Studio Technologies 45DR - Manual (Page 7)

Model 45DR User Guide Issue 2, January 2015
Studio Technologies, Inc. Page 7
A significant capability of the Model 45DR’s
party-line interface is its ability to supply
DC power and 200 ohm AC terminations
to “create” an intercom circuit. The 29 volt
output can power a moderate number of
devices such as beltpacks. With up to 240
milliamperes (mA) of current available, a
typical broadcast application which uses
two or three BP-325 beltpacks can be
supported. In many applications this can
eliminate the need for an external intercom
power supply, reducing total system cost,
weight, and required mounting space. The
power supply output is monitored for over-
current and short-circuit conditions. Under
firmware (embedded software) control the
output will automatically cycle off and on
to help prevent damage to the circuitry and
connected equipment.
Dante Audio-over-Ethernet
Audio data is sent to and from the Model
45DR using the Dante Audio-over-Ethernet
media networking technology. Audio
signals with a sample rate of 48 kHz
and a bit depth of up to 24 are supported.
Audio input (receiver) and output (transmit-
ter) channels on associated Dante-enabled
devices can be assigned to the Model
45DR using the Dante Controller applica-
tion. This makes it simple to select the way
in which a Model 45DR fits into a specific
application.
Analog Hybrids with Auto
Nulling
Circuits referred to as “hybrids” interface
the Dante input and output channels with
the two party-line channels. The hybrids
provide low noise and distortion, good
frequency response, and high return-loss
(“nulling”), even when presented with a
wide range of party-line conditions. Unlike
telephone-line (“POTS”) oriented DSP-
based hybrid circuits, the Model 45DR’s
analog circuitry maintains extended fre-
quency response. With a passband of
100 Hz on the low end and 8 kHz on the
high end, natural-sounding voice signals
can be sent to and received from a party-
line circuit.
The Model 45DR’s sophisticated hybrid
auto nulling function uses a combination
of digital and analog circuitry under micro-
processor control to achieve significant
trans-hybrid loss. This return-loss “null” is
achieved by making a series of firmware-
directed adjustments to account for the
resistive, inductive, and capacitive condi-
tions that are present on the connected
party-line cabling and user devices. When-
ever the Model 45DR’s auto null button is
pressed, digital circuitry adjusts the hybrids
to achieve their maximum return-loss in
less than 15 seconds. While the nulling
process is automatic, it only takes place
upon user request. The resulting null pa-
rameters are stored in non-volatile memory.
Pro Audio Quality
The Model 45DR’s audio circuitry was
designed in the spirit of professional audio
equipment rather than that found in typi-
cal party-line intercom gear. High-perfor-
mance components are used throughout,
providing low-distortion, low-noise, and
high headroom. Using active filters the
frequency response of the audio channels
is limited to nominally 100 Hz to 8 kHz.
This range was selected to provide excel-
lent performance for human speech while
maximizing the ability of the hybrid circuits
to create substantial “nulls.” Moreover,
the Model 45DR’s party-line intercom
power source offers a unique level of