Electrical audio signal processing systems and devices – Binaural and stereophonic – Quadrasonic
Patent
1981-09-24
1983-11-08
Pellinen, A. D.
Electrical audio signal processing systems and devices
Binaural and stereophonic
Quadrasonic
H04R 504
Patent
active
044144300
DESCRIPTION:
BRIEF SUMMARY
This invention relates to sound reproduction systems and more particularly to sound reproduction systems which enable a listener to distinguish sound from sources extending over 360.degree. of azimuth. Such systems are hereinafter called surround sound systems. The invention is also applicable to surround sound systems which, in addition, enable the listener to distinguish sound from sources at different heights.
Surround sound systems for loudspeaker arrays in which the loudspeakers are disposed at the corners of a geometrically regular polygon, or, in the case of with-height surround sound systems, the corners of a regular solid, are already known. Such systems are also known for loudspeaker arrays where the loudspeakers are disposed to corners of a rectangle or rectangular cuboid. The present invention is concerned with the provision of a decoder for use in a surround sound system where the loudspeakers are disposed at other locations. Such loudspeaker arrays will hereinafter be referred to as irregular loudspeaker arrays and it should be understood that this term excludes rectangular and rectangular cuboid arrays in spite of the fact that these are, in strict mathematical terms, not regular shapes.
It has already been proposed in U.K. Pat. No. 1,411,994 to feed each loudspeaker of an irregular array with a signal having an effective directional pick-up characteristic for encoded sounds which points in the direction of that loudspeaker. However, the results achieved with irregular arrays are not psychoacoustically correct.
Two important theories of sound localisation are the "Makita" theory and the "energy vector" theory. The "Makita" theory is applicable to frequencies less than 700 Hz and has some applicability up to about 1500 Hz. According to this theory, for a loudspeaker array with n loudspeakers all placed at the same distance r from a central reference point at positions indicated by respective rectangular cartesian co-ordinates (x.sub.i, y.sub.i, z.sub.i) where i=1, 2, . . . , n, the localisation of the sound fed to these loudspeakers, where g.sub.i is the complex gain of the sound emerging from the ith loudspeaker, is given by: ##EQU1## where "Re" means "the real part of" and (x.sub.o, y.sub.o, z.sub.o) is a vector pointing to the apparent localisation of the sound with respect to the origin of the cartesian co-ordinates.
For frequencies in the range from approximately 700 Hz to 5 kHz, the "energy vector" theory of localisation is appropriate, the apparent sound direction being the direction of the vector sum of a set of vectors, one pointing to each loudspeaker with a respective length equal to the energy gain of the sound at that loudspeaker. Then, with a loudspeaker array as described above, the energy vector localisation is the direction of the vector (x.sub.E, y.sub.E, z.sub.E) given by: ##EQU2##
The present invention is concerned with the provision of a decoder for an irregular loudspeaker layout which satisfies both the "Makita" and the "energy vector" theories.
According to the invention, there is provided a decoder for feeding an irregular array (as hereinbefore defined) of m (being three or more) pairs of diametrically opposite loudspeakers, each loudspeaker being disposed substantially at an equal distance r from a common reference point, comprising an amplitude matrix circuit so arranged that, in operation, the sum of the signals S.sub.i.sup.+ and S.sub.i.sup.- fed to the loudspeakers of each pair is the same for all pairs of loudspeakers, and such that, if the ith pair of loudspeakers has cartesian coordinates (x.sub.i, y.sub.i, z.sub.i) and (-x.sub.i, -y.sub.i, -z.sub.i) with respect to rectangular cartesian axes x, y and z at the reference point, Z'-.delta..sub.i jW.sub.i " Z'+.delta..sub.i jW.sub.i " reference point and is independent of i,
X', Y' and Z' are signals representative of the components of a desired acoustical velocity along the x, y and z axes and are independent of i,
jW.sub.i " is any signal bearing a 90.degree. phase relationship to W' for all encoded sound dire
REFERENCES:
patent: 4095049 (1978-06-01), Gerzon
Gerzon, "Surround Sound Decoders-6", Wireless World, vol. 83, No. 1499, Jul. 1977, pp. 43-47, S74520140g.
Gerzon, "Surround Sound Decoders-7", Wireless World, vol. 83, No. 1500, Aug. 1977, pp. 69-73, S74660033m.
National Research Development Corporation
Pellinen A. D.
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