adaptive directional microphones – directional microphone system which, when activated, can adapt based on the location of the noise.

adaptive feedback cancellation – a digital process that creates a filter within the amplifier of the hearing aid to cancel feedback the moment it is detected without reducing or altering the hearing aid’s response. The filter will automatically change (or adapt) if the feedback is caused by a different or changing situation.

ASP/AGC-Input – an acronym for the Automatic Signal Processing / Automatic Gain Control-Output. This circuit automatically reduces the volume of a hearing aid in response to the sound which has exceeded a certain level. With the ASP/AGC-Output circuit, loud sounds are reduced after the amplifier.

ASP (BILL Circuitry) – stands for the Automatic Signal Processing Bass Increases at Low Levels. This circuit also decreases the bass at high levels. BILL circuitry is often marketed under the trademark name “Manhattan” circuit. BILL circuitry is intended for wearers who frequently find themselves in noisy environments, especially environments where low-frequency noise is a constant factor. Harsh or shrill sounds are not amplified but are actually reduced by this circuit.

ASP (PILL Circuitry) – stands for Automatic Signal Processing Programmable Increases at Lower Levels. This type of circuitry is more versatile than TILL or BILL circuitry because it can be programmed by computer to automatically perform as a BILL circuit on one channel and a TILL circuit on another. The user can switch between circuits as listening environments change.

ASP (TILL Circuitry) – stands for the Automatic Signal Processing Treble Increase at Low Levels. This circuit also decreases the high-frequency column at high levels. TILL circuitry is often marketed under the trademark name “K-AMP.” TILL circuitry is intended for wearers who need more volume to hear the quiet sounds than they do for loud sounds. Harsh or shrill sounds are not amplified but pass through the circuit unaltered.

audiogram – a graph on which to record the auditory threshold by frequency of a patient’s hearing.

audiology – the science or study of hearing

audiometry – the measurement of hearing.

aural – having to do with the ear or hearing.

auditory nerve – connects the inner ear and the brain; serves in hearing and balance.

automatic directional microphones – directional microphone technology that is automatically engaged or disengaged without user direction.

automatic signal processing *(ASP) – the family of hearing aid circuits which automatically change the gain (volume) and frequency response (tones such as bass, midrange and treble) as a function of the sound entering the hearing aid microphone.


BiCROS – stands for Bilateral Contralateral Routing of Signal. A hearing aid with two microphones, one at each ear and one receiver. Used for hearing aid wearer who has one aidable ear and one that is not aidable.

Bluetooth compatibility – uses Bluetooth technology to allow digital instruments to communicate wirelessly

body hearing aid – a hearing aid with a microphone, amplifier, and battery worn on the chest and connected to an ear-worn receiver with a cord.

BTE – a behind the ear hearing aid system. Also called post-auricular hearing aid.


canal hearing aid – a custom hearing aid that fits mostly in the ear canal with a small part extending into the concha area.

class A circuits – have as their defining feature the characteristic of amplifying loud sounds and quiet sounds with equal intensity. For this reason, some patients may find that class A circuits provide either too little sound or too much sound to comfortably reach a listening comfort for their particular hearing loss. The class A circuit provides basic linear amplification and is found in lower-priced hearing aids.

class B circuits – recommended for only the most severe hearing losses. This circuit contains two additional transistors, one to push the signal and one to pull the signal, for the purpose of generati9ong more power. This gives the greatest power and volume for patients with more advanced losses. In some cases, the class B circuit may not be available because of the limited space within the hearing aid shell.

class D circuits – provide clear, undistorted sound and emphasize the high frequencies. The result is a hearing aid with ability to limit the level of incoming sound volume. This delivers a more natural loudness throughout the patient’s entire listening range, without getting too loud or too quiet as can be the case with linear hearing aids.

class H circuits – feature a “sliding” bias, or governor of the current drain, that adjusts the current based upon the strength of the incoming sound. Softer sounds which require less battery power, cause the governor to reduce battery drain. The result is current savings and increased battery life. When the sound level increases, the governor automatically increases, thereby maintaining a proper balance between battery drain and output level.

cochlea – part of the inner ear that is shaped like a snail. Vibrations in the fluid-filled cochlea cause tiny hair cells to vibrate and generate nerve impulses that then travel to the brain.

completely-in-the-canal hearing aid (CIC) – the smallest hearing aid which fits beyond the visual opening of the ear canal. Also called deep canal hearing aid.

compression amplification – has as its defining feature the characteristic of decreasing (or compressing) volume as the loudness of sound increases at the hearing user’s ear. The goal of compression ampli8fication is to deliver a more natural loudness through the wearer’s entire listening range without under-amplification or over-amplification

CROS – stands for Contralateral Routing of Signal. A hearing aid designed for a person with normal hearing in one ear and an unaidable ear on the other side.


dB – decibel, a unit for measuring and describing sound intensity or loudness; named after Alexander Graham Bell.

digital hearing aid – an instrument that converts the electric signal from the microphone to digital values for processing, then converts them back to electric signals for the ear.

direct audio input – the hearing aid has a jack to receive sound directly from another device such as a TV or a personal entertainment system.

directional microphone – a microphone that is more sensitive to sound approaching from one direction

dynamic range – the difference in dB between the threshold of hearing and discomfort level.


earmold – an impression of your ear canal used to mold the shell of the hearing aid. It is made using silicone or other impression material.

expansion technology – a digital process that allows the hearing aid to provide less gain for sounds that are softer than conversational speech. This improves the quality of sound fro the hearing aid when worn in quiet situations by reducing low-level noise.

external receiver – an instrument design that features a processor worn behind-the-ear and a speaker inserted in the ear canal.


feedback – the squeal produced when a sound that has been amplified is picked up by the microphone and reamplified in a loop.

filter – a device that allows some frequencies to pass through while others are attenuated (as in high pass, low pass, bandpass, high cut, low cut).

FM integration – the hearing aid contains an FM receiver to pick up signals from an FM transmitter. There is no additional hardware to plug into the hearing aid. The transmitter can be given to a speaker at a lecture or in a noisy situation in order to isolate the speaker’s voice.

frequency – the number of complete oscillations per unit of time, measured in the number of cycles per second and expressed in Hertz (Hz).


gain – the amount of dB that the sound has been increased.

gain control – a device that allows the gain to be adjusted (such as volume control or potentiometer).

gain reduction – used in multi-channel hearing aids to automatically lower the gain in a specific channel in order to control feedback.


hearing aid – also called hearing instrument, means any wearable instrument or device designed for, or represented as aiding, improving or correcting defective human hearing.

helix – shell style with a free field design allowing for maximum venting of the ear canal.

high pass filter – a filter that allows high frequencies to pass through and attenuates low frequencies.


in-the-ear hearing aid (ITE) – a custom hearing aid that fits entirely in the concha bowl of the ear (same as full shell).

in-the-canal hearing aid (ITC) – same as canal aid.


K-AMP circuit (TILL) – causes the Treble to Increase at Low Levels and to decrease at high levels. Name after its inventor, Dr. Mead Killion, this circuit is designed to amplify more in quite environments and less in loud environments. It was designed for people who need amplification for soft sounds but who hear loud sounds normally. The K-AMP circuit regulates the volume automatically and does not amplify loud sounds.

kneepoint – also called a compression threshold. It is the point, in sound decibels, that a compression circuit begins to reduce the gain. Some circuits allow this point to be digitally programmed, being customized to the user’s needs.


limiting compression circuits – automatically limit volume as it enters the hearing aid microphone. This circuit is designed for patients who have mild to moderately severe, sharply or gently sloping high frequency and flat losses.

linearity – the condition where a change in input level causes a similar change in output

low pass filter – a filter that allows low frequencies to pass through and attenuates high frequencies.

low profile – shell size of hearing aid that is between the full ITE and the half shell.


mixed hearing loss – a hearing loss which is a combination of conductive and sensorineural impairments.

multi-channel adaptive directional microphones – an adaptive directional microphone system which can manage multiple noise sources at the same time.

multiple directional microphones – see Omni-directional microphone.

multi-channel technology – technology that electronically separates the incoming sound into bands and adjusts the sound intensity in each band independently. The benefit is a hearing aid that more finely tailors the frequency response and compression characteristics to each user’s unique hearing needs.


narrowband filter – a filter that allows a specific restricted frequency range to pass through while attenuating adjacent frequencies on each side of the filter.

noise management – a digital process that automatically alters the response of the hearing aid in a noisy situation in order to unsure the listener’s comfort.

non-programmable multi-channel – technology that electronically separates the incoming sound into bands and adjusts the sound intensity in each band independently. The benefit is a hearing aid that more finely tailors the frequency response and compression characteristics to each user’s unique hearing needs. These hearing aids are adjusted manually by a potentiometer.


omnidirectional microphone – also called multiple directional microphones. A microphone that picks up sound from all directions.

open-fit – a class of hearing aids that do not occlude the ear canal.


potentiometer – a volume wheel or screw set to control which allows for fine adjustments to a hearing aid.

presbycusis – a sensorineural hearing loss related to aging.

prove microphone a – microphone with a long tube that is used in Real-Ear testing.

programmable circuitry – a feature that allows the hearing aid to be digitally programmed using a computer. Advantages are the preciseness of electroacoustic adjustments at the time of the fitting and ease of access to different types of signal processing for different listening conditions.


ration (compression ration) – the degree to which loud sounds are reduced. It is a ratio relationship, A:B, where A is the amount of original gain into the hearing aid and B is the amount of gain applied after compression.

real ear testing – the measure of sound in the ear canal by means of a probe tube and computerized equipment.

rechargeable – a hearing instrument designed with a rechargeable battery.

remote volume control – wireless, remote control device that allows the user to adjust hearing aid.


speech discrimination – a test which measures the subject’s ability to distinguish words.

speech recognition threshold (SRT) – the lowest level at which the subject can correctly repeat spondaic (two syllables) words.

static feedback cancellation – a digital process that creates a filter in the hearing aid amplifier and is programmed into the hearing aid during the fitting. The filter cancels feedback that is occurring at that time. The filter will continue to cancel feedback that occurs in the same situation, but will not adapt to changing situations.


telecoil – an induction coil in a hearing aid which picks up the electromagnetic signal from a telephone or loop amplification system.

threshold – the level above which the subject gives a positive response and below which the subject does not give a response

toggle – a switch on a hearing aid that allows the user to employ different memories for different listening situations. One memory might be set for a quiet office, while another may be set for a noisy restaurant.

tympanogram – a graphical representation of the changes in acoustic immittance of the middle ear in response to changes in pressure.

tympanometry – the measure of sound flowing through the middle ear in response to changes in pressure.


variable release compression – compression technology which reduces volume in loud circumstances continuously until the sound falls below a predetermined decibel level. With a long, loud sound, release is delayed based on the decibel level entering the hearing aid. The benefit is that it virtually eliminates the “pumping” sound associated with peak clipping in more primitive compression circuits. This circuit helps the user obtain comfortable listening in various levels of noise.

vent – a hole drilled the length of an earmold or ITE shell to allow sound to escape.

video otoscope – a miniaturized camera that the hearing processional inserts into the subject’s ear to view and photograph the ear canal and eardrum


wireless technology – technology that allows the digital instruments to wirelessly communicate information