Studio Technologies 76B 2012 - Manual (Page 38)

Issue 3, August 2012 Model 76B/77B User Guide
Page 38 Studio Technologies, Inc.
for Surround
by the Model 77B Control Console. It can
also be used to control the level of the sur-
round monitor output.
Technically, the metadata is in the form
of a 115.2 kbit/s RS-485/RS-422 signal
that contains a number of data elements,
including one or more that represent the
average dialog level (dialog normaliza-
tion or dialnorm) in the audio program
signals being carried over the digital audio
portion of the related Dolby E interface.
These dialnorm levels are associated with
specific programs within the 8-channel
audio “stream.” Firmware within the Model
76B is able to parse (separate) the data
elements, specifically separating the first
dialnorm level value in the metadata frame
from the one or more that may be present
later in the frame. To clarify, any dialnorm
level elements that occur later in the same
metadata frame are ignored. This method
was selected as it was assumed that the
first dialnorm level element will always be
associated with a 5.1 program. There’s
a technical basis for why this should be
true. In Dolby E a 5.1 program is always
assigned to the first six channels (chan-
nels 1-6). While there may be separate
dialnorm values associated with audio
channels 7 and 8, they are not relevant for
correct StudioComm system operation.
Downmix
The downmix functions are implemented
in the Model 76B Central Controller’s
hardware using analog circuitry. The 5.1
to stereo downmix function performs this
action: center (C) input dropped in level by
6 dB and routed to the left (L) and right (R)
surround monitor outputs; left surround
(LS) input dropped in level by 3 dB and
routed to the L surround monitor output;
right surround (RS) input dropped in level
by 3 dB and routed to the R surround moni-
tor output; low-frequency-enhancement
(LFE) input is muted; C, LFE, LS, and RS
surround monitor output channels are mut-
ed. The resulting stereo signal is sometimes
known as LoRo.
The stereo to mono downmix function per-
forms this action: L input dropped in level
by 3 dB and routed to the C surround moni-
tor output; R input dropped in level by 3 dB
and routed to the C surround monitor output;
C, LS, RS, and LFE inputs mute.
“Hot” Disconnection of the
Model 77B Control Consoles
There’s no problem relocating one or more
Model 77B Control Consoles while the
StudioComm system is operating. You
can disconnect the 9-pin interconnecting
cable, move the unit (or units), and then
re-connect without issue. Upon disconnec-
tion of all control consoles the Model 76B
Central Controller will mute the monitor out-
put channels as well as saving the current
operating parameters. No clicks, pops, or
other noises will occur when the Model 77B
units are again connected. The Model 77B
units will go through their standard power-
up sequence and then normal operation will
resume.
Monitor Output Transient
Protection
The Model 76B Central Controller contains
a power-up/power-down transient protec-
tion feature. This limits the chance of dam-
age to the monitor loudspeakers during the
time when AC mains voltage is connected,
disconnected, or has changed significantly
from nominal. A combination of hardware
and software is used to monitor one of the
power supply “rails.” Until the AC mains input