Pandurangarao N. Kulkarni

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.

Optimizing the Comb Filters for Spectral Splitting of Speech to Reduce the Effect of Spectral Masking

Sensorineural hearing impairment is associated with widening of auditory filters, resulting in poor frequency selectivity with an increased susceptibility to masking. Earlier studies have shown that binaural dichotic presentation, using critical bandwidth based spectral splitting with perceptually balanced comb filters, helps in reducing the effect of spectral masking for persons with moderate bilateral sensorineural hearing impairment In spectral splitting, the speech signal is filtered using a pair of linear phase FIR comb filters with complementary magnitude responses for binaural dichotic presentation. The objective of the present study is to optimize the comb filters with respect to the number of bands and bandwidth. Three different pairs of comb filters are investigated: constant bandwidth filters, critical band based filters, and 1/3 octave bandwidth filters. Evaluation of spectral splitting schemes, using these filters, through listening tests, indicate that 1/3 octave band and critical band based filters are superior to constant bandwidth filters.

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.

FPGA-based implementation of comb filters using sequential multiply-accumulate operations for use in binaural hearing aids

Sensorineural hearing loss, caused by damage to the cochlea in the inner ear or to the auditory nerve, is associated with reduced dynamic range and increased spectral and temporal masking and results in degraded speech perception. For listeners using binaural hearing aids, spectral splitting of the speech signal can be used to reduce the effects of increased intraspeech spectral masking thereby improving speech perception. It has been reported that a pair of linear-phase comb filters, with auditory critical bandwidth based complementary magnitude responses selected for perceptual balance of loudness, resulted in a significant improvement in speech perception without affecting localization of broadband sound sources. The paper presents an investigation for FPGA-based implementation of these comb filters for use in binaural hearing aids. It is shown that a processing architecture employing sequential multiply-accumulate operations results in an efficient implementation.

FPGA based implementation of comb filters for use in binaural hearing aids for reducing intraspeech spectral masking

Sensorineural hearing impairment is associated with decreased speech perception due to increased intraspeech spectral masking. For persons with moderate bilateral sensorineural loss, binaural dichotic presentation using a pair of complementary comb filters can reduce the effects of increased intraspeech spectral masking and thereby improve speech perception. It has been earlier shown that use of comb filters based on auditory critical bandwidths, with magnitude responses designed for perceptual balance of loudness and linear phase responses, resulted in a significant improvement in speech perception without adversely affecting localization of broadband sound sources. An FPGA-based implementation of these 513-coefficient filters with sampling frequency of 10 kHz is carried out for use in binaural hearing aids. Implementation using a 16bit codec and 15-bit integer filter coefficients used 47%, 34%, and 53% of combinational functions, logic registers, and logic elements, respectively, available on “Altera Cyclone II EP2C70F896C6” FPGA. The resulting magnitude responses have a close match to the offline floating-point implementation.