Rocktron's Hush system has been around for a number of years, and although patented, it is broadly similar to the system used by Symetrix and Drawmer in their own DNR (Dynamic Noise Reduction) processors, in that it combines a downward expander and a dynamic filter. The IICX is a two-channel, 1U, rackmount processor powered via an external adaptor, with both inputs and outputs on unbalanced, quarter-inch jacks. A high input impedance of 470k(omega) means that electric guitars can be plugged directly into the unit if required.

The two channels may be linked by means of the Master button, for stereo operation, or they may be used independently -- each channel has separate controls for expander threshold and filter sensitivity, as well as switchable +4dB/-10dB operation. Channel bypass buttons are fitted, but it isn't possible to bypass the expander and filter separately, something I like to do while setting up if possible. Neither does the expander have a variable ratio or release time, though a button does provide a choice of preset Fast or Slow release times.

So that you can see what's going on while using the IICX, both the expander and filter are furnished with simple four-LED meters. The expander meter shows how much gain reduction is being applied to low-level signals, while the filter's meter shows the cutoff frequency. This will normally vary, as the incoming signal varies in level and frequency content; the optimum setting is usually with filter fully open during all louder passages, only closing during obvious pauses or at the end of a piece. The expander should be set to apply little or no gain reduction during playback, unless a total pause is encountered.

A Class-A VCA is used in the expander circuitry, in order to maintain the highest possible signal quality. Bearing in mind that very often the whole mix will be going through this unit, that's an important consideration.

SPECIFICATIONS

Input

Input Impedence: 470K ohms

Maximum Imput Level: +18dBu (+4 ref) +5dBu (-10 Ref)

Input Jack: 1/4'' Mono

Frequency Response: + 0.5dB 30Hz to 20KHz

Total Harmonic Distortion: Less than 0.03% at 0dBu, 1KHz +4 Ref level (threshold at minimum)

Dynamic Range: 114dB Peak signal to A-weighted noise floor

Effective Noise Reduction: >60dB

Filter: Two pole Class A, 12dB per octave slope. Quiescent cut-off 700Hz. Maximum Bandwidth 50KHz

Expander VCA: Class A

Output

Maximum +4 Ref Output Level: +18dBu

Maximum -10 Ref Output Level: +5dBu

Output Impedance: <100 ohms

Output Jack: 1/4'' Mono

Power Requirements: 9VAC RMS 750mA

Note: 0dBu = .775V RMS