18WuD2x

48 audio oscillator • auroral propagation
audio oscillator 1. An oscillator that delivers an
output signal in the frequency range 20 Hz to 20
kHz. 2. An audio-frequency (AF) signal generator.
Some instruments of this type operate above and
below the limits of the common audio-frequency
spectrum (e.g., 1 Hz to 1 MHz).
audio output The output of an audio-frequency
oscillator or amplifier. It can be measured in
terms of peak or rms volts, amperes, or watts.
audiophile A sound-reproduction hobbyist.
audio power Alternating-current power at frequencies
roughly between 20 Hz and 20 kHz. When
used in connection with transmitters and other
modulated radio-frequency (RF) equipment, the
term refers to modulator power output.
audio response unit A device that links digitized
responses, held in computer storage, to a telephone
set or line to answer incoming calls and inquiries.
audio signal generator See AUDIO OSCILLA-
TOR, 2.
audio spectrum The range of sine-wave frequencies
detectable by the human ear when they occur
as acoustic vibrations. This range is about 20
Hz to 20 kHz.
audio squelch A squelch circuit that operates only
on the audio channel of a receiver.
audio system 1. The portion of any electronic assembly
that is used to process sound. 2. Special
computer equipment capable of storing and processing
digitized audio-frequency (AF) data.
audiotape Magnetic tape for the recording and reproduction
of data in the audio-frequency (AF)
range.
audio taper In potentiometers, a semilogarithmic
variation of resistance versus rotation. Used in
volume and tone controls for audio circuits. At
midposition (the halfway point), the counterclockwise
portion of the device has about 1⁄10 the
resistance of the clockwise portion. A listener will
hear sound at half-volume because of the logarithmic
nature of the human audibility curve.
audio-visual Pertaining to a combination of sound
and sight (e.g., television and sound motion pictures).
auditory backward inhibition A subjective phenomenon,
in which a sound is erased from the
memory of a listener by a second sound arriving
about 60 milliseconds later.
auditory inhibition The tendency of sound waves
to be partially or totally canceled by the
ears/mind of a listener, depending on the waves’
intensity, relative phase, and/or direction of impact.
auditory mirage See ACOUSTIC MIRAGE.
audit trail A history of the processes relating to a
record, transaction, or file in a computer system.
Created during the routine processing of data,
the trail is stored as a file. The audit trail allows
auditing of the system or the subsequent recreation
of files.
augend In a calculation, the number to which another
is to be added. Compare ADDEND.
augend register In a digital computer, the register
that stores the augend. Compare ADDEND REG-
ISTER.
aural Pertaining to sound actually heard, as opposed
to sound that exists only as audiofrequency
currents or waves.
aurora A phenomenon sometimes called the northern
lights or southern lights, as seen in the night
sky. In the Northern Hemisphere, it is known as
Aurora Borealis; in the Southern Hemisphere, it
is called Aurora Australis. It generally occurs a
few hours after a solar flare, when charged particles,
emitted from the sun, arrive at the earth,
and are accelerated in the vicinity of the the geomagnetic
poles.
auroral absorption Radio wave absorption by an
aurora.
auroral flutter Rapid fading of a signal at high or
very high frequencies, so-called because it often
imparts a fluttering quality to the signal that is
caused by phase distortion and Doppler shift
when the waves are reflected from the aurora.
auroral interference 1. Interference to highfrequency
radio propagation and also occasionally
to medium-frequency and low-frequency
propagation, caused by the activity of the aurora.
2. Auroral flutter on a signal.
auroral opening A condition in which radio communication
becomes possible via AURORAL
PROPAGATION. It can occur when communication
between two points is normally impossible at
a certain frequency. Auroral openings allow longdistance
communication well into the very-highfrequency
(VHF) spectrum.
auroral propagation Reflection of radio signals
from aurora that occur during geomagnetic
storms. Theoretically, auroral propagation is possible
when the aurora are active, between any two
points on the earth’s surface from which the same
part of the aurora lie on a line of sight. This type
of propagation seldom occurs when one end of the