AUDIO TIPS: Processors
Audio Tip #13: COMPRESSORS
- 1. Threshold sets the level where compression starts to take effect. Sounds below the threshold pass through unaltered and only sounds above the threshold are compressed.
- 2. Ratio sets the degree of compression above the threshold level. A ratio of 2:1 represents mild compression and means that when the incoming level (above the threshold) rises by 10dB, the outgoing level will only rise by 5dB. Ratios of up to 5:1 are regularly used for vocals and other instruments, and can pass by unnoticed by the listener if the other controls are set properly. Higher ratios are used for more serious limiting, where the level needs more severe control. Ratios of 10:1 and higher are nearly always noticeable to the listener.
- 3. Attack is measured in milliseconds and determines the time taken for the compressor to start working once the signal has passed the threshold level.
- 4. Release sets the length of time it takes for the compressor to return to its normal state once the signal has gone back below the threshold.
- 5. Gain is provided because compression always reduces the peak level: the more compression, the lower the level of the outgoing signal. This control is sometimes referred to as 'make-up' gain because it makes up the level that is inevitably lost during the compression process.
- 6. Knee is the place where the signal hits the threshold and it can be adjusted to be A hard knee or a soft knee.
Most compressors have pretty much the same controls:
A 2:1 ratio is probably the most common setting for a compressor
recording or playing back nearly anything. This makes it a great
starting point. What this means is simply, that it takes 2 decibels of
sound energy to raise the output meter by 1db. You can read the 1st
number as the dB IN and the second as the dB OUT. Again, 2db IN equals 1
dB OUT.
Gates have two parameters: 1) the noise floor
threshold, and the rate. The noise floor threshold eliminates the entire
signal when it dips below the threshold, which is set from 50db to
-10db. If the gate is set too high, then the attack of the vocalist's
words may be cut off or come in too abruptly. The rate parameter "fades
out" the audio signal as the gate clamps down on the signal source.
This is effective to prevent the gate from chopping off the tails of
the words. Usually a rate of 1-1.5 sec is enough.Some producers are
known to use noise gates after the Mic preamp. The gate can be set to
cut out the entire signal unless it gets a really loud burst. That
takes a bit of trial and error to set up, but if done well it can
improve the separation at the board. That way you can, for example,
add a big sounding reverb to just the snare as many 70's rock ballads
did, or further process your snare with lower mid frequency EQ for a
more contemporary sound.
The Threshold is the all-important
level at which the compressor kicks in. If you set the threshold to
-10, it will leave the entire signal under -10 alone. When the signal
exceeds -10 then it starts compressing at the ratio. Minus 10 is an
excellent place to start. Don't confuse this with the fact that your
gear is outputting -10 or +4 impedance-wise. Though the threshold
seems like it is a volume control, it is not. It is merely telling the
compressor at what level compression takes over the signal.
Effects should be used minimally. If a stereo effect is so great that
you can no longer pinpoint the instrument, you used too much. Another
tip here is doubling and de-tuning. You can make any instrument
dramatically wide, yet centered, by putting the same instrument far
right (127) and far left (0) and slightly detuning them by about 5-7
cents. This is a great technique for 'wall of sound' like mixes that
have strings that appear to float on the mix. Use it sparingly though,
as hard panned doubles can easily take up sonic space where other
instruments need to go.
If you are using a digital audio
workstation and all of your processing is being done with Pro Tools or
some other sequencing software you probably won't need a patch bay.
However, if you have many external rack-mount processors you may want
to consider a normaled patch bay. The patch bay is primarily designed
to route the inputs and outputs of the external rack-mounted hardware
to an easily accessible, centralized area for convenience, so you
don't have to keep climbing behind your equipment and pulling
in-and-out, the cables.
In a patch bay there are many cable
types, sizes and lengths, but the two most common are the balanced and
unbalanced types. An unbalanced cable is a tip-and-sleeve,
quarter-inch connector plug but does not have the ability to inhibit
humms, buzzes and annoying air born frequencies from intruding in the
signal. However, balanced TRS (tip,ring and sleeve) cables do inhibit
radio frequencies producing a cleaner signal.