Attack And Release; Setting The Attack Rate; Setting The Release Rate; Make-Up Gain - Focusrite Red Series Manual

compressor/limiter

Attack and Release

The attack and release controls determine how quickly
the compressor switches on and off at the threshold.
Without an attack control, full compression would be
applied to the signal as soon as it got louder than the
threshold. Similarly, without a release control, the
compressor would switch off as soon as the signal got
quieter than the threshold. While this is fine in some
recording situations, in most it gives an unnatural
sound to the signal, so you can use the attack and
release controls to modify this.
Note that the optimum attack and release rates vary with
the instrument being recorded, and with the perfor-
mance. For example, when recording a snare drum, a
fast attack and release are needed - a slow release over-
compresses the signal, with all beats after the first
dulled slightly because the compressor is still on.

Setting the Attack Rate

By slowing the attack rate, the compressor gradually
comes to full compression, instead of compressing
Before Attack During
Compression Compression
Attack times do not need to be very fast when
recording onto analogue tape - you can use slower
attack times of around 1 ms. The fastest transients are
lost by saturation of the tape and become inaudible,
and longer duration peaks can be controlled by the
compressor, giving a more natural sound.

Setting the Release Rate

By slowing the release rate, the compressor recovers
more slowly from compression, so it does not turn off
completely when the signal returns below the threshold.
The release rate is
probably the most
important variable
when recording
rock music, since it
controls loudness.
immediately.
Transient response
is less affected,
so maintaining
the presence of
each note.
During Release After
Compression Compression
Loudness is determined by the maintenance of high
mean levels: compression increases the proportion of
high-level signal
content, and as the
diagram shows,
the faster the unit
releases, the more
low-level signal is
brought to a higher
level. Therefore, the
faster the release
rate, the higher the
perceived loudness
of the recording.
You do not have to
set a permanent
release time for the whole input signal; instead, you
can use the Auto button. Auto reacts to the dynamic
range of the input, so the higher the signal is above the
threshold, the longer the release. This means that fast
signals that aren't compressed hard have a fast release
time, while longer signals release more slowly, which
makes the compression in context with the signal.

Make-up Gain

Compressing a
signal makes it
quieter. After you
have set the
compression on the
signal, use the make-
up gain to restore
the signal's original volume.
For example, in the diagram the compressor reduces
the signal by 20 dB, which reduces the dynamic range
of the input and in so doing makes the signal quieter.
AFTER MAKE UP
+20
2:1
0
20dB of 1:1
Make up
gain
-20
p a g e 8
Original Signal
Compression
Threshold
Fast Release
Overall Level Louder
Compressed
Level
Slow Release
This Portion Compressed
Over Compressed
Overall Level Quieter
BEFORE MAKE UP
+20
1:1
Max Level
Now 20dB Lower
0
New Dyamic
2:1
Range
-20
Using the make-
up gain restores
Max Level
the volume of the
Now Restored
to 20dB
compressed
But with smaller
Dynamic Range
signal.
Original
Range