thickness in the longitudinal y'y direction of the support S as low as possible, so as not to disturb the acoustic characteristics of each microphone.

In addition, as shown in FIG. 4a, the acoustic antenna, object of the present invention, can advantageously include a set of switches, denoted I ₀ to I ₈ , a switch of this set of switches being placed in serial link on the connection for example to the corresponding delay circuits D ₀ to D ₇ or to the element summator S ₁ . Each switch I ₀ to I ₈ ensures the connection or non-connection of at least one microphone to the summing circuit Σ via the elementary summing circuits. This operating mode then makes it possible to modify the reception diagram of the acoustic antenna according to the invention as a function of the configuration of connection or non-connection of the microphones of the antenna. In fact, the switching to a different antenna diagram can also be carried out by switching at the level of the output signals delivered by the sub-antennas, that is to say by the summers S ₁ to S ₃ . To this end, specific switches IS ₁ to IS ₃ can be provided, as shown in FIG. 4a. For example, a larger lobe, for the case where several people are present in front of the work station, can be obtained by replacing the sum at the output of the summator Σ by the signal delivered by the summator S ₃ , that is to say say by the smaller sub-antenna. The transfer function of the filter associated with the aforementioned sub-antenna is modified accordingly. In this hypothesis, the switch IS ₃ is closed and the switches IS ₁ and IS ₂ open, the signal delivered by the summator S ₃ being alone transmitted to the summator Σ. This procedure appears interesting for the antenna "broadside" in particular, as shown in Figure 3b, the switch being made from switches I ₀ to I ₈ and / or IS ₁ to IS ₄ for example.

In general, with regard to the implementation of the straight antenna which is the subject of the present invention, it is indicated, both with regard to "broadside" type antennas and to "end-fire" type antennas, that there is a minimum condition relating to the distance between microphones so as to avoid the disturbance phenomenon, known by the English name of " aliasing ".

For "broadside" type antennas, the condition is d <λ where λ denotes the wavelength of the incident sound wave.
For an end-fire antenna, this condition is written d <λ / 2.
Consequently, it follows that an "end-fire" type antenna has a smaller size than a "broadside" type antenna, which of course makes it possible to obtain a better compactness of the antenna thus produced.

In either case, once the signals are delivered by microphones have been digitized, the elementary delay permit is equal to the sampling period previously mentioned in the description. This elementary delay proves, however, insufficiently precise to ensure the pointing the antenna in the direction of the speaker. according to an advantageous characteristic of acoustic antennas, objects of the present invention, a way of making such delays is to arrange these microphones so delays are multiple of the sampling period supra. It is no longer necessary, for pointing in the direction of the speaker, use expensive interpolation techniques in computation time term.

In Figures 5a to 5b, there are shown different directivity diagrams in reception for an antenna of "broadside" type, FIG. 5a, using microphones omnidirectional, 9 microphones as shown in Figure 2a. The directivity diagram thus represented, the microphones being aligned on the axis of symmetry x'x, present, as previously mentioned, substantially the appearance of a vertical disc, but more particular, that of a torus, at least for the lobe main as shown in Figure 5a. We indicate however, depending on the grouping of microphones and of their spacing, the directivity diagram includes also degenerate lateral lobes extending into the direction x'x, these side lobes, although present, however, not being significantly represented in FIG. 5a, these being hidden in the representation chosen.

In FIG. 5b, on the contrary, the directivity diagram of an antenna of the "end-fire" type has also been represented, also comprising 9 microphones placed as shown in FIG. 2b. The microphones are of course placed and aligned in the direction y'y as shown in FIG. 5b, the directions x'x, y'y and z'z in FIG. 5a and in FIG. 5b being identical in order to facilitate the comparison. . In the case of FIG. 5a and of FIG. 5b, it is indicated that the reference microphone M _ir is placed in the vicinity of the origin of the axes OXYZ, the corresponding directivity diagrams being those carried out in the far field.

In FIG. 5b, it can be seen that the directivity diagram has substantially the shape of a cylinder for which the opening of the main lobe is much greater than that of the opening of the main lobe of the directivity diagram of the "broadside antenna""shown in Figure 5a. In both cases, the speaker is, with respect to the reference microphone M _ir , in the direction y'y.

In FIGS. 5c and 5d, there is shown, with a view to above, a top view respectively of FIG. 5a in which the lateral lobes of the directivity diagram are apparent, and from FIG. 5b in which the lobe rear has been removed by judicious choice of spacings microphones and delays that are applied to speech signals generated by them. Microphones used in this case are unidirectional.

In FIG. 5d, the diagram of directivity of an end-fire antenna for which the microphones are distributed in the direction y'y. From a broadside antenna, for which the microphones are distributed in the direction x'x and whose directivity diagram is shown in Figure 5c, it is possible, according to a remarkable aspect of the antenna object of the invention, to obtain a diagram of directivity similar to that of an end-fire antenna such as shown in Figure 5d, but subject to a rotation of π / 2 by the introduction of delays on the signals delivered by the microphones, the axis of symmetry of the diagram directivity then being the axis x'x.

In both cases, the spatial selectivity of acoustic antennas used is linked to the ratio of their size at the wavelength considered. In the field at low frequencies, the antennas used reduce little effect of the acoustic environment of these.

In the case of the implementation of an antenna "broadside" type as shown in Figure 2a, adding two side microphones, as shown in figure 3, partially alleviates this defect.

However, with regard to the acoustic antenna of end-fire type, increased selectivity at low frequency requires a noticeable increase in the size of the antenna so of course we want to keep the same structure. In the case of the end-fire type acoustic antenna in which the digitization of all the signals of speech delivered by each microphone is performed it is possible to implement treatment techniques for very sophisticated speech signal, likely to improve rejection of noise and room effect. These treatment techniques may consist of techniques filtering of Wiener or Ephraim and Malah.

In the same way and in particular in the case of the end-fire antenna, it is possible to modify the shape of the main lobe of the directivity diagram, especially in the case where several people located in front the work computer terminal wish to take part communication, especially in the case of an application video conferencing. Switching can be performed on a sub-antenna. In addition, quality improvement provided by the acoustic antenna, object of this invention of either type is also significant for a remote speaker.

In such a case, the switches mentioned above can then be used so as to switch on demand the antenna of the "end-fire" type or, if necessary, the antenna of the "broadside" type on a preferred microphone, the reference microphone M _ir , all the other microphones being for example disconnected.

A certain spatial selectivity can however be kept by switching to a specific sub-antenna smaller.

Compared to a single microphone, the antenna acoustics, object of the present invention, whether in its "broadside" or "end-fire" embodiment, improves echo control since this type of antenna increases, by its spatial selectivity, the decoupling between the speaker and the sound system.

However, when an echo canceller is used, the reduction in coupling is greater in the high frequencies than in the low frequency domain, and there it is therefore necessary to provide for an adaptation of the parameters echo canceller accordingly.

Similarly, in the case of modification of the main lobe of the receiving pattern or in the case of the orientation thereof, it is necessary to adapt the operation of the echo canceller to these changes. This adaptation is necessary, in particular in video conferencing applications or even in the case individual computer terminal applications.

• à replier l'antenne "broadside" à 180° autour du microphone de référence M_ir, M_i0 ;
• à décaler les microphones confondus de la distance séparant ces derniers du microphone adjacent, avant repliement, les microphones étant bien entendu réorientés par rotation vers la direction de l'onde sonore incidente OSI.

In addition, it is indicated that obtaining a directivity diagram in reception approaching that of an “end-fire” type antenna can be carried out using a “broadside” type antenna, except in this case. which relates to the rejection of rear waves, as previously mentioned in connection with FIGS. 5c and 5d. Indeed, it is understood that it is possible, in accordance with a particularly remarkable aspect of the acoustic antenna, object of the present invention, to switch from the "broadside" type antenna as shown in FIGS. 3a, 3b, to l 'antenna of the "end-fire" type as represented in FIGS. 4a, 4b, by a geometrical adaptation or transformation consisting of:

• folding the broadside antenna 180 ° around the reference microphone M _ir , M _i0 ;
• to shift the combined microphones by the distance separating them from the adjacent microphone, before folding, the microphones being of course reoriented by rotation towards the direction of the incident sound wave OSI.

Of course, the reverse transformation allows switch from the "end-fire" type antenna to the type "Broadside".

The aforementioned transformation results in the delay phase propagation of the incident sound wave OSI being compensated, on the "end-fire" type antenna, by the circuits delay, to produce directivity diagrams in reception approaching in either case, under the conditions previously described in the description, with increased ease of integration, respectively a much more discreet appearance.

Finally, the electronic orientation of the main lobe antenna can be realized thanks to the implementation of devices for interpolating the delivered speech signals by each microphone, such an orientation function main lobe electronics that can only be optimized in the event that a speaker locator system is used. Such an electronic orientation function of the main lobe finds a privileged application in the context of use and application for videoconferencing.

Claims (8)

1. An acoustic antenna for computer workstation including a display screen and comprising a plurality of microphones connected to a summator circuit, said microphones being distributed in a layout so as to form at least one straight line and each of said microphones being intended to be spaced, with respect to a reference microphone placed in the vicinity of the vertical axis of symmetry of the screen, according to a specified law, said layout comprising a plurality of microphones distributed over a first line substantially horizontal and intended to be placed at the upper part of said screen,
      wherein said layout further comprises at least one microphone placed on a second and a third line respectively, said second and third lines being placed perpendicularly to the ends of the said first line, said microphones of the first, second and third lines being arranged in a same plane, said layout exhibiting a substantially cylindrical directivity pattern whose axis of revolution is formed by said first straight line.
2. The antenna according to Claim 1, wherein said microphones are arranged on an antenna support intended to be arranged in the upper part of the filter of the display screen, of this screen or of the monitor which includes this screen.
3. Computer workstation including a display screen and an acoustic antenna, and comprising a plurality of microphones connected to a summator circuit, said microphones being distributed in a layout so as to form at least one straight line and each of said microphones being spaced, with respect to a reference microphone placed in the vicinity of the vertical axis of symmetry of the screen, according to a specified law, said layout comprising a plurality of microphones arranged on a straight support, wherein said straight support is placed substantially in the vertical plane of symmetry of said display screen, said microphones being spaced with respect to said reference microphone according to a specified law so as to form an antenna of the "end-fire" type, said antenna being subdivided into sub-antennas, each sub-antenna comprising microphones spaced apart on the straight support, by a specified distance, said layout exhibiting thus a substantially cylindrical directivity pattern whose axis of revolution is formed by said at least one straight line.
4. The antenna according to one of Claims 1 and 2 or antenna in a workstation according to Claim 3, wherein said antenna including means of analogue/digital conversion of the sound signal delivered by each microphone by sampling at a given sampling frequency Fe, each microphone is distanced from said reference microphone according to a distance law such that the delays in reception by each microphone of an incident sound wave are multiples of the sampling period corresponding to said sampling frequency.
5. The antenna according to Claim 4, wherein said microphones are successively spaced apart on said straight support by a distance which is in arithmetic progression with common difference a multiple of the smallest distance separating the neighbouring microphone from the reference microphone, the distance separating two successive microphones being of the form: x = kd = k c/Fe with k an integer, c denoting the speed of propagation of the incident sound wave.
6. Workstation according to Claim 3, wherein said antenna comprises:

   a rigid rod forming said straight support;

   a plurality of microphone supports, each microphone support being formed by a substantially symmetric double structural element mechanical piece, a first element being intended to provide for the placement of said microphone support on said rigid rod, and a second element being intended to receive and provide for the retention of a microphone.
7. Workstation according to Claim 6, wherein said rod is hollow and includes a central bore, said rod furthermore being furnished on one of the generator lines of its lateral surface with a plurality of through holes communicating between said central bore and the outside part of the rod, allowing thus passage of the connection wires of each microphone into said central bore.
8. The antenna according to Claims 1, 2, 4 and 5 or antenna in a workstation according to Claims 3, 6 and 7, wherein said antenna furthermore includes a gang of switches making it possible to provide for the connection of at least one microphone or one sub-antenna to said summator circuit, the transfer function of the filter associated with this sub-antenna being modified, thereby allowing to modify the reception pattern of said antenna as a function of the configuration of connection or nonconnection of the microphones of said antenna.

Images