Transcript presentation_pnk_ica2010

ICA 2010 : 20th Int. Congress on Acoustics, 23-27 August 2010, Sydney, Australia
[Tues, 24thAug, R.201, Speech Perception 1, 08:20]
Study of Perceptual Balance for
Designing Comb Filters
for Binaural Dichotic Presentation
P. N. Kulkarni
P. C. Pandey
D. S. Jangamashetti
{pnkulkarni,pcpandey}@ee.iitb.ac.in, [email protected]
http://www.ee.iitb.ac.in/~spilab
IIT Bombay, India
♠♠ 1Intro 2.Loudness 3.Method. 4.Results 5.Concl.
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OUTLINE
1 Introduction
2 Loudness of binaural presentation
3 Methodology
4 Results & discussion
5 Conclusions
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Intro.1/2
1 INTRODUCTION
Binaural dichotic presentation by spectral splitting,
using a pair of complementary comb filters,
to reduce the effect of increased spectral masking
in sensorineural hearing loss
Comb filter
Left ear
>
Input
signal
Comb filter
Right ear
Left ear
Right ear
Magnitude (dB)
0
-20
-40
-60
0
1
2
3
Frequency (kHz)
4
5
Spectral components of the speech signal in the alternate bands presented
to the left and the right ears, and those in the transition bands presented to
both the ears.
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Intro. 2/2
Comb filter responses
● Linear phase response.
● Magnitude responses selected for band separation and
perceptual balance of spectral components
▪ Low pass-band ripple, large stop-band attenuation.
▪ Perceived loudness for spectral components in the transition bands
should be the same as those in pass bands.
● Mixed results in earlier studies: from no advantage to
improvements corresponding to SNR advantage of 2 – 9 dB.
Variation in the results may be attributed to the different
magnitude responses of the comb filters in different studies.
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Loudness1/2
2 LOUDNESS OF BINAURAL PRESENTATION
Some earlier studies
Scharf (1968). Binaural level difference for equal loudness (BLDEL): 5 dB at low
presentation levels, 7 dB at moderate and 6 dB at high presentation levels.
Marks (1978). Binaural summation of loudness (0.1, 0.4, 1 kHz): linear additivity of
the numerical responses for loudness. BLDEL: 5 – 7 dB.
Hall & Harvey (1985). BLDEL (2 kHz tone, 70 and 80 dB SPL): 3 - 4 dB for h.i. S’s,
8–9 dB for n.h. S’s. BLDEL(2 kHz tone, 90 dB SPL): 9 dB for both groups.
Hawkins et al. (1987). BLDEL (4 kHz, MCL) 5 – 12 dB for both n.h. & h.i. S’s.
Zwicker and Henning (1991). BLDEL (250 Hz, 710 Hz, 2 kHz): 10 dB.
Cheeran (2005): BLDEL (0.25, 1, 2, 4 kHz, /a/, 85 dB SPL): 4 – 12 dB.
Whilby et al. (2006): for 1 kHz pure tone, BLDEL (1 kHz): 2 – 15 dB for n.h. S’s, and
1.5 – 12 dB for h.i. S’s.
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Loudness 2/2
Objective of the present study
To find the relation between comb filter gains for perceptually
balanced loudness of spectral components.
Investigations
▪ Perceptual balance in binaural hearing: relation between signal
amplitudes presented to the the left and right ears to evoke the
same loudness as monaural presentation.
▪ Comparison of filter responses used in the earlier studies.
▪ Design of perceptually balanced comb filter pair based on critical
bandwidth, and evaluation by conducting listening tests on n.h.
S’s (in noise) and h.i. S’s (in quiet).
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Method.1/2
3 METHODOLOGY
×
To left ear
a
>
Input
signal
β
×
To right ear
Listening tests
Monaural vs. binaural loudness comparison (L, E, H) , using 3I - 3AFC paradigm
▪ Presentation: ref. (mono) –– test (binaural) – ref. (mono), 0.5 s silence separation.
▪ Scaling factors α and β selected randomly over 0 to 1 in steps of 0.1 .
▪ Gain compensation for the imbalance in the headphone responses.
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Method.2/2
Experiment I
0.25, 0.5, 1, 2 kHz tones, MCL, 8 n.h. S’s
No. of presentations/subject = 484
(4 test frequencies × 11 values of α × 11 values of β)
Experiment II
0.5 kHz tone, MCL – 6 dB, MCL, MCL + 6 dB, 6 n.h. S’s
No. of presentations/subject = 363
(3 presentation levels × 11 values of α × 11 values of β)
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Results 1/6
4 RESULTS
1.0
(different
test tones,
MCL, 8 n.h. S’s)
Approx. linear
relation between
the scaling factors
Right ear scaling factor
250 Hz
Exp. I
500 Hz
0.8
1 kHz
2 kHz
0.6
0.4
0.2
0.0
0.0
0.2
0.4
0.6
0.8
Left ear scaling factor
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1.0
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Results 2/6
Exp. II
Approx. linear
relation between
the scaling factors
Right ear scaling factor
(500 Hz,
3 present. levels,
6 n.h. S’s)
1.0
MCL + 6 dB
0.8
MCL
MCL - 6 dB
0.6
0.4
0.2
0.0
0.0
0.2
0.4
0.6
0.8
1.0
Left ear scaling factor
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Results 3/6
10
Relation on
dB scale
0
Right ear scaling factor (dB)
(all test tones,
presentation
levels)
-10
MCL, 250 Hz
-20
MCL, 500 Hz
MCL, 1 kHz
-30
MCL, 2 kHz
MCL+6, 500 Hz
-40
MCL- 6, 500 Hz
Shifted curves,
(Marks,1978)
-50
-30
-25
-20
-15
-10
-5
0
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Left ear scaling factor (dB)
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Results 4/6
Monaural vs. binaural loudness match
▪ Binaural loudness ≈ linear sum of left and right ear loudness
▪ Loudness  (amplitude)p
 Monaural vs binaural loudness match: a p   p  1
0.6
Min. error for p ≈ 1
 Filter responses
should be
complementary on a
linear scale.
250 Hz
500 Hz
1 kHz
0.4
2 kHz
RMS error
Plot of error in β
(estimated – observed)
vs. p
0.2
0.0
0.0
0.5
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1.0
p
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1.5
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Results 5/6
Design of comb filter pair
Critical bandwidth (CB) based comb filter pair, designed as 512-coeff. linear
phase FIR filters, using freq. sampling technique (S.R. = 10 kHz, pass band
ripple < 1 dB, stop band attenuation > 30 dB).
Comparison
of filter
responses
ACB: CB based filters with
complementary gains
CHE: Cheeran & Pandey (2004)
LUN: Lunner et al. (1993)
LYR: Lyregaard (1982)
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Results 6/6
Evaluation by listening tests
Consonant recognition using modified rhyme test (MRT)
 6 n.h. S’s in the presence of broad-band masking noise: SNR
advantage of 12 dB at 75 % recognition score.
 11 S’s with moderate bilateral sensorineural loss: score
improvement of 14–31 %.
 Reduction in response time
0.04 – 0.33 s for n.h. S’s
0.04 – 0.57 s for h.i. S’s.
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Concl. 1/1
5 CONCLUSIONS
▪ Constant sum of the amplitudes of the left and right ear tones
resulted in loudness match in binaural presentation.
▪ For perceptually balanced dichotic presentation, the magnitude
responses of the comb filters should be approximately
complementary on a linear scale.
▪ Magnitude responses of the filters used in earlier studies
exhibited a large deviation from the condition of perceptual
balance.
▪ Evaluation of critical band based comb filters designed with
perceptually balanced responses, by conducting MRT, resulted in
a significant improvement in consonant recognition and a
reduction in response time.
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THANK YOU
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P. N. Kulkarni , P. C. Pandey, D. S. Jangamashetti, “Study of perceptual balance for designing comb
filters for binaural dichotic presentation”, Proc. 20th International Congress on Acoustics ( ICA
2010), 23-27 August 2010, Sydney, Australia.
Abstract -- Earlier studies on binaural dichotic presentation by spectral splitting of speech signal
using a pair of complementary comb filters, for improving speech perception by persons with
moderate bilateral sensorineural hearing loss, have shown mixed results: from no advantage to
improvements in recognition scores corresponding to an SNR advantage of 2 - 9 dB. The filters used
in these studies had different bandwidths and realizations. For an optimal performance of the
scheme, the perceived loudness of different spectral components in the speech signal should be
balanced, especially for components in transition bands which get presented to both the ears. For
selecting magnitude responses of such filters, we have investigated the relationship between the
signal amplitudes for binaural presentation of a tone to evoke the same loudness as that of monaural
presentation. Listening tests were conducted, on eight normal-hearing subjects, for comparing the
perceived loudness of monaural presentations to that of the binaural presentation with different
combination of amplitudes for the tones presented to the left and right ears, at 250 Hz, 500 Hz, 1 kHz,
and 2 kHz. The sum of the amplitudes of the left and right tones in binaural presentation being equal
to that of the monaural tone resulted in monaural-binaural loudness match, indicating that the
magnitude response of the comb filters used for dichotic presentation should be complementary on a
linear scale. An analysis of the magnitude responses of the comb filters used in earlier studies
showed large deviations from the perceptual balance requirement, and those with smaller deviations
were more effective in improving speech perception. A pair of comb filters, based on auditory critical
bandwidths and magnitude responses closely satisfying the requirement for perceptual balance, was
designed as 512-coefficient linear phase FIR filters for sampling frequency of 10 kHz. Listening tests
on six normal-hearing subjects showed improvements in the consonant recognition scores
corresponding to an SNR advantage of approximately 12 dB. Tests using 11 subjects with moderate
bilateral sensorineural hearing loss showed an improvement in the recognition score in the range 14 31 %. Thus the investigations showed that binaural dichotic presentation using comb filters designed
for perceptual balance resulted in better speech perception.
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REFERENCES
[1] P. E. Lyregaard, “Frequency selectivity and speech intelligibility in noise,” Scand. Audiol. Suppl. 15, 113 – 122 (1982).
[2] T. Lunner, S. Arlinger, and J. Hellgren, “8-channel digital filter bank for hearing aid use: preliminary results in monaural, diotic, and
dichotic modes,” Scand. Audiol. Suppl. 38, 75 – 81 (1993).
[3] D. S. Chaudhari and P. C. Pandey, “Dichotic presentation of speech signal using critical filter band for bilateral sensorineural hearing
impairment,” Proc. 16th Int. Congress Acoust. (ICA), Seattle, Washington (1998).
[4] A. N. Cheeran and P. C. Pandey, “Evaluation of speech processing schemes using binaural dichotic presentation to reduce the effect of
masking in hearing-impaired listeners,”Proc. 18th Int. Congress Acoust. (ICA), Kyoto, Japan, II, 1523 – 1526 (2004).
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[15] S. S. Stevens, “The direct estimation of sensory magnitudes- loudness,” Am. J. Psychol. 69, 1 – 15 (1956).
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[18] B. Scharf, and D. Fishken, “Binaural summation of loudness: Reconsidered,” J. Exp. Psychol. 86, 374 – 379 (1970).
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