Studio Technologies 742 2005 - Manual (Page 20)

Issue 2, May 2005 Model 742 User Guide
Page 20 Studio Technologies, Inc.
Model 742
world where maximum audio fidelity is the
goal, the LEDs should rarely, if ever, light.
Level Meters
Two 10-segment LED meters display the
level present on main outputs 1 and 2.
Each meter has seven green LEDs which
light in the presence of signals in the
normal operating range. Two yellow LEDs
light with signals slightly higher in level
than normal. One red LED lights when-
ever the signal level is in the “headroom”
area. The ballistics of the meters is a cross
between that of VU and a peak (PPM)
meters. (We affectionately refer to them as
“PU” meters!) The way the LEDs “move”
in response to signals should be comfort-
able for most users to observe.
While the meters are easy to interpret,
they are somewhat different from ones
that are marked with “VU” nomenclature.
The important thing to remember is that
the steps show level in dBu, rather than
VU units. So, for example, when the meter
step that is labeled “0” lights, it indicates
that 0 dBu is present on its associated
main output connector. It doesn’t indi-
cate 0 VU! (Remember that 0 VU typically
indicates a device’s reference operating
level—often +4 dBm.)
The seven green LEDs in each meter
display a dynamic range of 28 dB, with
thresholds of –24 dBu, –18 dBu, –12 dBu,
–8 dBu, –4 dBu, 0 dBu, and +4 dBu. This
is the range that typical signals should
display if correct settings have been made
to the input sensitivity switches, input level
controls, and master level controls. The
two yellow LEDs light when a signal level
has exceeded the Model 742’s nominal
+4 dBu output level. Their thresholds
are +8 dBu and +12 dBu, well within the
capabilities of the unit’s circuitry. The red
LED lights when signal on the main output
meets or exceeds +18 dBu. This is dan-
gerously close to the Model 742’s maxi-
mum output level and should be avoided.
But now back to reality when it comes to
how the meters will function during actual
Model 742 use. To a great degree meter
activity will depend on how the compres-
sors have been configured to operate.
As discussed in previous sections of this
user guide, a technician can set the Model
742’s compressors to operate from one of
three modes:
• If the factory-default compressor thresh-
old of +10 dBu is in effect, normal
audio content will cause each meter to
display a small to moderate amount of
dynamic range control. The yellow level
LEDs may light on peak signal levels,
along with the compressor active LED.
The red LED will essentially never light.
• If the thresholds are set for +6 dBu,
typically only a meter’s first yellow LED
will light. The second yellow LED will
rarely light; the red LED will probably
never light. With this configuration there
often may be a large amount of dynam-
ic range control being performed by
the compressors. Obviously the goal in
this case is for the operator to carefully
set the Model 742’s controls so that the
signal level generally stays below the
compressor’s threshold. But with the
fairly low threshold of +6 dBu, it may
be difficult to not have the compressors
active almost all the time.