WO2015114358A1

WO2015114358A1 - Audio communications system

Info

Publication number: WO2015114358A1
Application number: PCT/GB2015/050230
Authority: WO
Inventors: Habib Hussein; Chris Moore; Norman Davidson
Original assignee: Racal Acoustics Ltd.
Priority date: 2014-01-31
Filing date: 2015-01-30
Publication date: 2015-08-06
Also published as: GB201401705D0; GB2518024A

Abstract

An audio communications system comprising a plurality of stereo headsets linked through a communications network, wherein each of the stereo headsets comprises: a means of determining its own geographical location, a means of transmitting one or more signals, which include data indicating its own geographical location and a voice signal of the wearer, a means of determining its own orientation in two, three or more axes, a means for receiving signals from the other headset(s), a 3D audio engine, and a means for modifying a voice signal received from one of the other headset(s) using a received geographical location of the respective other headset, its own geographical location and its own orientation to provide an input to the 3D audio engine to place the received voice signal in a 3D audio space.

Description

Audio Communications System

The present disclosure relates to an audio communications system, in particular to an audio communications system comprising a plurality of stereo headsets, which audio communications system is configured such that the situational awareness of audio transmitted over the communications system, including voice communications, is improved for wearers of the headsets.

Present communications systems, which comprise stereo headsets that receive audio communications, play the received audio through speakers located in the headsets, which speakers are adjacent the user's ears. This is very different to the way a person perceives sounds ordinarily (without a headset). Sound is received direct from the source of the sound and the direction of the sound is readily perceived. Presently, the directional part of a sound is removed when transmitted over a communications system. This means the person listening to the sound/audio stream does not know where the sound originated from. If the location of the people using the communications system is a requirement in their operational environment, the individual person has to verbally communicate their location. The present invention arose in a bid to provide an improved communications system and offers a unique means of adding the directional part of a sound or voice into a communications system.

According to the present invention in a first aspect, there is provided an audio communications system as recited by Claim 1.

By virtue of such an arrangement, wearers of the stereo headsets are provided with the ability to communicate in a three-dimensional (3D) audio space. The wearers are provided with directional situational awareness of audio communications, including voice communications, which is lacking in prior art audio communications systems. According to the present invention in a further aspect, there is provided a method for providing situational awareness in a communications system using an audio

communications system as specified above. Further, preferred, features are presented in the dependent claims.

A non-limiting embodiment will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 shows a side view of a headset for use in the audio communications system of the present invention;

Figure 2 shows a front view of the headset of Figure 1;

Figure 3 shows a top view of the headset of Figure 1;

Figure 4 shows a side view of a helmet incorporating a headset for use in the audio communications system of the present invention;

Figure 5 shows a front view of the helmet of Figure 4;

Figure 6 shows a top view of the helmet of Figure 4;

Figure 7 shows an aerial map view of an audio communications system of the present invention in use; and

Figure 8 shows an aerial map view of an audio communications system of the present invention in use.

With reference to Figure 7, there is shown an audio communications system in accordance with an embodiment of the present invention, which comprises a plurality of stereo headsets (A, B, C, D) and a plurality of audio devices (E, F). It should be noted that more or less stereo headsets may be provided and more or less audio devices may be provided. It should further be noted that there may only be stereo headsets provided. The audio communications system may be configured to suit numerous different uses and scenarios, as will be readily appreciated by those skilled in the art and the specific configurations discussed herein are not to be construed as limiting.

Each of the stereo headsets and the audio devices comprises a means of determining its own geographical location, and a means of transmitting one or more signals, which include data indicating its own geographical location and an audio signal. The audio signal transmitted by each of the stereo headsets comprises a voice signal of the wearer. Further audio signals may also be transmitted by each of the first stereo headset and the further stereo headsets, as discussed below. Each of the stereo headsets further comprises: a means of determining its own orientation in two or more axes, a means for receiving signals from the other headsets and the communication devices, a 3D audio engine, and a means for modifying an audio signal received from one of the other headsets or the audio devices to place the received audio signal in a 3D audio space using a received geographical location of the respective other headset or audio device, its own geographical location and its own orientation.

The user of any one of the stereo headsets receives an audio signal passed across the communications network linking the headsets and audio devices by any of the other stereo headsets or audio devices. The audio signal passed across the communications network contains the geographical location of the headset/audio device transmitting the audio signal to the user's headset. By using the geographical location of the headset/audio device transmitting the audio signal, the geographical location of the user's headset receiving the signal, the orientation of the user's headset receiving the audio signal and a three-dimensional (3D) audio engine, the audio signal can be presented in a three- dimensional audio space to the user. The user will then perceive the direction of the transmitter of the audio signal as well as the audio signal itself.

Each headset is a stereo headset, wherein the headset can supply a different audio signal to the left and right ears of the user wearing the headset. The headset can be, but is not limited to, an in-the-ear headset, a circumaural headset (as discussed below with reference to Figures 1 to 3) or a supra-aural headset; or can be incorporated into a head protection device such as a helmet (as discussed below with reference to Figures 4 to 6). No matter what form they take, the headsets will each be arranged to capture their wearer's voice for transmission. One or more microphones/transducers may be provided for this purpose. The headsets may transmit and receive signals using two-way radios, a two-way intercom, a multicast system or Voice Over IP (VOIP) communications devices.

Devices that are capable of determining the orientation of the users head include, but are not limited to, 3-axis compasses, 6-axis compasses, 9-axis compasses, multiple axis accelerometers and multiple axis gyroscopic devices. If the transducer for reproducing sound does so by creating a magnetic field, the transducer and the head orientation device must either be positioned to ensure the magnetic field created by the transducers does not interfere with the head orientation device or must be suitably magnetically shielded.

The head orientation device must also be positioned in such a way as to accurately and repeatably determine the orientation of the users head in at least two and preferably three axes. The head orientation device must take into account different users as well as different fittings for an individual user and may be arranged accordingly. For circumaural and supra-aural headsets, the head orientation device may, for example, be mounted on a neckband (107, 308), on a headband (106, 206, 306), or within one or both of the earpieces (207, 308) of the headset. For in-the-ear headsets, the head orientation device can be mounted, for example, in a neckband, in an ear hanger or within one or both of the earpieces of the headset. For a helmet with an integrated headset, the head orientation device can be mounted anywhere in or on the helmet (404,506, 602) in one or more places or within one or both of the earpieces of the headset (403, 502, 606). Moreover, in any configuration of headset, multiple head orientation devices can be used to improve the head orientation readings and to provide backups. Alternative positioning of the head orientation device to those specified will also be readily appreciated by those skilled in the art.

Headsets may comprise, as an alternative or in addition to any of the one or more head orientation devices mentioned above, a single or dual axis inclinometer for further determining the orientation of the user's head and/or a barometer.

The audio devices can be, but are not limited to, listening devices, audio beacons or programmed geographical location beacons. As will be appreciated different combinations of audio devices may be used in a communications network in accordance with the present invention.

Listening devices comprise a geographical location device, a communications system and one or more transducers, such as one or more microphones, proximity detectors, IR sensors or combinations thereof. An audio signal captured by the microphone(s) or an audio signal indicative of a signal captured by an alternative form of sensor, along with the geographical location of the geographical location device may be transmitted over the communications system by a listening device.

Audio beacons, which act as reference points within the communications system, comprise a geographical location device and a communications system. Audio beacons transmit their geographical location over the communications system. An optional audio signal may be transmitted along with the geographical location over the communications system. If an audio signal is not transmitted the receiving system can impose its own audio signal based on the received geographical location signal. An audio beacon can be a standalone device or can be integrated into another device such as a health monitoring system or a casualty location system that is worn by a user. Programmable geographical location beacons operate in the same manner as an audio beacon, but without a physical device. A programmable geographical location can, for example, be sent over the communication link by a headset, based upon the location of the headset (as determined by the headset's means of determining its physical location) at the time of sending a signal, as a geographical location with an audio signal or as a geographical location only. A programmable geographical location can, however, be sent by any device(s) connected to the communications system, either locally or remotely. For example, a programmable geographical location or multiple geographical locations could be transmitted from a suitable computer connected to the communications system, wherein the computer can be located anywhere in the world.

A distance element can be added to the audio signal from the audio beacon or the programmable geographical location. A number of methods can be used to add a distance element, as will be readily appreciated by those skilled in the art. The volume of the audio signal can be caused to be adjusted, wherein the closer the audio beacon or programmable geographical location is to the headset of the user, the louder the audio signal.

Alternatively, the audio signal can be changed to indicate the change in distance with pitch changes, tonal changes, reverberation changes, Doppler effect changes or echo effects added, for example.

The means for determining geographical location provided in any of the headsets or audio devices may be, but is not limited to, a Global Positioning System (GPS) device, an Inertial Navigation System (INS), a simultaneous localization and mapping (SLAM) system or a combination of these. The means for determining geographical location that is associated with any one of the headsets or audio devices can be placed anywhere on that headset or audio device; or can be placed on a structure near that headset or audio device as long as that headset or audio device is to remain in close proximity to the means for determining geographical location. It is most preferable that the means for determining geographical location is mounted to the headset or audio device itself.

It should be noted that the location of a headset or audio device within the communications system can be a fixed location within the overall system. Any device (headset or audio device) at one of these fixed locations does not need a physical unit, such as a GPS device or INS, for the determination of its geographical location. For any such device, the means for determining its location may be considered to be a programmable fixed geographical location. For example, a wired headset may be connected to a specific connection point, wherein the location of that connection point is known and is taken as the geographical location of the wired headset that is programmed into the system.

In order to provide positional awareness to the wearer of a headset, the audio signal received by the headset needs to be placed in a three-dimensional audio environment. To correctly place the audio signal in a three-dimensional audio environment, the geographical location of the device (headset or audio device) transmitting the audio signal, the geographical location of the headset receiving the audio signal and the orientation of the headset receiving the audio signal are used to generate a directional input for a three- dimensional (3D) audio engine.

Figures 1, 2 and 3 show the three axes of orientation of a user's head when the user is wearing a stereo circumaural headset and Figures 4, 5 and 6 show the three axes of orientation of a user's head when the user is wearing a helmet with an integrated stereo headset, wherein the three axes are as follows: the positive (104, 405) or negative (105, 406) angle of the user's head (101, 401) with reference to a horizontal plane (103, 404), i.e. tilting of the user's head in a front/back direction (analogous to pitch); the positive (204, 504) or negative (205, 505) angle of the user's head (201, 501) with reference to a vertical plane (203, 503), i.e. the tilting of the user's head side to side (analogous to roll); and the positive (304, 604) or negative (305, 605) angle of the user's head (301, 601) in the horizontal plane with reference to a predefined direction (303, 603), i.e. the turning of the user's head (analogous to yaw). Note that the predefined direction is preferably

geographical north but can be input as any direction, and in the specific description that follows north is selected as the predefined direction, it must be understood that this can be altered however, as desired.

Note that the term vertical, as used herein, means a direction that is locally aligned with the gradient of the gravity field, i.e., with the direction of the gravitational force at that point. The term horizontal, as used herein, means a direction that is perpendicular to the vertical.

The three-dimensional audio engine, as will be understood by those skilled in the art, is audio processing software that is arranged to accept the received audio signal and the directional input, which is generated based upon the positional information and the head orientation information, and to use Head Related Transfer Functions (HRTFs) to create two audio streams that are passed to the respective left and right earpieces of the headset receiving the audio signal. The two audio streams create an effect that the user interprets as a single audio signal from a sound source at a specific position. It should be noted that a commercially available three-dimensional audio engine may be utilized in the present invention, which runs on a processor provided with each headset. The processing of the data relating to the geographical location of the device (headset or audio device) transmitting the audio signal, the geographical location of the headset receiving the audio signal and the orientation of the headset receiving the audio signal, to generate the directional input into the three-dimensional audio engine is now described in detail. It should be noted that each headset will be provided with a processor for generating the directional input for the 3D audio engine. A single processor may generate the directional input and run the 3D audio engine. The latitude, longitude and altitude of the transmitted audio signal have first to be adjusted to take into account the orientation of the receiving user's headset (and thereby the attitude of the receiving user's head). The receiving user's head can move in three axes (as defined above), therefore to adjust the latitude, longitude and altitude of the transmitted audio an adjustment in each axis is required. The equation for the adjustment can be built up by considering the rotation in one axis at a time.

An adjustment in the horizontal plane with reference to a predefined direction (303, 603), herein north, by an angle (304, 305, 604, 605) is determined by the equation:

0 0

cos a - sin a

sin a cos a where

• Rx is the rotation adjustment with reference to north.

• a is the angle of rotation with reference to north.

An adjustment with reference to a horizontal plane (103, 403) by an angle (104, 105,

404, 405) is determined by the equation:

where

• Ry is the rotation adjustment with reference to a horizontal plane.

• γ is the angle of rotation with reference to a horizontal plane.

An adjustment with reference to vertical plane (203, 503) by an angle (204, 205, 504, 505) is determined by the equation:

where

• Rz is the rotation adjustment with reference to a vertical plane.

• β is the angle of rotation with reference to a vertical plane.

An adjustment in all three axes is determined by the equation:

R— R_xR_yR_z

where

• R is the rotation adjustment for all three axes.

• Rx is the rotation adjustment with reference to north.

• Ry is the rotation adjustment with reference to the horizontal plane.

• Rz is the rotation adjustment with reference to the vertical plane. The equation can then be expanded to:

R =

The equation can be simplified by combining the equation elements as shown on the following two equations. 0 0 cos y cos β — cos y sin β sin y

R = cos a — sin a sin β cos ^ 0

sin a cos a - sin 7 cos β sin y sin β cos y.

cos y cos β —cos y sin β sin y

R = cos a sin β cos a cos β —sin a cos y sin a sin β— cos a sin y cos ? sin a cos β + cos a sin y sin ? cos a cos y .

Using the longitude, latitude and altitude of the transmitted audio as a vector the rotational adjustment can be applied using the following equations:

LongtitudeB

v = LatitudeB

AltitudeB

AdjustedLongitudeB

AdjustedLatitudeB = vR

AdjustedAltitudeB where

LongitudeB is the longitudinal element of the geographical location of the transmitter of the audio signal.

LatitudeB is the latitudinal element of the geographical location of the transmitter of the audio signal.

AltitudeB is the altitudinal element of the geographical location of the transmitter of the audio signal.

v is the vector of LongitudeB, LatitudeB and AltitudeB

AdjustedLongitudeB is the adjusted longitudinal element of the geographical location of the transmitter of the audio signal.

AdjustedLatitudeB is the adjusted latitudinal element of the geographical location of the transmitter of the audio signal.

AdjustedAltitudeB is the adjusted altitudinal element of the geographical location of the transmitter of the audio signal. Following adjustment of the transmitted audio the geographical position of the receiver is compared to the adjusted position of the transmitter, using the following equations:

Longitude A = Longitude A— AdjustedLongitudeB Latitude A = Latitude A— AdjustedLatitudeB AltitudeA = AltitudeA— AdjustedAltitudeB

where

• LongitudeA is the longitudinal element of the geographical location of the receiver of the audio signal.

• AdjustedLongitudeB is the adjusted longitudinal element of the geographical location of the transmitter of the audio signal.

• LatitudeA is the latitudinal element of the geographical location of the

receiver of the audio signal.

• AdjustedLatitudeB is the adjusted latitudinal element of the geographical location of the transmitter of the audio signal.

• AltitudeA is the altitudinal element of the geographical location of the

receiver of the audio signal.

• AdjustedAltitudeB is the adjusted altitudinal element of the geographical location of the transmitter of the audio signal.

Based on the values of LongitudeA and LatitudeA one of the four following equations is used to determine an angle in the horizontal plane relative to the predetermined direction (north):

If LongitudeA and LatitudeA > 0

LatitudeA

HorizontalAnqle = 90— tan (- :———)

LongitudeA

If LongitudeA > 0 and LatitudeA < 0 LatitudeA

Horizontal Angle =—90— tan ^x(-

LongitudeA

If LongitudeA < and LatitudeA > 0

LatitudeA

Horizontal Angle = 180— tan ¹ ^■)

LongitudeA

If LongitudeA and LatitudeA < 0

LatitudeA

Horizontal Angle =—180— tan ^x(-

LongitudeA 0

The geographical locations of the respective headset(s)/audio device(s) are input into the equations above as three value geographical co-ordinate locations, comprising longitude, latitude and altitude. If the overall system does not need an altitude element then it is possible that only latitude and longitude are used, which provides two value coordinate locations, more preferably, however, three value co-ordinate locations are used wherein the third co-ordinate corresponding to altitude is input as a zero value each time. As will be readily appreciated by those skilled in the art the input can be varied to suit the requirements of the system. The requirement for an altitude element will be dependent on the specified use of the system and may be omitted (by use of a two-value co-ordinates or a zero value for the third co-ordinate). For the purposes of describing the invention three value co-ordinate geographical locations have been used.

The following equation is used to determine the vertical angle from a horizontal plane, which is then input to the three-dimensional audio engine along with the angle in the horizontal direction from the pre-determined direction. In accordance with the discussion above, the altitude value will be entered as a zero where an altitude element is not required.

-1 AltitudeA

VerticalAngle = tan

^LongitudeA² + LatitudeA²

The directional data (the HorizontalAngle and the VerticalAngle) may be used to provide a point on the surface of an imaginary sphere surrounding the head of the user of the headset receiving the audio signal, wherein the centre of the user's head is located at the centre point of the sphere. The directional data may be considered to provide a straight line extending between the centre point of the imaginary sphere and the surface of the imaginary sphere, such that the directional data provides a point on the surface of the imaginary sphere. In a first implementation the radius of the imaginary sphere is fixed. In this implementation only the direction of the transmitted audio signal is presented to the user. All audio signals will be presented to the user at the same signal level as they were received at. There is no distance element provided. In a second implementation a distance element is introduced, wherein the level of the received audio signal is adjusted to provide a distance as well as direction element, wherein in this arrangement the radius of the sphere is changed in dependence on the distance from the receiving headset of the audio device or headset transmitting the audio signal thereto. The sphere radius is larger when the transmitting headset or audio device is further away and smaller when it is closer. The first implementation, with no distance element provided, is preferable in most implementations where the receiving headset may be large distances from the audio device or headset transmitting an audio signal. The specific implementation may be adapted to suit the specific use of the system.

When the second implementation is implemented, the following equation is used:

Distance = Longitude A² + Latitude A² + Altitude A²

The present system, as herein described, thus provides as a directional input to the 3D audio engine, a horizontal angle of ±180 degrees from a predefined direction (north), a vertical angle of ±90 degrees from a horizontal plane and optionally a distance from the receiving headset.

Modifications of the directional input method for the three-dimensional audio engine will be appreciated by those skilled in the art. The above method provides an exemplary example only. Example communications systems in use will now be considered. Figure 7 shows the positions of four users (A, B, C and D), each of whom is wearing a stereo headset, as well as the positions of two audio devices, comprising an audio listening device (E) and an audio beacon (F). The arrows on users A, B, C and D indicate the direction they are facing, and thereby their head orientation direction.

The users may be soldiers in the present example, however, the present invention will find application in numerous non-military applications. The headsets may be connected to two-way radios or other suitable communication devices, as mentioned herein, for transmitting and receiving live voice signals.

By way of example, and using Figure 7 as positional reference, user A will perceive voiced communication from user D as being from behind left and slightly above, voiced communications from user B or user C as being from behind; user B will perceive voiced communications from user D as being from directly behind and slightly above, voiced communications from user A as being from the left and voiced communications from user C as being from the right; and user D will perceive voiced communications from user C as being from the right front and slightly below, voiced communications from user B as being from directly in front and slightly below and voiced communications from user A as being from the left front and slightly below, and so on.

As is clear, any of the users may send or receive signals, including data indicative of geographical location and a voice signal, to any of the other users and vice versa. Again by way of example, and using figure 7 as a positional reference, user D or any of users A, B and C can use the audio listening device E to provide out-of-sight/distance audio monitoring.

Finally by way of example, and using Figure 7 as a positional reference, if audio beacon F is activated, then user D will hear an audio cue approximately 45 degrees to the right with a long distance indication, user C will hear an audio cue in front but slightly to the right and a closer distance indication than user D, and so on. Figure 8 shows how a series of programmable geographical locations can be used to guide a user from one point to another. User A is facing in a NW direction as shown in figure 8, when a series of programmable geographical locations is received. User A will hear an audio signal to the front right, and slightly below (if an altitude element is received), from the first programmable geographical location, Point X. As user A turns towards Point X the audio signal will be perceived as being directly in front. As user travels towards point X the audio signal is adjusted either in volume or by another means, as discussed above, to indicate the distance to Point X is reducing. For example, if the audio signal is a single beep repeated three times, the interval between beeps can be reduced to indicate the distance is reducing or the interval between beeps increased to indicate the distance is increasing.

When user A reaches Point X the programmable geographical location can be removed/deleted either manually or automatically, in a manner as will be appreciated by those skilled in the art. Removing/deleting a programmable geographical location will cause the next programmable geographical location to become active. In the example shown in Figure 8, Point Y will be perceived as being to the right of user A, and on the same level (if an altitude element is present). The user does not have to follow as straight path towards an audio beacon or programmable geographical location. Figure 8 shows two paths (801, 802) between points Y and Z. User A can follow the contours of the land by taking path 802 or up and over the ridge by following path 801. The audio signal will always point towards point Z regardless of the path taken by user A.

Numerous alternatives and modifications within the scope of the appended claims are possible, as will be readily appreciated by those skilled in the art.

Claims

1. An audio communications system comprising a plurality of stereo headsets linked through a communications network,

wherein each of the stereo headsets comprises:

a means of determining its own geographical location,

a means of transmitting one or more signals, which include data indicating its own geographical location and a voice signal of the wearer,

a means of determining its own orientation in two, three or more axes,

a means for receiving signals from the other headset(s),

a 3D audio engine, and

a means for modifying a voice signal received from one of the other headset(s) using a received geographical location of the respective other headset, its own geographical location and its own orientation to provide an input to the 3D audio engine to place the received voice signal in a 3D audio space.

2. A system as claimed in Claim 1, wherein the audio communications system is configured such that any one of the headsets may transmit the one or more signals across the communications network and any of the other headsets may receive those one or more signals and place the included voice signal in a 3D audio space.

3. A system as claimed in Claim 1 or 2 comprising at least three stereo headsets.

4. A system as claimed in any preceding claim, wherein each of the stereo headsets comprises a transducer for capturing the voice of the wearer for transmission.

5. A system as claimed in Claim 4, wherein the transducer comprises at least one microphone. 6. A system as claimed in any preceding claim, wherein the means of transmitting and receiving signals for one or more or all of the stereo headsets comprises a two-way radio, a two-way intercom, a multicast system or a Voice Over IP (VOIP) communications device.

7. A system as claimed in any preceding claim, wherein the means for modifying the voice signal is arranged to apply an adjustment to the geographical location of the stereo headset transmitting the audio signal to provide an adjusted geographical location of the stereo headset transmitting the audio signal, based upon the orientation of the stereo headset receiving the audio signal.

8. A system as claimed in Claim 7, wherein the means for modifying the voice signal is arranged to adjust the geographical location of the stereo headset transmitting the audio signal based upon the orientation in three axes of the stereo headset receiving the audio signal.

9. A system as claimed in Claim 8, wherein the three axes are the three axes of orientation of the head of a user who is wearing the stereo headset, the three axes comprising: the positive or negative angle of the user's head in a horizontal plane with reference to a predefined direction, the positive or negative angle of the user's head with reference to the horizontal plane, and the positive or negative angle of the user's head with reference to a vertical plane. 10. A system as claimed in any of Claims 7 to 9, wherein the means for modifying the voice signal is arranged to compare the geographical location of the stereo headset receiving the voice signal to the adjusted geographical location of the stereo headset transmitting the voice signal. 11. A system as claimed in Claim 10, wherein the means for modifying the voice signal is arranged to generate directional data based upon the comparison of the geographical location of the stereo headset receiving the voice signal and the adjusted geographical location of the stereo headset transmitting the voice signal, and to input the directional data to the 3D audio engine.

A system as claimed in any of Claims 7 to 11, wherein the audio communications m is arranged to provide all geographical locations to the means for modifying the voice signal as three value co-ordinates representing longitude, latitude and altitude, wherein zero values are input for the co-ordinate values corresponding to altitude if the altitude of the stereo headset transmitting the voice signal relative to the altitude of the stereo headset receiving the voice signal is not required.

13. A system as claimed in any preceding claim, wherein the stereo headset receiving the voice signal is arranged to present voice signals to the user at a constant volume irrespective of the distance of the stereo headset receiving the voice signal from the stereo headset transmitting the voice signal.

14. A system as claimed in any of Claims 1 to 12, wherein the stereo headset receiving the voice signal is arranged to present voice signals to the user at different volumes in dependence on the distance of the stereo headset receiving the voice signal from the stereo headset transmitting the voice signal, wherein the closer the stereo headset transmitting the voice signal, the louder the voice signal.

15. A system as claimed in any preceding claim, wherein the means for modifying a voice signal comprises a processor that is arranged to process the audio in real time. 16. A system as claimed in Claim 15, wherein the processor runs the 3D audio engine.

17. A system as claimed in any preceding claim, wherein the 3D audio engine is incorporated into the stereo headsets or is provided in a switch box, a communications hub or a management system associated, respectively, with any of the headsets.

18. A system as claimed in any preceding claim, wherein the means of determining the geographical location comprises a Global Positioning System (GPS) device, an Inertial Navigation System (INS), a simultaneous localization and mapping (SLAM) system, a programmable fixed geographical location or a combination of 2 or more of these.

19. A system as claimed in any preceding claim, wherein means of determining the orientation comprises a multiple axis compass, a multiple axis accelerometer or a multiple axis gyroscopic device or a combination of 2 or more of these. 20. A system as claimed in any preceding claim, wherein each of the stereo headsets further comprises an inclinometer and/or a barometer.

21. A system as claimed in any preceding claim, wherein the means of transmitting and receiving signals is wired.

22. A system as claimed in any of Claims 1 to 20, wherein the means of transmitting and receiving signals is wireless.

23. A system as claimed in any preceding claim, wherein each of the stereo headsets comprises any of an in-the-ear headset, a supra-aural headset or a circumaural headset.

24. A system as claimed in any preceding claim, wherein the geographical location may comprise latitude and longitude or latitude, longitude and altitude. 25. A system as claimed in Claim 24, wherein the geographical location may comprise a two or three value geographical co-ordinate.

26. A helmet comprising an integrated headset as claimed in any preceding claim. 27. An audio communications system as claimed in any preceding claim, which further comprises one or more audio devices, each audio device comprising a means of transmitting one or more signals, which include data indicating its own geographical location and an audio signal, wherein the means for receiving signals from the other headsets and the means for modifying an audio signal received from one of the other headsets of each of the stereo headsets are arranged to receive and modify audio signals received from the one or more audio devices and to place those audio signals in a 3D audio space.

28. An audio communications system as claimed in Claim 27, wherein each of the one or more audio devices comprises a one way radio, a two-way radio, a multicast system or a Voice Over IP (VOIP) communications device.

29. A system as claimed in Claim 27 or 28, wherein each of the one or more audio devices comprises any of an audio beacon emitting an audio guidance signal, a

programmable geographical location arranged to emit an audio guidance signal or an audio listening device employing one or more acoustic transducers.