Dakshayani S. Jangamashetti

Binaural dichotic presentation to reduce the effects of spectral masking in moderate bilateral sensorineural hearing loss.

Abstract Objective: The objective of the study was to evaluate the effectiveness of binaural dichotic presentation using comb filters with complementary magnitude responses, based on fixed bandwidth and auditory critical bandwidth, in improving speech perception by persons with moderate bilateral sensorineural hearing loss, and to assess its effect on localization of the sound source. Design and Study sample: Listening tests involving consonant recognition and source direction identification were conducted on six normal-hearing subjects under simulated hearing loss and on eleven subjects with moderate bilateral sensorineural loss in quiet. Results: The tests on normal-hearing subjects showed higher recognition scores and smaller response times for the comb filters based on the auditory critical bandwidth. The tests using these comb filters on the hearing-impaired subjects resulted in an increase of 14%–31% (mean: 22%) in recognition scores and a significant decrease in response times, with no significant effect on the identification of the direction of broadband sound sources. Conclusions: The results show that dichotic presentation may be useful for speech processing in binaural hearing aids.

Multi-band frequency compression for improving speech perception by listeners with moderate sensorineural hearing loss

In multi-band frequency compression, the speech spectrum is divided into a number of analysis bands, and the spectral samples in each band are compressed towards the band center by a constant compression factor, resulting in presentation of the speech energy in relatively narrow bands, for reducing the effect of increased intraspeech spectral masking associated with sensorineural hearing loss. Earlier investigation assessing the quality of the processed speech showed best results for auditory critical bandwidth based compression using spectral segment mapping and pitch-synchronous analysis-synthesis. The objective of the present investigation is to evaluate the effectiveness of the technique in improving speech perception by listeners with moderate to severe sensorineural loss and to optimize the technique with respect to the compression factor. The listening tests showed maximum improvement in speech perception for a compression factor of 0.6, with an improvement of 9%-21% in the recognition scores for consonants and a significant reduction in response times.

Perceptually balanced filter response for binaural dichotic presentation to reduce the effect of spectral masking

Earlier investigations show that the scheme of binaural dichotic presentation with spectral splitting of speech signal helps in reducing the effect of spectral masking for persons with moderate bilateral sensorineural hearing impairment. Speech perception improved by employing filters with interband crossover gain adjusted between 4 and 6 dB below the pass band gain. The relationship between scaling factors for a tone presented to the two ears, so that perceived loudness is that of a monaural presentation, is investigated for design of comb filters with improved perceptually balanced response. Results from the listening tests show that, for perceptual balance, the sum of the two scaling factors should be constant, indicating that the magnitude response of the comb filters should be complementary on a linear scale.

Multi-band frequency compression for reducing the effects of spectral masking

Sensorineural hearing loss is associated with widening of auditory filter bandwidths, leading to increased spectral masking and degraded speech perception. Multi-band frequency compression can be used for reducing the effects of spectral masking. In this technique, the speech spectrum is divided into a number of analysis bands and spectral samples in each of these bands are compressed towards the band center by a constant compression factor. Implementation of the scheme with different types of frequency mappings, bandwidths, and segmentation for processing is investigated. Listening tests conducted for assessing the quality and intelligibility of the processed speech gave best results for critical bandwidth based compression using spectral segment mapping and pitch-synchronous processing.

Multi-band frequency compression for sensorineural hearing impairment

Sensorineural hearing loss is associated with widening of the auditory filters, leading to increased spectral masking and degraded speech perception. Multi-band frequency compression can be used for reducing the effect of spectral masking. The speech spectrum is divided into a number of bands and spectral samples in each of these bands are compressed towards the band center, by a constant compression factor. In the present study, we have investigated the effectiveness of the scheme for different compression factors, in improving the speech perception. Evaluation of the scheme using the modified rhyme test showed maximum improvement in recognition scores for compression factor of 0.6: about 17 % for the normal-hearing subjects under simulated hearing loss, and 6–21 % for the subjects with moderate to severe sensorineural hearing loss.

Binaural dichotic presentation to reduce the effect of increased temporal and spectral masking in sensorineural hearing impairment

Sensorineural hearing loss is characterized by increased temporal and spectral masking, resulting in degraded speech perception. Earlier investigations have shown that binaural dichotic presentation using comb filters with complementary magnitude responses improved speech perception, particularly the place feature. Further, inter‐aural switching with periodic trapezoidal fading functions improved the perception of duration feature. For simultaneously reducing the effect of the two types of masking, a scheme has been devised with a pair of time‐varying comb filters, with bands corresponding to auditory critical bands. Thus the spectral components in neighboring critical bands do not mask each other, and the sensory cells on the basilar membrane get a relaxation time due to sweeping of the filter passbands. The scheme was implemented using linear phase 256‐coefficient FIR filters. Magnitude responses were cyclically swept with 20‐ms period, in steps by selecting the filter coefficients for each step from a pre‐calculated set. Listening tests involved closed set identification of 12 vowel–consonant–vowel syllables. The processing scheme resulted in the improvement of recognition scores, response time, and transmission of features, particularly place and duration, indicating reduction in the effect of spectral and temporal masking.

Design of comb filters based on auditory filter bandwidths for binaural dichotic presentation for persons with sensorineural hearing impairment

Splitting of speech into two signals by comb filters having complementary magnitude response and presenting these signals to the two ears has helped in improving the perception for persons with bilateral sensorineural hearing loss. An investigation is carried out to improve the comb filters based on auditory critical bands, with the objective of minimizing the perceived spectral distortion. Listening tests were conducted to find the difference in intensity with monaural and binaural presentations for equal loudness perception. Based on the results obtained, 256-coefficient linear phase FIR comb filters were designed using a frequency sampling technique, to obtain magnitude response with pass band ripple of 1 dB, stop band attenuation of 30 dB, and crossovers adjusted to lie between -4 dB and -6 dB with respect to pass band response. Listening tests involving closed set identification of 12 vowel-consonant-vowel syllables were conducted, to compare the performance of the new comb filter with the filter with sharp transitions. The new comb filters resulted in a higher improvement of recognition scores and relative information transmission.

Optimal sweep cycle for time‐varying comb filters for binaural dichotic presentation to improve speech perception in sensorineural hearing impairment

In a previous investigation [P. C. Pandey et al., J. Acoust. Soc. Am. 110, 2705 (2001)], a scheme using binaural dichotic presentation was devised for simultaneously reducing the effect of increased temporal and spectral masking in bilateral sensorineural hearing impairment. Speech was processed by a pair of time‐varying comb filters with passbands corresponding to cyclically swept auditory critical bands, with the objective that spectral components in neighboring critical bands do not mask each other and sweeping of filter passbands provides relaxation time to the sensory cells on the basilar membrane. Presently investigation is carried out to find the optimal value of the sweep cycle. Comb filters used were 256‐coefficient linear phase filters, with transition crossovers adjusted for low perceived spectral distortion, 1 dB passband ripple, 30 dB stopband attenuation, and 78–117 Hz transition width. Acoustic stimuli consisted of swept sine wave and running speech from a male and a female speaker. Bilater...

Comb filters for binaural dichotic presentation to improve speech perception by persons with bilateral sensorineural hearing impairment

Intelligibility of speech for persons with sensorineural hearing impairment gets reduced due to increased spectral masking. For persons with bilateral loss, improved speech perception has been reported with binaural dichotic presentation using comb filters having complementary magnitude responses, based on auditory critical bands. In this scheme, spectral components in adjacent critical bands do not mask each other as they get presented to different ears. The objective here was to design a set of comb filters with transition crossovers adjusted for a low perceived spectral distortion. For this, a slowly swept tone presented through the two comb filters should not have a change in its perceived loudness at crossover frequencies. Experiments showed that the change in loudness was negligible with crossover response lying between −4 dB and −6 dB with respect to passband response. With this constraint for response at the crossover frequencies, comb filters with responses corresponding to 18 critical bands were...