ASP Hearing 2007

7/31/2019 ASP Hearing 2007

1/136

Meena Ramani4/2/2007

EEL 6586Automatic Speech Processing

7/31/2019 ASP Hearing 2007

2/136

7/31/2019 ASP Hearing 2007

3/136

Best example of speech recognition Mimic human speech processing

Speech coding e.g. mp3Hearing aids/ Cochlear implants

7/31/2019 ASP Hearing 2007

4/136

7/31/2019 ASP Hearing 2007

5/136

Audible frequency range: 20Hz-20kHzIntensity dynamic range: 0-130 dBJND frequency: 5 cents *JND intensity: ~1dBSize of cochlea: D=2mm L uc=27mm

~Tip of your tiny finger

* one octave=12 equally tempered semi tonesone equally tempered semi tone=100 cents

7/31/2019 ASP Hearing 2007

6/136

7/31/2019 ASP Hearing 2007

7/136

A

N

A

T

O

M

Y

7/31/2019 ASP Hearing 2007

8/136

Function: Focuses sound pressure waves into the ear canal Sound localizationHuman Pinna structure: Symmetrical, curved and pointed forward More sensitive to sounds in front Pinna size: Inverse square lawOthers: Dogs/ Cats: Movable Pinna Elephants: Hear LF sound from up to 5 miles away Barn Owl: Left ear opening is higher than the right

Improvement in localization

Pinna

Auditory Canal

7/31/2019 ASP Hearing 2007

9/136

Interaural differences

1. Horizontal localization2. Vertical localization

PinnaPinna sound localizationsound localization

Is the sound on your right or left side?

7/31/2019 ASP Hearing 2007

10/136

Signal needs to travel further to the more distant earTime difference

More distant ear is partially occluded by the headIntensity differenceInteraural time difference (ITD)Interaural intensity difference (IID)

7/31/2019 ASP Hearing 2007

11/136

Illustration of Illustration of interauralinteraural differencesdifferences

Left

ear

Rightear

soundonset

left right

time

7/31/2019 ASP Hearing 2007

12/136

LeftLeft

earear

RightRightearear

soundsoundonsetonset

timetime

arrival timedifference

Illustration of interaural differencesIllustration of interaural differences

7/31/2019 ASP Hearing 2007

13/136

Left

ear

Rightear

soundonset

time

ongoing timedifference


7/31/2019 ASP Hearing 2007

14/136

Left

ear

Rightear

soundonset

time

i n t e n s i t y d i f

f e r e

n c e


7/31/2019 ASP Hearing 2007

15/136

Interaural time differences (ITDs)Threshold ITD 10-20 ms (~ 0.7 cm)

Interaural intensity differences (IIDs)Threshold IID 1 dB

Just noticeable thresholdsJust noticeable thresholds

7/31/2019 ASP Hearing 2007

16/136

Interaural time differences (ITDs)Used for low frequency sound localizationValid up to around 1000 HzSensitivity declines rapidly above 1000 Hz

Smallest phase difference corresponds to true ITD

Interaural intensity differences (IIDs)Used for high frequency sound localizationLess than 500 Hz, IIDs are negligible (due to diffraction)Attenuation varies with frequencyIIDs can reach up to 20 dB at high frequencies

DD

UU

PPLL

EE

XX

TT

HH

EE

OO

RR

YY

Horizontal localizationHorizontal localization

7/31/2019 ASP Hearing 2007

17/136

Pinna directional filtering

Pinna amplifies sound above and below differently Selective spectral amplification

Is sound above or below?

1. Horizontal localization2. Vertical localization

PinnaPinna sound localizationsound localization

7/31/2019 ASP Hearing 2007

18/136

Function: Boosts energy between 2-5Khz by 15dB 2-5kHz region is important for understanding speechStructure:

Auditory canal length: 2.7cm Closed tube resonance: wave resonator Broad peak since the closed end is a pliant ear drum Resonance frequency: ~ 3Khz

Pinna

Auditory Canal

7/31/2019 ASP Hearing 2007

19/136

A

N

A

T

O

M

Y

7/31/2019 ASP Hearing 2007

20/136

Impedance matching Acoustic impedance of the fluid is 4000 x that of air

Need amplification

Amplification By lever action ~ 3x Area amplification [55mm 2 3.2mm 2] 15xStapedius reflex Protection against low frequency loud sounds

Tenses muscles stiffens vibration of Ossicles Reduces sound transmitted (20dB)

Eardrum

Ossicles

Oval windowTranslation of sound wave to vibrations in cochlea

Eardrum Ossicles Oval WindowOssicles: Malleus, Incus, Stapes

7/31/2019 ASP Hearing 2007

21/136

A

N

A

T

O

M

Y

7/31/2019 ASP Hearing 2007

22/136

Semicircular Canals

Cochlea

Function: Keeps body in balance

Canals: Accelerometers in 3 perpendicular planesStructure:

3 perpendicular fluid-filled canals Hair cells in canal detect fluid movements Connected to the auditory nerve

7/31/2019 ASP Hearing 2007

23/136

Function: Cochlea is the body's microphone Converts mechanical movement to electrical action potentialsStructure:

Cochlea is a snail-shell like structure 2.5 turns

(1) Organ of Corti (fluid-filled)

(2) Scala tympani (fluid-filled)

(3) Scala vestibulli (fluid-filled)

(4) Spiral ganglion

(5) Auditory nerve fibers

Semicircular Canals

Cochlea

Inner earInner ear

7/31/2019 ASP Hearing 2007

24/136

[16,000 -20,000] Inner hair cells and Outer hair cells along BM 1 row of IHC, 3 rows of OHCs

IHC: Transmit signals to the brain via auditory nerves ( Afferent )OHC: Transmit feedback signals from the brain via auditory nerves ( Efferent )

7/31/2019 ASP Hearing 2007

25/136

Each hair cell has 100s of tiny stereocilia

7/31/2019 ASP Hearing 2007

26/136

Vibrations of the oval window causes the cochlear fluid to vibrate

BM vibration produces a traveling wave OHCs amplify and sharpen the vibration of the BM Bending of the IHC cilia (in one direction-HWR) produces action potentials Action potentials travel via the auditory nerve to the brain

7/31/2019 ASP Hearing 2007

27/136

7/31/2019 ASP Hearing 2007

28/136

Tonotopic mapping along the BM and for the AN fibers

7/31/2019 ASP Hearing 2007

29/136

Each position along the BM has a characteristic frequency formaximum vibrationFrequency of vibration depends on the place along the BMAt the base , the BM is stiff and thin (more responsive to high Hz )At the apex , the BM is wide and floppy (more responsive to low Hz )

32-35 mm long

Base Apex

7/31/2019 ASP Hearing 2007

30/136

7/31/2019 ASP Hearing 2007

31/136

Human ear resolves 1500 pitches

One pitch every .002cm!Possible by OHC feedback results in sharper response peaks along BM

7/31/2019 ASP Hearing 2007

32/136

The ear produces some sounds! By-product of electro-motile vibrations of the OHCsUses: To test hearing for infants To check if patient is feigning a loss

7/31/2019 ASP Hearing 2007

33/136

Each hair cell has about 10 AN fibersAN fibers carry impulses from cochlea and semicircular canalsAN makes connections with both auditory areas of the brain

Tonotopic mappingNeurons encode Steady state sounds (phase, frequency, intensity) Onsets

Auditory Area of Brain

7/31/2019 ASP Hearing 2007

34/136

Why do your ears pop while on an airplane?Does the pinna continue to grow?Why do you hear waves when you couple a sea-shell to

your ear?How do you perceive pitch while on a telephone?

7/31/2019 ASP Hearing 2007

35/136



7/31/2019 ASP Hearing 2007

36/136

Anatomy e.g. Cochlea

Psychoacoustics e.g. MaskingEngineering Applications e.g. Hearing aids and Cochlear implants

7/31/2019 ASP Hearing 2007

37/136

7/31/2019 ASP Hearing 2007

38/136

Outer ear: Pinna and Auditory canal Horizontal localization: IID, ITD Vertical localization: Pinna spectral amplification Auditory canal resonance ~3 kHz

Middle ear: Tympanic membrane, Ossicles, Oval window Translates sound pressure to cochlea fluid vibration Ossicles- Lever (15x) and Area amplification (3x) Stapedius reflexInner ear: Cochlea, Semicircular canals Semi-circular canals keep the body in balance Cochlear hair cells convert BM vibration to electrical impulses Impulses are transmitted via auditory nerve to the brain

7/31/2019 ASP Hearing 2007

39/136

7/31/2019 ASP Hearing 2007

40/136

The study of how sounds entering the ear are processed by the ear and the brain in order to give the listener useful information

Measurement of the sensitivity of listeners to changes in theauditory spectrum

The study of the relationship between acoustics and perception

The study of the structures and processes which convert soundsinto sensations and then into our perceptions

7/31/2019 ASP Hearing 2007

41/136

Auditory nerve codingHearing thresholdsPsychoacoustics basic phenomena

7/31/2019 ASP Hearing 2007

42/136

Each hair cell has about 10 auditory nerve fibers Bending of the IHC cilia produces action potentials Action potentials travel via the auditory nerve to the brain Tonotopic mapping for AN response

Auditory Area of Brain

7/31/2019 ASP Hearing 2007

43/136

Neurons encode Steady state sounds (phase, frequency, intensity) Onsets

At stimulus onset, AN firing rate increases rapidly For constant stimulus, the rate decreases exponentially Spontaneous rate: AN firing rate in the absence of stimulus

Neuron is more responsive to changes than to steady inputs

7/31/2019 ASP Hearing 2007

44/136

To determine the tonotopic map of AN: Apply 50ms tone bursts every 100ms Increase SPL till spike rate increases by 1

Repeat for all frequencies AN characteristic frequency

~=BM resonance frequency

Tuning curves are BPFs with almostconstant Q (=f 0/BW)

7/31/2019 ASP Hearing 2007

45/136

Minimum intensity of sound needed at a particular frequency to just stimulate an AN above spontaneous activity

HF slopes are very steep (c. 300 dB/oct) LF slopes generally have a steep tip followed by a flatter base Damage to the cochlea abolishes the tip

7/31/2019 ASP Hearing 2007

46/136

Play a tone above a particular (CF) ANs threshold, it will fire If a second tone is played, at a frequency and level in the shaded

area, then the firing rate of the first neuron will be reduced Auditory system is non-linear Contention for same neurons to encode both frequencies

7/31/2019 ASP Hearing 2007

47/136

ANs tend to fire at a particular phase of LF stimulus Inter Spike Intervals (ISI) occur at integer multiples of the tone period >3kHz phase locking gets weaker because of neuron refractory period

7/31/2019 ASP Hearing 2007

48/136

As the amplitude of a tone increases, the firing rate of a AN neuronat that CF increases up to saturation High spontaneous rate neurons code low level intensity changes Low spontaneous rate neurons code high level intensity changes High spontaneous rate neurons are more in number

7/31/2019 ASP Hearing 2007

49/136

Coding of frequencyPhase-locking for low frequenciesPlace (tonotopic) theory

Coding of phasePhase-lockingbinaural localization (ITD)

Coding of intensityRate of firing above thresholdSpread of firing

7/31/2019 ASP Hearing 2007

50/136

Matlab code available:http://www.ece.mcmaster.ca/~ibruce/Input: wav fileOutput: PSTH [post stimulus time histogram]

AuditoryAuditory- -periphery modelperiphery model

(Zhang et al. ~2001)

7/31/2019 ASP Hearing 2007

51/136


7/31/2019 ASP Hearing 2007

52/136

Threshold of hearing at 1,000 Hz is 0 dB

7/31/2019 ASP Hearing 2007

53/136

Loudness is not simply sound intensity!

Factor of ten increase in intensity for the sound to be twice as loud Unit of loudness: Phon [Reference: SPL at 1,000 Hz] The Bass loss problem: discrimination against LF

7/31/2019 ASP Hearing 2007

54/136

Presbycusis: hearing loss due of aging Hearing sensitivity decreases especially at HFs Threshold of pain remains the same Reduced dynamic range

7/31/2019 ASP Hearing 2007

55/136

a) Normal hearing b) Severe hearing loss

c) Fused cilia of IHC-Noise induced loss

7/31/2019 ASP Hearing 2007

56/136

7/31/2019 ASP Hearing 2007

57/136

Occupational Safety & Health Administration (OSHA)OSHA Noise exposure computation standard- 1910.95

Noise dosimeters: Microphone and noise processor Memory for storing results and time history

7/31/2019 ASP Hearing 2007

58/136


7/31/2019 ASP Hearing 2007

59/136

Critical bands and loudnessMonoaural beatsMasking effect Frequency masking, temporal masking

7/31/2019 ASP Hearing 2007

60/136

Psychoacoustic experimentsEqually loud, close in frequency ( A,B)

Same IHCs Slightly louder

Equally loud, separated in freq. ( C,D) Different IHCs Twice as loud

Critical bands of frequency(Proposed by Fletcher )

7/31/2019 ASP Hearing 2007

61/136

Center Freq(Hz)

Critical BW(Hz)

100 90

200 90

500 110

1000 150

2000 280

5000 700

10000 1200

How to measure?Signal threshold in noise vs. BW CB ~= 1.5mm spacing on BM 24 such band pass filters

BW of the filters increases with f c Weber: Logarithmic relationship Psychoacoustical scale: bark scale

7/31/2019 ASP Hearing 2007

62/136

Loudness increases when bandwidth exceeds a critical band

7/31/2019 ASP Hearing 2007

63/136

7/31/2019 ASP Hearing 2007

64/136


7/31/2019 ASP Hearing 2007

65/136

If two tones are presented monaurally with a smallfrequency difference, a beating pattern can be heard

500 & 502 Hz 500 & 520 Hz

Interaction of the two tones in the same auditory filter Beating arises from neural interaction Only perceived if the tones are sufficiently close in frequency

7/31/2019 ASP Hearing 2007

66/136



7/31/2019 ASP Hearing 2007

67/136


7/31/2019 ASP Hearing 2007

68/136

A loud sound makes a weaker sound imperceptibleCategories and aspects of masking

Frequency masking Temporal maskingFrequency selectivity of the auditory system

Psychophysical tuning curves

MAS KING

7/31/2019 ASP Hearing 2007

69/136

Masking occurs because two frequencies lie within a critical band and the higher amplitude one masks the lower amplitudesignalTypes of maskers:

Broad band noise, narrowband noise, pure & complex tonesLow frequency broad band sounds mask the mostMasking threshold : Amt of dB for test tone to be just audible in noise

MAS KING

MAS KING

7/31/2019 ASP Hearing 2007

70/136

White noiseMasked thresholds are a function of frequencyTOQs frequency dependence almost completely disappearsLow and very high frequency almost same as TOQ Above 500Hz, thresholds increase with increase in frequency by10dB/decade

M AS KING

MAS KING

7/31/2019 ASP Hearing 2007

71/136

Narrow band

7/31/2019 ASP Hearing 2007

72/136

Noise (Varying Amplitude, Fixed Frequency) 1KHz noise; 20-100dBSlope of rise seems independent of amplitudeBut slope of fall is dependent on amplitudeNon-Linear frequency dependenceStrange effect at high masker amplitudes: At high amplitudes ear begins to listen to anything audible!! Begin to hear difference noise (noise and testing tone)

M AS KING

MAS KING

7/31/2019 ASP Hearing 2007

73/136

Previously assume long lasting test and masking soundsSpeech has a strong temporal structure Vowels= Loudest parts; Consonants=faint parts Consonants are masked by preceding loud vowel

M AS KING

MAS KING

7/31/2019 ASP Hearing 2007

74/136

Post-stimulus/Forward/Post-masking 1st Masker 2 nd test tonePre-Stimulus/Backward/Pre-masking 1st test tone 2 nd MaskerSimultaneous Masking Test tone and Masker together

M AS KING

MAS KING

7/31/2019 ASP Hearing 2007

75/136

Simultaneous masking Duration >200ms, constant test tone threshold Assume hearing system integrates over a period of 200ms

Postmasking Decay in effect of masker for 100ms More dominant effect

Premasking Takes place 20ms before masker is on!! Each sensation is not instantaneous, requires build-up time

Quick build up for loud maskers; Slower build up for softer maskers Less dominant effect

M AS KING

MAS KING

7/31/2019 ASP Hearing 2007

76/136

Procedure

Masker: A narrowband noise of variable center freq is the maskerTarget: A fixed freq and fixed level pure toneLevel of masker that just masks the tone for different masker freqs.

Inference:

Masking curves tell much about auditory selectivity Psychophysical tuning curves match with physiological curves

M AS KING

7/31/2019 ASP Hearing 2007

77/136

Anatomy e.g. CochleaPsychoacoustics e.g. MaskingEngineering Applications e.g. Hearing aids and Cochlear implants

7/31/2019 ASP Hearing 2007

78/136

7/31/2019 ASP Hearing 2007

79/136

Normal Hearing

Sensorineural Hearing LossMild to Severe Loss[10 20 30 60 80 90] dB HL

Time (s)

F r e q u e n c y

( H z

)

Cell phone speech for normal hearing

0 0.5 1 1.5 2

0

500

1000

1500

2000

2500

3000

3500

4000

-250

-200

-150

-100

-50

0

Time (s)

F r e q u e n c y

( H z

)

Cell phone speech for SNHL

0 0.5 1 1.5 20

500

1000

1500

2000

2500

3000

3500

4000

-250

-200

-150

-100

-50

0

What do the hearingWhat do the hearingimpaired hear?impaired hear?

7/31/2019 ASP Hearing 2007

80/136

One in every ten (28 million) Americans has hearing loss

95% of those with hearing loss can have their hearing losstreated with hearing aids

Only 6 million use HAs

Factors for HAs not being used: stigma, cost and inefficiency

7/31/2019 ASP Hearing 2007

81/136

1. Decreased audibility2. Loudness recruitment3. Decreased frequency resolution4. Decreased temporal resolution

A good hearing loss (HL) compensation algorithm shouldcompensate for all the above four factors but often not possible

Most HAs compensate for 1 and 2

7/31/2019 ASP Hearing 2007

82/136

Effect:More loss at HFPossible solution:Frequency dependent gainMeasured by:Audiograms

2) Loudness recruitment2) Loudness recruitment

102

103

104-1 0

0

10

20

30

40

50

60

70

80

90

Frequency (Hz)

T h r e s

h o

l d o

f h e a r i n g

( d B

S P L )

Thresholds of hearing for normal & HI listeners

Normal hearingHearing impaired

20 40 60 80 100 120

Very soft

Soft

Comfortable

Loud

Very loud

Too loud

Input level (dB SPL)

L o u

d n e s s r a

t i n g

Loudness growth curves for normal & HI listeners


Effect:Loud sounds are just as loudPossible solution:CompressionMeasured by:Loudness growth curves

7/31/2019 ASP Hearing 2007

83/136

3) Frequency resolution3) Frequency resolution 4) Temporal resolution4) Temporal resolution

Effect:Upward spread of masking increasesPossible solution:Sharper and narrower filter banksMeasured by:Psychoacoustic tuning curve

103

1040

10

20

30

40

50

60

70

80

90

Desired tone frequency (Hz)

D e s

i r e

d t o n e

t h r e s

h o

l d ( d B

S P L )

4 kHz tuning curve for normal & HI listeners

Masker Normal hearingHearing impaired

0 20 40 60 80 100 120 1400

10

20

30

40

50

60

70

80

Desired-Masker tone separation (ms)

D e s

i r e

d t o n e

t h r e s

h o

l d ( d B

S P L )

Temporal resolution at 4 kHz for normal & HI listeners


Effect:Temporally masking of weak soundsPossible solution:Vary gain to get normal masking thresholdMeasured by:Psychoacoustic tuning curve

7/31/2019 ASP Hearing 2007

84/136

Behind The ear In the Ear

In the Canal Completely in the canal

7/31/2019 ASP Hearing 2007

85/136

MicrophoneTone hook

Volume controlOn/off switch

Battery compartment

d fd f

7/31/2019 ASP Hearing 2007

86/136

Ear mold measurements

Hearing aid fittingHearing aid fitting

7/31/2019 ASP Hearing 2007

87/136

So, do you want your HA to:1) Be comfortably loud2) Have loudness Equalization3) Have loudness Normalization

?

?

Which fitting methodology is theWhich fitting methodology is the bestbest ??

7/31/2019 ASP Hearing 2007

88/136

O/P

H1(w )

LevelDetector

GainComputation

H2(w )

LevelDetector

GainComputation

Hn(w )

LevelDetector

GainComputation

O/P LimitingCompression

I/P

HA parameters optimizationHA parameters optimization

7/31/2019 ASP Hearing 2007

89/136

HA parameters optimizationHA parameters optimization

Factors contributing to optimization complexity: Dimensionality of the parameter space is large The determinants of hearing-impaired user satisfaction are unknown Satisfaction evaluation through listening tests is costly and unreliable Acclimitization

7/31/2019 ASP Hearing 2007

90/136

Speech Intelligibility

Objective Measures

AI, STI

Speech Quality

Objective MeasuresPESQ

Subjective MeasuresMOS

Speech Intelligibility (SI): The degreeto which speech can be understood

Performance metricsPerformance metrics

Subjective Measures

HINT

Speech Quality: Does the speech

match your expectations?

Spectrograms and sound filesSpectrograms and sound files

7/31/2019 ASP Hearing 2007

91/136

Sensorineural Hearing Loss [10 20 30 60 80 90] dB HLNoise level =65 dBA and Speech level=65dBA

Spectrograms and sound filesSpectrograms and sound files

HI with Linear gainNormal hearing

HI with RBC gain HI with NR-RBC gain

7/31/2019 ASP Hearing 2007

92/136

7/31/2019 ASP Hearing 2007

93/136

First functional Brain Machine Interface (BMI)First functional Brain Machine Interface (BMI)

Definition:

A device that electrically stimulates the auditory nerve

of patients with severe-to-profound hearing loss toprovide them with sound and speech information

7/31/2019 ASP Hearing 2007

94/136

Severe-to profound sensorineural hearing lossLimited benefit from hearing aidsHearing loss did not reach severe-to-profoundlevel until after acquiring oral speech andlanguage skills

7/31/2019 ASP Hearing 2007

95/136

Worldwide: Over 100,000 multi-channel implants

At Univ of Florida: Implanted first patient in 1985 Currently follow over 400 cochlear patients

Magnetic Resonance Imaging

Surgical issues

Technical and Safety IssuesTechnical and Safety Issues

7/31/2019 ASP Hearing 2007

96/136

7/31/2019 ASP Hearing 2007

97/136

Parts of a CIParts of a CI

7/31/2019 ASP Hearing 2007

98/136

7/31/2019 ASP Hearing 2007

99/136

7/31/2019 ASP Hearing 2007

100/136

7/31/2019 ASP Hearing 2007

101/136

1. Electrode design Number of electrodes, electrode configuration

2. Type of stimulation

Analog or pulsatile3. Transmission link

Transcutaneous or percutaneous

4. Signal processing

Waveform representation or feature extraction

7/31/2019 ASP Hearing 2007

102/136

Compressed Analog (CA)Continuous Interleaved Sampling (CIS)Multiple Peak (MPEAK )

Spectral Maxima Sound Processor (SMSP)Spectral Peak (SPEAK)

7/31/2019 ASP Hearing 2007

103/136

7/31/2019 ASP Hearing 2007

104/136

7/31/2019 ASP Hearing 2007

105/136

7/31/2019 ASP Hearing 2007

106/136

6 channel PR: 100-2500 pulses/sec

7/31/2019 ASP Hearing 2007

107/136

7/31/2019 ASP Hearing 2007

108/136

F0/F1/F2 +HFs Unvoiced: 250 pps 4 electrodes

7/31/2019 ASP Hearing 2007

109/136

7/31/2019 ASP Hearing 2007

110/136

16 bands [16/22 electrodes] 6 max O/P every 4ms PR: 250 pps

7/31/2019 ASP Hearing 2007

111/136

7/31/2019 ASP Hearing 2007

112/136

Strategy: MPEAK or SPEAK Vary selected maxima: 5-10 Vary PR: 180-300pps

For BB: more maxima, less PR For NB: less maxima, more PR Preserves temporal and spectral data

7/31/2019 ASP Hearing 2007

113/136

7/31/2019 ASP Hearing 2007

114/136

Wide range of successMost score 90-100% on AV sentence materials

Majority score > 80% on high contextPerformance more varied on single word tests

7/31/2019 ASP Hearing 2007

115/136

7/31/2019 ASP Hearing 2007

116/136

Definition:The ABI is a surgically implanted device that bypasses thedamaged auditory nerves by providing electrical stimulation tothe cochlear nucleus of the brainstem

Who is a candidate?ABI is designed to provide sound to people withNeurofibromatosis Type II (NF2) who become deaf whentumors are removed from their ANBe at least twelve years of ageHave the ABI placed during tumor removal surgeryHave appropriate expectations and be prepared to participatein a follow-up program

7/31/2019 ASP Hearing 2007

117/136

The first patient was implanted with the MultichannelABI in 1992.So far over 100 NF2 patients have received the device.

How does an ABI work?How does an ABI work?

7/31/2019 ASP Hearing 2007

118/136

How does an ABI work?How does an ABI work?

How does an ABI work? (contd )How does an ABI work? (contd )

7/31/2019 ASP Hearing 2007

119/136

Ventral cochlear nucleus (VCN) transmitssound frequencyinformation to higher auditory centers VCN is tonotopically organized

How does an ABI work? (contd.)How does an ABI work? (contd.)

7/31/2019 ASP Hearing 2007

120/136

Approved October 20, 2000Uses the Nucleus 24 system processorsPlate array with 21 electrodesMost commonly used: Mode: Monopolar Coding strategy: SPEAK No of electrodes: 8

7/31/2019 ASP Hearing 2007

121/136

82% of the implanted subjects were able to perceivesound and use the device postoperatively85% of the subjects demonstrated statistically significantimprovements in open-set sentence understanding whenusing the Nucleus ABI in conjunction with lip-reading.

7/31/2019 ASP Hearing 2007

122/136

7/31/2019 ASP Hearing 2007

123/136

Speaker tracking is not possible with singlemicrophoneMultiple microphones facilitate spatiotemporalfilteringSetup consists of two microphones with the first

microphone assumed as originDistance of the wavefront from microphone is:

The direction of source is given by:

sk dF m

Nc

)1(sin

k d sin

7/31/2019 ASP Hearing 2007

124/136

Differentiate speech source from noise sourceOvercome problems of signal distortion due to noisePrevent loss of accuracy due to room reverberations

Types of DOA estimation aTypes of DOA estimation algorithmslgorithms

7/31/2019 ASP Hearing 2007

125/136

DOA Algorithms

Spatial Correlationmethods

Subspace decompositionmethods

MUSICMultiple Signal Estimation

ESPRITEstimation of Signal parametersusing rotational invariance

Delay and Sum Minimum Variance

Coherent MUSIC

Root MUSIC

ypyp g g

DOA implementation equationsDOA implementation equations

7/31/2019 ASP Hearing 2007

126/136

DOA Method Equation for Implementation

Delay and Sum

MinimumVariance

MUSIC

CoherentMUSIC

Root MUSIC

ESPRIT

*( ) ( ) ( ) P a Sa

*

1( )

( ) ( ) ( ) P

a inv s a

*

* *

( ) ( )( )( ) ( ) N N

a a P a EEa

'( )

' ' N N

a a P

a E E a

1 0sin . ( ) /( ) K c angle z d

1 0sin arg( ) /( ) K K c d

p qp q

7/31/2019 ASP Hearing 2007

127/136

Responsible factorsSampling rateBaseline distanceNumber of microphones

7/31/2019 ASP Hearing 2007

128/136

1. Delay-and-sum:Require prior knowledge of the direction of propagationof signals i.e. delay per microphone

2. Minimum variance:These algorithms adapt their computations to thecharacteristics of the signal

3. Generalized side-lobe cancellers:Uses the delay-and-sum technique for beamforming and

adaptively cancels noise

7/31/2019 ASP Hearing 2007

129/136

The oldest and simplest beamforming technique

Add incoming signals with appropriate delay to reinforce signal withrespect to noise

))(()( 01

0

t ywt z m M

mm

)(1 t y

7/31/2019 ASP Hearing 2007

130/136

Setup similar to delay-and-sum beamformer

Weights are chosen to minimize the weighted array power output fornon-desired look directions

The weights maintain unity gain along desired direction andconstructively add the signal

11)( e Re P e Re

e Rw 11

0

7/31/2019 ASP Hearing 2007

131/136

Target-SignalFilter [H 1]

Signal Blo cking [B] Adaptive Filtering[H2]

Speech

Delay Compensation

Noise wave front

+

-

Speech wave front

Best performance among the three algorithms Adaptive filtering decreases throughput Mismatch in delay lowers array gain Reverberations reduce the effectiveness of adaptive filtering

7/31/2019 ASP Hearing 2007

132/136

Poor performance at low frequenciesSensitivity decreases as inter-microphone distance decreasesPoor noise cancellation at small baseline

7/31/2019 ASP Hearing 2007

133/136

Phase lag of border frequencies isBeampattern chosen to have null at90 degree and unity gain atbroadside

The weights are calculated atindividual frequency binsSignal is multiplied by weights infrequency domain and broughtback to time domain via IFFT

cd L

L

sinc

d U U

sin

S N

N

jkd jkd

jkd

eee

w sinsin

sin

1

S N jkd jkd eew sinsin2

1

t jnd

j M

mm eewt y

sin21

0)(

7/31/2019 ASP Hearing 2007

134/136

7/31/2019 ASP Hearing 2007

135/136

Frequency independent beamformer outperforms othertechniques in terms of recognition improvement.

7/31/2019 ASP Hearing 2007

136/136

Anatomy e.g. Pinna, Ossicles, CochleaPsychoacoustics e.g. AN coding, MaskingEngineering Applications e.g. Hearing aids, Cochlear implants, ABI

http://www.cnel.ufl.edu/~meena/ppt.htmContact: meena[@]cnel.ufl.edu

ASP Hearing 2007

Documents

Transcript of ASP Hearing 2007