Like most other people,
engineers are creatures of habit and convention. When we think of frequency-conscious
compression, the first thing that pops into our minds is de-essing vocals.
Not surprising, as this is arguably the most common application for the
technique. But there are many others, and if we think outside the box,
we can discover ways to use frequency-conscious compression to tame boomy
acoustic and electric bass guitars and cello, blaring vocals and ear-splitting
wind instruments. Much of this is familiar to veteran engineers, but lets
look at some refinements that should at the very least jar your memory
and tune up your chops.
First, a brief refresher for newcomers to the technique. To perform frequency-conscious
compression, youll need to patch an equalizer into the sidechain
of your compressor; of course, the track you want to process gets patched
through the audio path via the I/O. While listening to the audio track,
determine what frequencies you want to tame. Then simply boost those frequencies
on your equalizer to make the compressor more sensitive to them. For example,
you might boost 7 kHz to 13 kHz by 6 to 12 dB in order to de-ess a female
vocalist. When searing sibilance rears its ugly head, the audio in the
compressors sidechainwhich is hearing an exaggerated
response in this frequency band, courtesy of the EQ boostwill exceed
the threshold and make the compressor reduce the level of the audio signal.
To be sure, the compressor attenuates not only the high frequencies, but
the whole enchilada. The trick is to set up the compressor so that it
releases and returns the track to unity gain immediately after the sibilance
has ceased. Usually, an attack time of around 50 µsec (.05 ms) and
a release time of 50 to 60 ms gets the compressor in and out fast enough
to attenuate the sibilant portion, yet passing the rest of the vocal through
The quality of the equalizer is not critical for this purpose, as it is
not in the audio path. For de-essing male or female vocals, I typically
start by boosting all frequencies above 5 kHz. Such a broad-stroke approach
is usually okay, because theres generally not enough energy above
the sibilance band to unintentionally trigger the compressor, even with
12 dB of equalizer boost. This way, I dont need to fuss with the
high-frequency cutoff, and I know any and all sibilance will be nabbed.
In addition, I usually cut all frequencies below 5 kHz to decrease the
compressors sensitivity to those lower frequencies so that it does
not kick in when the spectral balance is okaysuch as during vowel
sounds and nonfricative consonants.
As for compression ratios, I usually start with infinity:1 to really hear
the effect and then back it off to where it sounds right. I might even
go as low as 3:1 to perform subtle de-essing on a track that just needs
a pinch of control.
Reprinted with permission
Magazine, October, 2000
© 2000, Intertec Publishing, A Primedia Company All Rights Reserved