Dynamic information storage or retrieval – Storage or retrieval of spatially related acoustic signals – Quadraphonic
Patent
1987-07-22
1989-02-21
Sikes, William L.
Dynamic information storage or retrieval
Storage or retrieval of spatially related acoustic signals
Quadraphonic
369 90, 381 1, 381 20, 381 22, H05B 7094, H04R 500, G06K 950, G06K 948
Patent
active
048072176
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to multi-channel stereo reproducing apparatus and particularly to a multi-channel stereo reproducing apparatus which can selectively reproduce a recording medium such as a video disc or the like (a so-called Dolby surround-phonic sound system stereo) on which a multi-channel stereo signal is recorded such that a high frequency component of its rear signal is pre-emphasized for listeners to enjoy screen music reproduced at a concert hall and a movie theater, and a recording medium on which a standard 2-channel stereo signal is recorded.
BACKGROUND ART
When a motion picture is shown at a concert hall and a movie theater, an audio signal is generally reproduced by means of Dolby surround-phonic sound system 4-channel stereo reproducing system to urge audiences to feel as if they were in the very place shown on the picture screen.
When a motion picture for a movie theater is produced, a video signal is recorded and at the same time, left front sound, right front sound, center front sound and rear sound are recorded respectively. In this case, a left front signal L.sub.F, a right front signal R.sub.F, a center front signal F and a rear signal B are encoded respectively and then recorded on a video disc or a magnetic tape as LT and RT signals, respectively. In this case, in order to improve a signal-to-noise ratio, or a so-called S/N ratio of the rear signal B, there is employed a so-called modified B-type Dolby system in which a high frequency component higher than 1 kHz is emphasized (pre-emphasis) by a predetermined amount and then recorded. FIG. 3 illustrates frequency vs. response characteristics in the case where the recording level is at 0 dB, -10 dB, -20 dB and -30 dB in this modified B-type Dolby system. Then, the left front signal L.sub.F, the right front signal R.sub.F, the center front signal F and the rear signal B thus recorded are further encoded to a left composite signal L.sub.T and a right composite signal R.sub.T which are respectively expressed as L.sub.T =L.sub.F +(F/2+2) and R.sub.T =R.sub.F +(F/2)-(B/2). These left and right composite signals L.sub.T and R.sub.T are optically recorded, in the case of, for example, a 35 mm film, at a sound track portion located at a predetermined position of the film according to the brightness change system which carries out the recording on the basis of the change of light and shade of, for example, the coloring. Accordingly, when a motion picture is shown, the left and right composite signals L.sub.T and R.sub.T thus optically recorded are decoded so as to produce four signals of the left composite signal L.sub.T, the right composite signal R.sub.T, a sum signal L.sub.T +R.sub.T of the left composite signal L.sub.T and the right composite signal R.sub.T and a difference signal L.sub.T -R.sub.T of the left composite signal L.sub.T and the right composite signal R.sub.T. Then, these four signals are reproduced by a left front loudspeaker, a right front loudspeaker, a center front loudspeaker and a rear loudspeaker. In this case, since the high frequency component of the rear signal B is pre-emphasized by the modified B-type Dolby system as described hereinabove, upon reproducing, the high frequency component of the difference signal L.sub.T -R.sub.T is attenuated (de-emphasized) so as to make a total frequency characteristic flat relative to the rear signal B. When the audio signal is reproduced by such 4-channel stereo reproducing system, the sound effect is enhanced to provide presence so that the listeners are urged to feel as if they were in the very place shown on the picture screen.
By the way, a magnetic tape and a video disc by which the user can enjoy the screen music recorded thereon for the motion picture or the mortion picture itself are now available on the market. In this case, since the recorded signals recorded on the magnetic tape and the video disc are the composite signals L.sub.T and R.sub.T as described hereinabove, there is proposed a multi-channel stereo reproducing apparatus illustra
REFERENCES:
patent: 3971890 (1976-07-01), Bauer
patent: 4303800 (1981-12-01), DeFreitas
patent: 4525855 (1985-06-01), Willcocks
patent: 4532647 (1985-07-01), Willcocks
Sikes William L.
Sony Corporation
Ullah Akm E.
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