Page 63 - The Illustrated Dictionary of Electronics

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48 audio oscillator • auroral propagation

audio oscillator 1. An oscillator that delivers an augend In a calculation, the number to which an-
output signal in the frequency range 20 Hz to 20 other is to be added. Compare ADDEND.
kHz. 2. An audio-frequency (AF) signal generator. augend register In a digital computer, the register
Some instruments of this type operate above and that stores the augend. Compare ADDEND REG-
below the limits of the common audio-frequency ISTER.
spectrum (e.g., 1 Hz to 1 MHz). aural Pertaining to sound actually heard, as op-
audio output The output of an audio-frequency posed to sound that exists only as audio-
oscillator or amplifier. It can be measured in frequency currents or waves.
terms of peak or rms volts, amperes, or watts. aurora A phenomenon sometimes called the north-
audiophile A sound-reproduction hobbyist. ern lights or southern lights, as seen in the night
audio power Alternating-current power at frequen- sky. In the Northern Hemisphere, it is known as
cies roughly between 20 Hz and 20 kHz. When Aurora Borealis; in the Southern Hemisphere, it
used in connection with transmitters and other is called Aurora Australis. It generally occurs a
modulated radio-frequency (RF) equipment, the few hours after a solar flare, when charged parti-
term refers to modulator power output. cles, emitted from the sun, arrive at the earth,
audio response unit A device that links digitized and are accelerated in the vicinity of the the geo-
responses, held in computer storage, to a tele- magnetic poles.
phone set or line to answer incoming calls and in- auroral absorption Radio wave absorption by an
quiries. aurora.
audio signal generator See AUDIO OSCILLA- auroral flutter Rapid fading of a signal at high or
TOR, 2. very high frequencies, so-called because it often
audio spectrum The range of sine-wave frequen- imparts a fluttering quality to the signal that is
cies detectable by the human ear when they oc- caused by phase distortion and Doppler shift
cur as acoustic vibrations. This range is about 20 when the waves are reflected from the aurora.
Hz to 20 kHz. auroral interference 1. Interference to high-
audio squelch A squelch circuit that operates only frequency radio propagation and also occasion-
on the audio channel of a receiver. ally to medium-frequency and low-frequency
audio system 1. The portion of any electronic as- propagation, caused by the activity of the aurora.
sembly that is used to process sound. 2. Special 2. Auroral flutter on a signal.
computer equipment capable of storing and pro- auroral opening A condition in which radio com-
cessing digitized audio-frequency (AF) data. munication becomes possible via AURORAL
audiotape Magnetic tape for the recording and re- PROPAGATION. It can occur when communica-
production of data in the audio-frequency (AF) tion between two points is normally impossible at
range. a certain frequency. Auroral openings allow long-
audio taper In potentiometers, a semilogarithmic distance communication well into the very-high-
variation of resistance versus rotation. Used in frequency (VHF) spectrum.
volume and tone controls for audio circuits. At auroral propagation Reflection of radio signals
midposition (the halfway point), the counter- from aurora that occur during geomagnetic
clockwise portion of the device has about 1⁄10 the storms. Theoretically, auroral propagation is pos-
resistance of the clockwise portion. A listener will sible when the aurora are active, between any two
hear sound at half-volume because of the loga- points on the earth’s surface from which the same
rithmic nature of the human audibility curve. part of the aurora lie on a line of sight. This type
audio-visual Pertaining to a combination of sound of propagation seldom occurs when one end of the
and sight (e.g., television and sound motion pic-
tures).
auditory backward inhibition A subjective phe-
nomenon, 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 im-
pact.
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 recre-
ation of files.