Mixing Tips
Compression:
When you play an instrument or sing,
there are natural peaks in the volume level when you attack
notes. When you record, these peaks in signal can result
in clipping. To get rid of the clipping, you have to set
input and output levels on pre-amps to proper volume levels.
Once the sound is recorded you end up with a quieter volume
level. Clipping can be especially noticable on drums and
bass. To get the tracks up to the proper volume levels without
clipping you need to use compression. Compression takes
the peaks in the signal and lowers them to the average signal
level for a track. Usually the peaks in volume that cause
clipping are not audible but rather, they happen for mere
milliseconds. With light to medium compression, you don't
miss them at all. Compressing a track allows you to get
the overall volume of a track up in a mix, without clipping.
Without compression, you wouldn't be able to get drums very
loud in a mix, unless everyone had speakers capable of very
high SPL. Compression can be thought of as an automatic
volume knob. As soon as the volume gets above a certain
level, the gain is reduced by the compressor. Compression
normally has a few different adjustments to make.
Threshold is the volume level in
dB which you don't want the signal to exceed. Attack time
is the speed at which the compression kicks in, and release
time is the speed at which the compression disengages. Compression
ratio is the ratio to which you want the track compressed.
A 2:1 compression ratio is much lighter than a 4:1. You
need to be careful not to use more compression than necessary
because it can get rid of dynamics, which are an important
part of music performance.
You may want to use light compression
on vocals to bring the high frequency peaks down a little.
You will probably use a little more compression on female
vocals than on male vocals. You might start at around a
3:1 ratio. Bass guitar generally calls for about a 4:1 ratio,
with short attack times of 8-25 milliseconds, and release
times of around 250-500 milliseconds. Drums usually call
for a heavier ratio, because you attack them a lot harder
and the signal dies out almost immediately. Usually, a ratio
of between 5:1 and 10:1 works well. You want to set the
attack time short, to around 4 or 5 milliseconds, and the
release time to around 10 milliseconds. You can also set
attack and release times to "auto" in most software
compressors, which may or may not work well for you.
We've covered the basics of compression
but the actual values you use will vary, depending on the
performer and the style of music. Also, it depends on the
ears of the mixer. A lot of pop musicians prefer a heavily
compressed sound, while jazz and classical musicians tend
to prefer a much lighter compression sound. They usually
don't actually want to hear the compression at all. Compression
can be best when used behind the scenes.
