Recording - October 2013 - 66

At the other end of the level spectrum lies
the noise floor. All audio devices inherently
create some amount of noise, and therefore
levels need to be kept high enough so
unwanted crud is not heard in a recording.
Level setting is thus the art of placing a signal
at a point safely between the noise floor and
clipping. For most devices this magic location
is called the standard operating level and on
professional equipment it is usually about 18

were listenable on all formats. Compression also was, and continues to be, a critical element in radio and TV broadcasting. Regulated by the FCC in output power
and limited by budgets and physics, broadcasters use compressors to achieve maximum loudness and therefore increase effective transmission distance.
Today’s radio is ridiculously compressed, often triggering frustration from mix
engineers who hear their work squashed to death when played over the airwaves.
These complaints are usually ignored, though, as both stations and record labels
desire their product to be as loud as possible in order jump out of the speakers and
grab as many listeners as possible. The quest for increased loudness reached new
heights in the late 1990s and 2000s, triggering what are usually termed the loudness wars. A topic of its own, this column will visit the loudness wars later in this
multi-part series.
Consumer audio devices also rely on compression. Cell phones, for example, are
expected to be audible in both crowded bars and quiet bedroom settings, and thus
internal compressors are necessary to maximize vocal intelligibility. Real-world listening environments also need compression. Many locations, especially in mechanized
and crowded settings, are significantly curtailed in available dynamic range. Whether

Fig 1

The top screenshot (courtesy of the Audio Mastering app for iOS reviewed in this issue) shows a song with relatively
unclipped waveforms. The bottom screenshot shows extreme clipping; this song is much louder than the one shown up top,
and it is distorted and unpleasant to the ear. (By the way, in case you were wondering, it’s a current Top 40 hit...)
to 24 dB below clipping. Since each audio
device is slightly different in dynamic range,
experienced engineers learn how to gain
stage—that is, to set the levels in each individual device in a signal chain so both clipping and noise are consistently avoided.
Gain staging is a key element in producing
amazing sounding audio, and compressors
can help in this task by keeping peak levels
from clipping, and by raising average levels
to be farther from the noise floor.
Clarity in the face of chaos
Compression is nothing new—it was
already hugely important in the analog era.
Restricted in dynamic range, vinyl records
and analog tape were notoriously noisy. To
maximize fidelity, engineers used compressors in tracking, mixing, and mastering to
reduce dynamic range and ensure recordings
66

RECORDING October 2013

inside a shopping mall, airport, or an automobile, audio must be heard against background distractions such as talking, motor, and road noise. Processing is therefore
required to ensure audio is always above the chaos. The loudness of our modern world
is relentless, and compression is the key to keeping audio controlled and audible.
Control
The use of compression is not limited to the prevention of noise and distortion.
With the incredible dynamic range available in modern 24-bit digital recording,
engineers usually do not need compression to help keep signals clean. Instead,
when mixing, compression offers control over unwieldy elements. Most lead vocal
recordings, for example, are notoriously wide in dynamic range, with quieter
words often covered up by the music bed while louder notes jump out of the mix.
Compression is therefore an essential step in vocal processing, especially in rock,
pop, and hip hop styles in which lyrics must compete with an onslaught of multitracked instruments.
Other instruments also benefit from dynamic control. Electric basses, especially
inexpensive models, tend to vary in loudness across their range. Bass compression
is thus a common mix solution. With the bass tracked compressed, every note can
contribute equally to the foundation of the mix. Drum tracks are also frequently
squashed. Snares in particular are famous for wide dynamic ranges, with drummers

Recording - October 2013

Table of Contents for the Digital Edition of Recording - October 2013