Audio system for a computer display

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 "beeps".
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)