Abstract:
An interactive spatialized audiovisual system links a plurality of remote used terminals. The system comprises a networked computer having an associated user database including user status information. Input means are provided at the computer for receiving a plurality of audio streams and associated locating data from the remote user terminals for, virtually locating the users relative to one another within a virtual user environment such as a chat room environment Selection means are provided for enabling selection of at least the first group of the audio streams in a first selection process based on status information in the user database. Output means output the selected group of audio streams and associated locating data for spatialization of the audio streams relative to a first listener-based audio reference frame which is substantially coherent with visual representations of the audio sources defined by the locating data at the first user terminal. Merging means are provided for merging at least some of the audio streams into a merged audio stream for transmittal to the first and other user terminal, with the merged audio stream being spatialized so as to provide for a spatialized background audio effect in the audio reference frame at the user terminal.

Description:
FIELD OF THE INVENTION 
     The present invention relates to an interactive spatialized audiovisual system for conducting chat room type conversations in a three dimensional audio environment. 
     BACKGROUND OF THE INVENTION 
     Recently, chat rooms have become a very popular forum for intercommunication over the Internet. Normally, these chat rooms involve users typing in information using a computer type device interconnected to a computer network such as the Internet. 
     The use of chat rooms allows for an increased level of personal intercommunication and on-line discussion. Normally, the chat room may be discussion topic based. 
     Conventional chat programs provide a text input-based chat environment. Participants can either choose to chat with an individual, or within a group. A messaging service is also provided to enable short messages of limited length to be sent between two parties. This online program has proved itself to be very popular over time and has gained many users. 
     Unfortunately, the chat room scenario has a number of drawbacks. These include the need to type information on a keyboard type device for entering to the chat room. Typing is often a laborious and non-spontaneous process when compared merely to the process of talking. Further, chat room conversations can often become confusingly intermingled, and it is accordingly difficult to keep track of multiple participants in a particular discussion. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the invention there is provided an interactive spatialized audiovisual system for linking a plurality of remote user terminals, the system comprising:
         a networked computer;   an associated user database including user status information;   input means for receiving at the computer a plurality of audio streams and associated locating data from the remote user terminals for virtually locating the users relative to one another within a virtual user environment;   selection means for enabling selection of at least a first group of the audio streams in a first selection process based on status information in the user database;   output means for outputting the selected group of audio streams and associated locating data for spatialization of the selected group of audio streams relative to a first listener-based audio reference frame which is substantially coherent with visual representations of the audio sources defined by the locating data at a first user terminal.       

     Conveniently, the system includes first spatialization means for spatializing the selected group of audio streams. 
     Preferably, the system includes merging means for merging at least some of the audio streams into a merged audio stream for transmittal to the user terminal, and second spatializing means for spatializing the merged stream so as to provide for a background audio effect in the audio reference frame at the user terminal. 
     Conveniently, the selection means are arranged to select different groups of audio streams according to different selection processes based on the user status information in the user database, for transmission to the corresponding user terminals. 
     The user status information typically includes user location data for locating the user in the virtual environment, user orientation data for orientating the user both with respect to the other users and to the virtual environment, user listening status information and user talking status information. 
     The user listening status information is arranged to allow the user to listen to other selected users or groups in the environment. 
     The user listener status may be based on at least one of the following:
         the selection of M closest audio sources from N audio sources;   the selection of M loudest sources based on the amplitude of the source signal and/or the distance of the source from the listener;   a user-driven selection process determined by the subject user or other users;   a moderator-driven selection process in which a “moderator” in the environment is able to control the talk and listen status of the other users;   the geography or topology of the virtual environment, in which barriers and openings such as walls and doorways and other features of the environment are arranged realistically to affect the listening capability of a particular user;   the creation of temporary “soundproof” barriers around user groups.       

     The barriers may define one or more chat rooms, with at least some of the audio streams in a particular room being summed or merged and spatialized to achieve a background reverberation effect characteristic of that particular room. 
     The audio streams in adjoining rooms or areas may also be merged and spatialized to create “threshold” effects at entrance/exit points. 
     “Dry” and “wet” room signals may be respectively be generated using summed non-reverberated audio sources and audio sources which have been summed and reverberated. 
     In general terms, the invention seeks to provide a virtual environment in which there is a measure of coherence between the visible and audible effects within the virtual environment. 
     Typically, the user database utilizes a plurality of different selection criteria based on the status of the particular user to whom the selected audio streams and associated locating information is being transmitted. 
     Conveniently, the first spatialization means are provided at each of the user terminals for processing of selected groups of audio streams from the networked computer. 
     Alternatively, the first spatialization means are arranged to process selected groups of audio streams at the networked computer to derive spatialized audio streams for onward transmission to at least the first selected user terminal. 
     In one form of the invention, the second spatializing means are arranged to process the merged group of audio streams at the networked computer to derive a spatialized merged audio stream for onward transmission to at least the first selected user terminal. 
     Alternatively, the second spatialization means are provided at each of the user terminals for spatializing merged groups of audio streams at each user terminal. 
     Typically, the second spatialization means includes a binaural reverberation processor. 
     The invention extends to a method of providing an interactive spatialized audio facility comprising:
         receiving from a plurality of user-based audio sources a plurality of corresponding audio streams and associated locating data capable of virtually locating the audio sources relative to one another within a virtual environment;   determining user status data;   selecting at least some of the audio streams based on the user status data;   transmitting the locating data and selected audio streams to a first listener destination for enabling the display of visual representations of the virtual locations of at least some of the audio sources within the virtual environment, and   spatializing the selected audio streams relative to a first listener-based audio reference frame which is substantially coherent with the visual representations of the audio sources either before or after the audio streams are transmitted to the first listener destination.       

     Preferably, the method includes:
         enabling the user status data to be altered,   reading the altered user status data, and   selecting at least one of the audio streams based on the altered user status data, wherein at least one of the audio streams selected using the altered user status data is different to the prior selected streams.       

     Conveniently, the method includes the steps of:
         merging at least some of the audio streams,   transmitting the merged audio streams to the first listener destination, and   spatializing at the first listener destination the merged audio streams so as to provide a background audio effect within the virtual environment.       

     The merged audio stream may include audio streams which have not been individually selected. 
     The invention extends to a method of providing an interactive spatialized audiovisual facility comprising:
         receiving from a plurality of user-based audio sources a plurality of corresponding audio streams and associated locating data capable of virtually locating the audio sources relative to one another within a virtual environment;   determining user status data;   selecting at least some of the audio streams based on the user status data in a first selection process;   transmitting the selected audio streams and associated locating data to a first listener destination for enabling the display of visual representations of the virtual locations of at least some of the selected audio sources within the virtual environment;   spatializing the selected audio streams relative to a first listener-based audio reference frame which is substantially coherent with the visual representations of the audio sources either before or after the transmitting said streams;   selecting at least some of the audio streams in a second selection process; and   transmitting the selected audio streams and associated locating information to a second listener destination for enabling the display of visual representations of the locations of at least the selected audio sources, and spatializing at the second listener destination the selected audio streams in an audio reference frame which is substantially coherent with the visual representations of the audio sources, either before or after transmitting said streams.       

     In accordance with a further aspect of the present invention, there is provided a system for providing for spatialized conversation over a network environment, the system comprising:
         at least one user terminal;   a computer network capable of streaming audio streams to the user terminals, each of the audio streams including associated spatialization information;   a rendering system for rendering the audio streams to predetermined virtual locations around a user; and   a user interface for virtually spatially locating a user amongst the audio streams;       

     wherein the rendering system spatializes the audio streams so as to maintain a substantially spatially coherent audio reference frame around the user, the user interface includes a visual indicator of the spatial position of each of the audio streams around a listener and the rendering system substantially maintains a spatially coherent audio reference frame relative to the visual indicator. 
     Each stream preferably includes user ownership information and the system preferably includes audio stream access interface for granting access to the audio streams. 
     The rendering system can attenuate audio sources located virtually remotely from a current user and merge audio sources located virtually remotely from a current user. In one embodiment the rendering system can be located adjacent a user and the audio sources are preferably streamed over a computer network. 
     In one form of the invention, multiple selection processes are used to select the audio streams according to at least one predetermined algorithm, the selected audio streams and associated locating information are transmitted to multiple listener destinations, and visible representations of the locations of at least the selected audio sources are displayed at the multiple listener destinations, with each of the selected audio streams being spatialized at the multiple listener destinations in audio reference frames which are substantially coherent with the visible representations of the audio sources. 
     The invention further provides a computer-readable medium having stored thereon executable instructions for causing a computer to provide an interactive spatialized audiovisual facility, the instructions being arranged to:
         receive from a plurality of user-based audio sources a plurality of corresponding audio streams and associated locating data capable of virtually locating the audio sources relative to one another within a virtual environment;   determine user status data;   select at least some of the audio streams based on the user status data;   transmit the locating data and selected audio streams and associated to a first listener destination for enabling the display of visual representations of the virtual, locations of at least some of the audio sources within the virtual environment, and   spatialize the selected audio streams relative to a first listener-based audio reference frame which is substantially coherent with the visual representations of the audio sources.       

     The invention still further provides a computer-readable medium having stored thereon executable instructions for causing a computer to provide an interactive spatialized audiovisual facility, the instructions being arranged to:
         receive from a plurality of user-based audio sources a plurality of corresponding audio streams and associated locating data capable of virtually locating the audio sources relative to one another within a virtual environment;   determine user status data;   select at least some of the audio streams based on the user status data in a first selection process;   transmit the selected audio streams and associated locating data to a first listener destination for enabling the display of visual representations of the virtual locations of at least some of the selected audio sources within the virtual environment;   spatialize the selected audio streams relative to a first listener-based audio reference frame which is substantially coherent with the visual representations of the audio sources;   select at least some of the audio streams in a second selection process; and   transmit the selected audio streams and associated locating information to a second listener destination for enabling the display of visual representations of the locations of at least the selected audio sources, and spatializing at the second listener destination the selected audio streams in an audio reference frame which is substantially coherent with the visual representations of the audio sources.       

     According to a yet further aspect of the invention, there is provided a method of operating an interactive spatialized audio facility including a networked computer and a plurality of user terminals linked to the networked computer, the method comprising:
         transmitting from a user terminal to the networked computer an audio stream generated by the user and associated locating data capable of virtually locating the audio stream generated by the user within a virtual environment for selective combination with corresponding audio streams, associated locating data and user status data at the networked computer;   receiving at the user terminal a plurality of audio streams selected on the basis of the user status data and associated locating data for virtually locating the users relative to one another within a virtual user environment;   generating at the user terminal visual representations of the locating data, and   spatializing the selected group of audio streams relative to a user based audio reference frame which is substantially coherent with the visual representations of the audio sources of the users as defined by the locating data for playback to the user.       

     Conveniently, the method includes receiving at the user terminal a merged audio stream which is spatialized before or after receipt thereof to provide a spatialized background audio effect in the audio reference frame at the user terminal for playback to the user. 
     The invention extends to a computer-readable medium having stored thereon executable instructions for causing a computer to provide or operate an interactive spatialized audiovisual facility, the instructions including program segments arranged to implement any one of the methods set out above. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Notwithstanding any other forms which may fall within the scope of the present invention, preferred forms of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: 
         FIG. 1  illustrates schematically a first embodiment of a user interface for an audio chat room of the preferred embodiment; 
         FIG. 2  illustrates schematically a streaming environment of the first embodiment; 
         FIG. 3  illustrates a schematic flowchart showing the operation of a rendering computer of the first embodiment; 
         FIG. 4  illustrates a highly schematic functional block diagram of a second embodiment of a spatialized audio conversation system of the invention; 
         FIG. 5  shows a more detailed functional block diagram of an audio component of a streaming server; 
         FIG. 6  shows a more detailed functional block diagram of a user terminal adapted to be connected to the streaming server of  FIG. 5 ; 
         FIG. 7  shows a more detailed block diagram of a second embodiment of an audio component of a streaming server; 
         FIG. 8  shows a functional block diagram of a second embodiment of a user terminal adapted to be connected to the streaming server of  FIG. 7 ; 
         FIG. 9  shows a functional block diagram of an audio component of a third embodiment of a streaming server of the invention; 
         FIG. 10  illustrates a schematic view of a user interface screen which corresponds to the server configuration illustrated in  FIG. 9 ; and 
         FIG. 11  shows a functional block diagram of an audio component of a fourth embodiment of a streaming server of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     In the preferred embodiment, there is provided a chat room facility which includes audio spatialization and rendering technologies to provide for a spatialized form of audio chat room. The preferred embodiment can be implemented via suitable C++ programming of standard high end personal computer equipment. 
     Turning now to  FIG. 1 , there is illustrated an example of a user using the interface screen for utilization with a first embodiment of the invention. 
     A user  1  enters a virtual chat room which comprises a two dimensional array  2  on the user&#39;s screen. The chat room in this particular case is one dealing with the “LINUX” operating system. The chat room consists of a number of groups  5 ,  6 ,  7  and  8  of users  9  discussing various topics. The user interface includes a mouse pointer  4  which can be utilised in conjunction with a mouse to grab the user  1  and move the user towards different groups such as group  5  and further orient the user relative to the group. The user  1  is equipped with a set of headphones and, as the user approaches the group  5 , the conversation of that group initially appears in the distance and the conversation comes closer to the individual. Further, the conversation can be spatialized such that the conversations of the group  5  appear on the left hand side of the user  1  and the conversations of the group  6  appear on the right hand side of the user. The user is equipped with a microphone and, as a result, can thereby contribute to the conversation. Further, alternative audio inputs such as music tracks can be provided for the other listeners in the environment. 
     Each listener in the virtual environment is provided with a similar screen with a clearly identified current position locater. Listeners move around in the space defined by the “wall”  10  of the chat room listening to various conversations and contributing to the conversations. Each member of the chat room is able to take part in localised spatialized conversations with other members. 
     Turning now to  FIG. 2 , there is illustrated schematically a basic implementation of the arrangement of  FIG. 1 . The system can be based around a personal computer  11  having sound card processing capabilities so as to provide for output audio over headphones  12  in addition to a microphone input  13 . The rendering computer  11  is interconnected with a streaming server  14  which streams the audio channels of each participant over a streaming network which is in this case the Internet  15 . A series of other users  16  are similarly interconnected to the streaming server  14  which streams audio dialogue in addition to dialogue position information. The audio dialogue of the user  17  is also forwarded back to the server  14  for streaming to each participant. 
     The rendering computer can therefore operate as illustrated in  FIG. 3 . From the network stream  20  there is provided a series of chat room occupant streams  21 . Each chat room occupant stream contains a voice channel and the position and orientation of the user of the voice channel. Similarly, output  22  from the rendering computer is the local user&#39;s voice channel and associated positional information. The position and orientation information is utilised to update a display  23  so as to update the current position and orientation of each individual. The position information is also forwarded to relative position determination unit  24  for determining a current position of each listener relative to the current listener. 
     The relative position determination output is forwarded to an optional voice channel culling unit  26 . Voices that are attenuated with distance may be culled in accordance with the preset preferences. Additionally, a group or cluster of distant voices can be combined into a single voice or quasi-voice via superposition of the voice channels. The utilization of culling and combining operates to reduce the number of voice channels that must be subjected to spatialized audio rendering  27 . 
     The spatialized audio rendering takes the voice channel inputs in addition to the relative location information and culling information and utilises techniques for spatialization to place the voices around a listener at predetermined locations. 
     Suitable techniques for spatialization include those disclosed in PCT publication no. WO99/49574 entitled “Audio Signal Processing Method and Apparatus”, filed 6 Jan. 1999 and assigned to the present applicant, the contents of which are specifically incorporated by cross reference. The spatialization techniques disclosed allow a voice to be located relative to a headphone listener. Each of the input audio channels can be separately spatialized or can be first rendered to a standard reference frame such as a Dolby® Surround Sound five channel reference frame and then rotated to an absolute reference frame before a final rotation to the relative reference frame of the listener. The signals are combined and then output to the listener. 
     The spatialized conversation system can also be combined with binaural rendering technologies to provide for fully immersive behaviour. For example, U.S. Standard application Ser. No. 08/893,848 which claims priority from Australian Provisional Application No. PO0996, both contents of which are specifically incorporated by cross reference, discloses a system for rendering a B-formatted sound source in a head tracked environment at a particular location relative to a listener. Hence, if the audio tracks are stored in a B-format then such a system, suitably adapted, can be used to render the audio tracks. One example of where such a system is suitable is where the B-format part of the rendering is to be done centrally, and the headtracking part (which is applied to the B-format signal to generate a headphone signal) is done locally. B-field calculation can be expensive and is best done centrally. Central computation incurs communication delays, and this has the effect of introducing latency in position, which is not too detrimental. Headtracking is done locally because this is very sensitive to latency. 
     PCT publication no. WO99/51063 discloses an alternative system for Headtracked Processing for headtracked playback of audio in particular in the presence of head movements. Such a system could be used as the rendering engine by rendering the audio track to a predetermined format (e.g. Dolby™ 5.1 channel surround) so as to have a predetermined location relative to a listener, and, in turn, utilising the system described in the PCT application to then provide for the localisation of an audio signal in the presence of head movements. 
     Various user interface modifications to the preferred embodiment are also possible. For example, an announcer audio channel can also be provided which provides a “god-like” voice which announces the entrance and exit of users. A joystick or mouse can be provided so that a user can “walk” around the environment. Other users can have a choice of accepting or declining chat requests. 
     Hence, in the above embodiment, users conduct their conversation/chat sessions in the conventional way—through speech. The user wears a set of headphones with a transmitter attached which communicates with a receiver connected to a phone line, establishing the Internet online connection. As new users log onto the chat program, or so-called ‘chat-rooms’, they receive a voice announcement of the existing users in the room and their details. The display also shows where the user is located with respect to all other existing users in the chat room. The user can ‘move’ around the room (located on the display) and can walk up to any users in trying to set up an individual conversation. In one form of the embodiment all users have a choice of accepting or declining chat requests. 
     Referring now to  FIG. 4 , a streaming server  30  is shown connected via the internet to a number of user terminals  32 . 1  to  32 .N. The streaming server incorporates a user status database  34  which is typically SQL-based. The user status database is constantly updated with user location and status information via inputs  36  from each of the user terminals  32 . 1  to  32 .N. The user location data includes the position and orientation of each user both with respect to the other users and to the chat room(s) within the chat room environment. The status information includes the particular status of the user at a particular time. For example, the user may have various categories of listener status allowing the user to listen to other selected users or groups in the chat room. Similarly, the talk status of the user may be altered from the lowest “mute” status to, say, a highest “voice of god”, “soapbox” or “moderator” status in which that particular user may be in a position, respectively, to talk at will, to broadcast a message or speech throughout the chat room environment, or to control the talk and listen statuses of other users within the chat room environment. Multiple outputs  38  from the user status database lead to multiplexer-type select M functions  40 . 1  to  40 .N connected to the respective user terminals  32 . 1  to  32 .N via user location and status inputs  41  and via audio inputs  42  through an audio engine  43 . 
     The operation of the audio component of the streaming server will now be described in more detail with reference to  FIG. 5 . In the server, an audio bus  44  is provided comprising all of the audio channels of the N users. Each of the channels, such as those indicated at  44 . 1  and  44 . 2 , have corresponding audio or microphone inputs  46 . 1  and  46 . 2 . Outputs  48 . 1  to  48 .N from each of the lines in the audio bus  44 .N are fed into the select M fictions  40 . 1  to  40 .N. M output audio channels  50  are fed from the select M functions to each of the user terminals  32 . 1 - 32 .N of  FIG. 4 . There are various different methods or algorithms that can be used to control exactly which audio channels are selected for a particular user. Two of the main control criteria are the manner in which the user or listener obtains permission to enter a chat room, and exactly who gets heard by whom in each chat room. 
     Typically, a new entrant to the room will go through an approval process prior to being allowed entry. As a result, private conversations can be held between participants in the particular room, safe in the knowledge that new entrants can not “sneak in” without prior notification to the existing participants. The selection process may be autocratic, via a moderator or chairman, or may be democratic, by way of a users&#39; vote. User entry could also be password controlled in the case of a regular chat group. 
     Referring back to  FIG. 1 , a new entrant  52  would position himself or herself at the entrance  54  of the virtual chat room  3  appearing on the user interface screen and would request entry into the room, by, say, clicking on a “request entry” icon. One of the processes described above could then take place. As an alternative, a particular group  7  could, by mutual consent, erect a “sound proof” barrier  56  around their conversation. Similar entry criteria would apply if a user was in the room and wanted to join in the discussion. 
     Once the user  52  has entered the chat room, various other methods can be used to determine exactly who the user or listener will hear. In one version, the M closest sources can be selected from the N sources. Alternatively, the M loudest sources may be selected, where loudness is based on the amplitude of the source signal as well as the distance of the source from the listener. 
     A moderator, which could be user  1 , could also be used to select who is to be heard, on behalf of all listeners in the room. A further variation is that the moderator could select M′ sources on behalf of the group, and listener-individualised selection could be used for the remaining M-M′ sources. 
     As far as talking status is concerned, listeners may request permission to speak, by signalling to the moderator  1  their desire. The moderator can then review the “queue” of listeners and select who is to be heard by heard the group. One method of selection could be for each of the prospective talkers to provide a brief textual precis of their proposed contribution. Where there are several groups in the chat room, with several different conversations going on simultaneously, each of the groups  5 ,  6 ,  7  and  8  may have a group moderator or chairperson to control the flow of the discussion within a particular group. 
     Referring back to  FIG. 5 , all of the audio channels to the audio bus  44  are combined at a summer  58 , and the summed signal  60  undergoes a binaural reverberation process, such as the B-format rending process described above with reference to U.S. Ser. No. 08/893,848. The left and right binaural reverberation outputs  64  and  66  effectively form part of the audio bus  44 , with left and right summed binaural reverberation inputs  64 . 1  to  64 .N and  66 . 1  to  66 .N being fed to each of the user terminals  32 . 1  to  32 .N. 
     Referring now to  FIG. 6 , the user terminal  32 . 1  is shown having M audio channel inputs  50 . 1  to  50 .M which are separately spatalized by binaural rending using HRTF processes  68 . 1  to  68 .M. The binaurally rendered signals are summed at left and right summers  70  and  72  which are fed to the respective left and right earpieces of a set of headphones  74  worn by the user. The left and right binaural reverberation signals  64 . 1  and  66 . 1  are also fed to the respective left and right summers  70  and  72 . The summed binaural reverberation signals  64 . 1  and  66 . 1  produce background reverberation which allows the user to experience not only, say, the three or four closest voices in the room, but also the background hubbub representative of all of the summed voices in the chat room environment. This makes for an audio experience which is far more realistic without requiring an inordinate number of input audio channels. 
     In the embodiment of  FIGS. 5 and 6 , the bulk of the digital signal processing and channel selecting occurs at the streaming server, to the extent that the audio signal processing functions illustrated in  FIG. 6  can be incorporated into the right and left earpieces of the headphone  74 , which is in turn connected to the rendering computer. The rendering computer in turn incorporates the visual user interface, providing user location and status information to update the user status database  34 . It also receives the updated user location and status information from the demultiplexer function  40 . 1  to  40 .N so that the user interface screen can be constantly updated with the whereabouts and statuses of the other users in the chat room. 
     Referring now to  FIG. 7 , a second embodiment of an audio component of a streaming server  76  is shown which is similar to the first embodiment, save that the binaural reverberation function has been removed. Instead, the summed output signal  60  from the summer  58  is fed as an unprocessed summed input signal  60 . 1  to  60 .M to each of the user terminals, one of which is shown at  78 . 1  in  FIG. 8 . The binaural reverberation function  80  of the summed signal  60 . 1  takes place at the user end either within the rendering computer or within the headphones  74 , together with the HRTF functions  68 . 1  to  68 .M. In this way, the number of input channels is reduced, at the expense of additional processing power at the user end. 
     In  FIGS. 9 and 10 , a more sophisticated version of a spatalized conversation system is illustrated. The audio component of the streaming server  82  comprises an audio bus  84  having source signal channels from eight users numbered from  91  to  98 . In  FIG. 10 , a user interface screen is shown comprising chat rooms A and B divided by a wall  100  having an interleading doorway  102 . Users  91 ,  92 ,  94  and  96  are located in room A, and users  93 ,  95 ,  97  and  98  are located in room B. The audio channels to and from the users  92 ,  93  and  95  are shown. Each of the users feeds his or her microphone signal into the server as a mono signal, as is shown at  104 . Each of the users  92 ,  93  and  95  is fed with the three closest or chosen sources, including signals from other users or from the doorway  102 . The summed room hubbub for room A is summed at  106 , and includes audio channels from the users  91 ,  92 ,  94  and  96 , together with a so-called “wet room” signal  108  from room B. This signal is made up of the signals from the users  93 ,  95 ,  97  and  98  which are summed at  110 , together with the “wet room” signal  112  from room A. The directly summed output signal  116  from the summer  110  constitutes a “dry room” signal for room B. The “dry room” signal for room B is fed through a mono-reverberator  118  to provide a “wet room” signal output  120  for room B. This is in turn fed into the summer  106  for room A. The directly summed output  122  from the summer  106  is a “dry room” signal in respect of room A, with the “dry room” signal being processed by a mono-reverberator  124  to become a wet room signal  126  for room A. 
     The user  95  thus has as inputs the closest three users  93 ,  97  and  98  in room B, as well as the summed room hubbub constituted by the dry room signal  116  for room B. The user  93 , on the other hand, has as inputs the closest two users  97  and  95 , together with a doorway signal  128  constituted by the “wet room” reverberated output  126  from room A. In addition, user  93  in room B receives as an input a dry room input  130  representative of the background noise or hubbub in room B. 
     The user  92  in room A receives as inputs voice channels from the closest two users  91  and  96 , together with a doorway signal constituted by a “wet room” signal  132  from the “wet room” output  120  of room B, together with a “dry room” output signal  134  from room A representative of the background noise in that room. 
     An audio experience which is consistent with a dual chat room environment is achieved, in that users in one room which are close to the doorway receive “wet room” input from the other room as a dedicated input channel. For users further away from the doorway and the other room, a reduced input from the other room is still achieved by virtue of the feedback of “wet room” signals  108  and  112  which are combined at the respective summers  106  and  110 . This feature gives the user the ability to hear distant hubbub transmitted through multiple rooms and doors, and to navigate by sound to find the room with the greatest level of audible activity. 
     The gain of the fed back door signals  108  and  112  may be modified at  138  depending on whether the door is partly or fully open or closed, thereby enhancing the realism of the chat room environment and selectively allowing or preventing eavesdropping, in particular where it is possible for one or more of the users to “close” or “open” doors. 
     Referring now to  FIG. 11 , a further embodiment of a streaming server  136  is shown which is substantially identical to the  FIG. 9  embodiment save that binaural processing is performed at the server. In particular, binaural processors  138  are provided for receiving and processing the various wet and dry room signals and the source signals. The user terminal-based binaural reverberation and HRTF processing shown in  FIG. 8  can accordingly be arranged to take place at the server-based binaural processors  138 . The L and R binaural signals from the server can thus be fed directly to the headphones of each of the users  92 ,  93  and  95 , thereby reducing the hardware, signal processing and network bandwidth requirements at each of the user stations, in that only two input audio channels are required. 
     It will be appreciated that, in the case of HRTF processing user orientation and position on the graphic display on the user&#39;s screen  2  may be governed by a joystick or mouse pointer  1 , as has previously been described. The position and orientation signals are transmitted to the streaming server for processing, inter alia, at the binaural processors, and may be augmented by head tracking signals to achieve a more realistic effect as the user rotates his or her head to address other individuals in the group. The head tracking signals derived from a head tracking unit may be used intuitively to effect both rotational and translational motion of the user representation by corresponding head rotation and translation. This may be supplemented by the mouse pointer  4  or joystick. The resultant orientation and positional signals may be transmitted back to the streaming server for processing, and may also be processed locally at the user terminal to achieve the desired spatialization effects. 
     It will be understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention. 
     The foregoing describes embodiments of the present invention and modifications, obvious to those skilled in the art can be made thereto, without departing from the scope of the present invention.