Maximizing Audibility and Speech Recognition with Non-Linear Frequency Compression by Estimating Audible Bandwidth

Objective—Nonlinear frequency compression attempts to restore high-frequency audibility by lowering high-frequency input signals. Methods of determining the optimal parameters that maximize speech understanding have not been evaluated. The effect of maximizing the audible bandwidth on speech recognition for a group of listeners with normal hearing is described. Design—Nonword recognition was measured with twenty normal-hearing adults. Three audiograms with different high-frequency thresholds were used to create conditions with varying high-frequency audibility. Bandwidth was manipulated using three conditions for each audiogram: conventional processing, the manufacturer’s default compression parameters, and compression parameters that optimized bandwidth. Results—Nonlinear frequency compression optimized to provide the widest audible bandwidth improved nonword recognition compared to both conventional processing and the default parameters. Conclusion—These results showed that using the widest audible bandwidth maximized speech identification when using nonlinear frequency compression. Future studies should apply these methods to listeners with hearing loss to demonstrate efficacy in clinical populations

The influence of audibility on speech recognition with nonlinear frequency compression for children and adults with hearing loss

Objective—The primary goal of nonlinear frequency compression (NFC) and other frequency lowering strategies is to increase the audibility of high-frequency sounds that are not otherwise audible with conventional hearing-aid processing due to the degree of hearing loss, limited hearing aid bandwidth or a combination of both factors. The aim of the current study was to compare estimates of speech audibility processed by NFC to improvements in speech recognition for a group of children and adults with high-frequency hearing loss. Design—Monosyllabic word recognition was measured in noise for twenty-four adults and twelve children with mild to severe sensorineural hearing loss. Stimuli were amplified based on each listener’s audiogram with conventional processing (CP) with amplitude compression or with NFC and presented under headphones using a software-based hearing aid simulator. A modification of the speech intelligibility index (SII) was used to estimate audibility of information in frequency-lowered bands. The mean improvement in SII was compared to the mean improvement in speech recognition. Results—All but two listeners experienced improvements in speech recognition with NFC compared to CP, consistent with the small increase in audibility that was estimated using the modification of the SII. Children and adults had similar improvements in speech recognition with NFC. Conclusion—Word recognition with NFC was higher than CP for children and adults with mild to severe hearing loss. The average improvement in speech recognition with NFC (7%) was consistent with the modified SII, which indicated that listeners experienced an increase in audibility with NFC compared to CP. Further studies are necessary to determine if changes in audibility with NFC are related to speech recognition with NFC for listeners with greater degrees of hearing loss, with a greater variety of compression settings, and using auditory training

FORUM:Remote testing for psychological and physiological acoustics

Acoustics research involving human participants typically takes place in specialized laboratory settings. Listening studies, for example, may present controlled sounds using calibrated transducers in sound-attenuating or anechoic chambers. In contrast, remote testing takes place outside of the laboratory in everyday settings (e.g., participants' homes). Remote testing could provide greater access to participants, larger sample sizes, and opportunities to characterize performance in typical listening environments at the cost of reduced control of environmental conditions, less precise calibration, and inconsistency in attentional state and/or response behaviors from relatively smaller sample sizes and unintuitive experimental tasks. The Acoustical Society of America Technical Committee on Psychological and Physiological Acoustics launched the Task Force on Remote Testing (https://tcppasa.org/remotetesting/) in May 2020 with goals of surveying approaches and platforms available to support remote testing and identifying challenges and considerations for prospective investigators. The results of this task force survey were made available online in the form of a set of Wiki pages and summarized in this report. This report outlines the state-of-the-art of remote testing in auditory-related research as of August 2021, which is based on the Wiki and a literature search of papers published in this area since 2020, and provides three case studies to demonstrate feasibility during practice

Maximizing Audibility and Speech Recognition with Non-Linear Frequency Compression by Estimating Audible Bandwidth

Objective—Nonlinear frequency compression attempts to restore high-frequency audibility by lowering high-frequency input signals. Methods of determining the optimal parameters that maximize speech understanding have not been evaluated. The effect of maximizing the audible bandwidth on speech recognition for a group of listeners with normal hearing is described. Design—Nonword recognition was measured with twenty normal-hearing adults. Three audiograms with different high-frequency thresholds were used to create conditions with varying high-frequency audibility. Bandwidth was manipulated using three conditions for each audiogram: conventional processing, the manufacturer’s default compression parameters, and compression parameters that optimized bandwidth. Results—Nonlinear frequency compression optimized to provide the widest audible bandwidth improved nonword recognition compared to both conventional processing and the default parameters. Conclusion—These results showed that using the widest audible bandwidth maximized speech identification when using nonlinear frequency compression. Future studies should apply these methods to listeners with hearing loss to demonstrate efficacy in clinical populations

The influence of audibility on speech recognition with nonlinear frequency compression for children and adults with hearing loss

Objective—The primary goal of nonlinear frequency compression (NFC) and other frequency lowering strategies is to increase the audibility of high-frequency sounds that are not otherwise audible with conventional hearing-aid processing due to the degree of hearing loss, limited hearing aid bandwidth or a combination of both factors. The aim of the current study was to compare estimates of speech audibility processed by NFC to improvements in speech recognition for a group of children and adults with high-frequency hearing loss. Design—Monosyllabic word recognition was measured in noise for twenty-four adults and twelve children with mild to severe sensorineural hearing loss. Stimuli were amplified based on each listener’s audiogram with conventional processing (CP) with amplitude compression or with NFC and presented under headphones using a software-based hearing aid simulator. A modification of the speech intelligibility index (SII) was used to estimate audibility of information in frequency-lowered bands. The mean improvement in SII was compared to the mean improvement in speech recognition. Results—All but two listeners experienced improvements in speech recognition with NFC compared to CP, consistent with the small increase in audibility that was estimated using the modification of the SII. Children and adults had similar improvements in speech recognition with NFC. Conclusion—Word recognition with NFC was higher than CP for children and adults with mild to severe hearing loss. The average improvement in speech recognition with NFC (7%) was consistent with the modified SII, which indicated that listeners experienced an increase in audibility with NFC compared to CP. Further studies are necessary to determine if changes in audibility with NFC are related to speech recognition with NFC for listeners with greater degrees of hearing loss, with a greater variety of compression settings, and using auditory training

Do "Optimal" Conditions Improve Distortion Product Otoacoustic Emission Test Performance?

Objectives: To determine whether an "optimal" distortion product otoacoustic emission (DPOAE) protocol that (1) used optimal stimulus levels and primary-frequency ratios for each f 2 , (2) simultaneously measured 2f 2 Ϫ f 1 and 2f 1 Ϫ f 2 distortion products, (3) controlled source contribution, (4) implemented improved calibration techniques, (5) accounted for the influence of middle ear reflectance, and (6) applied multivariate analyses to DPOAE data results in improved accuracy in differentiating between normal-hearing and hearing-impaired ears, compared with a standard clinical protocol. Design: Data were collected for f 2 frequencies ranging from 0.75 to 8 kHz in 28 normal-hearing and 78 hearing-impaired subjects. The protocol included a control condition incorporating standard stimulus levels and primary-frequency ratios calibrated with a standard SPL method and three experimental conditions using optimized stimuli calibrated with an alternative forward pressure level method. The experimental conditions differed with respect to the level of the reflection-source suppressor tone and included conditions referred to as the null suppressor (i.e., no suppressor tone presented), low-level suppressor (i.e., suppressor tone presented at 58 dB SPL), and high-level suppressor (i.e., suppressor tone presented at 68 dB SPL) conditions. The area under receiver operating characteristic (A ROC ) curves and sensitivities for fixed specificities (and vice versa) were estimated to evaluate test performance in each condition. Results: A ROC analyses indicated (1) improved test performance in all conditions using multivariate analyses, (2) improved performance in the null suppressor and low suppressor experimental conditions compared with the control condition, and (3) poorer performance below 4 kHz with the high-level suppressor. As expected from A ROC , sensitivities for fixed specificities and specificities for fixed sensitivities were highest for the null suppressor and low suppressor conditions and lowest for standard clinical procedures. The influence of 2f 2 Ϫ f 1 and reflectance on test performance were negligible. Conclusions: Predictions of auditory status based on DPOAE measurements in clinical protocols may be improved by the inclusion of (1) optimized stimuli, (2) alternative calibration techniques, (3) low-level suppressors, and (4) multivariate analyses

Distribution of standing-wave errors in real-ear sound-level measurements

Standing waves can cause measurement errors when sound-pressure level (SPL) measurements are performed in a closed ear canal, e.g., during probe-microphone system calibration for distortion-product otoacoustic emission (DPOAE) testing. Alternative calibration methods, such as forward-pressure level (FPL), minimize the influence of standing waves by calculating the forward-going sound waves separate from the reflections that cause errors. Previous research compared test performance (Burkeet al., 2010) and threshold prediction (Rogerset al., 2010) using SPL and multiple FPL calibration conditions, and surprisingly found no significant improvements when using FPL relative to SPL, except at 8 kHz. The present study examined the calibration data collected by Burkeet al. and Rogerset al. from 155 human subjects in order to describe the frequency location and magnitude of standing-wave pressure minima to see if these errors might explain trends in test performance. Results indicate that while individual results varied widely, pressure variability was larger around 4 kHz and smaller at 8 kHz, consistent with the dimensions of the adult ear canal. The present data suggest that standing-wave errors are not responsible for the historically poor (8 kHz) or good (4 kHz) performance of DPOAE measures at specific test frequencies