ick potentiometers 1651, 1652 respectively.
As examples of image placement, Table 3 shows settings and corresponding image positions to "fly" a sound image corresponding to a helicopter at positions well above the plane including the loudspeakers and the listener. To obtain the required monophonic signal for the process according to the present invention, the stereo tracks on the sound effects disc were summed. With the equipment shown set up as tabulated, realistic sound images are projected in space in such a manner that the listener perceives a helicopter at the locations tabulated.
TABLE 1______________________________________Filter # 1 2 3 4 5 6______________________________________Capacitor 1631 100 47 33 15 10 4.7Value, nF______________________________________
TABLE 2______________________________________Switch 1642Position # 1 2 3 4 5______________________________________Resistor # 1637 1638 1639 1640 1641Resistor 4700 1000 470 390 120value, Ohms______________________________________
TABLE 3______________________________________Filter 1630 element 1 switch pos. 5 5Filter 1630 element 2 switch pos. 5 5Filter 1630 element 3 switch pos. 5 5Filter 1630 element 4 switch pos. 5 5Filter 1630 element 5 switch pos. 5 5Filter 1630 inverting switch 1622 norm. norm.Potentiometer 1652 ratio 0.046 0.054Potentiometer 1654 ratio 0.90 0.76Potentiometer 1658 ratio 0.77 0.77Inverting switch 1691 position inv. inv.Selector switch 1685 position 1601 1601Output attenuator 1686 ratio 0.23 0.23Output attenuator 1687 ratio 1.0 1.0Image azimuth a, degrees -45 -30Image altitude b, degrees +21 +17Image range r remote remote______________________________________ Note to table 3: setting of reversing switch 1659 in both cases is such that signals from element 1657 drive element 1660, and those from element 1658 drive element 1670.
By addition of two extra elements to the above circuits, an extra facility for lateral shifting of the listening area is provided. It should be understood, however, that this is not essential to the creation of images. The extra elements are shown in FIG. 19, in which left and right signals 1701, 1702 may be supplied from the outputs 1688, 1689 respectively of the signal processor of FIG. 16. In each channel a delay 1703, 1704 respectively is inserted, and the output signals from the delays 1703, 1704 become the sound processor outputs 1705, 1706.
The delays introduced into the channels by this additional equipment are independent of frequency. They may thus each be completely characterized by a single real number. Let the left channel delay be t(1), and the right channel delay t(r). As in the above case, only the differential between the delays is significant, and we can completely control the equipment by specifying the difference between the delays. In implementation, we will add a fixed delay to each channel to ensure that at least no negative delay is required to achieve the required differential. Defining a differential delay t(d) as:
If t(d) is zero, the effects produced will be essentially unaffected by the additional equipment. If t(d) is positive, the center of the listening area will be displaced laterally to the right along dimension (e) of FIG. 3. A positive value of t(d) will correspond to a positive value of (e), signifying rightward displacement. Similarly, a leftward displacement, corresponding to a negative value of (e), may be obtained by a negative value of t(d). By this method the entire listening area, in which listeners perceive the illusion, may be projected laterally to any point between or beyond the loudspeakers. It is readily possible for dimension (e) to exceed half of dimension (s), and good results have been obtained out to extreme shifts at which dimension (e) is 83% of dimension (s). This may not be the limit of the technique, but represents the limit of current experimentation.
Two ordinary, spaced-apart loudspeakers can produce a sound image that appears to the listener to be emanating from a location other than the actual location of the loudspeakers. The sound signals are process