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Glossary
musical scale; a note which is an octave higher
than another note is twice the frequency of the
first note.
Expander
An expander is an amplifier that increases its
gain as the level of the input signal increases, a
characteristic that "stretches" the dynamic
range of the program (see "expansion"). An ex-
pander may operate over the entire range of
input levels, or it may operate only on signals
above and/or below a given level (the thresh-
old level). ·
Expansion
Expansion is a process whereby the dynamic
range of program material is increased. In other
words, the difference between the lowest and
highest audio level is "stretched" into a wider
dynamic range. Expansion is sometimes used
to restore dynamic range that has been lost
through compression or limiting done in the
original recording or broadcast; expansion is an
integral part of compander-type noise reduc-
tion systems, including dbx. Expansion is
achieved with an expander, a special type of
amplifier that increases its gain as the level of
the input signal increases. The amount of ex-
pansion is expressed as a ratio of the input dy-
namic range to the output dynamic range; thus,
an expander that takes a program input with
50dB of dynamic range and yields an output
Glossary
Harmonic Distortion
Harmonic distortion consists of signal compo-
nents appearing at the output of an amplifier or
other circuit that were not present in the input
signal, and that are whole-number multiples
(harmonics) of the input signal. For example,
an amplifier given a pure sine-wave input at
100Hz may produce 200Hz, 300Hz, 400Hz,
500Hz, 600Hz and even 700Hz energy, plus
lOOHz, at its output (these being the 2nd, 3rd,
4th, 5th, 6th and 7th order harmonics).
Usually, only the first few harmonics are signifi-
cant, and even-order harmonics (i.e., 2nd and
4th) are less objectionable than odd-order har-
monics (i.e., 3rd and 5th); higher harmonics
may be negligible in comparison to the funda-
mental (100Hz) output. Therefore, rather than
specifying the level of each harmonic compo-
nent, the distortion is usually expressed as
T.H.D., or Total Harmonic Distortion. While
T.H.D. is the total power of all harmonics gener-
ated by the circuitry , expressed as a percentage
of the total output power, the "mixture" of dif-
ferent harmonics may vary in different equip-
ment with the same T.H.D. rating.
"Hard Knee" Compression
"Hard Knee" compression refers to the com-
pression characteristic curve of a compressor.
When a signal crosses the threshold, the com-
pression circuitry responds to the signal almost
program of 100dB dynamic range may be said
to have a 1 :2 compression ratio.
Fundamental
A musical note is usually comprised of a basic
frequency, plus one or more whole-number
multiples of that frequency. The basic fre-
quency is known as the fundamental, and the
multiples are known as the harmonics or over-
tones. A pure tone would consist of only the
fundamental.
Gain Reduction Display:
Indicator of current amount of compression or
limitin g. On the 160XT, this display is a 12 seg-
ment LED display.
Ground Compensated Output
This is a sophisticated output circuit that senses
the potential difference between the ground of
the dbx unit and the shield ground of unbal-
anced inputs to which the dbx unit is con-
nected. Ideally, the dbx unit and the input of
the following device should be at the same
level (potential). However, where grounding is
not "right" (where so-called "ground loops"
exist), the circuit calculates the ground ertor
and adds a correction signal to the high side of
the output, thereby cancelling much of the
hum, buzz and noise that might otherwise
have been introduced by ground loops.
dbx 160XT
instantaneously, creating an abrupt level
change at the audio output. This type of com-
pression is most desireable for speaker protec-
tion, transmitter protection from overmodu la-
tion and protection from saturation on digital
or analog tape recorders and producing popu-
lar instrument "sounds" (particularly drums) ..
Harmonics
Overtones which are integral multiples of the
fundamental.
Headroom
Headroom refers to the "space," usually ex-
pressed in dB, between the nominal operating
signal level and the maximum signal level. The
input headroom of a circuit that is meant to ac-
cept nominal-lOdB levels, but can accept up to
+18dB (from-lOdB to +18 equals 28dB). Simi-
larly, the output headroom of a circuit that is
meant to supply nominal +4dBm drive levels,
but that can produce +24dBm before clipping is
20dB. A circuit that lacks adequate headroom is
more likely to distort by clipping transient
peaks, since these peaks can be 10 to 20dB
above nominal operating levels.
IM (Intermodulation Distortion)
Intermodulation distortion consists of signa l
components appearing at the output of an am-
plifier or other circuit that were not present in
the input signal, that are not harmonically re-
lated to the input, and that are the result of in-
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