Ashly LIMITER/COMPRESSORS CL-100 - Manual (Page 17)

GLOSSARY
ACTIVE
Etectranic circuits which use devices such as
transistors and integrated circuits, and which
are capable of voltage and power gain as well
as loss. Circuits using only resistors, capacitors,
transformers, etc., are referred to as passive.
AMPLITUDE
The voltage level of a sigruiL May be measured
in volts or decibels. Generally corresponds to
the vrdume or intensity of an audio signal.
ATTACK TIME
The amount of time that elapses before a
compressor 1 limiter begins to attenuate the
output level after threshold has been reached.
BALANCED
3-wire circuit arrangement in which two
conductors are designated as signal lines (+
and -f, and the third is a shield and chassis
ground. The sigruzl lines are of opposite polarity
at any given moment, and are of equal potential
with respect to ground. Balanced input
amplifiers are u.'sed in all Ashly products to
improve hum and noise rejection. Jumpering
signal minus (-) to ground provides an
unbalanced input.
BREATHING
A usually undesirable fluctuation of background
noise resulting from compressor action. (Also
called ‘Pumping,’)
CENTER FREQUENCY
The frequency (or pitch) at which o filter is
most effective. In a parametric equalizer, it
refers to the frequeruy where a particular boost/
cut control has maximum effect.
COMPRESSOR
An amplifier which reduces its gain as its
input is increased beyond a predetermined
“threshold. ’
dB
A unit by which audio levels can be
COMPARED. Often thoroughly misunderstood
are the concepts that decibels represent the
level of a signal compared to some reference
level (IS dB cut rtwans a certain level less
than a previous level
— the absolute level of
the signal need not be known}, and that decibels
are a logarithmic unit.
Some handy numbers to remember when
dealing with decibels:
+3 dB = Double Power
+6 dB = Double Amplitude, Quadruple
+B dB = Power
+10 dB = lOX Power
+20 dB = lOXAmplitude, KX)X Power
dBm
j 4 unit of measuremerti in decibels where 0
dBm = a power level of I milliwatt into a 600
ohm load. Originally defined by the telephone
company to measure line levels.
dBV
Decibel Volts, an update of the dBm definition
where 0 dBV = the same voltage level as 0
dBm, but with no regard to power or
impedance. 0 dBV = 0.778 V oîîsl This unit is
much more appropriate for modem audio
equipment with high impedance inputs and
tow impedance outputs.
DISTORTION
Generally refers to ANY modification of an
audio signal which produces new frequencies
which were not in the originaL Examples are
harmonic distortion, where a circuit adds
overtones to a fundamental signal, and
intermodulation or IM distortion, where two
frequencies beat together to produce sum and
difference frequencies.
EQUALIZATION
Modification of the frequency response of an
audio
system for eifAer corrective or
enhancement purposes.
FEEDBACK
Generally refers to any process where an output
is in some form routed back to an input to
establish a loop. N^ative feedback tends to
be be self stabilizing, while positive feedlxick
causes instability.
30 ASHLY
FREQUENCY
T7ie
repetition rate of a wavefiorm. Frequency
is measured in Hertz. One cycle per second
(cps) is one Hertz (Hz). The higher a note on a
musical scale, the higher its frequency.
FREQUENCY RESPONSE
Refers to relative gain and loss at various
frequencies
across the audio band. May be
illustrated by a graph called a frequency
response plot, usually graphing decibels
us.
hertz or octaves.
GAIN REDUCTION
77ic amount (expressed in dB) by which a
compressor/limiter’sou^puihasbeenreduced
in level with respect to Us uncompressed
level
HEADROOM
Refers to the increase in level above normal
operating level that can be obtained without
clipping. Usually
eapnessed in dB.
IMPEDANCE
Essentially the AC equivalent of resistance.
It describes the drive capability o/’an output,
or the amount of drive required for an input
at any given signal level.
RH t .
Kilohertz. 1,000 Hertz.
LEVEL
The magnitude of a sigruzl, expressed in
decibels or ixdts.
LINE LEVEL
Meaning ‘somewhere around OdEV as
opposed to MIC level of around -40dBV.
LIMITER
An amplifier which reduces its gain as its
input is increased beyond a predetermined
threshold. Usually used to protect audio
systems against sudden, high level sigrutls,
and possible overload.
OCTAVE
A logarithmic unit to compare frequencies.
+1 Octave means double frequency,-1 Octave
means half frequency.
OHM
77ie
unitofelectricalresistanceorimpedance.
PREAMPLIFIER
The first stage of amplification, designed to
boost very low level signals to line level
RATIO
77ie relationship between change in input
level and resultant change in output level
RELEASE TIME
The time required for a compressor/limiter
to restore system gain to normal after the
input signal has fallen below threshold
SATURATION
The point at which the magnetic storage
capability of a piece of recording tape is
exceeded
SmiLANCE
TTtedistortioncausedbyioudhigh/rvquency
signals, suchasthe ‘Ssss... “soundsin human
speech.
THRESHOLD
The level above which a compressor/limiter
begins la reduce gain.
TRANSIENT
A sudden burst of energy in an audio signal
such as a breath blast in a microphone, the
sound of a snare drum, or a deep scratch in
a record Transients frequently reach peak
levelst^IOtoSOdBabovestandardoperating
levelandmaycausedistortionorevendamage
to equipment
UNITY GAIN
Output level = Input level.
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