r graphic display means 905, a multi-axis control 906, and a keyboard 907 are provided, along with suitable computing and storage facilities to support them.
Computer graphic display means 905 may provide a graphic representation of the position or trajectory of the image in space as shown, for example, in FIGS. 10 and 11. FIG. 10 shows a display 1001 of a listening situation in which a typical listener 1002 and an image trajectory 1003 are presented, along with a representation of a motion picture screen 1004 and perspective space cues 1005, 1006.
At the bottom of the display is a menu 1007 of items relating to the particular section of sound track being operated upon, including recording, time synchronization, and editing information. Menu items may be selected by keyboard 907, or by moving cursor 1008 to the item, using multi-axis control 906. The selected item can be modified using keyboard 907, or toggled using a button on multi-axis control 906, invoking appropriate system action. In particular, a menu item 1009 allows an operator to link the multi-axis control 906 by software to control the viewpoint from which the perspective view is projected, or to control the position/trajectory of the current sound image. Another menu item 1010 allows selection of an alternate display illustrated in FIG. 11.
In the display of FIG. 11 the virtually full-screen perspective presentation 1001 shown in FIG. 10 is replaced by a set of three orthogonal views of the same scene; a top view 1101, a front view 1102, and a side view 1103. To aid in interpretation the remaining screen quadrant is occupied by a reduced and less detailed version 1104 of the perspective view 1001. Again a menu 1105, substantially similar to that shown at 1007 and with similar functions, occupies the bottom of the screen. One particular menu item 1106 allows toggling back to th display of FIG. 10.
In FIG. 12, sound sources 1201, 1202, and 1203 in a first room 1204 are detected by two microphones 1205 and 1206 that generate right and left stereo signals, respectively, that are recorded using conventional stereo recording equipment 1207. If replayed on conventional stereo replay equipment 1208, driving right and left loudspeakers 1209, 1210, respectively, with the signals originating from microphones 1205, 1206, conventional stereo images 1211, 1212, 1213 corresponding respectively to sources 1201, 1202, 1203 will be perceived by a listener 1214 in a second room 1215. These images will be at positions that are projections onto the line joining loudspeakers 1209, 1210 of the lateral positions of the sources relative to microphones 1205, 1206.
If the two pairs of stereo signals are processed and combined as detailed above using sound processor 1216, and reproduced by conventional stereo playback equipment 1217 on right and left loudspeakers 1218, 1219 in a third room 1220, crisp spatially localized images of the sound sources are apparent to listener 1226 at positions unrelated to the actual positions of loudspeakers 1218, 1219. Let us suppose that the processing was such as to form an image of the original right channel signal at position 1224, and an image of the original left channel signal at 1225. Each of these images behaves as if it were truly a loudspeaker; we may think of the images as "virtual loudspeakers"
A transfer function in which both differential amplitude and phase of a two-channel signal are adjusted on a frequency dependent basis across the entire audio band is required to project an image of a monaural audio signal to a given position. For general applications to specify each such response, the amplitude and phase differential at intervals not exceeding 40 Hz must be specified independently for each of the two channels over the entire audio spectrum, for best image stability and coherence. For applications not requiring high quality and sound image placement the frequency intervals may be expanded. Hence specification of such a response requires about 1000 real numbers (or equivalently, 500 complex ones). Differences for human perception of a