audioscan RM500SL User Manual page 105

User's Guide Version 3.4 © June 2011
RM500SL ®
Loop System, an assistive listening device that uses magnetic induction to carry a signal
from a microphone/amplifier to a wire loop. The signal is picked up from the loop by a
hearing aid set to the telecoil position or by a receiver with built-in telecoil, volume control,
and earpiece. Loops are either worn around an individual's neck or can encircle a room,
such as a classroom, providing an excellent signal-to-noise ratio.1
MAF, minimum audible field, SPL of a tone at the threshold of audibility measured in a
free sound field for a subject listening with both ears and facing the sound source. The SPL
is measured with the subject removed from the field at the midpoint of an imaginary line
joining the centers of the ear canal openings.
MAP, minimal audible pressure, SPL of a tone, measured or inferred at the tympanic
membrane, at the threshold of audibility.
MPO, Maximum Power Output, the maximum SPL that a hearing aid can deliver in
response to a steady narrow band input. The stimulus may be pulsed (a tone burst) to avoid
discomfort and to approximate an aided UCL measurement stimulus.
Modulation, the process of varying a characteristic of one signal with another.
NAL, National Acoustic Laboratories (Australia)
NCA, National Centre for Audiology (Canada)
Nonlinear Region, that portion of the input-output function which is not a straight line at
45 degrees.
OSPL90 (output SPL for 90-dB input SPL), The SPL developed in a 2cc coupler when the
input SPL is 90 dB, with the gain control of the hearing aid full-on (ANSI S3.22).
Oscillation, in audiology, refers to the undesired tonal output of an amplifier behaving
unstably as a result of feedback; whistling.1
Output Compression, a form of AGC in which the signal level is regulated at the output.
OLC, Output-limiting Compression (compression limiting), a form of AGC with a high
kneepoint and high compression ratio.
PC, Peak-clipping, a method of limiting MPO by truncating the electrical signal supplied
to the output transducer. The resulting acoustic signal may not be truncated but will be
distorted.
Probe microphone, microphone (which may include an extension tube) having a sound
inlet which is small enough to be acoustically unobtrusive when inserted into the ear canal
(ANSI S3.46).
Pure tone, a signal containing one, and only one, frequency; a sinusoidal acoustic signal.1
REAG, Real-Ear Aided Gain, difference, in dB as a function of frequency, between the
SPL (or BSPL) at a specified measurement point in the ear canal and the SPL (or BSPL) at
the field reference point, for a specified sound field, with the hearing aid in place and
turned on (ANSI S3.46).
REAR, Real-ear Aided Response, the SPL (or BSPL) as a function of frequency, at a
specified measurement point in the ear canal for a specified sound field, with the hearing
aid in place and turned on (ANSI S3.46).
RECD, Real-Ear-to-Coupler Difference, difference, in dB as a function of frequency,
between the SPL (or BSPL) produced by an insert transducer at the eardrum and in a 2cc
coupler. HA-1 or HA-2 coupler should be specified.
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