 Some or all of them may also be applied to the inputs of a storage system 805. This system is capable of storing complete processed stereo audio signals, and of replaying them simultaneously to appear at outputs 806. Typically this storage system amy have different numbers of input channel pairs and output channel pairs. A plurality of outputs 806 from the storage system are applied to further inputs of stereo mixer 804. Stereo mixer 804 sums all left inputs to produce left output 807, and all right inputs to produce right output 808, possibly modifying the amplitude of each input before summing. No interaction or coupling of left and right channels takes place in the mixer.
A human operator 809 may control operation of the system via human interface means 810 to specify the desired image position to be assigned to each input channel.
It may be particularly advantageous to implement signal processors 802 digitally, so that no limitation is placed on the position, trajectory, or speed of motion of an image. These digital sound processors that provide the necessary differential adjustment of phase and amplitude on a frequency dependent basis will be explained in more detail below. In such a digital implementation it may not always be economic to provide for signal processing to occur in real time, though such operation is entirely feasible. If real-time signal processing is not provided, outputs 803 would be connected to storage system 805, which would be capable of slow recording and real-time replay. Conversely, if an adequate number of real-time signal processors 802 are provided, storage system 805 may be omitted.
In FIG. 9, operator 901 controls mixing console 902 equipped with left and right stereo monitor loudspeakers 903, 904. Although stability of the final processed image is good to a loudspeaker spacing (s) as low as 0.2 m, it is preferable for the mixing operator to be provided with loudspeakers placed at least 0.5 m apart. With such spacing, accurate image placement is more readily achieved. A computer 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 signal