Dolby Laboratories DA20, Руководство по установке

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6-4
Digital Status Indicators
These LEDs indicate the format of the audio coming from the DA20. When the upper
(green)
LED is on, Format 10 has been selected, and the DA20 is producing decoded
digital audio. When the lower (yellow) LED is on, Format 10 has been selected but the
DA20 is unable to decode digital information from the film (either the film is not a Dolby
Digital print, or the data is unreadable) and has switched to the analog track. When
neither LED is on, a format other than 10 has been selected, and the digital audio track is
not being reproduced.
Projector Changeover and Motor Running Indicators
The Projector1 and Projector2 LEDs indicate the status of the changeover line from the
Cinema Processor. Motor1 and Motor2 LEDs indicate which projector motor(s) are
running. The motor running signals are used in the timing of changeovers in a two
projector system.
Power Rail Indicators
These LEDs indicate the presence of the three power supply rails in the DA20. All three
should be lit when power is applied to the DA20.
Front Panel Switches
The five rotary switches shown on the DA20 front panel are for use by technicians when
the DA20 is first installed and adjusted. Changing the delay switches requires the use of
special test equipment. Do not arbitrarily adjust these switches.
6.4 Format Control and Auto Digital Modes
The DA20 can operate in either of two basic modes: Auto Digital and Auto Digital
Disabled. These are described below:
When the CP Type switch on the DA20 is set to Auto Digital mode for a particular cinema
processor type, the DA20 will automatically assert Format 10 and switch the Cinema
Processor to Format 10 under certain conditions.
When the CP Type switch is set to an Auto Digital Disabled mode, the format selection is
controlled by the Cinema Processor alone and the DA20 will assert no formats except
when switched to Format 10 and a reversion is required. Details of operation differ
depending on the type of Cinema Processor used and are described later.
When Format 10 Dolby Digital is selected, the DA20 will output decoded digital audio
whenever valid digital data is being read by the soundhead. Receipt of valid digital data
is indicated on the DA20 front panel when the green ‘Digital’ LED lights. When valid
digital data is not available (for example, while playing an analog only film), the output of
the DA20 / CP system will be switched to analog (Format 05, Dolby SR). The DA20 uses
very sophisticated error correction techniques to allow the data to be read perfectly, even
in the presence of heavy scratching or dirt. As with any digital system, the performance
is perfect up to the limits of the error correction, and then degrades very rapidly. Should
the digital data become corrupted beyond correction through perforation damage, then
concealment techniques are applied for up to 4 perforations (40ms), then the DA20 forces
the Cinema Processor to Format 05 (Dolby SR). This is referred to as a ‘reversion to
analog’ or simply ‘reversion’. Reversion is indicated on the front panel of the DA20 when