"Among the cleanest, most foul creature!"
This was our first foray into the world of Rupert Neve Design. After countless performances and shows of using UA 1176LN, LA2A, Distressor, Presonus ACP88, including the ubiquitous Art Pro-VLA II, we decided that a cleaner and more transparent compressor was needed in our selections.
RND's Portico 543 particularly excelled in the category of sounding clean without having the pumping effect of an overly-compressed signal box. The first exception was it's high-pass sidechain parameter that enables all frequencies under 250Hz to pass through untouched. What this does is allow the compressor to work on only the mids and upper transients of the signal, thus, giving a much smoother and uniform body. Very similar to having a multiband compressor across your signal, ie bass, kick, mix buss, and boosting the lower frequencies for a fuller soundtrack.
The second most important feature is the feedback and feedforward parameter. The feedback mode is very gentle, while the feedforward mode has a higher compression effect. With feedback mode engaged and high compression ratio, the signal still retains most of it's dynamics except for the slightest transients that gets smoothed out.
In all, RND's 543 is by far the most transparent compressor we've ever heard to date. It's not unlikely that one would fill a whole 500 series rack full of 543's.