Space-mapping sound system

Encoder apparatus for a three-dimensional position-mapping stereo sound reproduction system using a pair of transmission or storage channels, said apparatus comprising a hemispherical sound location encoder having input(s) for sound signals designated for reproduction from selected positions within or on the periphery of a volume representing a playback space, and having at least two-channel output, said encoder including:

• means for hemispherical directional encoding of a sound input signal to apply said signal with a selected differential phase shift to the transmission or storage channels, said differential phase shift having a first sense of phase-leading vs. phase-lagging (positive vs. negative imaginary signal component in the differential phase shift), where said differential phase shift represents spherical elevation angle of the sound input signal on the surface of a hemispherical dome bounded on the bottom by the plane of the audience in the playback area, said elevation angle measured around the left/right central axis of the audience plane;
• and further having means for hemispherical directional encoding of a sound input signal to apply said signal with a selected amplitude ratio and relative polarity (positive vs. negative real signal component in the differential phase shift) to said transmission or storage channels where said amplitude ratio and relative polarity represent azimuth angle of said sound input signal;
• means for audience-plane positional encoding of a sound input signal to apply said signal with a selected differential phase shift to the transmission or storage channels, said differential phase shift having a sense of phase-leading vs. phase-lagging (positive vs. negative imaginary signal component in the differential phase shift) opposite to that used for hemispherical directional encoding, where said differential phase shift represents front/back position of the sound input signal on the audience plane;
• and further having means for audience-plane positional encoding of a sound input signal to apply said signal with a selected amplitude ratio to said transmission or storage channels where said amplitude ratio represents left/right position of said sound input signal on the audience plane;
• means for vertical positional encoding of a sound input signal to apply said signal to the transmission or storage channels with selected quasi-decorrelation involving variation with frequency of differential phase in said channels, where said quasi-decorrelation represents at least proximity of the sound input signal to the midpoint of a vertical axis within a hemispherical volume bounded on the top by said hemispherical dome, and on the bottom, by said audience plane;
• means for positional encoding of a sound input signal in the transmission or storage channels to apply said signal to said channels with a substantially 90.degree. differential phase shift in one sense of phase-leading vs. phase-lagging, and to have equal amplitudes in both channels, said 90.degree. differential phase shift and equal amplitudes representing a "Center Up" direction and a full or nominally unity radius or distance with respect to the center of the audience plane corresponding to a "center top" location on a unit-radius hemispherical dome;
• and means for encoding a sound input signal in the transmission or storage channels to apply said signal to said channels with a substantially 90.degree. differential phase shift in the opposite sense of phase-leading vs. phase-lagging, and to have equal amplitudes in both channels, said opposite 90.degree. differential phase shift and equal amplitudes representing a Center position in the audience plane having a substantially zero radius or distance with respect to the center of the audience plane;
• and further having means for encoding a sound input signal in the transmission or storage channels to apply said signal so as to be quasi-decorrelated in respective said channels, where quasi-decorrelation involves variation with frequency of differential phase in said channels, and to have approximately equal overall amplitudes in both channels, said quasi-decorrelation and approximately equal overall amplitudes representing a position, within a hemispherical volume, substantially at the midpoint of a central vertical axis connecting the Center Top of the hemispherical dome with the Center of the audience plane.

The process of decoding positions associated with sound signals contained in two or more transmission or storage channels and having 3-dimensional sound-source position information encoded by at least phase-amplitude relationships in said channels comprising the steps of:

• (a) applying said transmission or storage channels to a two-or-more-channel input and four-or-more-channel output 3-dimensional decoder in which the dominant or strongest one(s) of outputs intended for reproduction on the periphery of the horizontal plane of the audience are determined by amplitude ratio and polarity difference (sign of real component of difference) between the signals in said transmission or storage channels, degree of dominance decreasing as amplitude ratio between said signals approaches unity in combination with phase difference approaching ninety degrees in either sense (.+-.90.degree.);
• and amplitude of an output intended for overhead reproduction increasing relative to that of the audience-plane outputs as amplitude ratio between said signals approaches unity in combination with phase difference approaching ninety degrees in one sense;
• with reproduction of quasi-decorrelated signals in said transmission or storage channels (signals whose different spectral components have different relative phases in said channels) obtained in both audience-plane and overhead outputs;
• (b) providing the four or more output signals from the previous step to transducers with position designations including at least three audience-plane positions and at least one overhead position.