Rupert Neve 543 - 500 Series Mono Compressor-Limiter - Manual (Page 8)

8
GAIN
Often referred to as Make Up Gain. Considering the compressor’s VCA is generally being forced to
attenuate louder signals some method of returning the average level to a volume comparable with the
compressor bypassed is desirable. The GAIN control is mostly used for this purpose especially for those
of us that depend on comparing compression to bypass. GAIN is often pushed for even more level than
“bypass” because it is understood that the compressor should be providing some effective headroom
(besides “louder is better” being the oldest trick in the book).
ATTACK
This sets how quickly the compressor reacts and starts attenuating. If set fast (20mS) the compressor
should react to very quick transients like the initial stick hit of a snare drum and can attenuate the “hit”
so the “note” of the drum seems relatively emphasized. If set slower, the compressor will tend to ignore
the fastest transients and react more to the drum resonance and attenuate the “note” of the drum so that
the hit seems more emphasized. Similarly, on a mixed track, if a compressor is set too fast, it will tend to
remove drums, which may help to explain why mastering engineers tend to use medium to slow attack
times and lower ratios.
RELEASE
This sets how fast the compressor returns back to zero after attenuating. Typically engineers have used
quite slow releases when the need is to minimize any obvious compressor action or gains changing. For
modern pop music quite often the goal is to have the compressor change gains approximately in time
with the music and the RELEASE control setting becomes important for this. On the other hand, many
of us were trained to avoid having compressors “pump” and sound like they are breathing. Another
(maybe too) common use of compressors is to maximize the apparent volume and for this one generally
wants very fast release settings so that after reducing peaks the compressor returns to maximum levels
as quickly as possible. And by “as possible” there is a practical matter regarding the tendency of
compressor/limiters to introduce a nasty form of distortion called “modulation distortion” when they are
set for a combination of fast attacks, fast releases and high ratios.
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 FAST 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.
Side Chain HPF
This routes a high pass filter set to 250 Hz into the circuit that the compressor uses to determine level,
commonly 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