6. The method of claim 5, wherein the predetermined phase and amplitude transfer functions are constructed on a frequency dependent basis of 40 Hz intervals.
7. A system for conditioning a signal for producing and locating, using two transducers located in free space, an auditory sensory illusion of an apparent origin for at least one selected sound at a predetermined localized position located within the three-dimensional space containing a listener from a single electrical signal corresponding to the selected sound, comprising: first and second channel means both receiving the same single electrical signal, said first and signal channel means including respective first and second sound processor means each for altering the amplitude and shifting the phase angle of the respective electrical signal on a frequency dependent basis for successive discrete frequency intervals across the audio spectrum to produce a respective modified signal wherein the amplitude alteration differential and the phase angle shift differential occurring between the two channels are respective predetermined values for each said successive frequency interval of the audio spectrum, said sound processor means shifting the phase angle such that each successive phase angle shift is different and independent of a preceding phase angle shift relative to zero degrees, and said first and second channels being maintained separate and apart prior to being fed to the two transducers.
8. A system as in claim 7 further including storage means connected to said sound processor means for storing said modified signals in a medium capable of regenerating said stored signals at a subsequent selected time.
9. A system as in claim 7 wherein the sound processor means comprises a sound processor having a predetermined amplitude transfer function for producing the amplitude differential on a frequency dependent basis and having a predetermined phase transfer function for producing the phase angle differential on a frequency dependent basis.
10. A system as in claim 9, wherein the frequency dependent basis is made up of said intervals being 40 Hz wide.
This is a continuation of application Ser. No. 07/398,988, filed Aug. 28, 1989 now abandoned.
Field of the Invention
This invention relates generally to a method and apparatus for processing an audio signal and, more particularly, to processing an audio signal so that the resultant sounds appear to the listener to emanate from a location other than the actual location of the loudspeakers.
Human listeners are readily able to estimate, the direction and range of a sound source. When multiple sound sources are distributed in space around the listener, the position of each may be perceived independently and simultaneously. Despite substantial and continuing research over many years, no satisfactory theory has yet been developed to account for all of the perceptual abilities of the average listener.
A process that measures the pressure or velocity of a sound wave at a single point, and reproduces that sound effectively at a single point, will preserve the intelligibility of speech and much of the identity of music. Nevertheless, such a system removes all of the information needed to locate the sound in space. Thus, an orchestra, reproduced by such a system, is perceived as if all instruments were playing at the single point of reproduction.
Efforts were therefore directed to preserving the directional cues contained inherently in the sounds during transmission or recording and reproduction. In U.S. Pat. No. 2,093,540 issued to Alan D. Blumlein in September, 1937 substantial detail for such a two-channel system is given. The artificial emphasis of the difference between the stereo channels as a means of broadening the stereo image, which is the basis of many present stereo sound enhancement techniques, is described in detail.
Some known stereo enhancement systems rely on cross-coupling the stereo channels in one way or another, to emphasis the existing cues to spatial location contained in a stereo recording. Cross-coupling and