HP RM500SL - Manual (Page 94)

22 Glossary
AGC, Automatic Gain Control, the means by which gain is automatically controlled by the level of the
signal being amplified. (ANSI S3.22)
AGC-I, input-controlled AGC (see "input compression").
AGC-O, output controlled AGC (see "output compression").
AGRAM, Abbreviation for audiogram.
ANSI, American National Standards Institute.
Attack Time, the time required for HA output to reach +/- 3dB of its steady state level in response to an
input step from 55 to 90dB SPL. (ANSI S3.22)
ASP, Automatic Signal Processing, In hearing aids, level dependent frequency response shaping.
AVC, Automatic Volume Control, slow-acting AGC that attempts to maintain a constant average signal
level.
BSPL, Band Sound Pressure Level, the SPL within a restricted frequency band.
BTE, Behind-The-Ear (hearing aid).
Compression, a type of AGC in which an incremental change in the input level produces a smaller
incremental change in the output level.
CR, Compression Ratio, the ratio of incremental change in input SPL to the resulting incremental
change in output SPL. Used to characterize steady state AGC action; can be a function of input level,
duration and frequency.
CROS, Contralateral Routing Of Signals; a type of hearing aid in which the microphone is at the ear
opposite to the one receiving the amplified sound.
CORFIG, Coupler Response for Flat Insertion Gain; the transformation added to real-ear insertion gain
to obtain 2-cc coupler gain. Assumes linear amplification.
Coupler, a device used to acoustically couple an earphone or hearing aid to a measurement microphone
and to provide an acoustic load.
DSL, Desired Sensation Level Method, a systematic eardrum (SPLogram) approach to the hearing aid
fitting process that seeks to ensure amplified speech will be audible and comfortable while loud sounds
will not be uncomfortable.
Directional hearing aid, a hearing aid for which the gain is dependent on the direction of sound
incidence when measured under free-field conditions (ANSI S3.22).
Equalization, process of controlling the SPL (or band SPL) of the stimulus, as a function of frequency, at
the field reference point (ANSI S3.46).
Expansion, a type of AGC in which an incremental change in the input level produces a larger
incremental change in the output level.
FM, frequency modulation, a method of transmitting information in which the frequency of a radio wave
(carrier) is varied (modulated) by the information (signal). Also, a method of reducing standing waves in a
sound field in which the frequency of a test tone (carrier) is varied by a low frequency triangle or sine
wave.
FM System, an assistive listening device consisting of a microphone, an fm radio transmitter and an fm
receiver. The microphone and transmitter are worn by the speaker and the receiver is worn by the
listener.