The X-Rack Dynamics Module, XR 618 from Solid State Logic provides a single channel of dynamics for an X-Rack or Mynx enclosure. The unit was designed around the same SuperAnalogue circuitry as used in SSL's XL 9000 K console, and provides compression, limiting, expansion and gating.
The compressor/limiter and a gate/expander both share the same gain element. The compressor normally has an "over-easy" characteristic, but can be switched to peak sensing, which replaces the "over-easy" characteristic with a "hard knee." With a number of options for hard or soft knee operation, and peak or RMS sensing, the module is able to deliver fantastic sound quality, with very low noise and distortion.
The gate/expander section can act as an infinity:1 gate, or as a 2:1 expander. Variable hysteresis (dependence of the state of a system on the history of its state) is incorporated in the threshold circuitry to prevent spurious triggering of the gate when the signal is close to the threshold level. This means that the signal has to decay roughly 2dB below the threshold level before the gate will start to close.