Dolby Laboratories SDU4

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The matrix format used on Dolby soundtracks is compatible with both

monophonic and conventional stereo playback.

Many home viewers have purchased Dolby Surround decoding equipment

for use during playback of prerecorded videotape or videodisk program

material. These consumer grade decoders are being manufactured by the

many companies who are licensed by Dolby Laboratories. Viewers are

finding that the Dolby Surround decoders are also capable of effectively

decoding broadcasts of Dolby films and Dolby Surround productions. The

SDU4 gives the broadcast station a means of monitoring the correct spatial

decoding of this material in the professional broadcast environment.

The SDU4 is simply installed in the monitor system, typically between the

stereo replay machine or stereo program buss. Its output is used to drive the

monitor system’s power amplifiers, either directly or through an audio

routing system. Surround encoded material will usually be decoded using

the Dolby Surround mode; however, it may be evaluated for conventional

stereo and mono compatibility as well. Proper decoding of Dolby Surround

encoded material is, of course, the preferred way of evaluating the overall

quality of the material. All stereo program material, regardless of whether

it is specifically surround encoded or not, can be evaluated for compatibility

in mono, stereo and surround playback.

Conventionally recorded stereo material, i.e., originally recorded for two

loudspeaker playback, may be checked for acceptability using the Dolby

Surround mode. In this case, center and surround channels will be extracted

from the stereo mix as if they were specifically encoded as such.

Note: If a center loudspeaker is not used, i.e., the internal Center speaker

switch S301 is in the “no” position, the decoded center output is re-summed

with the left and right decoder output signals, giving effectively the same

front stereo image as with normal stereo playback. In this case, the decoder

will extract the phase-difference information from the stereo input material

and send it to the rear loudspeakers.

As most conventional stereo material contains some valid phase difference

information, due to the microphone techniques, the reproduction of this

phase difference information to the rear of the viewer will usually lead to an

overall pleasing effect. On the other hand, artificially induced phase-

differences, created either by alignment errors or by some special effects

processors (such as stereo synthesizers) can cause erroneous and

inappropriate sound elements at the rear of the viewer. Conventional stereo

material may be evaluated for compatible playback using the Dolby Surround

mode.

In audio post-production environments, it is recommended that all stereo

material be evaluated through the SDU4 in the Dolby Surround mode as a

means of verifying mono compatibility. Conventional monophonic

recording, i.e., equal phase at equal level, can be considered a subset of the

Dolby Surround encoding matrix, as its occurrence will be reproduced as

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