Electrical audio signal processing systems and devices – Binaural and stereophonic – Quadrasonic
Reexamination Certificate
1999-02-05
2004-07-06
Harvey, Minsun Oh (Department: 2644)
Electrical audio signal processing systems and devices
Binaural and stereophonic
Quadrasonic
C381S020000, C381S022000, C381S306000, C381S307000
Reexamination Certificate
active
06760448
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the field of multichannel audio. More particularly the invention relates to matrix-encoded surround-sound channels in a discrete typically digital sound format for motion picture soundtracks.
DESCRIPTION OF RELATED ART
Optical soundtracks for motion pictures were first demonstrated around the turn of the century, and since the 1930's have been the most common method of presenting sound with motion pictures. In modern systems, the transmission of light through the film is modulated by variations in soundtrack width, where an ideally transparent varying width of soundtrack is situated within an ideally opaque surrounding. This type of soundtrack is known as “variable area”.
In an effort to reduce distortion due to non-uniform light over the soundtrack width and other geometric distortion components, the “bilateral” variable area track was introduced. This format has two modulated edges, identical mirror images around a fixed centerline. A later development, which is now the standard monophonic analog optical soundtrack format, is called “dual bilateral” (or “double bilateral” or “duo-bilateral”) sound track. This format has two bilateral elements within the same soundtrack area, thus providing further immunity from illumination non-uniformity errors. A useful discussion of the history and potential of optical soundtracks can be found in “The Production of Wide-Range, Low-Distortion Optical Sound Tracks Utilizing the Dolby Noise Reduction System” by Ioan Allen in
J. SMPTE
, September 1975, Volume 84, pages 720-729.
In the mid 1970's Stereo Variable Area (SVA) tracks became increasingly popular, in which two independently modulated bilateral soundtracks are situated side by side in the same area as the normal monophonic (mono) variable area track.
In 1976, Dolby Laboratories introduced its four-channel stereo-optical version of Dolby Stereo, which employed audio matrix encoding and decoding in order to carry 4 channels of sound on the two SVA optical tracks. “Dolby” and “Dolby Stereo” are trademarks of Dolby Laboratories Licensing Corporation. Dolby Stereo for SVA optical tracks employs the “MP” matrix, a type of 4:2:4 matrix system that records four source channels of sound (left, right, center and surround) on the two SVA tracks and reproduces four channels. Although the original Dolby Stereo stereo-optical format employed Dolby A-type analog audio noise reduction, in the mid-1980's Dolby Laboratories introduced an improved analog audio processing system, Dolby SR, which is now used in Dolby Stereo optical soundtrack films.
Multichannel motion picture sound was employed commercially at least as early as “Fantasound” in which the four-channel soundtrack for the motion picture Fantasia was carried in respective optical tracks on a separate film synchronized with the picture-carrying film. Subsequently, in the 1950s, various “magnetic stripe” techniques were introduced in which multiple channels of sound were recorded in separate tracks on magnetizable materials affixed to the picture-carrying film. Typically, magnetic striped 35 mm film carried three or four separate soundtracks while magnetic striped 70 mm film carried six separate soundtracks.
Although most motion picture films with magnetic striped soundtracks carried a separate channel in each magnetic track, at least one film released in the mid-1970s (Tommy in “Quintaphonic” sound) employed matrix encoding—the normally left and right tracks were matrix encoded with left front, left rear, right front and right rear sound channels. The third, center channel remained discrete. The phase sensitive matrix system suffered from sound image wandering due to variations in phasing between the matrix-encoded tracks.
In a variation of PerspectaSound used in some prints of the motion picture Around the World in Eighty Days, four magnetic tracks on 35 mm carried left, center, right and surround channel information, respectively. In addition to the surround information, the fourth track carried subaudible tones for directing the surround sound to a selected bank of three banks of surround sound loudspeakers. Early forms of PerspectaSound employed a subaudible control tone on the monaural soundtrack in order to direct the sound to selected loudspeakers behind the screen.
Magnetic striped 35 mm films became obsolete after the introduction of the Dolby Stereo 35 mm optical format.
In another version of Dolby Stereo introduced in the 1970s, Dolby noise reduction was applied to four of the six discrete audio tracks of magnetic striped 70 mm motion picture film. As a feature of this Dolby Stereo format, tracks
1
and
2
(recorded in the magnetic stripe located between the left edge of the film and the left-hand sprocket holes) carry the left main screen channel and low-frequency-only “bass extension” information, respectively; track
3
(recorded in the magnetic stripe located between the left-hand sprocket holes and the picture) carries the center main screen channel; track
4
(recorded in the magnetic stripe located between the picture and the right-hand sprocket holes) also carries low-frequency-only “bass extension” information; and tracks
5
and
6
(recorded in the magnetic stripe located between the right sprocket holes and the right edge of the film) carry the right main screen channel and the single surround channel, respectively. Dolby noise reduction is not applied to the bass extension information.
In a variation of Dolby Stereo for 70 mm magnetic soundtrack motion picture films, two surround channels are provided instead of one (referred to as “split surrounds” or “stereo surrounds”). Tracks
1
,
3
,
5
and
6
are the same as in conventional Dolby Stereo 70 mm; however, mid- and high-frequency left surround information is recorded (with Dolby noise reduction) in track
2
along with the low-frequency bass information, and mid- and high-frequency right surround information is recorded (with Dolby noise reduction) in track
4
along with the low-frequency bass information. When reproduced in a theater, the mid- and high-frequency stereo surround information on tracks
2
and
4
is fed to the left and right surround speakers, respectively, combined with monophonic surround bass information from track
6
. This variation of Dolby Stereo 70 mm was an early form of the now-common “5.1” channel (sometimes referred to as six channel) configuration: left, center, and right main screen channels, left and right surround sound channels and a low-frequency bass enhancement (LFE) or subwoofer channel. The LFE channel, which carries much less information than the other full-bandwidth channels, is now referred to as “.1” channels.
In spite of these advances in analog soundtrack fidelity, film soundtracks had long been considered a candidate for digital coding due to the high cost of 70 mm magnetic soundtrack films and the perceived limitations of the matrix technology employed in 35 mm optical soundtrack films. In 1992, Dolby Laboratories introduced its Dolby Digital optical soundtrack format for 35 mm motion picture film. Dolby Digital is a trademark of Dolby Laboratories Licensing Corporation. 5.1 channel (left, center, right, left surround, right surround and LFE) soundtrack information is digitally encoded employing Dolby Laboratories AC-3 perceptual encoding scheme. That encoded information is in turn encoded as blocks of symbols optically printed between the film's sprocket holes along one side of the film. The analog SVA tracks are retained for compatibility. Details of the Dolby Digital 35 mm film format are set forth in U.S. Pat. Nos. 5,544,140, 5,710,752 and 5,757,465. The basic elements of the Dolby AC-3 perceptual coding scheme are set forth in U.S. Pat. No. 5,583,962. Details of a practical implementation of Dolby AC-3 are set forth in Document A/52 of the United States Television Systems Committee (ATSC), “Digital Audio Compression Standard (AC-3),” Dec. 20, 1995 (available on the world wide web of the Internet at3 atsc dot org and at dolby dot com. The Dol
Dolby Laboratories Licensing Corporation
Gallagher Thomas A.
Gallagher & Lathrop
Harvey Minsun Oh
Jacobson Tony M.
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