Frequency Lowering Research Articles

Effects of Frequency-Composition Algorithm and Phoneme-Based Auditory Training in Older Hearing Aid Users.

Frequency-lowering (FL) algorithms improve the audibility of high-frequency sounds by shifting inaudible high-frequency components to audible low-frequency regions. However, the FL algorithm has yielded mixed findings. This study involved two experiments. The first experiment investigated whether objective and subjective auditory outcomes would be enhanced by activating frequency composition (Fcomp), which is a type of FL technique. The second experiment determined whether auditory training with Fcomp activation would provide perceptual benefits to older hearing aid users. Twelve older hearing aid users with moderate to profound high-frequency sensorineural hearing loss participated in this study. In Experiment I, all participants received a 4-week adaptation period to Fcomp before the measurement, and then the influence of Fcomp was evaluated. In Experiment II, among the 12 participants in Experiment I, five received 8-week phoneme-based auditory training while activating Fcomp, whereas the remaining seven did not receive training but continued to use Fcomp as non-trained controls. In Experiment I, 4-week passive accli-matization period to Fcomp did not improve speech-in-quiet recognition or self-perceived sound quality. In Experiment II, active pho-neme-based training enhanced recognition of consonants and words as well as better speech-quality ratings for trained participants. The consecutive use of Fcomp did not lead to any differences for non-trained participants. Overall, phoneme-based auditory training would allow older hearing aid users to relearn frequency-lowered speech sounds and reduce phonetic confusion. However, the analytical training approach did not lead to transfer to sentence recognition or overall satisfaction with the hearing aids.

Sound Quality Effects of an Adaptive Nonlinear Frequency Compression Processor with Normal-Hearing and Hearing-Impaired Listeners.

Frequency lowering (FL) technology offers a means of improving audibility of high-frequency sounds. For some listeners, the benefit of such technology can be accompanied by a perceived degradation in sound quality, depending on the strength of the FL setting. The studies presented in this article investigate the effect of a new type of FL signal processing for hearing aids, adaptive nonlinear frequency compression (ANFC), on subjective speech quality. Listener ratings of sound quality were collected for speech stimuli processed with systematically varied fitting parameters. Study 1 included 40 normal-hearing (NH) adult and child listeners. Study 2 included 11 hearing-impaired (HI) adult and child listeners. HI listeners were fitted with laboratory-worn hearing aids for use during listening tasks. Speech quality ratings were assessed across test conditions consisting of various strengths of static nonlinear frequency compression (NFC) and ANFC speech. Test conditions included those that were fine-tuned on an individual basis per hearing aid fitting and conditions that were modified to intentionally alter the sound quality of the signal. Listeners rated speech quality using the MUlti Stimulus test with Hidden Reference and Anchor (MUSHRA) test paradigm. Ratings were analyzed for reliability and to compare results across conditions. Results show that interrater reliability is high for both studies, indicating that NH and HI listeners from both adult and child age groups can reliably complete the MUSHRA task. Results comparing sound quality ratings across experimental conditions suggest that both the NH and HI listener groups rate the stimuli intended to have poor sound quality (e.g., anchors and the strongest available parameter settings) as having below-average sound quality ratings. A different trend in the results is reported when considering the other experimental conditions across the listener groups in the studies. Speech quality ratings measured with NH listeners improve as the strength of ANFC decreases, with a range of bad to good ratings reported, on average. Speech quality ratings measured with HI listeners are similar and above-average for many of the experimental stimuli, including those with fine-tuned NFC and ANFC parameters. Overall, HI listeners provide similar sound quality ratings when comparing static and adaptive forms of frequency compression, especially when considering the individualized parameter settings. These findings suggest that a range in settings may result in above-average sound quality for adults and children with hearing impairment. Furthermore, the fitter should fine-tune FL parameters for each individual listener, regardless of type of FL technology.

Difference limens for noise bandwidth discrimination in listeners with normal and impaired hearing

Frequency-lowering (FL) in hearing aids is often used to move inaudible high-frequency energy from sibilant fricatives to spectral regions where hearing better. Clinically, FL settings that maximize the spectral separation between these sounds, which can be modeled as bands of noise, are assumed to maximize discrimination between them and other speech contrasts. The purpose of this study was to quantify the minimum spectral differences for normal-hearing and hearing-impaired listeners to discriminate between bands of frozen noise. Noise bands corresponded to the average frequency and bandwidth of sibilant fricatives after undergoing FL using settings appropriate for mild-to-moderate, moderately-severe, and severely-profound hearing losses. Noise bands differed on the low- and/or the high-frequency edges. Discrimination in normal-hearing listeners was constant across presentation level and the three frequency ranges. Discrimination was also better for high-frequency edge differences. Neural excitation patterns generated from an auditory nerve model account for these findings. Neural excitation patterns generated for the three severities of hearing loss indicate that hearing-impaired listeners will rely heavily on spectral differences on the low-frequency edge and indicate that sibilant fricatives processed with FL will not be able to be discriminated solely on the basis of high-frequency edge differences. [Grant supported by Sonova USA, Inc.] Frequency-lowering (FL) in hearing aids is often used to move inaudible high-frequency energy from sibilant fricatives to spectral regions where hearing better. Clinically, FL settings that maximize the spectral separation between these sounds, which can be modeled as bands of noise, are assumed to maximize discrimination between them and other speech contrasts. The purpose of this study was to quantify the minimum spectral differences for normal-hearing and hearing-impaired listeners to discriminate between bands of frozen noise. Noise bands corresponded to the average frequency and bandwidth of sibilant fricatives after undergoing FL using settings appropriate for mild-to-moderate, moderately-severe, and severely-profound hearing losses. Noise bands differed on the low- and/or the high-frequency edges. Discrimination in normal-hearing listeners was constant across presentation level and the three frequency ranges. Discrimination was also better for high-frequency edge differences. Neural excitation patt...

The effects of frequency lowering on speech perception in noise with adult hearing-aid users

Objective: Frequency lowering (FL) strategies move high frequency sound into a lower frequency range. This study determined if speech perception differences are observed between some of the different frequency lowering strategies that are available. Design: A cross-sectional, repeated-measures design was used to compare three hearing aids that used wide-dynamic range compression (WDRC) and either non-linear frequency compression (NFC), linear frequency transposition (LFT), or frequency translation (FT). The hearing aids were matched to prescriptive real ear targets for WDRC. The settings for each FL strategy were adjusted to provide audibility for a 6300 Hz filtered speech signal. Sentence recognition in noise, subjective measures of sound quality, and a modified version of the speech intelligibility index (SII) were measured. Study sample: Ten adults between the ages of 63 to 82 years with bilateral, high frequency hearing loss. Results: LFT and FT led to poorer sentence recognition compared to WDRC for most individuals. No difference in sentence recognition occurred with and without NFC. The quality questionnaire and SII showed few differences between conditions. Conclusion: Under similar fitting and testing conditions of this study, FL techniques may not provide speech understanding benefit in certain background noise situations.

The Performance of Music and Speech with Different Frequency Lowering Devices

Objective: Previous research studies have documented the benefits of both frequency transposition (FT) and non-linear frequency compression (NLFC) for patients with different degrees of hearing loss, however, very few studies directly compare the effect of two different frequency lowering (FL) techniques on the same population to investigate if superior performance in terms of speech and music perception exists. Design and Sample: The aim of the study was to determine whether people with a moderate to severe hearing loss have improved music perception and speech intelligibility with the use of FL and if the benefits is dependent on a specific FL strategy. A parallel research design was implemented and a purposive sampling method was used. Participants (n=20) were experienced hearing aid users with bilateral, moderate to severe hearing losses and no FL experience. A music perception questionnaire were completed by participants to rate their perception of music and the Music Perception Test (MPT) were used to assess participants’ musical performance. The Phoneme Perception Test (PPT) and Hearing-in-Noise Test (HINT) were used to assess participants’ speech perception abilities. Two commercial hearing aid devices with different FL approaches (FT and NLFC) were used. Results and Conclusion: Results indicate that participants distinguish high frequency sounds better with both FL strategies than without it resulting in better speech intelligibility in quiet and in noise. Greater speech scores with NLFC compared to FT was evident. Participants that used FT showed more confusion regarding speech perception. In terms of music perception the study shows that NLFC improves participants’ pitch and melody perception whereas mostly no musical improvement was observed with FT. With the use of FT participants’ ability to identify melodies decreased. A strong preference to listen to classical music with NLFC compared to FT was noted. Therefore it is evident that FL can improve speech and music perception for people with moderate to severe hearing losses but the perceived benefit seems to be dependent on the specific FL strategy implemented.

Benefits of Nonlinear Frequency Compression in Adult Hearing Aid Users.

Frequency-lowering (FL) algorithms are an alternative method of providing access to high-frequency speech cues. There is currently a lack of independent research addressing: (1) what functional, measureable benefits FL provides; (2) which, if any, FL algorithm provides the maximum benefit, (3) how to clinically program algorithms, and (4) how to verify algorithm settings. Two experiments were included in this study. The purpose of Experiment 1 was to (1) determine if a commercially available nonlinear frequency compression (NLFC) algorithm provides benefit as measured by improved speech recognition in noise when fit and verified using standard clinical procedures; and (2) evaluate the impact of acclimatization. The purpose of Experiment 2 was to (1) evaluate the benefit of using enhanced verification procedures to systematically determine the optimal application of a prototype NLFC algorithm, and (2) determine if the optimized prototype NLFC settings provide benefit as measured by improved speech recognition in quiet and in noise. A single-blind, within-participant repeated measures design in which participants served as their own controls. Experiment 1 included 26 participants with a mean age of 68.3 yr and Experiment 2 included 37 participants with a mean age of 68.8 yr. Participants were recruited from the Audiology and Speech Pathology Center at Walter Reed National Military Medical Center in Bethesda, MD. Participants in Experiment 1 wore bilateral commercially available hearing aids fit using standard clinical procedures and clinician expertise. Participants in Experiment 2 wore a single prototype hearing aid for which FL settings were systematically examined to determine the optimum application. In each experiment, FL-On versus FL-Off settings were examined in a variety of listening situations to determine benefit and possible implications. In Experiment 1, speech recognition measures using the QuickSIN and Modified Rhyme Test stimuli were obtained at initial bilateral fitting and 3-5 weeks later during a follow-up visit. In Experiment 2, Modified Rhyme Test, /sə/, /∫ə/ consonant discrimination task, and dual-task cognitive load speech recognition performance measures were conducted. Participants in Experiment 2 received four different systematic hearing aid programs during an initial visit and speech recognition data were collected over 2-3 follow-up sessions. Some adults with hearing loss obtained small-to-moderate benefits from implementation of FL, while others maintained performance without detriment in both experiments. There was no significant difference among FL-On settings systematically obtained in Experiment 2. There was a modest but significant age effect in listeners of both experiments that indicated older listeners (>65 yr) might benefit more on average from FL than younger listeners. In addition, there were reliable improvements in the intelligibility of the phonemes /ŋ/ and /b/ for both groups, and /ð/ for older listeners from the FL in both experiments. Although the optimum settings, application, and benefits of FL remain unclear at this time, there does not seem to be degradation in listener performance when FL is activated. The benefits of FL should be explored in older adult (>65 yr) listeners, as they tended to benefit more from FL applications.