Transcript Amplification systems: Hearing aids

Amplification systems: Hearing aids
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May be analog or digital
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Consists of a microphone, amplifier, and loudspeaker.
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Earlier: Linear. Now, compressive with automatic gain
control
Directional microphones
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Different types of hearing aids: Body level, BTE, ITE,
ITC, CIC, Bone-conduction, Eyeglass, disposable, CROS.
http://www.nidcd.nih.gov/health/hearing/hearingaid.htm#4
http://www.ahaanet.com/hearingaidstyles.asp
Hearing aid characteristics
OSPL
 Gain:
 Full on gain versus reference test gain
 Functional gain versus insertion gain
 Frequency response
 Distortion
 Battery drain, equivalent input noise level
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Implants
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Bone-conduction implants
http://products.cochlearamericas.com/baha/introduction-to-baha-baha-and-natural-hearing
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Middle ear implants
http://www.hearingcenteronline.com/newsletter/august00c.shtml
 Auditory brainstem implants
http://www.earinstitute.org/news/facts/abifact.htm
Cochlear implants
Direct stimulation of the auditory nerve
http://www.nidcd.nih.gov/health/hearing/coch.asp
http://www.mayoclinic.com/health/medical/IM02586
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Consists of external and internal units.
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External: Microphone that picks up acoustic signals, converts it to
electrical signals and feeds it to a speech processor. Speech
processor then delivers these coded signals to a transmitter, which
converts it to magnetic impulses
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Internal: Receiver and electrode array.
Candidacy issues: Age, hearing loss
Cochlear implant
Issues in amplification
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Candidacy: Should depend on individual’s specific needs.
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Goal of amplification: To restore sensitivity, clarity (in
quiet and noise) and to prevent amplification to
intolerable levels.
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Earlier: Comparative methods
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Now: Prescriptive methods
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Verification of hearing aid performance very important.
Compensate for insertion loss. Real ear measures.
Assistive listening devices
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Allows the signal to be closer to the amplification
system.
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Interface can be FM, infrared, or
electromagnetic coupling .
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Other types: For awareness. Example: Visual or
vibrotactile devices.