For us guitarists, the word compression is one
of those terms thrown around in the audio
field that seems to have multiple meanings.
From stompbox pedals to plug-ins to classic
analog outboard gear, its fundamental use is
to control the level of an audio signal and its
dynamic range. But before leaping forward
into some of its studio applications, let’s take
a step back for a brief review.
Simply put, dynamic range can be thought
of as the ratio (measured in dB or decibels)
between the softest and loudest parts of an
audio signal (when speaking of music). Just
think about the sonic difference between
which parts are loud and which are soft—I’m
oversimplifying here, but you get the point.
This can apply to individual instruments, like
drums, bass, vocals and guitars, or to the
full stereo mix. When people bitch about
the Metallica disc having no dynamic range,
it means that the stereo signal is squashed
as loud as it can go, which for the most
part fatigues the ears after a brief time.
Everything is loud. This is generally done at
the mix stage but the mastering engineer can
also do it (though they hate to). Compare
that to Led Zeppelin II, which you have to
turn up to hear loud. I don’t mind twisting my
volume knob, do you? The dynamic range on
that disc effortlessly goes from loud to soft,
and I can (and have) listened to it countless
times. It seems to make for an easy listen.
Back in the studio, when we think about
applying some compression to our recorded guitar parts, it involves tweaking the
Threshold, Ratio, Attack and Release and
Makeup Gain functions (among others).
Threshold can be described as the level
above which the signal is reduced, usually
set in dBs. So, if your guitar signal spikes on
a few notes above your threshold setting,
that signal will be decreased. The Ratio is
measured as the input/output ratio for the
audio that jumps above the threshold. So at
3: 1, that guitar peak that jumps 3 dB above
the threshold will squash to just 1 dB above
threshold. When a compressor has Attack
and Release adjustments, these help control how fast or slow the compressor “hits.”
Usually both set in ms (milliseconds), they
control the amount of time the compressed
signal squashes its signal and gets itself back
below threshold, or to 0dB.
work in different ways
and provide different
Clearly, they are also
affected by what type
of guitar signal you put
into them and how it
But what happens to your volume if your loud
parts all get squashed when compressed?
You can then use Makeup Gain to boost the
overall level by a fixed amount, again measured in dBs. I often think of the volume fader
as a compressor, which you can choose to
ride manually versus compressing a signal to
achieve a smoother overall sound. If you want
to keep a mix sounding “airy” or “open,”
try using no compression and just riding the
fader for the whole mix. However, compressing guitars can really help add character. An
excellent distorted/edgy guitar compressor
is the Universal Audio 1176. Both in plug-in
and hardware form, it provides an almost
indescribable sound that works perfectly on
guitars—squashing the stray peaks just right
while adding a nice beefy thickness. Watch
out though; sometimes it can be too much.
When compressing a doubled or tripled part,
I will set up an Aux (auxiliary) bus and use
a single UA 1176 (or Eventide Omnipressor
for extreme sounds) while sending all the
guitars to it. This helps even out the overall
guitar sound, and the compression settings
will usually react favorably because the signals should be similar (since it’s a double).
However, if the parts are different, sending
them to the guitar compression bus doesn’t
always work. This is because while the compressor’s attack and release may be reacting
to one sound, a part with different peaks and
valleys may begin to “confuse” the compressor. In these cases, I will usually apply a separate compressor directly to the track itself, or
if you’re short on processor power, set up a
second, lighter guitar compressor bus.
With acoustic guitars, I’ve found that the
character of the Sonnox Dynamics or Waves
Renaissance compressors work great because
they almost invisibly affect the signal. With
acoustics, I tend to like retaining as much
Dynamic Range as possible, and compressors such as the ones above allow the
compressed signal to still remain clean and
crisp. You can easily set a nice 4: 1 ratio with
a relatively fast attack and release and then
adjust the Threshold so that only the highest
peaks reduce themselves. The point is that
different compressors work in different ways
and provide different sonic characteristics.
Clearly, they are also affected by what type
of guitar signal you put into them and how it
was recorded. Strong aggressive compression
will help punch guitars through a dense mix,
while a light soft compression will retain more
dynamic range. The only way to know what
works best is to try out as many as you can
and see what sounds right to your ears.
Rich is a producer, engineer and mixer who has worked
with artists ranging from Al DiMeola to David Bowie . A
life-long guitarist, he’s also the auther of Pro Tools Surround
Sound Mixing and composes for such networks as Discovery
Channel, Nickelodeon and National Geographic.