Dolby Laboratories DA20 Manuale d'uso - Pagina 9
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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.
1.4
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:
Auto Digital—When the CP Type switch (See figure 1.3) is set to positions 1, 2 or 3,
depending on the cinema processor type, the DA20 will switch the cinema processor to
Dolby Digital, Format 10, under certain conditions.
Auto Digital Disabled—When the CP Type switch is set to position 5, 6 or 7, depending
on the cinema processor type, the format selection is controlled by the Cinema Processor
alone and the DA20 will assert no formats except when playing digital audio 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 digital audio whenever
it is available. When the DA20 is playing digital audio, the green 'Digital' LED on the
DA20 front panel will light. When digital audio is not available (for example, while
playing an analog only film), the DA20 will switch the cinema processor to Format 05,
Dolby SR, if Format 10 was selected previously.
If the Dolby Digital track becomes corrupted beyond correction through perforation
damage, then error concealment techniques are applied for up to 4 perforations (40ms). If
the data is still unreadable, the DA20 then switches 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 the yellow 'Analog" LED lights. This