Recording - December 2013 - 47

Suggested settings
From my vantage point, I see two schools
of thought on how to bus-compress a mix.
Before outlining these, the difference
between limiting and compression must be
addressed. As discussed last month, the two
processing types are essentially the same,
with no strict definition for either. Because of
the lack of clarity, the two terms are often
interchanged in conversation, in articles like
this, and in the names and descriptions of
various hardware and software processors.
This vagary acknowledged, there are a few
attributes that traditionally separate the two
effect types. Compression is traditionally
thought of as slower and with a lower ratio.
Thus compression is typically used for gentle
signal riding. Limiting, on the other hand, is
conventionally thought of as faster and with
a higher ratio. Therefore limiters are customarily employed to quickly clamp down
on errant signal peaks.
One bus-processing approach uses traditional compression to gently ride dynamic changes. Attack and release times are
typically moderate, around 50 milliseconds
and 250 milliseconds, respectively. Ratio is
usually low, typically 2:1 or less, and the
all-important threshold is set to reduce signal peaks by only a few dB. This technique
was the norm during the analog era, and
can add both punch and smoothness to a
mix. Gentle compression does not, however, significantly raise the overall loudness of
a mix. Beyond a few dB of manipulation,
traditional compression becomes audible.
The other major mix-bus method is to use a
traditional limiter. Limiters, faster and greater
in ratio, can be set to a higher threshold so
only signal peaks are affected. Typical settings see attacks in the 10-millisecond and
releases in the 50-millisecond ranges. Many
limiters employed for this application also
have automatic modes that can manipulate
attack and release settings dynamically, thus
helping the processing potentially achieve
greater transparency. Bus limiting has found
great popularity in the digital era, as it typically allows for more squash and thus greater
loudness than traditional compression.
Which method should you choose? Both,
actually. Not necessarily at the same time,
but you should experiment with both techniques to see what works best for you and
the song at hand. Surprisingly, depending
on music style and song complexity, you
might find yourself alternating between gentle punch-increasing compression and the
more extreme level-increasing limiting. Also
worth noting is that many professional mix
and mastering engineers chain two processors together to achieve the best of both
worlds. I like to employ this trick on individual instruments as well. Vocals, always a
challenge to fit into a dense mix, can sometimes benefit from gentle compression followed by peak limiting. Just be careful not
squash the life out of the performance...

The Golden Rule
No matter what approach you select,
be sure to always turn on the bus compressor and/or limiter at the start of the
mixing process. This is the golden rule,
and must be followed, or you will be an
unhappy engineer!
Why? Because bus processing affects
the level of every element in a mix at all
times. The punch of the kick, the thwack
of the snare, the intensity of the guitars,
and the loudness of individual lyrics are
all manipulated by the processor. Thus it
is mandatory to turn the effect on in the
beginning so you can "mix into the processing" and make fully informed decisions about how level and tonality will

change with compression. If you don't follow the rule, and save the limiting for
later, disaster might strike, as the processing will be indiscriminate in its reduction
of signal peaks, typically making the
effect much more obvious.
Take it from me, someone who once
waited to the end of a very long mix day
to engage a bus compressor. With my
ears tired I accidentally overdid it, my
hard work was destroyed, and since it
was an analog mix, there was no undoing
it later. The song, to my surprise, saw use
in both a regular TV series and in several
movies. I cringed every time I heard my
overcompressed nastiness! I was disappointed instead of proud.

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Recording - December 2013

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