1. ♠♠♠♠ 1Intro 2.Loudness 3.Method. 4.Results 5.Concl. ♦♦ ◄◄ ► ► 1/161Intro 2.Loudness 3.Method. 4.Results 5.Concl. ♦♦ ◄ ► IIT Bombay 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, dsj1869@rediffmail.com http://www.ee.iitb.ac.in/~spilab IIT Bombay, India

2. ♠♠♠♠ 1Intro 2.Loudness 3.Method. 4.Results 5.Concl. ♦♦ ◄◄ ► ► 2/161Intro 2.Loudness 3.Method. 4.Results 5.Concl. ♦♦ ◄ ► IIT Bombay OUTLINE 1Introduction 2Loudness of binaural presentation 3Methodology 4Results & discussion 5Conclusions

3. ♠♠♠♠ 1Intro 2.Loudness 3.Method. 4.Results 5.Concl. ♦♦ ◄◄ ► ► 3/161Intro 2.Loudness 3.Method. 4.Results 5.Concl. ♦♦ ◄ ► IIT Bombay 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 Intro.1/2 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.

4. ♠♠♠♠ 1Intro 2.Loudness 3.Method. 4.Results 5.Concl. ♦♦ ◄◄ ► ► 4/161Intro 2.Loudness 3.Method. 4.Results 5.Concl. ♦♦ ◄ ► IIT Bombay 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. Intro. 2/2

5. ♠♠♠♠ 1Intro 2.Loudness 3.Method. 4.Results 5.Concl. ♦♦ ◄◄ ► ► 5/161Intro 2.Loudness 3.Method. 4.Results 5.Concl. ♦♦ ◄ ► IIT Bombay 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. Loudness1/2

6. ♠♠♠♠ 1Intro 2.Loudness 3.Method. 4.Results 5.Concl. ♦♦ ◄◄ ► ► 6/161Intro 2.Loudness 3.Method. 4.Results 5.Concl. ♦♦ ◄ ► IIT Bombay 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). Loudness 2/2

7. ♠♠♠♠ 1Intro 2.Loudness 3.Method. 4.Results 5.Concl. ♦♦ ◄◄ ► ► 7/161Intro 2.Loudness 3.Method. 4.Results 5.Concl. ♦♦ ◄ ► IIT Bombay 3 METHODOLOGY 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. Method.1/2

8. ♠♠♠♠ 1Intro 2.Loudness 3.Method. 4.Results 5.Concl. ♦♦ ◄◄ ► ► 8/161Intro 2.Loudness 3.Method. 4.Results 5.Concl. ♦♦ ◄ ► IIT Bombay 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) Method.2/2

9. ♠♠♠♠ 1Intro 2.Loudness 3.Method. 4.Results 5.Concl. ♦♦ ◄◄ ► ► 9/161Intro 2.Loudness 3.Method. 4.Results 5.Concl. ♦♦ ◄ ► IIT Bombay 4 RESULTS Exp. I (different test tones, MCL, 8 n.h. S’s) Approx. linear relation between the scaling factors Results 1/6

10. ♠♠♠♠ 1Intro 2.Loudness 3.Method. 4.Results 5.Concl. ♦♦ ◄◄ ► ► 10/161Intro 2.Loudness 3.Method. 4.Results 5.Concl. ♦♦ ◄ ► IIT Bombay Exp. II (500 Hz, 3 present. levels, 6 n.h. S’s) Results 2/6 Approx. linear relation between the scaling factors

11. ♠♠♠♠ 1Intro 2.Loudness 3.Method. 4.Results 5.Concl. ♦♦ ◄◄ ► ► 11/161Intro 2.Loudness 3.Method. 4.Results 5.Concl. ♦♦ ◄ ► IIT Bombay Shifted curves, (Marks,1978) Results 3/6 Relation on dB scale (all test tones, presentation levels)

12. ♠♠♠♠ 1Intro 2.Loudness 3.Method. 4.Results 5.Concl. ♦♦ ◄◄ ► ► 12/161Intro 2.Loudness 3.Method. 4.Results 5.Concl. ♦♦ ◄ ► IIT Bombay Monaural vs. binaural loudness match ▪ Binaural loudness ≈ linear sum of left and right ear loudness ▪ Loudness  (amplitude) p  Monaural vs binaural loudness match: Plot of error in β (estimated – observed) vs. p Min. error for p ≈ 1  Filter responses should be complementary on a linear scale. Results 4/6

13. ♠♠♠♠ 1Intro 2.Loudness 3.Method. 4.Results 5.Concl. ♦♦ ◄◄ ► ► 13/161Intro 2.Loudness 3.Method. 4.Results 5.Concl. ♦♦ ◄ ► IIT Bombay 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 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) Results 5/6

14. ♠♠♠♠ 1Intro 2.Loudness 3.Method. 4.Results 5.Concl. ♦♦ ◄◄ ► ► 14/161Intro 2.Loudness 3.Method. 4.Results 5.Concl. ♦♦ ◄ ► IIT Bombay 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. Results 6/6

15. ♠♠♠♠ 1Intro 2.Loudness 3.Method. 4.Results 5.Concl. ♦♦ ◄◄ ► ► 15/161Intro 2.Loudness 3.Method. 4.Results 5.Concl. ♦♦ ◄ ► IIT Bombay 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. Concl. 1/1

16. ♠♠♠♠ 1Intro 2.Loudness 3.Method. 4.Results 5.Concl. ♦♦ ◄◄ ► ► 16/161Intro 2.Loudness 3.Method. 4.Results 5.Concl. ♦♦ ◄ ► IIT Bombay THANK YOU

17. ♠♠♠♠ 1Intro 2.Loudness 3.Method. 4.Results 5.Concl. ♦♦ ◄◄ ► ► 17/161Intro 2.Loudness 3.Method. 4.Results 5.Concl. ♦♦ ◄ ► IIT Bombay 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.

18. ♠♠♠♠ 1Intro 2.Loudness 3.Method. 4.Results 5.Concl. ♦♦ ◄◄ ► ► 18/161Intro 2.Loudness 3.Method. 4.Results 5.Concl. ♦♦ ◄ ► IIT Bombay 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). [5] A. Murase, F. Nakajima, S. Sakamoto, Y. Suzuki, and T. Kawase, “Effect and sound localization with dichoticlistening hearing aids,” Proc. 18th Int. Congress Acoust. (ICA), Kyoto, Japan, II-1519 – 1522, 2004. [6] P. N. Kulkarni, P. C. Pandey, and D. S. Jangamashetti, “Perceptually balanced filter response for binaural dichotic presentation to reduce the effect of spectral masking,” (abstract) J. Acoust. Soc. Am. 120, 3253 (2006). [7] B. Scharf, “Binaural loudness summation as a function of bandwidth,” Proc. 6th Int. Congress Acoust. (ICA), Tokyo. 25 – 28, 1968. [8] B. Scharf, “Dichotic summation of loudness,” J. Acoust. Soc. Am. 45, 1193 – 1205 (1969). [9] J. H. Hall, and A. D. Harvey, “Diotic loudness summation in normal and impaired hearing,” J. Speech Hear. Res. 28, 445 – 448 (1985). [10] D. B. Hawkins, R. A. Prosek, B. E. Walden, and A. A. Montgomery, “Binaural loudness summation in hearing impaired, ” J. Speech Hear. Res. 30, 37 – 43 (1987). [11] E. Zwicker, and G. B. Henning, “On the effect of interaural phase differences on loudness,” Hearing Research. 53, 141 – 152 (1991). [12] A. N. Cheeran, Speech processing with dichotic presentation for binaural hearing aids for moderate bilateral sensorineural loss, Ph.D. Thesis, School of Biosciences and Bioengineering, Indian Institute of Technology Bombay, India, 2005. [13] S. Whilby, M. Florentine, E. Wagner, and J. Marozeau, “Monaural and binaural loudness of 5 and 200 ms tones in normal and impaired hearing,” J. Acoust. Soc. Am. 119, 3931 – 3939 (2006). [14] L. E. Marks, “Binaural summation of the loudness of pure tones,” J. Acoust. Soc. Am. 64, 107 – 113 (1978). [15] S. S. Stevens, “The direct estimation of sensory magnitudes- loudness,” Am. J. Psychol. 69, 1 – 15 (1956). [16] G. S. Reynolds and S. S. Stevens, “Binaural summation of loudness,” J. Acoust. Soc. Am. 32, 1337 – 1344 (1960). [17] J. C. Stevens, and M. Guirao, “Individual loudness functions,” J. Acoust. Soc. Am. 36, 2210 – 2213 (1964). [18] B. Scharf, and D. Fishken, “Binaural summation of loudness: Reconsidered,” J. Exp. Psychol. 86, 374 – 379 (1970). [19] H. Fletcher, and W. A. Munson, “Loudness, its definition, measurement and calculation,” J. Acoust. Soc. Am. 5, 82–108 (1933). [20] R. P. Hellman and J. J. Zwislocki “Monaural loudness summation at 1000 cps and interaural summation,” J. Acoust. Soc. Am. 35, 856 – 865 (1963). [21] R. W. L. Kortekaas and A. Kohlrausch “Psychoacoustical evaluation of PSOLA II. Ddouble-formant stimuli and the role of vocal perturbation,” J. Acoust. Soc. Am. 105, 522-535 (1999).