Download 投影片 1 - National Taiwan University

Hearing and Hearing Aids
蘇璟瑋, 林宜宏, 李彥鋒
Department of Electrical Engneering
National Taiwan University
Monday, April 9, 2007
Outline
•
•
•
•
•
The Structure and Function of Ear
Hearing Loss
Hearing Aids
Summary
Reference
2
Su, Lin and Lee
Outline
Dept. of Electrical Engeering, NTU
The Structure and Function of Ear
• The ear of human can be classified into three parts :
external ear, middle ear and inner ear.
Outer ear
Su, Lin and Lee
Middle ear Inner ear
The Structure of Ear
3
Dept. of Electrical Engeering, NTU
The Structure and Function of Ear (Cont’d)
• External Ear : Preamplifier
 Pinna
Collects sound waves and amplifies sound
 Ear Canal :
Amplifies frequencies in the range 3 kHz to 12 kHz
4
Su, Lin and Lee
External Ear
Dept. of Electrical Engeering, NTU
The Structure and Function of Ear (Cont’d)
• External Ear : Preamplifier
 Pinna
Collects sound waves and amplifies sound
 Ear Canal :
Amplifies frequencies in the range 3 kHz to 12 kHz
Total gain
Gain from Pinna
Gain from Ear Canal
Frequency (kHz)
The frequency response of external ear
Su, Lin and Lee
External Ear
5
Dept. of Electrical Engeering, NTU
The Structure and Function of Ear (Cont’d)
• Middle Ear
 Conduction
Conduct sound from the outer ear to the inner ear
 Protection
Middle ear muscles provide protection from loud sounds
Barrier between external ear and inner ear
6
Su, Lin and Lee
Middle Ear
Dept. of Electrical Engeering, NTU
The Structure and Function of Ear (Cont’d)
• Middle Ear
 Transducer
Converts acoustic energy to mechanical energy
Converts mechanical energy to hydraulic energy
 Amplifier
The frequency response of Middle Ear
Su, Lin and Lee
Middle Ear
7
Dept. of Electrical Engeering, NTU
The Structure and Function of Ear (Cont’d)
• Inner Ear
 Hearing
 Frequency Selectivity
 Balance
8
Su, Lin and Lee
Inner Ear
Dept. of Electrical Engeering, NTU
Hearing Loss
• The type of hearing loss
 Conductive hearing loss
Sound cannot be conducted efficiently through the outer
ear canal to the eardrum and the tiny bones, or ossicles,
of the middle ear.
 Sensorineural hearing loss
There is damage to the inner ear (cochlea) or to the nerve
pathways from the inner ear (retrocochlear) to the brain.
Sensorineural hearing loss cannot be medically or surgically
corrected.
 Mixed hearing loss
9
Su, Lin and Lee
Hearing Loss
Dept. of Electrical Engeering, NTU
Hearing Loss (Cont’d)
(1) Decreased Audibility
 Conductive hearing loss
 Sensorineural hearing loss
10
Su, Lin and Lee
Decreased Audility
Dept. of Electrical Engeering, NTU
Hearing Loss (Cont’d)
(2) Decreased Dynamic Range
 Normally, the dynamic range of hearing equals
120dBs roughly.
11
Su, Lin and Lee
Decreased Dynamic Range
Dept. of Electrical Engeering, NTU
Hearing Loss (Cont’d)
(3) Decreased Frequency Resolution
 SNR Loss
 Sensitivity Loss
 Clarity Loss
(3) Decreased Temporal resolution
12
Su, Lin and Lee
Decreased Frequency Resolution
Dept. of Electrical Engeering, NTU
Hearing Aids
• Basic Structure and Design of Modern Hearing
Aids
Voice
Microphone
Pre-amplifier
Microprocessor
Audio
Amplifier
earphone
Voice
13
Su, Lin and Lee
Dept. of Electrical Engeering, NTU
Hearing Aids (Cont’d)
• The Function of Hearing Aids
 Compression
14
Su, Lin and Lee
Dept. of Electrical Engeering, NTU
Hearing Aids (Cont’d)
• The Function of Hearing Aids (Cont’d)
 Directional Microphone and Microphone array
This method enables the design of highly-directive-hearing
instruments which are comfortable, inconspicuous, and
convenient to use. The array provides the user with a dramatic
improvement in speech perception over existing hearing aid
designs, particularly in the presence of background noise,
reverberation, and feedback.
15
Su, Lin and Lee
Dept. of Electrical Engeering, NTU
Hearing Aids (Cont’d)
• The Function of Hearing Aids (Cont’d)
 Directional Microphone and Microphone Array (Cont’d)
16
Su, Lin and Lee
Dept. of Electrical Engeering, NTU
Hearing Aids (Cont’d)
• The Function of Hearing Aids (Cont’d)
 Noise Reduction
 Method 1
Using high pass filter, but the eliminates both speech and noise
in the frequency region between 0.4kHz and 1.0 kHz.
17
Su, Lin and Lee
Dept. of Electrical Engeering, NTU
Hearing Aids (Cont’d)
• The Function of Hearing Aids (Cont’d)
 Noise Reduction (Cont’d)
 Method 2
Adaptive noise cancellation, need at leat two microphones
18
Su, Lin and Lee
Dept. of Electrical Engeering, NTU
Hearing Aids (Cont’d)
• The Function of Hearing Aids (Cont’d)
 Speech Enhancement
19
Su, Lin and Lee
Dept. of Electrical Engeering, NTU
Hearing Aids (Cont’d)
• The Function of Hearing Aids (Cont’d)
 feedback cancellation
Acoustic feedback in hearing aids, which, if severe enough,
causes the aid to emit a high-intensity oscillation (known as
‘whistling,’ ‘screeching,’ or ‘howling’) is a persistent
and annoying problem.
Block diagram of amplification and
feedback in a hearing aid.
Continuous adaptation feedback
cancellation scheme
20
Su, Lin and Lee
Dept. of Electrical Engeering, NTU
Hearing Aids (Cont’d)
• The Function of Hearing Aids (Cont’d)
 feedback cancellation (Cont’d)
An adaptive algrithom attempts to identify the hearing-aid
feedback path. Once the feedback path has been identified, an
estimate of its output is subtracted from the microphone signal.
Thus the hearing-aid user hear the amplified input signal with a
reduction of the distortion caused by the feedback path.
Continuous adaptation feedback
cancellation scheme
Su, Lin and Lee
21
Dept. of Electrical Engeering, NTU
Hearing Aids (Cont’d)
• The types of Hearing Aid
 線性電路助聽器
 壓縮類比式電路助聽器
 電腦程控式助聽器
 Advantage
 價格低
 調整快速
 Disadvantage
 調整彈性低
22
Su, Lin and Lee
Dept. of Electrical Engeering, NTU
Hearing Aids (Cont’d)
• The types of Hearing Aid (Cont’d)
 數位助聽器
 Advantage
 價格較高
 Performance(清晰度、音質、SNR等)高
 Disadvantage
 調整彈性不易
23
Su, Lin and Lee
Dept. of Electrical Engeering, NTU
Summary
Although many techniques are provided to solve the problem
of hearing loss, but those methods are still poor for practical
application.
 Hearing aid makes sound too loud
 Poor performance in background noise
 Hear things, but not clear
 Acoustic feedback
 Cost
24
Su, Lin and Lee
Dept. of Electrical Engeering, NTU
Summary (Cont’d)
Hearing-aid design involves in many region
 Electronics (circuit, system, analog/digital signal processing etc.)
 Medicine
 Even though Art designer
25
Su, Lin and Lee
Dept. of Electrical Engeering, NTU
Reference
• Sound, http://www.britannica.com/ebc/article-64016
• Reliability of computer-automated hearing thresholds in cochlearimpaired listeners using ER-4B Canal Phone Earphones, James A.
Henry, PhD et al.,
http://www.rehab.research.va.gov/jour/03/40/3/henry.htm
• 富聆聽力中心, http://www.new-care.com.tw
• Suband Adaptive Filtering Applied to Acoustic Feedback Reduction
in Hearing Aids, M.G. Siqueira et al.,
http://citeseer.ist.psu.edu/siqueira96subband.html
• B. Widrow, “A microphone array for hearing aids,” IEEE Circuits Syst.
Mag., vol. 1, pp. 26-32, 2001.
• 人耳聽覺與聽力損失, http://www.iosh.gov.tw/netbook/noear2.htm
26
Su, Lin and Lee
Dept. of Electrical Engeering, NTU
Thank you for your attention.
27
Su, Lin and Lee
Dept. of Electrical Engeering, NTU