Ashly LIMITER/COMPRESSORS CL-100 - Manual (Page 7)

Comparison of the dynamic range of several common audio systems.
At the other end of the loudness spectrum, the limitation on dynamic
range is usually distortion, either in the form of amplifier overload or tape
saturatiorL In most transistorized equipment, the transition firom clean,
undistorted operation to severe distortion is very abrupt. Therefore, it is
common practice to operate a piece of equipment at a level that is somewhat
below the distortion point, leaving a margin of safety for unexpected,
transient volume peaks in the music. This safety margin is known as
headroom, and may range fix)m 10 to 25 dB. Lowering our standard
operating level to leave ourselves some headroom helps prevent distortion,
but at the same time it moves our average program level closer to the noise
floor, thereby compromising signal-to-noise performance. It becomes
apparent that to get the most out of an audio system, you have to keep your
standard operating level as high as possible without risking distortion.
Useabte
Dymamfc
Range
The useful dynamic range of any piece of audio equipment
is limited by noise and distortion.
10 ABHiy
Gain Riding
One solution to the noise vs. distortion trade^jBT is to keep your hand on
the level control and manually adjust gain to suit the program. Indeed, there
are times when this approach is entirely satis&ctory. However, in most types
of music there are instantaneous, short duration volume peaks, or Ixansients,
which would be diBBcult to anticipate and impossible to respond to with
manual gain riding, you simply could not bring the level down fast enough. In
many situations, this can present real problems. For example, in recording, an
extra burst of enthusiasm fi:t)m a lead singer might overload the capabilities of
your recording tape, causing rs^ged distortion and necessitating another take.
In sound reinforcement, a sudden burst of energy throu^ the system can
blow fuses or even damage loudspeakers.
In addition to the problem of response time with manual gain riding, it
also requires your constant attention, which takes you away fix)m more
important jobs. The need for a fast-acting, reliable, automatic gain control is
answered by limiters and compressors.
What Compressors and Umlters Do
limiting and Cknnpression are closely related effects, their differences
sometimes being very subtle. Since limiting is generally an easier concept to
deal with than compression, the Mowing sections will talk about hmiting first,
followed by a discussion of compression. The use of (he fiunt panel controls is
discussed in terms of limiting also. Bear in mind that these controls wiU have
the same function when the CL-SERIES unit is used as a compressor.
ijiniting
In any musical program there are constant changes in loudness. It is the
job of a limiter to detect when the volume has exceeded a predetermined level,
and to then turn down the volume. When the incoming signal returns to its
original safe level, the limiter should respond by restoring the gain to normal.
Thus, when the level is within a specified “safe" range, the limiter has no
effect. When an occasional peak occurs, the limiter responds. This situation is
completely analogous to manual gain riding, except that it occurs faster and
more consistently.
ASHLV 11