Studio Technologies 76 V.1.10 - Manual (Page 15)

Model 76/77 User Guide Issue 7, August 2012
Studio Technologies, Inc. Page 15
for Surround
Stereo Output
In addition to a 6-channel surround monitor
output, a separate 2-channel stereo out-
put is also provided. By default the stereo
output can be enabled by an operator. In
applications where stereo monitor loud-
speakers are not connected to the stereo
output, the stereo output can be disabled.
This can minimize confusion, preventing
an operator from attempting to select the
stereo output.
Digital Input Reference Level
Configuring the digital input reference level
to match the sources associated with a
specific installation is an important step
toward achieving optimal audio perfor-
mance. This ensures that the Model 76’s
digital audio receiver integrated circuits
are configured to match the digital input
source’s “0 VU” or average point. The digi-
tal input reference level can be selected
from four choices: –20.0, –18.0, –16.0, and
–14.0 dBFS. The Society of Motion Picture
and Television Engineers (SMPTE) rec-
ommends a reference level of –20 dBFS,
a value which is also extensively used
in professional audio applications. The
recommended digital reference level for
PAL broadcast applications is –18 dBFS.
The other two levels were included be-
cause… well, we can’t remember why! But
it seemed like a good idea at the time. If
you end up using the –16.0 or –14.0 dBFS
settings please let us know why and we’ll
add that information to the next version of
this user guide!
Monitor Output Nominal Level
The nominal level of the surround (5.1) and
stereo output channels is configured, as
a group, matching the requirements of an
installation. This setting defines the analog
output level when a digital input source, at
its reference level, is connected and the
monitor output level is at its maximum. The
choices are 0.0 or +4.0 dBu. Most applica-
tions will find the +4.0 dBu setting correct
as it meets the dominant worldwide audio
standards. For broadcast applications that
follow the PAL standards the 0.0 dBu set-
ting may be appropriate.
While sometimes not fully understood,
using the term dBu is more in line with
contemporary audio applications than the
outdated dBm and the “semi-pro” dBV
references; dBu refers to audio levels
without regard to their load impedance,
typical of situations where an output has a
low source impedance and is connected to
a high-impedance input. An analog audio
signal with a level of +4 dBu has an RMS
level of 1.228 volts. A 0 dBu signal has an
RMS level of 0.775 volts.
A final review of the two previously se-
lected settings might now be in order. The
most common input and output combina-
tion will have a digital input reference level
of –20.0 dBFS and a monitor output nomi-
nal level of +4.0 dBu. For PAL broadcast
applications a setting of –18.0 dBFS for
the digital input and 0.0 dBu for the analog
outputs would be typical.
Reference Level
For audio-with-picture applications it’s
often beneficial for monitoring to be done
in reference to a known loudspeaker
level. This is often referred to as “mixing
to 85 dB” on the monitors. The Studio-
Comm system allows a precise monitor
output level to be stored, and then enabled
by pressing the Model 77 button labeled
Reference Level. Setting the reference
level is very simple but care is required: