9
WHAT COMPRESSORS DO
There are four main reasons to use a compressor:
1.
Prevent loud transients
or volume bursts from overdriving a recording device or sound sys-
tem. These loud burst can completely destroy a digital recording by creating terrible sounding
distortion. Constant overdriving of a PA system can cause subtle, but ear fatiguing distortion
as well.
2.
Smooth out wide variations in volume
creating a more controlled sound. Useful when record-
ing a vocalist who has a wide dynamic range or to condition a pad or supporting musical part
(such as an acoustic rhythm guitar). Also useful for instrumentalists (such as horn players)
who move on and off the mic.
3.
Make a sound louder.
When the loudest peaks of a recording are turned down, then the
entire track can be turned up. This makes the softer sections and the average volume level
louder than they were before the signal was compressed. This is often the main reason many
engineers use compressors. When this is the goal, it’s often desirable for the compressor to be
“transparent” or unnoticeable. The LA-3A works particularly well for this application when the
PEAK REDUCTION meter shows -3 to -5 dB of gain reduction.
4.
Change the character of a sound.
All sounds have an “attack” and “decay”. The attack is
what we hear in the first fraction of a second when a snare drum is hit or a guitar string is
plucked. The decay is what we hear after the attack when the tone or pitch of a note fades
away. The decay can be fairly quick, such as the fading ring of a snare drum or quite long as
in the case of a piano chord being held while the sustain pedal held down.
Attack and Release
Most compressors have attack and release controls that will change the sound of an instruments attack and
decay (release). If the attack control is set to a “fast” setting, the compressor will instantly turn the signal
down which will attenuate the high frequency transients that are present in the initial attack. This is a good
way to warm up an overly bright or edgy acoustic guitar recording. If the attack control is set to a “slow” set-
ting, the natural full volume of the sounds attack will be heard and then the “slow acting compressor” will
get around to turning the volume down. This is often done when you want to hear the bright clean attack of a
percussion sound or the attack of an acoustic bass. Also, vocals often want a medium attack, as they sound
more natural with the full harmonic content of the articulation. If an attack is set too slow, then the compressor
will not attenuate loud attack transients. So, sometimes it’s a compromise between getting the right sound and
getting the desired amount of gain control.
The LA-3A does not have user controls for attack and release times. It’s attack and release times are automati-
cally controlled by the nature of the T4 Cell used in the LA-3A’s circuitry. The lack of controls has some benefits
and some disadvantages. On the plus side, the LA-3A will change the speed of it’s attack and release automat-
ically depending on the nature of the sound and the magnitude of compression. For instance, the release time
will be quick with occasional light compression (-3db) but slower if driven hard continuously (-7 to -10 dB).
Also, the release time has two stages. It releases quickly at first and then slower. See the Compression Basics
section starting on page 11 for more details. The lack of controls also prevents the user from setting them
incorrectly. Due to the automatic and extremely musical way the LA-3 rides level, it’s quick and easy to get good
results. The down side: sometimes you need a quicker release time or you want to manipulate the attack time
as mentioned previously. In this case the Universal Audio 1176, 2-1176 or 6176 may be the perfect tool.
