Studio Technologies 76 V.1.04 - Manual (Page 15)

Model 76/77 User Guide Issue 4, September 2008
Studio Technologies, Inc. Page 15
for Surround
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 confi gured, as
a group, matching the requirements of an
installation. This setting defi nes 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 fi nd 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outdated dBm and the “semi-pro” dBV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 fi nal review of the two previously selected
settings might now be in order. The most
common input and output combination will
have a digital input reference level of –20.0
dBFS and a monitor output nominal 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
benefi cial for monitoring to be done in refer-
ence to a known loudspeaker level. This is
often referred to as “mixing to 85 dB” on the
monitors. The StudioComm 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:
1. Set up a precision sound pressure level
(SPL) measuring device at the desired
listening location.
2. Place the StudioComm system in the
normal operating mode, not the con-
fi guration mode. Be certain that the dim,
mute all, reference level, and downmix
functions are not active. The remote
mute all or remote dim functions must
not be active.
3. Use the Model 77 Control Console to
select the input source that contains the
desired reference signal source, e.g.,
pink noise.
4. Observing the SPL meter, adjust the
Model 77’s rotary level control until the
desired reference monitor system level
has been reached.