Giso Grimm

Increase and Subjective Evaluation of Feedback Stability in Hearing Aids by a Binaural Coherence-Based Noise Reduction Scheme

The effect of a binaural coherence-based noise reduction scheme on the feedback stability margin and sound quality in hearing aids has been analyzed. For comparison, a conventional adaptive feedback canceler (AFC) and the combination of the adaptive filter with the binaural coherence filter have been tested. The observed quantities are feedback stability and target signal attenuation. An objective measure of feedback stability, i.e., the added stable gain (ASG) was obtained for a number of algorithmic settings and compared to a subjective measure of feedback stability, the added tolerable gain (ATG). In an attempt to eliminate the subjective bias in estimating the ATG, the ldquounbiased added gainrdquo (UAG) is introduced as a new method. Both, objective and subjective measures give similar results for feedback stability. This allows for a valid comparison across different feedback reduction schemes both in isolation and in combination: whereas the ASG of the coherence filter without combination with AFC is negligible, the results indicate that a robust feedback suppression in hearing aids can be achieved if the benefit of de-correlation and the head-shadow effect in binaural hearing aids is used in an advantageous way. The ASG reaches 23 dB for the best combination at the expense of an average target signal attenuation of 15 dB at critical frequencies. The attribute of the coherence filter is that it adaptively limits the maximum gain before feedback becomes audible. The UAG analysis revealed that subjects used a stable quality criterion across the conditions tested and that the group of subjects covered a large range of individual quality criteria.

Do hearing loss and cognitive function modulate benefit from different binaural noise-reduction settings?

Objectives: Although previous research indicates that cognitive skills influence benefit from different types of hearing aid algorithms, comparatively little is known about the role of, and potential interaction with, hearing loss. This holds true especially for noise reduction (NR) processing. The purpose of the present study was thus to explore whether degree of hearing loss and cognitive function modulate benefit from different binaural NR settings based on measures of speech intelligibility, listening effort, and overall preference. Design: Forty elderly listeners with symmetrical sensorineural hearing losses in the mild to severe range participated. They were stratified into four age-matched groups (with n = 10 per group) based on their pure-tone average hearing losses and their performance on a visual measure of working memory (WM) capacity. The algorithm under consideration was a binaural coherence-based NR scheme that suppressed reverberant signal components as well as diffuse background noise at mid to high frequencies. The strength of the applied processing was varied from inactive to strong, and testing was carried out across a range of fixed signal-to-noise ratios (SNRs). Potential benefit was assessed using a dual-task paradigm combining speech recognition with a visual reaction time (VRT) task indexing listening effort. Pairwise preference judgments were also collected. All measurements were made using headphone simulations of a frontal speech target in a busy cafeteria. Test–retest data were gathered for all outcome measures. Results: Analysis of the test–retest data showed all data sets to be reliable. Analysis of the speech scores showed that, for all groups, speech recognition was unaffected by moderate NR processing, whereas strong NR processing reduced intelligibility by about 5%. Analysis of the VRT scores revealed a similar data pattern. That is, while moderate NR did not affect VRT performance, strong NR impaired the performance of all groups slightly. Analysis of the preference scores collapsed across SNR showed that all groups preferred some over no NR processing. Furthermore, the two groups with smaller WM capacity preferred strong over moderate NR processing; for the two groups with larger WM capacity, preference did not differ significantly between the moderate and strong settings. Conclusions: The present study demonstrates that, for the algorithm and the measures of speech recognition and listening effort used here, the effects of different NR settings interact with neither degree of hearing loss nor WM capacity. However, preferred NR strength was found to be associated with smaller WM capacity, suggesting that hearing aid users with poorer cognitive function may prefer greater noise attenuation even at the expense of poorer speech intelligibility. Further research is required to enable a more detailed (SNR-dependent) analysis of this effect and to test its wider applicability.

Perceptual consequences of different signal changes due to binaural noise reduction: do hearing loss and working memory capacity play a role?

Objectives: In a previous study, Neher et al. (2013) investigated whether pure-tone average (PTA) hearing loss and working memory capacity (WMC) modulate benefit from different binaural noise reduction (NR) settings. Results showed that listeners with smaller WMC preferred strong over moderate NR even at the expense of poorer speech recognition due to greater speech distortion (SD), whereas listeners with larger WMC did not. To enable a better understanding of these findings, the main aims of the present study were (1) to explore the perceptual consequences of changes to the signal mixture, target speech, and background noise caused by binaural NR, and (2) to determine whether response to these changes varies with WMC and PTA. Design: As in the previous study, four age-matched groups of elderly listeners (with N = 10 per group) characterized by either mild or moderate PTAs and either better or worse performance on a visual measure of WMC participated. Five processing conditions were tested, which were based on the previously used (binaural coherence-based) NR scheme designed to attenuate diffuse signal components at mid to high frequencies. The five conditions differed in terms of the type of processing that was applied (no NR, strong NR, or strong NR with restoration of the long-term stimulus spectrum) and in terms of whether the target speech and background noise were processed in the same manner or whether one signal was left unprocessed while the other signal was processed with the gains computed for the signal mixture. Comparison across these conditions allowed assessing the effects of changes in high-frequency audibility (HFA), SD, and noise attenuation and distortion (NAD). Outcome measures included a dual-task paradigm combining speech recognition with a visual reaction time (VRT) task as well as ratings of perceived effort and overall preference. All measurements were carried out using headphone simulations of a frontal target speaker in a busy cafeteria. Results: Relative to no NR, strong NR was found to impair speech recognition and VRT performance slightly and to improve perceived effort and overall preference markedly. Relative to strong NR, strong NR with restoration of the long-term stimulus spectrum and thus HFA did not affect speech recognition, restored VRT performance to that achievable with no NR, and increased perceived effort and reduced overall preference markedly. SD had negative effects on speech recognition and perceived effort, particularly when both speech and noise were processed with the gains computed for the signal mixture. NAD had positive effects on speech recognition, perceived effort, and overall preference, particularly when the target speech was left unprocessed. VRT performance was unaffected by SD and NAD. None of the datasets exhibited any clear signs that response to the different signal changes varies with PTA or WMC. Conclusions: For the outcome measures and stimuli applied here, the present study provides little evidence that PTA or WMC affect response to changes in HFA, SD, and NAD caused by binaural NR. However, statistical power restrictions suggest further research is needed. This research should also investigate whether partial HFA restoration combined with some pre-processing that reduces co-modulation distortion results in a more favorable balance of the effects of binaural NR across outcome dimensions and whether NR strength has any influence on these results.

Spatial Acoustic Scenarios in Multichannel Loudspeaker Systems for Hearing Aid Evaluation

BACKGROUND Field tests and guided walks in real environments show that the benefit from hearing aid (HA) signal processing in real-life situations is typically lower than the predicted benefit found in laboratory studies. This suggests that laboratory test outcome measures are poor predictors of real-life HA benefits. However, a systematic evaluation of algorithms in the field is difficult due to the lack of reproducibility and control of the test conditions. Virtual acoustic environments that simulate real-life situations may allow for a systematic and reproducible evaluation of HAs under more realistic conditions, thus providing a better estimate of real-life benefit than established laboratory tests. PURPOSE To quantify the difference in HA performance between a laboratory condition and more realistic conditions based on technical performance measures using virtual acoustic environments, and to identify the factors affecting HA performance across the tested environments. RESEARCH DESIGN A set of typical HA beamformer algorithms was evaluated in virtual acoustic environments of different complexity. Performance was assessed based on established technical performance measures, including perceptual model predictions of speech quality and speech intelligibility. Virtual acoustic environments ranged from a simple static reference condition to more realistic complex scenes with dynamically moving sound objects. RESULTS HA benefit, as predicted by signal-to-noise ratio (SNR) and speech intelligibility measures, differs between the reference condition and more realistic conditions for the tested beamformer algorithms. Other performance measures, such as speech quality or binaural degree of diffusiveness, do not show pronounced differences. However, a decreased speech quality was found in specific conditions. A correlation analysis showed a significant correlation between room acoustic parameters of the sound field and HA performance. The SNR improvement in the reference condition was found to be a poor predictor of HA performance in terms of speech intelligibility improvement in the more realistic conditions. CONCLUSIONS Using several virtual acoustic environments of different complexity, a systematic difference in HA performance between a simple reference condition and more realistic environments was found, which may be related to the discrepancy between laboratory and real-life HA performance reported previously.

The personal hearing system: a software hearing aid for a personal communication system

A concept and architecture of a personal communication system (PCS) is introduced that integrates audio communication and hearing support for the elderly and hearing-impaired through a personal hearing system (PHS). The concept envisions a central processor connected to audio headsets via a wireless body area network (WBAN). To demonstrate the concept, a prototype PCS is presented that is implemented on a netbook computer with a dedicated audio interface in combination with a mobile phone. The prototype can be used for field-testing possible applications and to reveal possibilities and limitations of the concept of integrating hearing support in consumer audio communication devices. It is shown that the prototype PCS can integrate hearing aid functionality, telephony, public announcement systems, and home entertainment. An exemplary binaural speech enhancement scheme that represents a large class of possible PHS processing schemes is shown to be compatible with the general concept. However, an analysis of hardware and software architectures shows that the implementation of a PCS on future advanced cell phone-like devices is challenging. Because of limitations in processing power, recoding of prototype implementations into fixed point arithmetic will be required and WBAN performance is still a limiting factor in terms of data rate and delay.

Binaural noise reduction for hearing AIDS

Noise reduction algorithms have been proposed that try to imitate some aspects of the binaural information processing in the human hearing system by using two microphones at both ears and a central processor. Based on a two channel input, it is theoretically possible to cancel one interfering directional noise source at a time. Due to the relatively large distance between microphones, it should additionally be possible to detect and cancel reverberation based on coherence measures. In practice however, no significant increase in speech intelligibility has been shown so far with these schemes in acoustically complex environments characterized by diffuse noise and reverberation. This paper summarizes these results for a review. Furthermore, a localization algorithm is introduced, which uses a statistical description of the binaural signal differences in order to increase the robustness in estimating sound source incident directions in noisy environments. Possible noise reduction schemes based on this localization algorithm are discussed.

Evaluation of spatial audio reproduction schemes for application in hearing aid research.

Loudspeaker-based spatial audio reproduction schemes are increasingly used for evaluating hearing aids in complex acoustic conditions. To further establish the feasibility of this approach, this study investigated the interaction between spatial resolution of different reproduction methods and technical and perceptual hearing aid performance measures using computer simulations. Three spatial audio reproduction methods -- discrete speakers, vector base amplitude panning and higher order ambisonics -- were compared in regular circular loudspeaker arrays with 4 to 72 channels. The influence of reproduction method and array size on performance measures of representative multi-microphone hearing aid algorithm classes with spatially distributed microphones and a representative single channel noise-reduction algorithm was analyzed. Algorithm classes differed in their way of analyzing and exploiting spatial properties of the sound field, requiring different accuracy of sound field reproduction. Performance measures included beam pattern analysis, signal-to-noise ratio analysis, perceptual localization prediction, and quality modeling. The results show performance differences and interaction effects between reproduction method and algorithm class that may be used for guidance when selecting the appropriate method and number of speakers for specific tasks in hearing aid research.

Web-Based Live Speech-Driven Lip-Sync

Virtual characters are an integral part of many games and virtual worlds. The ability to accurately synchronize lip movement to audio speech is an important aspect in the believability of the character. In this paper we propose a simple rule-based lip-syncing algorithm for virtual agents using the web browser. It works in real-time with live input, unlike most current lip-syncing proposals, which may require considerable amounts of computation, expertise and time to set up. Our method generates reliable speech animation based on live speech using three blend shapes and no training, and it only needs manual adjustment of three parameters for each speaker (sensitivity, smoothness and vocal tract length). Our proposal is based on the limited real-time audio processing functions of the client web browser (thus, the algorithm needs to be simple), but this facilitates the use of web based embodied conversational agents.

Auditory Model-Based Dynamic Compression Controlled by Subband Instantaneous Frequency and Speech Presence Probability Estimates

Sensorineural hearing loss typically results in elevated thresholds and steepened loudness growth significantly conditioned by a damage of outer hair cells (OHC). In hearing aids, amplification and dynamic compression aim at widening the limited available dynamic range. However, speech perception particularly in complex acoustic scenes often remains difficult. Here, a physiologically motivated, fast acting, model-based dynamic compression algorithm (MDC) is introduced which aims at restoring the behaviorally estimated basilar membrane input-output (BM I/O) function in normal-hearing listeners. A system-specific gain prescription rule is suggested, based on the same model BM I/O function and a behavioral estimate of the individual OHC loss. Cochlear off-frequency component suppression is mimicked using an instantaneous frequency (IF) estimate. Increased loudness as a consequence of widened filters in the impaired system is considered in a further compensation stage. In an extended version, a subband estimate of the speech presence probability (MDC+SPP) additionally provides speech-selective amplification in stationary noise. Instrumental evaluation revealed that the IF control enhances the spectral contrast of vowels and benefits in quality predictions at higher signal-to-noise ratios (SNRs) were observed. Compared with a conventional multiband dynamic compressor, MDC achieved objective quality and intelligibility benefits for a competing talker at lower SNRs. MDC+SPP outperformed the conventional compressor in the quality predictions and reached comparable instrumental speech intelligibility as achieved with linear amplification. The proposed algorithm provides a first promising basis for auditory model-based compression with signal-type- and bandwidth-dependent gains.

Influence of Multi-microphone Signal Enhancement Algorithms on the Acoustics and Detectability of Angular and Radial Source Movements:

Hearing-impaired listeners are known to have difficulties not only with understanding speech in noise but also with judging source distance and movement, and these deficits are related to perceived handicap. It is possible that the perception of spatially dynamic sounds can be improved with hearing aids (HAs), but so far this has not been investigated. In a previous study, older hearing-impaired listeners showed poorer detectability for virtual left-right (angular) and near-far (radial) source movements due to lateral interfering sounds and reverberation, respectively. In the current study, potential ways of improving these deficits with HAs were explored. Using stimuli very similar to before, detailed acoustic analyses were carried out to examine the influence of different HA algorithms for suppressing noise and reverberation on the acoustic cues previously shown to be associated with source movement detectability. For an algorithm that combined unilateral directional microphones with binaural coherence-based noise reduction and for a bilateral beamformer with binaural cue preservation, movement-induced changes in spectral coloration, signal-to-noise ratio, and direct-to-reverberant energy ratio were greater compared with no HA processing. To evaluate these two algorithms perceptually, aided measurements of angular and radial source movement detectability were performed with 20 older hearing-impaired listeners. The analyses showed that, in the presence of concurrent interfering sounds and reverberation, the bilateral beamformer could restore source movement detectability in both spatial dimensions, whereas the other algorithm only improved detectability in the near-far dimension. Together, these results provide a basis for improving the detectability of spatially dynamic sounds with HAs.