Studio Technologies 212 2013 - Manual (Page 16)

Issue 5, May 2013 Model 212 User Guide
Page 16 Studio Technologies, Inc.
Microphone Preamplifier
Gain, Phantom Power, and
Compressor Threshold
Five switches are used to set the gain of
the microphone preamplifier. One switch
is used to select the on/off status of the
phantom power supply. Another switch
selects the threshold level of the compres-
sor circuit.
Microphone Preamplifier Gain
Switches SW1-1 through SW1-5 are used
to select the gain of the microphone pre-
amplifier. The choices are 10, 20, 30, 40,
50 dB; 0 dB (no gain) is also available.
Only one switch should be enabled at a
time. There’s no problem changing the
gain setting while the unit is operating.
Audio clicks or pops might occur during
gain transitions, but this shouldn’t be a
major issue as long as associated monitor
loudspeakers are temporarily attenuated
or muted.
Selecting the correct amount of gain for an
application might take a little experimenta-
tion. The goal is to bring the mic’s signal
up so that the main and talkback output
levels will match the Model 212’s nominal
digital output level which is –20 dBFS.
Operating at this signal level will help to
ensure the delivery of “clean” audio with
adequate level “headroom.”
The output of the Model 212’s microphone
preamplifier is used, by way of the com-
pressor circuit, by the main and talkback
outputs. So creating a nice “hot” signal
will help maintain audio quality, specifically
a high signal-to-noise ratio.
Unfortunately, there’s no “perfect” gain
setting that this guide can recommend.
The two issues that impact the setting are
output sensitivity of the connected micro-
phone and the acoustical output level of
the microphone’s user. With some headset
microphones, such as the Sennheiser
HMD 26, selecting an initial setting of 30
dB is appropriate. Users who speak loudly
might need to have the gain reduced to 20
dB. Quiet users might need 40 dB of gain.
An LED indicator is provided as an aid
in correctly setting the gain of the micro-
phone preamplifier. Red in color, this LED
is located adjacent to switch assembly 1.
It is visible by observing the bottom of the
Model 212’s enclosure when the security
plate has been removed. Technically, this
red LED lights whenever the compressor
circuitry is controlling the dynamic range
of the signal coming from the microphone
preamplifier. Using configuration DIP
switch SW1-7, the compressor’s thresh-
old will be set to either –14 or –4 dBFS.
(Details concerning setting the compress
threshold are discussed later in this user
guide.) If the threshold is set for –14 dBFS
a good “rule of thumb” is to adjust the
gain of the microphone preamplifier such
Figure 4. Microphone preamplifier gain switch
settings