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#1
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What is 2.0 surround?
I have a number of DVDs that have 2.0 surround. How does this provide
surround sound? ---MIKE--- In the White Mountains of New Hampshire (44=B0 15' N - Elevation 1580') |
#2
Posted to rec.audio.high-end
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What is 2.0 surround?
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#3
Posted to rec.audio.high-end
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What is 2.0 surround?
On Sat, 16 Apr 2011 12:29:02 -0700, MIKE--- wrote
(in article ): I have a number of DVDs that have 2.0 surround. How does this provide surround sound? ---MIKE--- In the White Mountains of New Hampshire (44=B0 15' N - Elevation 1580'), It's called matrix encoding and, without technical augmentation, is capable of only 4 channels: left, right, front center, and rear. The matrixing is a type of encoding where the localization of the channels is accomplished with signal phase. I.E., left and right are derived as usual from the two channels. The front center channel is the result of placing the same signal, such as a human voice, equally in both channels and in phase with each other. On playback, the two identical signals, left and right, are summed (L + R), and the sound comes from the center-front speaker. The rear channel is derived by the difference between the left and right channels (L - R). The drawback to this system is that the rear channel separation is only about 3 dB, which means that the wanted sound, whether in front or in back is only twice as loud as a "ghost" of that sound in the unwanted channel(s). This is just barely perceptible by the ear. Without some kind of electronic "channel separation enhancement" or "steering logic" circuitry in the decoder, the surround images will be unreliable and not a little ephemeral. IOW, if you hear a sound coming from the rear, and you turn your head to better focus on it, the image will as likely as not, seem to shift to the front. The separation enhancement logic such as that used by the Dolby Pro-Logic system works by detecting differences in phase of the stereo signal and steering slightly out of phase signals ( L - R, R - L) to the rear channels while simultaneously attenuating those same out-of-phase sounds in the front channels, This increases apparent separation to perhaps 15 dB or more, which will give a good, solid, localization. It is even possible by using the way that the out-of-phase material is combined in the main stereo channels and by using logic decoding, to derive both a left-rear and a right-rear channel from what is normally a mono rear channel in the simple matrix (without logic circuitry) configuration. While the equipment exists on the production end of this process to allow the producers to "pan" any sound, theoretically, to any point between any of the four (or five) speakers by design, one must keep in mind, that any random, extraneous out-of-phase info (such as sound bouncing off of the recording venue's walls) will be sent by the playback system to whatever channel the accidental phase anomalies tells the decode logic to steer them to. This can sound very impressive if the program material is simply music, as it mimics, to a certain extent, the acoustics in a concert hall, but in the case of a motion picture soundtrack, these random phase anomalies must be pretty carefully controlled to avoid any misplaced sounds showing up in channels where they aren't wanted. Discrete multi-channel sound such as DTS and Dolby Digital, SACD, or any of the newer discrete Blu-Ray formats are much better, |
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