500 Series Mono Compressor-Limiter based on the Portico 5043, 500 Series Mono Compressor-Limiter.
The Rupert Neve Designs Portico 543 Mono Compressor delivers the unobtrusive, musical-sounding dynamic control and brick-wall limiting made famous in the Portico 5043 to the 500 series format. The 543 features a fully controllable compressor-limiter with feed-forward / feedback modes, Peak / RMS detection and a built-in side chain high pass filter. With an unrivalled heritage and a tremendous feature set, the 543 yields a combination of rich warmth, flexibility and precision that is sure to resonate in the ears of sound engineers the world over.
Built around Mr Rupert Neve’s custom transformer designs, each 543 module encompasses individually controllable threshold, attack, release, makeup gain, ratio, side chain HPF, Feed-Forward / Feed-back selection and Peak/RMS detection modes. With the compressor inactive, the 543 may be used as a transformer-coupled, high-performance line amplifier, and two 543 may also be linked for stereo operation. The chassis is built to standard 500 series specifications, with power and I/O provided by the rack.
A V.C.A. or Voltage Controlled Amplifier (or Attenuator) is used to control gain. There are many types of V.C., including tubes, discrete and integrated solid-state circuits and naturally non-linear devices, each with the characteristic behaviour that reflects sonically on the final performance and gives it a character or signature that can be musically attractive or not! The Portico 543 uses a very accurate, low noise, low distortion V.C.A. having no signature of its own.
A part of the audio signal is rectified and smoothed to produce a suitable control voltage for the V.C.A., which has to respond very quickly and have low distortion. If the response is too fast, low-frequency signals will be gain controlled! If the response is too slow, the signal will overshoot, and the first few cycles will not get compressed. The speed and accuracy of the response, known as the “attack”, and the time frame that gain remains under the initial control, known as “release” or “recovery” plays a large part in the way a compressor sounds.
The 543 also can switch between feed-forward and feed-back modes. If the V.C.A. Control voltage is taken from the 543 output (i.e. after the V.C.A.) it cannot act immediately on the V.C.A. because it has already been modified by settings of the V.C.A. and circuits through which it has passed. This is known as a “Feed-Back” compressor. The two compression characteristics are quite different; there is more “Overshoot”, and both the attack and recovery ramps are changed, providing the user with powerful choices. For the FF / FB switch, both classic and modern VCA responses are available.
One of the more unique features of the 543 is the new Peak / RMS mode, also found in the Portico II Channel. This switch allows the VCA (voltage control amplifier) to respond to RMS (Root Mean Square) and peak levels. RMS circuits are considered to better mimic how the ears perceive apparent loudness. In contrast, peak circuits tend to respond directly to the waveform voltage, which may be more of a concern for preventing clipping and maximizing levels. In this case, peak mode combines both methods to get the best of both worlds and avoids the drawbacks of each method on its own.