UNIT 1 (i): SIGNAL-TO-NOISE RATIO ENHANCING TECHNOLOGIES

Although hearing aids continue to improve in quality and versatility, they typically
do not meet all of the communication needs of the hearing impaired individuals.
Multiple factors, both acoustic and non-acoustic, influence an individual’s success
and failure with amplification (McCarthy, Montgomery, and Meuller, 1990).

An assistive listening device (ALD) is any type of device that can help function
better in day-to-day communication situations. An ALD can be used with or
without hearing aids to overcome the negative effects of distance, background
noise, or poor room acoustics. So along with the hearing aid, ALDs can offer
greater ease of hearing (and therefore reduced stress and fatigue) in many day-to-
day communication situations. (ASHA).
CLASSIFICATION:
1. Assistive Listening Devices can be classified into four categories:
· Systems to assist in face-to –face communication.
· Systems to assist in the enjoyment of broadcast and other media.
· Systems to assist in telephone communication.
· Systems to assist in the awareness and identification of environmental
sounds and situations(alerting devices).
2. Leavitt(1987) classified ALD’s into 4 categories:
 Sound Enhancement Technology-specific amplification systems used to
assist in the reception of sound. Included are traditional systems, such as hearing
aids, as well as personal and group hardwire, infrared, induction loop and
frequency modulation(FM) systems.
· Television Enhancement Technology: equipment used to improve the auditory
perception of a television signal. This category includes tele-caption decoding any
many sound enhancement devices.
 · Telecommunication Technology: systems used to enhance telephone
communication. Included are text telephones (TT), built-in and portable amplifiers,
and induction systems.
· Signal/ Alerting Technology: the group of devices used to signal the presence of
sound to a hearing impaired listener. Included are visual and tactile aids or wireless
systems, as well as hearing ear dogs.

3) ALD’s can be separated into two broad and distinct categories:

 Communication devices
 Alarm/ alerting devices
I. SYSTEMS TO ASSIST IN FACE-TO-FACE COMMUNICATION/ SOUND
ENHANCEMENT TECHNOLOGY:
They include:
• Hardwire system
• Induction loop system
• Infrared systems
• FM systems
1. HARDWIRE SYSTEM:

Hardwire personal amplification system provides a direct physical connection from

the sound source to the listener.It consists of a direct wire connection from a
microphone, amplifier, and finally to a receiver. The receiver can be either personal
hearing aid or earphone. The microphone is placed by the desired sound source.The
signal is amplified through the body of the instrument and transmitted to the
listener.The hardwire coupling can be achieved through the use of earphones, ear
buds or if the listener wears hearing aids with a telecoil, via an induction loop.The
hardwire system can be divided can be divided into 2 systems:-
1. Hearing Aid Dependent System.
2. Hearing Aid Independent System.
Hearing Aid Dependant System: It means that listening system which can only
be used in connection with a hearing aid. It can again occur in 2 ways i.e. Direct
Audio Input (DAI) and Inductive Coupling.
Direct Audio Input (DAI) - It is considered as a manner of hardwire coupling. It is
available in most BTE hearing aid companies and some custom ITE companies, by
plugging directly into hearing aid via an audio shoe or a plug /jack interface. Also
available for CI, tactile aids and some body type hearing aids. In DAI, the
connection from sound source to listener is achieved by plugging an input cord
from sound source or subsequent amplification system, directly into a hearing via a
boot or audio shoe. Now a days because of impedance variations, any DAI system
cannot be used with any brand of hearing aids.
Inductive System: Hearing aid dependent inductive systems include plug in neck
loops and silhouette inductors that connect directly into the earphone jack of TV,
Radios, Dictaphones and other electronic devices and are powered by the voltage
from the devices.

Hearing Aid Independent Systems: It is also called Personal Amplification

systems or standalone systems. These battery powered hardwire systems have their
own microphone, amplifier and earphone headset. This can be also used with
hearing aids through DAI cords, neck loop, or silhouette inductor.

Uses Of Hardwire Systems

Nursing Homes: can be provided as loaners to those residents who have lost their
hearing aid , or to those residents who awaits the receipt of their own systems.
Physician’s Offices: Devices can assist the health care provider and hearing impaired
patients both in the history intake and the provision of medical information.
Automobiles: can be used in cars to enhance communication and reduce the
interference of wind and street noise.
Family: It can be particularly helped for one-to-one communication, especially at
social gathering where these can be great deal of background noise.
Advantages:
1. Small and Portable.
2. Light weight.
3. Inexpensive.
4. It can be used to access broadcast media via a direct plug-in connection or remote
microphone.
5. It has large volume controls and batteries, which make them simpler to manage
than many hearing aids, especially for individuals with manual dexterity problems
and physically handicapped.
Disadvantages:
1. Limited mobility – Direct wire coupling from the sound source to the listener may
contraindicate their use in such large areas as auditorium and meeting halls.
2. When used with large groups, care need to be taken to avoid accidental falls from
wires positioned along the floor.

WIRELESS SYSTEMS:
It consists of a battery or AC powered transmitter that sends some type of radio
signal to a battery powered receiver.It doesn’t require a cord between the sound
source and the listener.Its application includes large areas such as concert and
lecture halls, classrooms, churches and temples, theaters, museums, theme parks,
arenas, sports stadiums, ports of transportation, and retirement and nursing
homes.There are various wireless systems like Induction Loop systems, Infrared
systems Frequency Modulation systems.
A. Induction Loop Systems:

It is one of the oldest forms of assistive listening technology in use today.This

system consists of a microphone, an amplifier, and a length of wire that surrounds
a designated area, such as a theater or a classroom, for a large group of people. For
individual use, an induction Neckloop ( a loop of shielded wire worn around the
individual’s neck) can be used by the hearing impaired listener. A pick up
microphone is kept near the sound source, transmitting the signal via hard wire
coupling or FM radio waves to a receiver/ amplifier that transforms the signal into
electrical energy. This electric current flow through the wire loop, creating a
magnetic field that can be picked up by the telecoil of a conventional hearing aid or
a specially designed induction receiver.The placement of the loop of wire within a
listening environment is also extremely important. Within a given setting, there
may be areas that are not reached by the electromagnetic field. This will result in
“dead spots” that is area of no sound. When this situation occurs, one must either
relocate the loop of wire or reposition the seats, if possible, in a different manner.
For large area amplification stronger loop system is necessary.
USES OF INDUCTION LOOP SYSTEM:
1. Firstly they are used successfully in situations where groups of hearing-

impaired individuals gather, such as community hearing impaired consumer

group meetings
2. Secondly, induction technology can be used to couple other assistive device

neck-loop that is coupled directly to such assistive devices as hardwire,

infrared and FM systems.
3. Apart from this they can be used in service counters, pots of transportation

vehicles, tour buses, meeting rooms, conference rooms, auditoriums,

classrooms, courtrooms, churches and temples, theaters, museums, sports
stadiums, nursing homes, hospitals etc.
ADVANTAGES:

1. Relatively inexpensive and work well when properly installed.

2. They do not require maintenance of separate receivers, provided the listeners
have telecoil-equipped hearing aids.
3. Induction receivers are compatible with all loop systems.
4. May be used separately or integrated with existing PA-systems.
5. Portable systems are available for use with small groups of listeners. These
portable systems can be stored in a carrying case and set up temporarily as
needed.
DISADVANTAGES:
1. Spillover (i.e., a magnetic field generated in one room and picked by a
telecoil in an adjacent room) can be a major problem. This can be
particularly troublesome in settings where more than one room is looped,
such as in a school for the hearing impaired.
2. Induction systems are vulnerable to interference from a variety of sources
(fluorescent lights, transformers, and electric power wires) within a
designated area and take the form of a low frequency humor increased
distortion.
3. Requires installation of loop wire. Installation may be difficult in pre-
existing buildings. Skilled installation essential in historical buildings (and
may not be permitted at all).
4. If listener does not have telecoil-equipped hearing aid (cannot assume
everyone does), then requires administration and maintenance of receivers.

B.INFRARED SYSTEMS:
Infrared systems transmit sound in the form of harmless light waves that are
invisible to the human eye. After the desired sound is picked up, a
special transmitter/emitter sends the signal on invisible light waves to individual
wireless receivers that must be worn by each listener.These receivers contain a
photo detector diode or "eye" that picks up the infrared light and changes it into
sound. The receiver can be worn connected to earphones or ear buds or can be
 used with a hearing aid via inductive pickup (neck-loop or silhouette inductor) or
direct audio input.There are no seating restrictions with infrared transmission,
provided the room has a sufficient number of properly positioned infrared
transmitters. In addition, because infrared light will not penetrate solid barriers, it
can be used simultaneously in adjacent rooms without interference and is ideal for
use in the legitimate theater, courtrooms, larger conference rooms, cinema houses,
and other areas where security of the signal is a concern.

Uses of Infrared Systems:

1. Theaters: Infrared systems can be made available to impaired patrons at local
theater and movies houses, thus making entertainment more accessible.
2. Television: Personal infrared systems can be easily installed for use at home. Use
of such a system does not affect TV volume; therefore, viewing with friends and
family is possible.
3. Business: Infrared systems can be installed in offices and conference rooms to
allow the hearing impaired worker to participate in meetings.
4. Worship: Places of worship can have receivers available for the participants of
religious services.
 ADVANTAGES:
1. No spillover to adjacent room, etc
2. Infrared receivers compatible with most infrared emitters.
DISADVANTAGES:

1. Infrared systems cannot be used outside because they are subject to interference from
sunlight. They are ineffective in direct sunlight.
2. Infrared light also travels in a straight line, meaning that the strongest and clearest
signal is obtained when received from direct line of transmission.
3. In most applications, the infrared signal is also reflected by walls, ceilings, fur-
nishings, clothing, and so on, and the reception of the signal is not completely di-
rection.
4. However, in large-area applications where the coverage area of the emitters may be
pushed to its maximum, the infrared signal may prove to be more directional, re-
quiring the user to face in the direction of the emitters in order to receive a clear
signal.
5. Infrared transmitters cannot be efficiently operated by battery power because of
their comparatively high power needs.
6. Finally, the performance of an infrared transmitter in larger rooms without the
addition of remote emitters may provide a limited signal and a potentially inferior
performance.

C. FREQUENCY MODULATION SYSTEM (FM).

FM systems provide a wireless means of transmitting the sound source to the
listener.In FM system, the auditory signal is picked up by a microphone and is
transmitted in the form of radio frequency modulated carrier waves to a personal
receiver that is worn by the hearing impaired listener. Each FM consists of a
 transmitter with a specific radio carrier frequency, an antenna, and a compatible
receiver.
 There are essentially 2 types of FM systems:
1. The first one is a complete system consisting of an FM microphone located on the
transmitter with associated antenna, an environmental microphone on the FM
receiver and an amplifier sufficiently powerful to allow the receiver to function as a
hearing aid.
2. The second type of FM system, is often referred to as a personal FM system, involves
the coupling of the FM system to the client’s personal hearing aids.

USES OF FM SYSTEMS:
 Classrooms: FM systems can be used in classes for the hearing- impaired as well as
in mainstreamed classes for improving signal-to-noise ratio. They can also be used
as auditory trainers for speech therapy.
 Employment: use of these systems can help improve communication at meetings
and for one-to-one situations. A conference microphone can allow greater
participation.
  Infants: FM systems can help provide direct language stimulation between the
parents and the hearing impaired child.
 Travel: Any travel that requires listening to a tour guide presentation can be
improved by the use of wireless FM.
 Adult Education: FM systems have been used for adult continuing education, as
well as for use in college lecture hall settings.
 Arenas: Theaters, arenas and places of worship can be have FM system technology
available.
ADVANTAGES:
 Highly portable when used with body-worn, personal transmitter.
 Easy to install.
 May be used separately or integrated with existing PA-systems.

DISADVANTAGES:
 Signal spillover to adjacent rooms/listening areas(can prevent interference by using
different transmission frequencies for each room/listening area). Choose infrared if
privacy is essential.
 Receiver required for everyone/ requires administration and maintenance of
receivers.
 Susceptible to electrical interference when used with induction neck loop/
silhouette.
 Some systems are more susceptible to radio waves interference and signal drift
than others.

II. SYSTEMS TO ASSIST IN THE ENJOYMENT OF BROADCAST AND

OTHER MEDIA/ TELEVISION ENHANCEMENT TECHNOLOGY

This technology is mainly used to improve the perception of television signal.

 A .Real-Time Captioning. Captioning of live lectures has grown in popularity in
recent years and will continue to do so. Like-live captioning of television, real-time
captioning of lectures can be done in two ways.

1. In the first, a transcript of the person's speech is fed into a computer system and
then displayed on a projection screen (in sub- or surtitles), either alone or along
with a live picture of the lecturer.
2. In the second method, verbatim captioning of unscripted material is done by a
trained court reporter, using a special computerized system that can generate the
full text of the proceedings with only slight time delays.
III. SYSTEMS TO ASSIST IN TELEPHONE COMMUNICATION/
TELECOMMUNICATION TECHNOLOGY
 Auditory Telephone Devices: ALDs for the voice telephone can be used
with or without a hearing aid. When used with a hearing aid, they can be used
in conjunction with the hearing aid's microphone circuit (acoustic coupling)
or with the hearing aid's telecoil circuit (inductive coupling).
The appropriateness of each coupling method is largely dependent on the
individual's hearing impairment.
 Inorder to control the ringer pitch and volume control a switch can be
provided.
 Visual display: Light flashes whenever the telephone rings.
 Ring enhancers: Amplify the ring sound can be used.

IV. ALARM/ ALERTING DEVICES:

Uses devices which delivers signals through visual or tactile vibratory means so
has to enable the hearing impaired person to perceive them. It is a technology to
alert persons with HI to the presence of sound by converting the sound into
another form of energy (visual/vibration) which he/she can perceive.Alarm
clock with vibrators, baby cry systems, doorbell/ telephone alerts, smoke alarm.

Some of the alerting devices include:

• Wake-up systems include small, portable, battery-powered clocks that

shake a person awake as well as AC-powered clocks that can be connected
to a lamp, a strobe, a bed shaker. A very inexpensive system consisting of a
lamp, a lamp timer, and a flasher button placed in the lamp socket also can
be recommended.
• Baby monitor: detects the sounds of baby crying and provides visual
signals (flashlight).
• Smoke detector

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