Melinda C. Anderson

Effects of noise and distortion on speech quality judgments in normal-hearing and hearing-impaired listeners.

Noise and distortion reduce speech intelligibility and quality in audio devices such as hearing aids. This study investigates the perception and prediction of sound quality by both normal-hearing and hearing-impaired subjects for conditions of noise and distortion related to those found in hearing aids. Stimuli were sentences subjected to three kinds of distortion (additive noise, peak clipping, and center clipping), with eight levels of degradation for each distortion type. The subjects performed paired comparisons for all possible pairs of 24 conditions. A one-dimensional coherence-based metric was used to analyze the quality judgments. This metric was an extension of a speech intelligibility metric presented in Kates and Arehart (2005) [J. Acoust. Soc. Am. 117, 2224-2237] and is based on dividing the speech signal into three amplitude regions, computing the coherence for each region, and then combining the three coherence values across frequency in a calculation based on the speech intelligibility index. The one-dimensional metric accurately predicted the quality judgments of normal-hearing listeners and listeners with mild-to-moderate hearing loss, although some systematic errors were present. A multidimensional analysis indicates that several dimensions are needed to describe the factors used by subjects to judge the effects of the three distortion types.

Effects of noise, nonlinear processing, and linear filtering on perceived speech quality.

Objectives: The purpose of this study was to measure subjective quality ratings in listeners with normal hearing and listeners with hearing loss for speech subjected to a wide range of processing conditions that are representative of real hearing aids. Design: Speech quality was assessed using a rating scale in a group of 14 listeners with normal hearing and 15 listeners with mild to moderately severe sensorineural hearing loss. Controlled simulations of hearing aid processing were used to process speech that included speech subjected to (1) noise and nonlinear processing, (2) linear filtering, and (3) combinations of noise, nonlinear processing, and linear filtering. The 32 conditions of noise and nonlinear processing included stationary speech-shaped nose, multitalker babble, peak clipping, quantization noise, spectral subtraction, and dynamic range compression (in quiet, with babble, and with spectral subtraction). The 32 linear filtering conditions included high-pass filtering, low-pass filtering, band-pass filtering, positive and negative spectral tilt, and resonance peaks. Subsets of these conditions were used for the 36 conditions that combined noise and nonlinear processing with linear processing. Results: Both listeners with normal hearing and listeners with hearing loss gave consistent (reliable) ratings. In both listener groups, sound quality was significantly affected by the noise, nonlinear processing, and linear filtering conditions. Compared with the listeners with normal hearing, the listeners with hearing loss showed significantly lower ratings of sound quality in nearly all of the processing conditions. For the conditions included in the current hearing aid simulation, noise and nonlinear conditions had a greater effect on quality judgments than did the linear filtering conditions. Conclusions: The data reported here provide a comprehensive dataset of speech quality ratings for simulated hearing aid processing conditions. The results indicate that quality ratings by listeners with hearing loss are significantly lower than quality ratings by listeners with normal hearing. In addition, quality ratings by listeners with hearing loss are impacted by signal processing at least as much as, and often more than, the quality ratings by listeners with normal hearing. Finally, quality ratings for speech processed with a simulated hearing aid are impacted more by noise and nonlinear signal processing than by linear filtering.

Working memory and intelligibility of hearing-aid processed speech

Previous work suggested that individuals with low working memory capacity may be at a disadvantage in adverse listening environments, including situations with background noise or substantial modification of the acoustic signal. This study explored the relationship between patient factors (including working memory capacity) and intelligibility and quality of modified speech for older individuals with sensorineural hearing loss. The modification was created using a combination of hearing aid processing [wide-dynamic range compression (WDRC) and frequency compression (FC)] applied to sentences in multitalker babble. The extent of signal modification was quantified via an envelope fidelity index. We also explored the contribution of components of working memory by including measures of processing speed and executive function. We hypothesized that listeners with low working memory capacity would perform more poorly than those with high working memory capacity across all situations, and would also be differentially affected by high amounts of signal modification. Results showed a significant effect of working memory capacity for speech intelligibility, and an interaction between working memory, amount of hearing loss and signal modification. Signal modification was the major predictor of quality ratings. These data add to the literature on hearing-aid processing and working memory by suggesting that the working memory-intelligibility effects may be related to aggregate signal fidelity, rather than to the specific signal manipulation. They also suggest that for individuals with low working memory capacity, sensorineural loss may be most appropriately addressed with WDRC and/or FC parameters that maintain the fidelity of the signal envelope.

Effects of noise, nonlinear processing, and linear filtering on perceived music quality.

Abstract Objective: The purpose of this study was to determine the relative impact of different forms of hearing aid signal processing on quality ratings of music. Design: Music quality was assessed using a rating scale for three types of music: orchestral classical music, jazz instrumental, and a female vocalist. The music stimuli were subjected to a wide range of simulated hearing aid processing conditions including, (1) noise and nonlinear processing, (2) linear filtering, and (3) combinations of noise, nonlinear, and linear filtering. Study sample: Quality ratings were measured in a group of 19 listeners with normal hearing and a group of 15 listeners with sensorineural hearing impairment. Results: Quality ratings in both groups were generally comparable, were reliable across test sessions, were impacted more by noise and nonlinear signal processing than by linear filtering, and were significantly affected by the genre of music. Conclusions: The average quality ratings for music were reasonably well predicted by the hearing aid speech quality index (HASQI), but additional work is needed to optimize the index to the wide range of music genres and processing conditions included in this study. Sumario Objetivo: El propósito de este estudio fue determinar el impacto relativo de diferentes formas de procesamiento de señal de los auxiliares auditivos en cuanto a la calificación cualitativa de la música. Diseño: la calidad de la música se evaluó utilizando una escala de calificación para tres tipos de música: clásica orquestral, jazz instrumental y mujer vocalista. Los estímulos musicales estuvieron sujetos a un amplio número de simulaciones de procesamiento de los auxiliares auditivos, incluyendo (1) ruido y procesamiento no-linear, (2) filtración linear y (3) combinaciones de ruido, no-linear y filtración linear. Mestra: Se obtuvieron los índices de calidad en un grupo de 19 sujetos normoyentes y otro grupo de 15 sujetos con hipoacusia sensorineural. Resultados: Las calificaciones cualitativas en ambos grupos fueron generalmente comparables, confiables en las diferentes sesiones, fueron más alteradas por el ruido y por el procesamiento no linear de la señal que por la filtración linear y fueron afectadas significativamente por el género de la música. Conclusiones: El índice de calidad del lenguaje de los auxiliares auditivos (HASQI), pronosticó razonablemente bien el promedio de calificación de la calidad de la música, pero todavía es necesario continuar la investigación para optimizar el índice para que éste pueda cubrir una gama más amplia de géneros y condiciones de procesamiento incluidas en este estudio.

The acoustic and peceptual effects of series and parallel processing

Temporal envelope (TE) cues provide a great deal of speech information. This paper explores how spectral subtraction and dynamic-range compression gain modifications affect TE fluctuations for parallel and series configurations. In parallel processing, algorithms compute gains based on the same input signal, and the gains in dB are summed. In series processing, output from the first algorithm forms the input to the second algorithm. Acoustic measurements show that the parallel arrangement produces more gain fluctuations, introducing more changes to the TE than the series configurations. Intelligibility tests for normal-hearing (NH) and hearing-impaired (HI) listeners show (1) parallel processing gives significantly poorer speech understanding than an unprocessed (UNP) signal and the series arrangement and (2) series processing and UNP yield similar results. Speech quality tests show that UNP is preferred to both parallel and series arrangements, although spectral subtraction is the most preferred. No significant differences exist in sound quality between the series and parallel arrangements, or between the NH group and the HI group. These results indicate that gain modifications affect intelligibility and sound quality differently. Listeners appear to have a higher tolerance for gain modifications with regard to intelligibility, while judgments for sound quality appear to be more affected by smaller amounts of gain modification.

Chosen Listening Levels for Music With and Without the Use of Hearing Aids.

PURPOSE The objective of this study was to describe chosen listening levels (CLLs) for recorded music for listeners with hearing loss in aided and unaided conditions. METHOD The study used a within-subject, repeated-measures design with 13 adult hearing-aid users. The music included rock and classical samples with different amounts of audio-industry compression limiting. CLL measurements were taken at ear level (i.e., at input to the hearing aid) and at the tympanic membrane. RESULTS For aided listening, average CLLs were 69.3 dBA at the input to the hearing aid and 80.3 dBA at the tympanic membrane. For unaided listening, average CLLs were 76.9 dBA at the entrance to the ear canal and 77.1 dBA at the tympanic membrane. Although wide intersubject variability was observed, CLLs were not associated with audiometric thresholds. CLLs for rock music were higher than for classical music at the tympanic membrane, but no differences were observed between genres for ear-level CLLs. The amount of audio-industry compression had no significant effect on CLLs. CONCLUSION By describing the levels of recorded music chosen by hearing-aid users, this study provides a basis for ecologically valid testing conditions in clinical and laboratory settings.

The effects of noise vocoding on speech quality perception.

Speech perception depends on access to spectral and temporal acoustic cues. Temporal cues include slowly varying amplitude changes (i.e. temporal envelope, TE) and quickly varying amplitude changes associated with the center frequency of the auditory filter (i.e. temporal fine structure, TFS). This study quantifies the effects of TFS randomization through noise vocoding on the perception of speech quality by parametrically varying the amount of original TFS available above 1500Hz. The two research aims were: 1) to establish the role of TFS in quality perception, and 2) to determine if the role of TFS in quality perception differs between subjects with normal hearing and subjects with sensorineural hearing loss. Ratings were obtained from 20 subjects (10 with normal hearing and 10 with hearing loss) using an 11-point quality scale. Stimuli were processed in three different ways: 1) A 32-channel noise-excited vocoder with random envelope fluctuations in the noise carrier, 2) a 32-channel noise-excited vocoder with the noise-carrier envelope smoothed, and 3) removal of high-frequency bands. Stimuli were presented in quiet and in babble noise at 18dB and 12dB signal-to-noise ratios. TFS randomization had a measurable detrimental effect on quality ratings for speech in quiet and a smaller effect for speech in background babble. Subjects with normal hearing and subjects with sensorineural hearing loss provided similar quality ratings for noise-vocoded speech.

Long-Term Outcome Data in Patients following One Year's Use of a Fully Implantable Active Middle Ear Implant.

This study examined the safety and efficacy of a fully implantable active middle ear (AMEI) system. Outcome measures assessed AMEI performance compared with an optimally fitted conventional hearing aid (CHA). Fifty adults with stable, symmetric moderate-to-severe sensorineural hearing loss were implanted at 9 ambulatory settings. Consonant-Nucleus-Consonant (CNC) words, Bamford-Kowel-Bench Speech in Noise test (BKB-SIN), Abbreviated Profile of Hearing Aid Benefit (APHAB), and unaided hearing thresholds in the implanted ear were compared to baseline measures obtained using a personal CHA. Changes in thresholds were observed from pre- to 12-month postoperative assessments. CNC word scores decreased (within 10%), and the BKB-SIN showed no change from pre- to 12-month postoperative time points. The APHAB revealed improvement. Findings suggest no difference in performance between an appropriately fit CHA and the AMEI at 12 months. This study indicates AMEIs have the potential to help individuals who choose not to use CHAs.

Quality judgments for music signals by normal‐hearing and hearing‐impaired listeners.

Noise, distortion, nonlinear signal‐processing algorithms, and linear filtering can all affect the sound quality of a hearing aid or other audio device. Most hearing‐aid research concentrates on speech, but music reproduction can also be an important factor in user satisfaction. In this presentation, quality judgments are made for several different music signals by normal‐hearing and hearing‐impaired listeners. The music signals include orchestral classical music, jazz instrumental, and vocal. The signal processing uses a simulated hearing aid. The noise and nonlinear signal degradations include additive noise, multitalker babble, peak‐clipping distortion, quantization noise, multichannel compression, spectral subtraction. Linear filtering conditions include bandwidth limitation, spectral resonance peaks, and spectral tilt. Conditions combining noise and nonlinear processing with linear filtering are also included. Subject ratings of the degraded music will be presented, along with comparisons of the rati...

Predictions of speech quality under conditions of noise and distortion

Noise and distortion reduce speech intelligibility and quality in audio devices such as hearing aids. The purpose of this study is to quantify and model the effects of signal degradation on the perception of speech quality in normal‐hearing and hearing‐impaired listeners. The stimuli were sentences subjected to eight different levels of additive noise, peak clipping, and center clipping distortion. The subjects listened to all possible comparisons of pairs of the 24 degraded sentences, and for each comparison indicated their preference. Multi‐dimensional analysis is used to model the subject decision spaces, and the data are also modeled using a one‐dimensional metric to predict the subject quality judgments. The one‐dimensional metric is an extension of the procedure developed by Kates and Arehart [J. Acoust. Soc. Am. 117, 2224–2237 (2005)] to model speech intelligibility. That approach is based on dividing the speech signal into three amplitude regions, computing the coherence for each region, and then ...