The Rupert Neve 543 Mono Compressor delivers the unobtrusive, musical-sounding compression and limiting made famous in the Portico 5043 to 500 series.
The 543 has a fully controllable compressor limiter with feed-forward / feedback modes, Peak / RMS detection and a built-in side chain highpass filter.

Specifications:
Gain Range:
Continuously variable from 6 dB to +20 dB. Threshold Range:
Continuously variable from 36 dB to +22 dB. Ratio Range:
Continuously variable from 1.1:1 to Limit (40:1). Attack Range:
Continuously variable from 20mS to 75mS
Release Range:
Continuously variable from 100mS to 2.5 Seconds. FF/FB:
Feed-Forward or Feed-Back VCA control. Maximum Output Level:
Balanced and Floating Transformer Output
Maximum output from 20 Hz to 40 kHz is +23 dBu. Total Harmonic Distortion and Noise:
@ 1kHz, +20 dBu output level, no load. Main Output, compressor bypassed
Better than 0.0006%.

Main Output, compressor engaged
Better than 0.02%
Noise:
Measured at Main Output, un-weighted, 22Hz-22kHz, Terminated 40 Ohms. With Gain at Unity, Compressor disengaged
Better than 103 dBu. With Gain at Unity, Compressor engaged: Better than 92 dBu
Frequency Response:
Main Output, Unity Gain
@ 18Hz, +/- .1dB
@ 150kHz -3dB. Cross talk
Measured Channel to Channel:
Better than 90 dB @ 15kHz. METERS: Monitor INPUT LEVEL and GAIN REDUCTION

With Gain at Unity, Compressor engaged: Better than 92 dBu Frequency Response: Main Output, Unity Gain @ 18Hz, +/- .1dB @ 150kHz -3dB. Cross talk Measured Channel to Channel: Better than 90 dB @ 15kHz. METERS: Monitor INPUT LEVEL and GAIN REDUCTION