 conventional stereo signal is treated as a monophonic signal, and the channels are imaged to two different positions in the listener'space, a complete conventional stereo image along the line joining the positions of the images of the channels will be perceived. In addition, at the time the stereo record or disc is being recorded on multitrack tape, having for example twenty-four channels, each channel can be fed through a transfer function processor so that the recording engineer can locate the various instruments and voices at will to create a specialized sound stage. The result of this is still two-channel audio signals that can be played back on conventional reproducing equipment, but that will contain the inventive auditory imaging capability.
FIG. 1 is a plan view representation of a listening geometry for defining parameters of image location;
FIG. 2 is a side view corresponding to FIG. 1;
FIG. 3 is a plan view representation of a listening geometry for defining parameters of listener location;
FIG. 4 is an elevational view corresponding to FIG. 4;
FIGS. 5a-5k are plan views of respective listening situations with corresponding variations in loudspeaker placement and FIG. 5m is a table of critical dimensions for three listening rooms;
FIG. 6 is a plan view of an image transfer experiment carried out in two isolated rooms;
FIG. 7 is a process block diagram relating the present invention to prior art practice;
FIG. 8 is a schematic in block diagram form of a sound imaging system according to an embodiment of the present invention;
FIG. 9 is a pictorial representation of an operator workstation according to an embodiment of the present invention;
FIG. 10 depicts a computer-graphic perspective display used in controlling the present invention;
FIG. 11 depicts a computer-graphic display of three orthogonal views used in controlling the present invention;
FIG. 12 is a schematic representation of the formation of virtual sound sources by the present invention, showing a plan view of three isolated rooms;
FIG. 13 is a schematic in block diagram form of equipment for demonstrating the present invention;
FIG. 14 is a waveform diagram of a test signal plotted as voltage against time;
FIG. 15 tabulates data representing a transfer function according to an embodiment of the present invention;
FIG. 16 is a schematic in block diagram form of a sound image location system according to an embodiment of the present invention;
FIGS. 17A and 17B are graphical representations of typical transfer functions employed in the sound processors of FIG. 16;
FIG. 18A-18C are schematic block diagrams of a circuit embodying the present invention; and
FIG. 19 is a schematic block diagram of additional circuitry which further embodies the present invention.
In order to define terms that will allow an unambiguous description of the auditory imaging process according to the present invention, FIGS. 1-4 show some dimensions and angles involved.
FIG. 1 is a plan view of a stereo listening situation, showing left and right loudspeakers 101 and 102, respectively, a listener 103, and a sound image position 104 that is apparent to listener 103. For purposes of definition only, the listener is shown situated on a line 105 perpendicular to a line 106 joining loudspeakers 101 and 102, and erected at the midpoint of line 106. This listener position will be referred to as the reference listener position, but with this invention the listener is not confined to this position. From the reference listener position an image azimuth angle (a) is measured counterclockwise from line 105 to a line 107 between listener 103 and image position 104. Similarly, the image slant range (r) is defined as the distance from listener 103 to image position 104. This range is the true range measured in three-dimensional space, not the projected range as measured on the plan or other orthogonal view.
In the present invention the possibility arises of images substantially out of the plane of the speakers. Accordingly, in FIG. 2 an altitude angle (b) for the image is defined. A listen