Abstract:
An audio system for a computer visual display unit (VDU), providing four loudspeakers 1 to 4 at the corners of the VDU screen. Sound is distributed to the loudspeakers under computer program control, to simulate the emission of sound from an image on the VDU screen.

Description:
FIELD OF THE INVENTION 
     The invention relates to an audio system for a computer display. 
     BACKGROUND OF THE INVENTION 
     A personal computer usually includes a loudspeaker and audio circuitry for generating sounds in conjunction with programs as they are run. Speech or music may be simulated or played from a digital recording. A growing application for computers is in conferencing, where several users may be connected together in a network, each with a terminal. Each screen may contain representations of the users such as icons, photographic representations, or freeze-frame or even real-time video pictures. Each user will generally have a particular region of the screen devoted to him, with the program typically running under a windows environment. 
     It is found that there is enhancement of a user interface if the sound associated with a window appears to emanate from the position of the window. The invention provides a means of achieving this and in more general terms provides a means of generating sound which is spatially associated with the position of the image of the sound source on the screen. It will be seen that such a facility has application in various types of computer displays including games with moving sound sources and video type displays 
     SUMMARY OF THE INVENTION 
     The present invention provides an audio system for a computer visual display unit (VDU), the system comprising a plurality of loudspeakers distributed around the screen of the VDU, audio circuitry for driving the loudspeakers including means to allow a sound source signal to be variably distributed to the loudspeakers. 
     The screen coordinates of the image provided by a computer program and related to a sound source are processed to provide a control input to the audio circuitry whereby sound is generated which appears to emanate from a position spatially coordinated with the position of the image. 
     The image position and the apparent sound position may be aligned with respect to their distances from the center of the screen. Alternatively, it may be desirable to exaggerate the apparent position of the sound so that there is not spatial coordination, the position of the sound being further from the center of the screen than the position of the corresponding image. Exaggeration may be provided in one dimension only, for example the &#34;up-down&#34; dimension. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     The invention will further be described with reference to the accompanying drawing, of which the sole figure is a schematic diagram of an audio system in accordance with the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to the drawing there is shown an essentially rectangular screen S of an VDU. Loudspeakers 1 to 4 are situated at the corners of the screen. The computer C associated with the VDU is running a networked conferencing program which operates in a windows environment. Two windows A and B are shown at the top left and bottom right of the screen respectively. 
     Although any number of loudspeakers may be distributed around the VDU, in preferred embodiments four are placed at respective corners of the screen. Other examples include only three loudspeakers arranged in a triangle and one loudspeaker placed at the middle of each side of the screen. 
     The system is able to distribute sound between the four loudspeakers to give the impression that sound is emanating from the screen at a position corresponding to the position of the appropriate window. For window A the sound will come predominantly from loudspeaker 1. If the window moves so will the apparent position of the sound source. Any number of windows can be present at once and the sound will be positioned independently for each window. So, for example, the sound associated with window B would come mainly from speaker 3. 
     This scheme would work equally well for speech, and other complex sounds, as well as for more primitive sounds such as &#34;beeps&#34;. 
     A window is of width dx and height dy. The origin is defined as the upper left hand corner of the screen. The left hand edge of a window is distance x from the origin and the top edge of a window is distance y for each channel. Audio circuitry is provided for each channel A and B, which comprises sets of four variable gain amplifiers aG1 to aG4 and bG1 to bG4 for each window and adding units 5 for each loudspeaker. 
     The operation of the system may best be understood by the following illustrative example. 
     In providing sound corresponding to window A the followinq steps are taken: 
     In Software 
     1. The center of the window is calculated by the coordinates (x+dx/2), y+dy/2). For example, if the top left hand corner of window A is 50,50 and the width dx, and height dy are 150 and 100 respectively, then the center of the window will be (50+150/2), 50+100/2), or 125, 100. 
     2. The gain for the amplifiers (aG1, aG2, aG3, aG4) is determined by the sound distribution over the four speakers with reference to the size of the screen. 
     The distribution of the sound left and right (i.e., between the vertically aligned pairs of speakers 1 and 4, 2 and 3) will be proportional to the ratio: ##EQU1## for the left side, and ##EQU2## for the right side. 
     If for example, the size of the display is the same as VGA screens (768×480), then the width of the screen is 768 and the height 480. If the x coordinate of the center of the window is 125 then the ratio between speakers 1 &amp; 4, and 2 &amp; 3 (i.e. between left and right) is 84% to the left hand speakers and 16% to the right hand speakers. 
     Similarly, if the y coordinate of the center of the window is 100 and the height of the window is 480, then by the same method the ratio between speakers 1 &amp; 2, and 3 &amp; 4 (i.e. up and down) is 79% is to the upper speakers and 21% to the lower speakers. 
     Once the percentages of audi directed to the upper and lower speakers and left and right speakers are computed, the percentage of the sound going to each of the four speakers is determined. For example, of the 84% of the sound going to the left hand speakers 79% of this goes to the upper left hand speaker and 21% goes to the lower left hand speaker. Therefore, 66% (79% of 84%) goes to speaker 1 and 18% (21% of 84%) goes to speaker 4. 
     Using the same method the percentage going to speaker 2 and 3 is 13% (79% of 16%) and 3% (21% of 16%) respectively. 
     
         ______________________________________            left right______________________________________                  84%    16%up       79%           66%    13%down     21%           18%     3%______________________________________ 
    
     These percentage values can then be used to control the variable gain, aG1, aG2, aG3, and aG4. 
     In Hardware 
     The hardware, in preferred embodiments, is in the form of a card for the IBM PC-AT computer class. 
     1. The incoming audio is split into four and fed into four amplifiers. 
     2. The variable gains, aG1, aG2, aG3, and aG4, calculated in software control each amplifier. 
     3. The outputs of the amplifier are added by an adder 5, to the amplifier stages of the other channels. 
     4. Each adder 5 is coupled to a speaker. 
     In the figure only two channels are shown, however, a separate set of amplifiers may be provided for each additional channel.