Studio Technologies 47 - Manual (Page 7)

Model 47 User Guide Issue 1, August 2010
Studio Technologies, Inc. Page 7
this isolation, technically known as return-
loss or trans-hybrid loss, is measured in
dB. A high value is important, especially
in applications where multiple 2-wire-to-
4-wire interfaces are used together. Re-
mote sports broadcast applications are
especially sensitive to this requirement.
The Model 47’s sophisticated auto nulling
function uses analog circuitry under micro-
processor control to achieve significant
trans-hybrid loss. This return-loss “null”
is achieved by making a series of adjust-
ments to account for the resistive, induc-
tive, and capacitive conditions that are
present on the connected 2-wire party-line
circuit. A party-line’s condition is the sum
of the impact made by the type and quan-
tity of cable, the connected user devices,
and the intercom power source.
Whenever a user presses one of the
Model 47’s “auto null” buttons digital
circuitry adjusts the analog hybrids to
rapidly achieve their maximum return-loss.
The nulling process takes less than ten
seconds for each channel of an interface.
However, it’s important to note that while
the nulling process is automatic, it only
takes place upon user request. This can
lead to more stable and consistent audio
performance when a hybrid is exposed to
the varying 2-wire conditions often found
in broadcast applications. The param-
eters obtained during the nulling process
are stored in non-volatile memory; mains
power interruptions won’t require the auto
nulling function to again be performed.
A sine-wave audio tone is generated for
use during the auto nulling process. The
frequency is software-controlled to maxi-
mize the ability of the hybrid circuits to
reach a “deep” null. In addition, at the
beginning of each auto null sequence a
short period of 24 kHz tone is sent to the
associated 2-wire party-line interface. This
serves as a microphone disable (“mic kill”)
signal for user devices such as the RTS
BP325. By automatically disabling “open”
microphones the auto nulling process can
achieve better performance.
4-Wire Interfaces
Associated with the 4-wire portion of the
Model 47’s interfaces are analog line-level
inputs and outputs. These are intended
to interconnect with a variety of 4-wire
devices, including matrix intercom systems,
audio-over-fiber transmission systems, and
other specialized audio equipment. The
input and output circuitry is transformer-
coupled to minimize the chance of hum,
noise, or ground “loop” issues. A key
characteristic of the Model 47’s design is
the ability to select the 4-wire input and
output nominal levels. This helps to ensure
compatibility with virtually all audio equip-
ment. Front-panel-accessible DIP switches
allow the nominal levels to be configured
from among four choices: 0, +4, +6, or
+8 dBu. The 0 dBu setting was specifically
provided for compatibility with Clear-Com
matrix intercom systems. The +4 dBu set-
ting allows “standard” audio signals to be
directly connected. Digital matrix intercom
systems from Riedel® can be effectively
connected using the +6 dBu setting. And
the +8 dBu setting allows proper level
matching with the popular ADAM® series
of matrix intercom systems from RTS. This
setting also applies to the related RVON-I/O
VoIP product.
The Model 47 contains eight 5-segment
LED level meters. Four of the meters are
provided for each interface, with two
displaying the level of the signal being