BEL DIGITAL AUDIO BM-A1-S Operation
2004 BEL (Digital Audio) Ltd 3 Version 0.3
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The front panel user interface consists of 5 rotary controls, an alarms switch, and four
bargraphs. In addition there is a headphone output, two LEDs for sustained anti-phase, a
further five LED indicators and a 525/625 switch at the rear of the unit.
The BM-A1-S front control panel
Selecting sources
The audio source switch routes available sources to the speaker selectors, the bargaphs and
the monitoring line output. The possible choices are analog, AES, and embedded groups 1 to
4 from the SDI input. The AES/analog audio output, recovered from the SDI input, follows the
selected group but defaults to group 1 in the Analog and AES positions.
Note: To prevent de-muxed audio from being corrupted or muted, ensure that the 525/625
switch at the rear of the unit is correct for the SDI source.
Using alarms
The BM-A1-S can provide the following warnings:
Alarm event Notes Alarm indication
Audio loss The currently selected four audio channels are
monitored for persistent under-level. An alarm is
generated when an input is < -30dB (-50dB for
AES meter) for more than 15 seconds.
Bottom bargraph segment
flashes amber
Audio tone, TTL/serial o/p
Audio-over-
level
The currently selected four audio channels are
monitored for transient over-level. An alarm is
generated immediately when the first red
segment of the relevant bargraph is illuminated.
Bottom bargraph segment
flashes red
Audio tone, TTL/serial o/p
Audio anti-
phase
Audio pairs 1&2 and pairs 3&4 are monitored for
sustained anti-phase.
Phase LED illuminates
Audio tone, TTL/serial o/p
(if enabled)
Note: The over-level alarm threshold can be adjusted by moving the red bar transition point.
The anti-phase tone and external alarm can only be armed via serial control.
