Sonifex RB-ML2
Limiter,Mic and Line Level


The RB-ML2 is a stereo microphone and line level limiter. The unit is mainly used where assistance with level control is required, for protection of mixer inputs and to prevent distortion. Ideal for news-booths, and the input to PC workstations, it provides an economical level control solution.

The RB-ML2 has two electronically balanced XLR-3 inputs, which are routed to a line amplifier, or microphone amplifier, via a rear push-button. The microphone amplifiers have independent pre-set gain controls, and DIP switches for a high pass filter (low frequency roll-off at 125kHz) and phantom power to provide +48V to the connected microphones.

The outputs of these amplifiers are passed through a VCA limiter circuit that can operate jointly on the signals in stereo mode, or independently in dual mono mode. The rear panel mode switch changes the unit from dual mono to stereo. 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-ML2 as two separate mono mic/line limiters.

The characteristics of the limiter can be set via level threshold pre-sets. 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 two XLR-3 electronically balanced outputs can be set to either line or mic output levels via a push-button. This allows the RB-ML2 to be used in line with a line or mic input on a mixer, or similar equipment.


  • Maximum Input Level: -6dBu (mic), +28dBu (line), electronically balanced
  • Input Impedance: >20kohms balanced bridging
  • Input Gain Range: Adjustable +22dB to +67dB gain (mic) via 2 x pre-set pots (L and R), 0dB gain (line)
  • Maximum Output Level: -18dBu (mic), +28dBu (line), electronically balanced
  • Output Impedance: <50ohms
  • Output Gain Range: Adjustable -54dB to -24dB gain (mic), -8dB to +22dB gain (line), ref 0dBu line input, gain via 2 pre-set pots]
  • Limit Threshold: Adjustable -8dBu to +28dBu
  • Frequency Response: 20Hz - 20kHz +/-0.1dB (600ohm load, ref 1kHz)
  • Noise (RMS): <-70dB unity gain, ref +8dBu output
  • Distortion: <0.02% THD + N @ 1kHz, ref +8dBu output
  • Headroom: 27dB for 3mV input
  • Common Mode Rejection (Line): >66dB typically
  • Common Mode Rejection (Mic): >86dB typically
  • Phantom Power: +48V
  • LF Filter: 125Hz @ 6dB/octave

Connections and Controls:

  • Analogue Inputs: 2 x XLR 3 pin female mic or line switchable (balanced)(L and R)
  • Mic/Line Input Control: 2 x push-buttons for mic/line input
  • Analogue Outputs: 2 x XLR 3 pin male mic or line, switchable (balanced)(L and R)
  • Mains Input: Filtered IEC, switchable 110-120V or 220-240V, fused, 6W max
  • Mic/Line Output Control: 2 x push-buttons for mic/line output
  • Phanton Power and LF Filter: 1 x 4 way dip-switch
  • Mono/Stereo Mode Select: 1 x push-button
  • Limit Level Threshold Set: 2 x preset pots
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