14
DOLBY Encoded Signals
DOLBY Signal Indication
Illumination of the blue
DOLBY LED
underneath a channel pair indicates that a DOLBY encoded signal has been
detected on that channel pair.
What is a DOLBY Encoded Signal?
A DOLBY encoded signal is a bitstream that contains multi-channel audio data compressed to fit in a single AES/EBU
bitstream (one channel pair). A DOLBY bitstream can also be present in a pair of embedded audio channels in SDI
video. Unlike with regular uncompressed digital audio (PCM), this bitstream must be decoded into its discrete channels
before it can be monitored as audio. Up to 8 discrete channels may be decoded from a DOLBY signal.
The
ARDM-552 DOLBY Module
must be installed in the AR-DM2X-X audio monitor in order to decode DOLBY signals
from any input module. If this module is not present, the AR-DM2X-X will indicate DOLBY signal presence with the
aforementioned blue LED, but will not be able to decode the bitstream into discrete channels.
Decoding and Monitoring DOLBY Signals
■ Introduction
If your AR-DM2X-X has been configured with the optional
ARDM-552 DOLBY Module
, you will be able to decode and
monitor a DOLBY signal on any channel pair. Two varieties of DOLBY signals can be decoded: DOLBY DIGITAL (AC-
3), and DOLBY E.
What is DOLBY DIGITAL?
DOLBY DIGITAL, also known as AC-3, is an encoded bitstream that carries up to 6 discrete channels of audio.
DOLBY DIGITAL is typically used to transmit a multi-channel audio program to consumers on a DVD or through
DTV.
What is DOLBY E?
DOLBY E is an encoded bitstream that carries up to 8 discrete channels of audio. DOLBY E has several technical
advantages over DOLBY DIGITAL, which make it ideal for distributing multi-channel audio within a production
environment using an existing AES/EBU pair of audio channels.
■ Entering DOLBY Decoding Mode
Once a DOLBY signal is detected, use the following steps to enter DOLBY decoding mode:
1.
Press the
PAIR
button to enter the Pair monitor mode.
2.
Use the
LEFT
,
RIGHT
, and
9-16
buttons to select the channel pair containing the DOLBY bitstream.
3.
Press the
DOLBY
button to enter DOLBY decoding mode. Once this mode is entered, 8 channels of decoded
audio from the selected bitstream will appear on bar graphs 1-8 or 16-9, depending upon the source channel
of the bitstream.
4.
DOLBY decoding mode can be exited by pressing the
DOLBY
button again.
5.
Pressing the
DOLBY
button will have no effect without the
ARDM-552 DOLBY Module
installed, or if no
DOLBY bitstream is present.
■ Downmixing DOLBY Decoded Audio
As with non-encoded multi-channel audio, DOLBY decoded audio channels can be monitored in Single, Pair, or
Downmix modes. In Downmix mode, however, several additional downmix configurations are available, depending on
the program format as described in the metadata of the DOLBY bitstream. See the
DOLBY Downmix Configurations
table on
page 12
for a table of available downmix configurations
11
Basic Operation
Overview
Basic operation of the AR-DM2X-X Audio Monitor involves selecting an input module as the audio source, using the LED
presence indicators to monitor signal presence, or using the LED bar graphs to display signal levels, and choosing a
mode in which to monitor audio through the stereo speakers.
The user can switch between up to four installed I/O modules, each providing up to 16 channels of audio. The LED
presence indicators will then display signal presence, or the LED bar graphs will display VU/PPM levels for each audio
channel from the selected input module. Finally, audio channels from the selected module can then be monitored through
the stereo speakers in a variety of ways: Any single channel can be monitored in mono, any channel pair can be
monitored in stereo, and any group of eight channels can be down-mixed to stereo using a variety of configurations.
Selecting an Input Module
The
SRC
switch is used to select the source module from which to monitor audio.
•
Module slots are identified with numbers 1-4, from left to right when facing the rear panel of the audio monitor.
•
Only the selected module’s channel inputs can be monitored simultaneously. Audio channels from different input
modules cannot be monitored at the same time.
Loop-through outputs and dedicated output modules however will
function at all times regardless of the selected module.
See module specifications for details.
•
If the
SRC
switch is set to a module slot where an output module or no module is present, no audio will be visible on
the meters or audible from the speakers.
•
Each module location retains exclusive settings – Channel selections and mix configurations are saved separately
for each module (1-4) when switching modules. Settings are only reset once the module is removed from the audio
monitor.
Volume
,
Balance
, and
Mute
settings are common to all modules.
LED Bar Graphs
The
LED signal presence indicators
will display audio presence or the
LED bar graphs
will display signal level
information for each audio channel.
Once an input module is selected using the
SRC
switch, the LED signal presence indicators display signal presence or
the LED bar graphs immediately begin displaying signal level information for up to 16 channels of audio, depending on the
number of channels available from the module. The bar graph for each channel will function even if that channel is not
selected for monitoring through the stereo speakers as described in the
Audio Monitoring
section.
The LED bar graphs have the following functions:
Digital Audio Signal Presence
Unlike analog audio signals, digital audio signals contain a constant bit stream even when the audio content is silent.
Such bit stream presence during silence is indicated by red illumination of the first LED segment of the corresponding
channel’s bar graph. This feature is useful in differentiating between an accidentally disconnected cable from silence in
the audio programming. This feature is not available for analog audio inputs.
VU/PPM Signal Level
Each LED bar graph (if available) represents the full scale of dynamic range of the audio monitor (-66dBFS to 0dBFS).
Signal level is simultaneously displayed in two ways. Signal level is shown in Volume Units – the average volume of
the signal – reflecting the perceive loudness of the signal. The bar graphs also function as Peak Program Meters,
indicating signal peaks by displaying a single red bar at the peak level with a slow decay time.
