Rupert Neve Portico II - Master Buss Processor - Manual (Page 11)

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referred to as “the side-chain”. Note that the rest of the circuit and output will not have those lows
filtered out. This function tends to be very useful because typical sounds often have more energy in the
low octaves and can cause excessive compression. Our ears may tend to associate loudness with mids
or high mids for some sounds and one may be wanting the compressor to regulate and smooth perceived
loudness. Removing some amount of low frequencies that the compressor “sees” can help especially if
one is compressing deeply (-8 dB or more).
RMS / PEAK
This changes the compressor from essentially responding to the RMS level of the audio to also
responding to the PEAK level. RMS (root mean squared) circuits are considered to better mimic the
way the ears perceive apparent loudness, while Peak circuits tend to directly respond to the waveform
voltage which may be more of a concern for prevention of clipping and maximizing levels. In this case,
pushing RMS / PEAK uses a combination of both methods to get the best of both worlds and avoidance
of the drawbacks of each method on its own.
Do we recommend any particular compressor settings for particular instruments? No, but we will
recommend that you not depend on hear-say settings and that you always listen carefully to the levels
and mix values as you tweak. You can generally regard a compressor as a semi-automatic volume
control and be aware of the kinds of artifacts that you would get moving a fader quickly. You can also
listen for changes in tone that are probably due to altering the relative strength of transient hits and
plosives that often contain more high mid and highs.
LIMIT dBU
At first glance, one might scoff at the single knob operation, however the independent limiter is
extremely intelligent, knowing how to appropriately respond to the various signals presented to it. Our
new Serial Adaptive Release Technology is behind this revolutionary performance.
Using a blend of release time constants, this limiter will simultaneously respond quickly to transient
material (such as the “snap” of a snare drum) and slowly to more sluggish signals (such as a bass guitar)
when the set threshold is surpassed. This configuration allows the limiter to grab a transient and let go
just an instant later, while also dealing with more constant signals in a slower, more musical way. In
this manner, the MBP Limiter can provide a much more aggressive amount of limiting than typically
possible, while maintaining the essential character of the music and remaining free of the modulation
distortion usually found in a fast acting limiter.
Typically there is a trade-off between how fast limiter can react and the amount of modulation distortion
in the lower frequencies. This is due to the lower frequencies finding their way into the side chain
signal, triggering the compressor on and off very quickly, which ends up modulating the overall signal.
This is interesting to look at with sine waves, but sounds quite undesirable with music. The MBP does
not have this trade-off, and one is able to have the best of both worlds: a quick, snappy response while
maintaining the integrity and smoothness of the low end. In addition to the adaptive time constant
circuitry, the release time is also varied with the position of the knob. As the knob is turned counter
clock-wise, the release time is increased accordingly, as typically one would want a longer release time
with a larger amount of reduction.
The limiter found in the MBP is designed to respond as fast as .03 mS in order to reduce the first half
of a 20 kHz waveform over the threshold. It has a “medium knee” initial ratio and within 3 dB of the
threshold attains a better than 10:1 ratio. A soft clipper circuit catches transients that may have been in