Rupert Neve 543 - 500 Series Mono Compressor-Limiter - Manual (Page 6)

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“signature” of its own. This leaves the designer free to use amplifier and transformer combinations that
are well proven and produce the desired sonic quality.
All Portico™ modules use input and output transformers and almost entirely discrete component
amplifiers to produce the musical “signature” for which they are known. These are factors that enable
the Portico™ 543 to work unobtrusively within the context of a very high quality audio chain.
If the V.C.A. Control voltage is taken from the 543 input, (i.e. before the V.C.A.) the V.C.A. “knows” right
away that a gain change is required and there is almost immediate response. This is known, logically,
as a “Feed-Forward” compressor. 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. A choice between “Feed-
Forward” and “Feed-Back” circuitry is provided. Almost all Mr. Rupert Neve’s earlier designs were
“Feed-Back”. They were more musical and sweeter than with “Feed-
Forward” designs.