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center channel information. This, in effect, will cause the mono-compatible
elements of the mix to appear to always come from the center of the picture.
On the other hand, the incompatible elements (those that would cancel if the
two input channels were summed) would be reproduced around and
behind the listener. This spatial effect is useful as it instantly alerts sound
mixers to compatibility problems should inappropriate elements, such as
on-screen effects, or dialogue, suddenly appear in the rear.
Music Recording For Dolby Encoded Films
Music studios will find the SDU4 very useful when recording material
intended for integration into Dolby encoded soundtracks as it provides
accurate monitoring of two- or three-channel material in its final dimensional
perspective.
Typically, the SDU4 would be installed into the monitor system during the
music mix. Three equally balanced loudspeakers would be used in the front
driven by the L, C and R outputs, with the surround channel optionally used
to drive two or more speakers, wired as mono, in the rear.
The music pre-mix is usually recorded as three tracks with assignment
being made into L C and R tracks. Generally, no surround track is recorded
in advance. The three tracks can be recorded directly from the console mix
buss, but the discrete center track must be made into a “phantom”. This
requires the center track to be added back into the L and R channels at
precisely –3 dB into each. From this point, these two channels are sent to the
SDU4 Lt and Rt inputs for decoding into the spatially correct L,C,R and S
channels.
This fairly simple procedure allows the studio to simulate the action of the
Dolby encoder in respect to the generation of the center channel. It is not
possible, however, to pre-record an accurate discrete surround track using
this technique. Encoding of the surround channel requires the use of the
surround encoder due to the precise nature of the phase matching necessary
between the center and surround channels.
The three-track music mix would typically be transferred to magnetic film
and, subsequently, matched to the edited picture. In the film re-recording
studio it would be added with dialogue and effects keeping the same spatial
imaging characteristics.
Surround Productions
The SDU4 has been designed to interface with the Dolby Model SEU4
Surround encoding unit. Post-production facilities contemplating the
production of surround encoded programs should consider the installation
of the SDU4 and the establishment of a correct monitoring environment as
the first step in equipping for future surround productions.
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