Studio Technologies 212 2006 - Manual (Page 6)

Issue 3, July 2006 Model 212 User Guide
Page 6 Studio Technologies, Inc.
System Features
Microphone Input
A high-performance microphone pre-
amplifier circuit provides low-noise/low-
distortion amplification over a 10 to
50 dB gain range. The gain is adjustable
in 10 dB steps. The input is compatible
with balanced dynamic or condenser
microphones. The microphone power
source is 48 volts nominal and meets the
worldwide P48 phantom standard. An
LED indicator serves as an aid for optimiz-
ing the setting of the preamplifier’s gain.
The output of the microphone preamplifier
is routed to the compressor circuit that
supports the main and talkback audio
channels.
Dynamic Range Control
A studio-quality compressor circuit is
provided to control the dynamic range
of the analog signal coming from the
microphone preamplifier. Far from a
simple “clipper,” the circuit utilizes a
sophisticated laser-trimmed voltage-
controlled-amplifier (VCA) integrated cir-
cuit for quiet, low-distortion level control.
The output of the compressor is used by
the main and talkback channels, being
routed to the inputs of their respective
analog-to-digital converter circuits. The
threshold of the compressor can be con-
figured from among two values. When
configured for –4 dBFS, dynamic range
control will only take place as the signal
approaches the level limit of the digital
signal. During normal operation the com-
pressor would not be active. With the
compressor configured to –14 dBFS some
dynamic range control would be expected
during normal operation. While not appro-
priate for major on-air situations, having
dynamic range control of the signal can
offer increased performance for many
applications. This would be appropriate
for applications such as stadium an-
nouncement positions, sports events
using nonprofessional on-air talent, as
well as situations where the risk of digital
“clipping” is present.
Main and Talkback Audio
Channels
Internally, the Model 212 creates analog
main and talkback audio channels. The
main audio channel is designed to serve
as the on-air, stadium announcement,
or other primary audio feed. The talkback
audio channel is intended to provide
production trucks, control rooms, or
support personnel with a talent-originated
cue signal. The two analog channels are
converted to 24-bit PCM digital audio and
multiplexed and formatted into an AES
digital audio “stream.” The A/D converters
and digital transmitter circuitry is synchro-
nized (“locked”) to the selected digital
input signal. The system will automatically
revert to the internal clock, which provides
a 48 kHz sampling rate. The main audio
channel is assigned to digital channel 1
with talkback audio on digital channel 2.
The composite digital audio signal
is routed to two physical interfaces. One
output is AES3id compliant (unbalanced,
75 ohms) with a BNC connector for inter-
facing. This professional interface is trans-
former-coupled and capable of driving
long broadcast cable runs.
The digital audio output signal is also
routed to a unique bidirectional digital
interface. Similar to AES3id, it uses a
BNC connector and supports two chan-
nels of audio in each direction over a
single 75 ohm cable. The bidirectional