Silence Detect Unit
Silence Detect Unit
The RB-SD1 Silence Detect Unit is a 1U rack-mount
device used to monitor an unattended stereo studio feed
and in the event of the signal going “quiet” after a given
period the unit will switch through an alternative stereo
audio signal. This signal could be a recorded message
(e.g. “normal service will be resumed”, etc), a feed from a
CD player or minidisc machine, or an alternative recorded
program. Controls are provided to start external equipment
and to provide remote status indication.
It has 2 balanced stereo audio inputs with the maximum
input level being +28dBu. Each input is user-defined as
either the main source or auxiliary source and both
sources are monitored for failure, each having a remote
failure alarm. In the event of the main source dropping
below a pre-set level for a pre-determined amount of time,
the unit will automatically switch through to the auxiliary
The silence detect level is adjustable between -60dBu and
-15dBu in 3dB steps via a 16 position rotary switch on the
rear panel. The silence interval can be adjusted between 2
seconds to 30 seconds in 2 second steps, or, alternatively,
set to 2 minutes 5 seconds also via a 16 position rotary
switch on the rear panel. The audio outputs use stereo
professional balanced XLR-3 male connectors.
The unit can operate in 2 modes - automatic or manual. In
both modes it will automatically switch over to the auxiliary
source on detecting silence. When the main signal is again
detected it will either return to the main signal automatically
or manually depending on the mode chosen.
Audio Specification
Maximum Input Level:
Maximum Output Level:
Frequency Response:
The RB-SD1 has a number of remote operational features.
Remote outputs provide separate relay contact closures for
failure of the main and auxiliary inputs. You can also
control remotely all of the front panel switches for source
selection, mode selection and signal Restore. You can
remotely start and stop another piece of equipment on
alarm failure and main signal return respectively. Also, the
longest silence time (2min 5sec) can be set remotely,
which is useful if you are expecting to broadcast a long
The unit can be configured to alarm when either the left or
right channel of the main input source fails, or if the whole
stereo signal fails. There are also options to set the remote
start output as momentary or latched, to disable switching
to the auxiliary input on alarming and to increase the gain
on the auxiliary input so that an unbalanced input can be
used, for example, from a domestic minidisc player.
Front panel LED indicators show individually left and right
programme and alarm conditions for both the main and
auxiliary inputs. The status of the source, mode and alarm
state are also shown on the front panel with LED
The RB-SD1 has been designed to have a passive signal
path through the main input, so if power to the unit fails,
the signal input will still be routed through to the output.
This is essential for applications such as installation at
transmitter sites, where a power failure to the unit should
not prevent the audio input signal from being output to the
Input Impedance: >100k ohm balanced
Output Impedance: As input, except when using unbalanced auxiliary
20Hz - 20kHz ±0.1dB
input where output impedance <50 ohm
+12dB (for unbal input B - optional)
<-87dB, unity gain, ref +8dB output for unbal input
As input for balanced input, <0.05% ref +8dBu output for unbalanced input
Rear Panel Connections and Controls
Inputs (Main & Auxiliary): 4 x XLR 3 pin female (balanced, auxiliary can be unbalanced)
2 x XLR 3 pin male (balanced)
Filtered IEC, 110V-120V, or 220-240V, fused, 9W max
Alarm Threshold:
-15dBu to -60dBu in 3dB steps via rotary switch
Silence Detect Duration: 2 - 30 seconds in 2 second intervals & 125 second option via rotary switch
Detection Type:
Mono or stereo, via dipswitch
15 way D-type plug
Silence Switch Defeat:
Disable/enable silence switching, via dipswitch Remote Start:
Latched or momentary, via dipswitch
Front Panel Controls and Indicators
Controls (with indicators): Source select, mode select and restore
Program and alarm indicators for left and right
source for both main and auxiliary channels
Equipment Type
Physical Specification
Nett: 1.4kg Gross: 2.0kg
Dimensions (Raw): 48cm (W) x 10.8cm (D) x 4.2cm (H) (1U)
(Boxed): 53cm (W) x 20.5cm (D) x 6cm (H)
Silence detect unit, 230V (UK 3 pin to IEC)
Silence detect unit, 230V (European Schuko 2 pin to IEC)
Silence detect unit, 115V (USA 3 pin to IEC)
Stereo Limiter
Designed and manufactured to the highest
specifications, Redbox comprises of a range
of analogue and digital audio interfaces for
use in various professional applications
including installations at radio stations, TV
studios, home studios and video and
recording suites.
Twin Mono, Or Stereo Limiter
Range Features:
The RB-SL2 is a stereo, or twin independent mono, VCA
limiter for use in news-rooms and other locations where
the correct level into recording equipment is required, but
not necessarily under the control of an engineer, for
example, for overload protection. It can also be used as
an inexpensive main output limiter for small scale radio
stations, hospital radio and student radio.
All are equipped with IEC mains lead
and instruction manual.
The XLR-3 electronically balanced inputs and outputs
can be wired unbalanced to accept an output from
domestic equipment.
All are screw mountable as standard and
are either rack-mounted or have the
option to be rack-mounted.
In-house design and manufacture
ensures high quality control standards.
They are manufactured as either 115V
60Hz or 230V 50Hz and all have a front
panel LED power indicator.
Manufactured within ISO9000 standards
and guaranteed CE compliant.
Housed in eye catching red anodised
aluminium cases.
The Redboxes in this brochure can be rackmounted using the 1U RB-RK1 rack front kit,
except the RB-SD1 which is already rackmounted.
For each channel there is an input gain and a threshold
level control. With the limit threshold set to maximum, the
input through to output can be normalised using the input
potentiometers. Once the unit is acting as a buffer with
gain/attenuation, the limit threshold level can be set, with
the recovery adjusted for the application. The power LED
indicates limiting by flashing.
The rear panel mode switch changes the unit from dual
mono to stereo, when only the pre-sets for channel 1
(left) are active and apply to both channels. Stereo
limiting operates by limiting both left and right outputs if
either left or right input needs to be limited. Dual mono
limiting operates by limiting left and right signals
individually, so you can use the RB-SL2 as two separate
mono limiters.
Audio Specification
Maximum Input Level:
Maximum Output Level:
Input Gain:
Limit Threshold:
Frequency Response:
Common Mode Rejection:
Input impedance: 20 kohms balanced bridging
Output impedance: <50 ohms balanced
Adjustable -8dBu to +18dBu gain
Adjustable -8dBu to +28dBu
20Hz to 20kHz ±0.1dB (600 ohm load, ref 1kHz)
-100dB unity gain, ref +8dB output
0.01% THD @ 1kHz, ref +8dBu output, threshold set at +10dBu
>66dB typically
Mains Input:
Physical Specification
2 x XLR 3 pin female (Balanced, can be unbalanced) Weight:
Nett: 1.0kg Gross: 1.45kg
2 x XLR 3 pin male (Balanced, can be unbalanced) Dimensions (Raw): 28cm (W) x 10.8cm (D) x 4.2cm (H)
Filtered IEC, 110-120V, or 220-240V, fused, 6W max (Boxed): 36cm (W) x 20.5cm (D) x 6cm (H)
Equipment Type
Twin mono, or stereo, limiter, 230V (UK 3 pin to IEC)
Twin mono, or stereo, limiter, 230V (European Schuko 2 pin to IEC)
Twin mono, or stereo, limiter, 115V (USA 3 pin to IEC)
1U Rack-Mount Kit For Small Redboxes
mixing desks and studio furniture, or rack-mounted.
UK :
Sonifex Ltd, 61, Station Road,
Irthlingborough, Northants., NN9 5QE, UK
Tel : +44 (0)1933 650 700
Fax : +44 (0)1933 650 726
Email :
Internet :
Independent Audio, 43, Deerfield Road,
Portland, ME 04101-1805, USA
Tel : +1 207 773 2424
Fax : +1 207 773 2422
Email :
Internet :
The Redboxes are housed in red anodised aluminium
boxes which can be screw-mounted to the underside of
Physical Specification
Nett Weight:
Gross Weight:
Dimensions (Raw):
48cm (W) x 0.8cm (D) x 4.2cm (H) 1U
5.5cm (Diameter of tube) x 56cm (L)
Equipment Type
1U rack-mount for small Redboxes
The RB-DA6, RB-HD6, RB-UL4, RB-SD1 and RB-ADDA
are mounted in a 1U rack as standard. All the other small
Redboxes can be rack-mounted by fitting the RB-RK1
rack front kit.
Denmark :
Interstage AS, Phistersvej 31,
DK-2900 Hellerup, Denmark
Tel : +45 39 46 00 00
Fax : +45 39 46 00 40
Internet :
Brochure Stock Code : 30-203 Ref : AW10099A
In an effort to continually improve equipment
performance, Sonifex reserve the right to alter
the product specifications from those given in
this brochure. Errors and omissions excepted.
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