IIT Bombay {pcpandey, [email protected]} Intro. Proc. Schemes Evaluation Results Conclusion Intro. Proc. Schemes Evaluation Results Conclusion

I

IT B

omba

y{p

cpan

dey ,

alic

enc@

ee.ii

t b.a

c.in

}

• Intro. • Proc. Schemes • Evaluation • Results • Conclusion

ICA

200

4 , K

yoto

, Jap

an, A

pril

4 - 9

, 200

4

1

ICA 2004, Kyoto, April 4-9, 2004 / Session: HRS43 Paper No. 00413 (Tu.5.X2.5)

Evaluation of Speech Processing Schemes Using Binaural Dichotic

Presentation to Reduce the Effect of Masking in Hearing-Impaired Listeners

By

A.N. CheeranP.C. Pandey

IIT Bombay, Indiahttp://www.ee.iitb.ac.in

I

IT B

omba

y{p

cpan

dey ,

alic

enc@

ee.ii

t b.a

c.in

}


ICA

200

4 , K

yoto

, Jap

an, A

pril

4 - 9

, 200

4

2

Outline of the presentation

● Introduction ● Processing schemes ● Evaluation ● Test results ● Conclusion

I

IT B

omba

y{p

cpan

dey ,

alic

enc@

ee.ii

t b.a

c.in

}


ICA

200

4 , K

yoto

, Jap

an, A

pril

4 - 9

, 200

4

3

Introduction (1/9)

Outer ear Inner earMiddle ear

External canal

Pinna

Nasal cavity

Cochlea

Cochlear nerve

Vestibular nerve

Oval windowRound windowEustachian tube

Eardrum (Tympanicmembrane)

Vestibular apparatus with semicircular canals

MalleusIncusStapes

Hearing impairments• Conductive • Sensorineural • Central • Functional

Peripheral auditory system

I

IT B

omba

y{p

cpan

dey ,

alic

enc@

ee.ii

t b.a

c.in

}


ICA

200

4 , K

yoto

, Jap

an, A

pril

4 - 9

, 200

4

4

Introduction (2/9)

Causes of Sensorineural Loss----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

• Damage to hair cells in the cochlea

• Degeneration of auditory nerve fibers

Sensorineural Loss Characteristics-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

• Increased hearing thresholds

• Reduced dynamic range, loudness recruitment

• Poor freq. selectivity, increased spectral masking

• Poor time resolution, increased temporal masking

I

IT B

omba

y{p

cpan

dey ,

alic

enc@

ee.ii

t b.a

c.in

}


ICA

200

4 , K

yoto

, Jap

an, A

pril

4 - 9

, 200

4

5

Introduction (3/9)

Effects of Increased Spectral Masking----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

-

Broader auditory filters Smearing of spectral peaks & valleys Reduction in internal spectral contrast. Reduced discrimination of consonantal place feature.

Effects of Increased Temporal Masking----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

-

Forward & backward masking of weak segments by strong ones. Reduced ability to discriminate sub-phonemic segments

like noise bursts, voice-onset time, formant transitions. Reduced discrimination of duration & other

consonantal features.

I

IT B

omba

y{p

cpan

dey ,

alic

enc@

ee.ii

t b.a

c.in

}


ICA

200

4 , K

yoto

, Jap

an, A

pril

4 - 9

, 200

4

6

Introduction (4/9)

Dichotic Presentation for Bilateral Residual Hearing

Masking at the peripheral level.

Information integration from the two ears at higher levels.

Binaural dichotic presentation for bilateral residual hearing: speech signal split into a complementary form.

Signal components likely to mask each other presented to different ears.

Improved speech recognition due to reduction in the effects of masking.

I

IT B

omba

y{p

cpan

dey ,

alic

enc@

ee.ii

t b.a

c.in

}


ICA

200

4 , K

yoto

, Jap

an, A

pril

4 - 9

, 200

4

7

Introduction (5/9)

Binaural Presentation Schemes

Spectral SplittingFiltering by two complementary comb filters: Sensory cells corresponding to alternate filter bands on the basilar membrane not stimulated. Reduction in spectral masking. Better consonantal place reception.

Temporal SplittingGating by two complementary fading functions: Cyclic stimulation and relaxation of all the sensory cells Reduction in temporal masking Better duration and place reception

I

IT B

omba

y{p

cpan

dey ,

alic

enc@

ee.ii

t b.a

c.in

}


ICA

200

4 , K

yoto

, Jap

an, A

pril

4 - 9

, 200

4

8

Introduction (6/9)

Binaural Presentation Schemes (contd.)

Combined Splitting Processing by two time-varying complementary comb filters

Sensory cells in alternate bands in a given ear stimulated at a time. All the sensory cells on the basilar membrane get periodic relaxation from stimulation.

Reduction in spectral and temporal masking

Better reception of consonantal duration, place, and other features.

Better overall speech recognition & reduction in load on perception process

I

IT B

omba

y{p

cpan

dey ,

alic

enc@

ee.ii

t b.a

c.in

}


ICA

200

4 , K

yoto

, Jap

an, A

pril

4 - 9

, 200

4

9

Introduction (7/9)

Earlier Work

Lunner et al. [Linkoping, 1993]. • Comb filters using filter bank with constant BW (700 Hz) filters & band gain adjustment : Improvement of 2 dB in SNR. • Combined splitting by symmetrical switching (at 50 Hz) of comb filter bands: No further improvement. Poor sound quality due to switching.

Chaudhari & Pandey [IIT Bombay, 1998]. • Comb filters with auditory critical bands and sharp transitions. Improvement in reception of primarily the consonantal place feature. Reduction in response time. • Individually adjustable frequency response further improvement, but not distinctly for place.

I

IT B

omba

y{p

cpan

dey ,

alic

enc@

ee.ii

t b.a

c.in

}


ICA

200

4 , K

yoto

, Jap

an, A

pril

4 - 9

, 200

4

10

Introduction (8/9)

Earlier Work (contd.)Jangamashetti & Pandey [IIT Bombay, 2003]

Temporal splitting using symmetrical inter-aural switching of 20 ms along with overlap and various fading functions.

Improvement mainly in the reception of the duration feature

Jangamashetti, Cheeran & Pandey [IIT Bombay, 2003]

Combined splitting using time-varying comb filters with constant sweep cycle of 20 ms and with 2, 4, 8, & 16 shiftings

Improvement in reception of both duration & place features

I

IT B

omba

y{p

cpan

dey ,

alic

enc@

ee.ii

t b.a

c.in

}


ICA

200

4 , K

yoto

, Jap

an, A

pril

4 - 9

, 200

4

11

Introduction (9/9)

Objective of the present study

Implementation of binaural dichotic presentation schemes & evaluation through listening tests

Spectral splitting with perceptually balanced comb filters

Temporal splitting with trapezoidal fading functions of inter-aural switching periods of 20, 40, 80 ms

Combined splitting with cyclically swept comb filters with sweep cycle of 20, 40, 80 ms and 4, 8, and 16 shiftings

I

IT B

omba

y{p

cpan

dey ,

alic

enc@

ee.ii

t b.a

c.in

}


ICA

200

4 , K

yoto

, Jap

an, A

pril

4 - 9

, 200

4

12

Parameters:

Transition width: 78 Hz – 117 Hz, Inter-band crossover gains: -4 to -6 dB,

Pass band ripple < 1 dB.

Processing schemes (1/3)

Spectral Splitting with Perceptually Balanced Comb Filters

I

IT B

omba

y{p

cpan

dey ,

alic

enc@

ee.ii

t b.a

c.in

}


ICA

200

4 , K

yoto

, Jap

an, A

pril

4 - 9

, 200

4

13


Temporal Splitting with Trapezoidal Fading

Parameters:

Inter-aural switching period (N ) : 20, 40, 80 ms

Duty cycle (L) : 70 % of N , Transition duration (M ) : 3 ms

I

IT B

omba

y{p

cpan

dey ,

alic

enc@

ee.ii

t b.a

c.in

}


ICA

200

4 , K

yoto

, Jap

an, A

pril

4 - 9

, 200

4

14


Combined Splitting with Time-varying Comb Filters

Parameters: Sweep cycle duration : 20, 40, 80, 120, 160 ms No of shiftings (m) : 4, 8, 16

I

IT B

omba

y{p

cpan

dey ,

alic

enc@

ee.ii

t b.a

c.in

}


ICA

200

4 , K

yoto

, Jap

an, A

pril

4 - 9

, 200

4

15

Evaluation

Listening Tests for Evaluation

Type of evaluation: Open-set

Test material: Phonetically balanced set of monosyllables (used at AYJNIHH, Mumbai) in the first language of the subjects.

Subjects & listening condition: • Seven normal hearing S’s with loss simulated by adding Gaussian noise with short-time SNRs of, 3, 0, -3, -6, -9 dB. MCL (70-75 dB SPL).

Performance measurement: • Response time (indication of load on perceptual processing) • Recognition scores

I

IT B

omba

y{p

cpan

dey ,

alic

enc@

ee.ii

t b.a

c.in

}


ICA

200

4 , K

yoto

, Jap

an, A

pril

4 - 9

, 200

4

16

Results (1/4) Listening test results

Averaged scores for normal hearing S’s (7) with simulated loss

I

IT B

omba

y{p

cpan

dey ,

alic

enc@

ee.ii

t b.a

c.in

}


ICA

200

4 , K

yoto

, Jap

an, A

pril

4 - 9

, 200

4

17

Results (2/4)

Averaged Recogn. Scores vs SNR

I

IT B

omba

y{p

cpan

dey ,

alic

enc@

ee.ii

t b.a

c.in

}


ICA

200

4 , K

yoto

, Jap

an, A

pril

4 - 9

, 200

4

18

Processing scheme Rel. imp. in rec. score (%)

-9 dB SNR -6 dB SNR -3 dB SNR

SS

TS-20

TS-40

TS-80

CS-20/4

CS-20/8

CS-20/16

CS-40/4

142.8 93.2 30.1

31.8 26.9 8.1

23.4 25.4 4.6

-30.4 -21.3 -9.5

82.2 54.5 10.5

83.8 61.4 12.5

90.3 54.1 17.4

97.5 69.3 17.4

Unprocessed (% rec. score) = 23.9 at –9dB, 39.9 dB at –6 dB & 66.3 at –3 dB

Results (3/4)

Relative improvements in recogn. scores

I

IT B

omba

y{p

cpan

dey ,

alic

enc@

ee.ii

t b.a

c.in

}


ICA

200

4 , K

yoto

, Jap

an, A

pril

4 - 9

, 200

4

19

Processing scheme Rel. imp. in rec. score (%)

-9 dB SNR -6 dB SNR -3 dB SNR

CS-40/8

CS-40/16

CS-80/4

CS-80/8

CS-80/16

CS-120/8

CS-120/16

CS-160/8

CS-160/16

88.6 64.0 16.4

110.6 68.1 21.6

106.8 71.6 27.1

130.2 75.4 26.3

118.2 81.0 27.4

100.9 70.1 22.6

108.5 65.0 24.6

104.3 79.0 24.8

103.4 73.1 22.8

Unprocessed (% rec. score) = 23.9 at –9dB, 39.9 dB at –6 dB & 66.3 at –3 dB

Results (4/4)

Relative improvements in recogn. Scores (contd.)

I

IT B

omba

y{p

cpan

dey ,

alic

enc@

ee.ii

t b.a

c.in

}


ICA

200

4 , K

yoto

, Jap

an, A

pril

4 - 9

, 200

4

20

Conclusion (1/2)

Summary of results

• Spectral splitting showed highest relative improvement at all SNR condition• For 60 % recognition score spectral splitting gave an improvement of 5 dB SNR

• Combined splitting at sweep cycle 80 ms with 8 and 16 shiftings showed improvements close to spectral splitting• Results similar for 8 and 16 shiftings

• Temporal splitting was best with inter-aural switching of 20 ms• Inter-aural switching of 80 ms showed degradation

I

IT B

omba

y{p

cpan

dey ,

alic

enc@

ee.ii

t b.a

c.in

}


ICA

200

4 , K

yoto

, Jap

an, A

pril

4 - 9

, 200

4

21

Conclusion (2/2)

Further work

Evaluation by conducting listening tests on moderate bilateral sensorineural hearing-impaired persons.

Combining audiogram dependant filtering and multi-band compression with dichotic presentation.

Implementation of dichotic presentation schemes in wearable hearing aids, with personalized parameter setting.

I

IT B

omba

y{p

cpan

dey ,

alic

enc@

ee.ii

t b.a

c.in

}


ICA

200

4 , K

yoto

, Jap

an, A

pril

4 - 9

, 200

4

22

Documents

IIT Bombay {pcpandey, [email protected]} Intro. Proc. Schemes Evaluation Results Conclusion Intro. Proc. Schemes Evaluation Results Conclusion