User Guide
Model 374A User Guide Issue 4, February 2021
Studio Technologies, Inc. Page 17
MODEL 374A
INTERCOM BELTPACK
presence of a call signal. Also, if channel 4
has been configured to the Call mode that
channel will not respond to a call signal on
audio input 4.
The Model 374A will not confuse a normal
talk audio signal with a call signal. Digital
filters within the unit’s processor integrated
circuit limits each channel’s high-frequency
response, helping to ensure that false call
detection won’t take place. Digital filtering
is also performed on the Dante receiver
(input) audio signals before they are sent
to the headphone outputs. This prevents
users with extended high-frequency sensi-
tivity, such as presenters and guests asso-
ciated with dog shows, from ever receiving
undesirable audio content.
By using 20 kHz tones for call signal-
ing the Model 374A is compatible with
legacy intercom equipment, including the
venerable RTS® BP-325 beltpack. When
interconnecting Model 374A and BP-325
units using an appropriate Dante-enabled
interface, such as the Studio Technologies’
Model 45DR Intercom Interface, call signal-
ing is fully compatible. Compatibility with
the Clear-Com® method of call function-
ality is also possible by using the Model
45DC Intercom Interface. (It converts the
DC call signal associated with pin 3 of a
Clear-Com party-line circuit to a 20 kHz
tone.)
Devices such as the Studio Technologies’
Model 44D Audio Interface will also send
and receive 20 kHz signals that are com-
patible with the Model 374A’s call function.
To generate a call signal a Model 44D will
respond to the activation of a GPI (gen-
eral-purpose input) signal by summing
(combining) a 20 kHz tone with the normal
audio signal that is being transported “in
band” via a Dante audio path. On the call
receive side, audio signals that enter the
Model 44D will be monitored for the pres-
ence of 20 kHz. If a call signal is detected
the GPO (general-purpose output) associ-
ated with that audio channel will activate.
Receive
Whenever a Model 374A’s Dante receive
(input) channel receives a valid 20 kHz
nominal call signal the action of the as-
sociated button’s LED will follow the unit’s
call indication configuration. This one con-
figuration will impact the action of all but-
ton LEDs. If the call indication function has
been configured for Disabled a button’s
LED will not respond to the presence of a
call signal. If the call indication configura-
tion has been selected for Flash then a
button’s LED will flash orange when a call
signal has been detected on its associated
audio input and the talk function is not
active. If a call tone is detected when the
talk function is active then the associated
button’s LED will flash, alternating be-
tween green and orange. If the call indica-
tion has been configured for Solid then a
button’s LED will light orange whenever a
call signal is detected. If Flash then Solid
is selected for the call indication configura-
tion a button’s LED will first flash orange
(or orange and green if the talk function
is active) and then light solid orange.
Send
The Model 374A allows a call signal to be
sent on channels 1, 2, and 3. This requires
that button 4 be configured to the Call
mode. To send a call signal is simple: just
enable any combinations of channels 1,
2, and/or 3 and simultaneously press and
hold button 4. When call sending is active
the orange LED associated with button 4
will light. At the same time the channel or
channels that are active in their talk mode