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0611 RM500SL User’s Guide Version 2.8 Page 95
FOG, Full On Gain, gain for a 50 dB input SPL with the gain control set to maximum ANSI S3.22)
Gain (in dB), output sound pressure relative to input sound pressure, expressed in decibels; gain =
20log
10
(output sound pressure / input sound pressure); also, gain = (output SPL) - (input SPL).
Gain control, a manually or electronically operated control for the adjustment of overall gain (ANSI
S3.22).
HA-1 Coupler, a coupler having a volume of 2 cubic centimetres with direct access to the cavity. Used for
testing in-the-ear and in-the-canal hearing aids; can also be used to test behind-the-ear hearing aids with
a custom earmold attached. Aka the ITE coupler.
HA-2 Coupler, a coupler having a volume of 2 cubic centimetres with access through a rigid tube. When
used for testing BTE hearing aids, the rigid tube consists of 18 mm of 3 mm tubing plus 25 mm of 2 mm
tubing (ANSI S3.22). When used for calibrating insert earphones, the 2 mm tubing is not used (ANSI
S3.6). Aka the BTE coupler.
Harmonic, a component of a tone complex that is an integer multiple of the lowest frequency component
(fundamental).
Harmonic Distortion, the addition of harmonic components to a signal. The rms value of a harmonic
component of a signal as a percentage of the rms value of the fundamental. If less than 20%, the rms
value of the total signal may be used instead of the fundamental.
HFA, High Frequency Average, the average of values in dB at 1000, 1600, and 2500 Hz. (ANSI S3.22).
HL, Hearing Level, the hearing threshold referenced to the threshold of normal hearing, expressed in dB.
HI, Hearing instrument.
HIT, Hearing instrument test.
Input Compression, a form of AGC in which the signal level is regulated before the volume control.
Input / Output function, steady state, single-frequency plot of the coupler SPL on the ordinate as a
function of input SPL on the abscissa with equal decibel scale divisions on each axis (ANSI S3.22).
ITE, In-The-Ear (hearing aid).
Kneepoint (compression threshold), the point on an input/output curve at which the slope digresses from
unity indicating the signal level at which a non-linear process begins to take effect.
1
LCD, liquid crystal display. A thin, planar information display.
Linear Region, that portion of the input-output function which is a straight line at 45 degrees.
Linear Amplification, amplification having the same gain for all input levels until the maximum output of
the device is reached.
LTASS, Long-term average speech spectrum, the rms level of a speech passage in 1/3
rd
octave
bands, averaged over the entire passage.
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.