Redbox RB-MM1
Redbox RB-MM1
Mix-Minus Generator
June 2012
Manufacturers of audio & video products
for radio & TV broadcasters
Audio & Video Interfaces
A unit for generating a suitable
mix to send to a telephone hybrid
or codec.
Whenever programming originates from
outside of the studio, or if listeners/viewers
are calling up a phone-in using telephone
hybrids or codecs, mix-minus feeds are
required. Most telephone lines incur delays
which prohibit off-air monitoring, because
the caller, or remote talent, would hear
their own voice in delay which is very
disconcerting. The solution is to feed a mix
back to the caller minus his or her own
voice. Some mixing desks do not have a
dedicated telco channel to generate a
clean-feed, or mix minus, so the RB-MM1
can be used.
The RB-MM1 is a unit for generating a
suitable mix to send to a telephone hybrid
or codec. A stereo output is taken from a
mixer, together with a post fader output
from the mono telephone fader on the
mixer. The caller audio is removed from the
station output so that it can be sent to the
telephone line via the hybrid.
Analogue audio inputs and outputs are via
Neutrik XLR connectors. The output level
to the TBU can be adjusted using a rear
panel pre-set potentiometer. To control
the cancellation null (the amount of the
telephone channel which is subtracted
from the mixer output signal), 2 multi-turn
potentiometers are provided, one for the
LF null and the other for the full-band
null. Additionally, a band pass filter can be
switched in and out, via a rear panel switch,
to condition the signal for the telephone
hybrid. To use the RB-MM1 unit with fullband ISDN codecs, the band pass filter
can be switched out. For stereo codecs, or
conference calls, multiple RB-MM1 units
can be used.
Audio Specification For RB-MM1
Input Level:
Input Impedance: >20kΩ
Output Level:
Output Gain
Adjustable -15dB to +12dB, ref 0dBu
gain via a multi-turn pot
Mode Rejection:
Band Pass
200Hz to 4kHz, 12dB/octave
Filter Range:
LF Null
Better than 40dB at 100Hz
Mix-Minus Null: Better than 40dB at 1kHz
20Hz - 22kHz ± 0.1dB
0.01% THD @ 1kHz, ref +8dBu
output (C-Message weighted)
-90dBu unity gain +6dBu
Analogue Inputs 2 x XLR 3 pin female (balanced) (L & R)
From Mixer Output:
Analogue Input 1 x XLR 3 pin female (balanced) (L & R)
From Telephone Fader:
1 x XLR 3 pin male (balanced) (L & R)
Output To TBU:
Mains Input:
Filtered IEC, switchable 110-120V,
or 220-240V, fused, 6W max.
Fuse Rating:
Anti-surge fuse 100mA 20 x 5mm
Anti-surge fuse 250mA 20 x 5mm
Equipment Type
Mix-minus generator
Physical Specification
28cm (W) x 10.8cm (D) x 4.3cm (H)
11” (W) x 4.3” (D) x 1.7” (H)
36cm (W) x 20.5cm (D) x 6cm (H)
14.2” (W) x 8” (D) x 2.4” (H)
Nett: 1.1kg Gross: 1.5kg
Nett: 2.4lbs Gross: 3.3lbs
Tel: +44 (0)1933 650 700 Fax: +44 (0)1933 650 726 Email: Internet:
Talkback & Communications
Mix-Minus Generator
t:+44 (0)1933 650 700
f:+44 (0)1933 650 726
61 Station Road
Nor thants NN9 5QE
United Kingdom
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