Jörg M. Buchholz

The effect of better-ear glimpsing on spatial release from masking

The current experiment investigated whether better-ear glimpsing can explain the spatial release achieved by normal-hearing adults when situations are high in informational masking. Both modeling and behavioral methods were used. The speech reception thresholds of 38 young adults were measured for co-located, spatially separated and two better-ear glimpsed conditions. In the better-ear glimpsed conditions the binaural signals were processed so that in each time-frequency segment, the signal with the better SNR (left or right ear) was presented diotically. To investigate the effect of widening auditory filters on better-ear glimpsing, adjacent frequency bands were combined in one of the better-ear glimpsing conditions. Twenty-two participants were tested with maskers high in informational masking, while 16 participants were tested with maskers lower in informational masking. The mean speech reception thresholds achieved in the glimpsed conditions were significantly worse than in the spatially separated condition. This suggests that better-ear glimpsing can explain some but not all of the observed spatial release from masking. The difference between performance in the spatially separated and glimpsed conditions was largest when informational masking was high, suggesting better-ear glimpsing may release energetic rather than informational masking. Reducing the number of frequency bands sampled had a small effect on performance.

The influence of spectral characteristics of early reflections on speech intelligibility

The auditory system takes advantage of early reflections (ERs) in a room by integrating them with the direct sound (DS) and thereby increasing the effective speech level. In the present paper the benefit from realistic ERs on speech intelligibility in diffuse speech-shaped noise was investigated for normal-hearing and hearing-impaired listeners. Monaural and binaural speech intelligibility tests were performed in a virtual auditory environment where the spectral characteristics of ERs from a simulated room could be preserved. The useful ER energy was derived from the speech intelligibility results and the efficiency of the ERs was determined as the ratio of the useful ER energy to the total ER energy. Even though ER energy contributed to speech intelligibility, DS energy was always more efficient, leading to better speech intelligibility for both groups of listeners. The efficiency loss for the ERs was mainly ascribed to their altered spectrum compared to the DS and to the filtering by the torso, head, and pinna. No binaural processing other than a binaural summation effect could be observed.

The importance of interaural time differences and level differences in spatial release from masking

Numerous studies have described improvements in speech understanding when interaural time differences (ITDs) and interaural level differences (ILDs) are present. The present study aimed to investigate whether either cue in isolation can elicit spatial release from masking (SRM) in a speech-on-speech masking paradigm with maskers positioned symmetrically around the listener. Twelve adults were tested using three presentations of the Listening in Spatialized Noise-Sentences Test, with each presentation modified to contain different interaural cues in the stimuli. Results suggest that ILDs provide a similar amount of SRM as ITDs and ILDs combined. ITDs alone provide significantly less benefit.

Binaural dereverberation based on interaural coherence histograms

A binaural dereverberation algorithm is presented that utilizes the properties of the interaural coherence (IC) inspired by the concepts introduced in Allen et al. [J. Acoust. Soc. Am. 62, 912-915 (1977)]. The algorithm introduces a non-linear sigmoidal coherence-to-gain mapping that is controlled by an online estimate of the present coherence statistics. The algorithm automatically adapts to a given acoustic environment and provides a stronger dereverberation effect than the original method presented in Allen et al. [J. Acoust. Soc. Am. 62, 912-915 (1977)] in most acoustic conditions. The performance of the proposed algorithm was objectively and subjectively evaluated in terms of its impacts on the amount of reverberation and overall quality. A binaural spectral subtraction method based on Lebart et al. [Acta Acust. Acust. 87, 359-366 (2001)] and a binaural version of the original method of Allen et al. were considered as reference systems. The results revealed that the proposed coherence-based approach is most successful in acoustic scenarios that exhibit a significant spread in the coherence distribution where direct sound and reverberation can be segregated. This dereverberation algorithm is thus particularly useful in large rooms for short source-receiver distances.

Flat-walled multilayered anechoic linings: Optimization and application

The concept of flat-walled multilayered absorbent linings for anechoic rooms was proposed three decades ago. Flat-walled linings have the advantage of being less complicated and, hence, less costly to manufacture and install than the individual units such as wedges. However, there are difficulties in optimizing the design of such absorbent linings. In the present work, the design of a flat-walled multilayered anechoic lining that targeted a 250 Hz cut-off frequency and a 300 mm maximum lining thickness was first optimized using an evolutionary algorithm. Sixteen of the most commonly used commercial fibrous building insulation materials available in Australia were investigated and fourteen design options (i.e., material combinations) were found by the evolutionary algorithm. These options were then evaluated in accordance with their costs and measured acoustic absorption performances. Finally, the completed anechoic room, where the optimized design was applied, was qualified and the results showed that a l...

Reproduction of Nearby Sound Sources Using Higher-Order Ambisonics with Practical Loudspeaker Arrays

loudspeaker arrays DTU Orbit (01/05/2019) Reproduction of nearby sound sources using higher-order ambisonics with practical loudspeaker arrays In order to reproduce nearby sound sources with distant loudspeakers to a single listener, the near field compensated (NFC) method for higher-order Ambisonics (HOA) has been previously proposed. In practical realization, this method requires the use of regularization functions. This study analyzes the impact of two existing and a new proposed regularization function on the reproduced sound fields and on the main auditory cue for nearby sound sources outside the median plane, i.e, low-frequencies interaural level differences (ILDs). The proposed regularization function led to a better reproduction of point source sound fields compared to existing regularization functions for NFC-HOA. Measurements in realistic playback environments showed that, for very close sources, significant ILDs for frequencies above about 250 Hz can be reproduced with NFC-HOA and the proposed regularization function whereas the existing regularization functions failed to provide ILDs below 500 Hz. A listening test showed that these lower-frequency ILDs provided by the proposed regularization function lead to a significantly improved distance perception performance. This test also showed that the distance of virtual sources are perceived less accurately than corresponding physical sources when amplitude cues are not available.

A dynamic speech comprehension test for assessing real-world listening ability

BACKGROUND Many listeners with hearing loss report particular difficulties with multitalker communication situations, but these difficulties are not well predicted using current clinical and laboratory assessment tools. PURPOSE The overall aim of this work is to create new speech tests that capture key aspects of multitalker communication situations and ultimately provide better predictions of real-world communication abilities and the effect of hearing aids. RESEARCH DESIGN A test of ongoing speech comprehension introduced previously was extended to include naturalistic conversations between multiple talkers as targets, and a reverberant background environment containing competing conversations. In this article, we describe the development of this test and present a validation study. STUDY SAMPLE Thirty listeners with normal hearing participated in this study. DATA COLLECTION AND ANALYSIS Speech comprehension was measured for one-, two-, and three-talker passages at three different signal-to-noise ratios (SNRs), and working memory ability was measured using the reading span test. Analyses were conducted to examine passage equivalence, learning effects, and test-retest reliability, and to characterize the effects of number of talkers and SNR. RESULTS Although we observed differences in difficulty across passages, it was possible to group the passages into four equivalent sets. Using this grouping, we achieved good test-retest reliability and observed no significant learning effects. Comprehension performance was sensitive to the SNR but did not decrease as the number of talkers increased. Individual performance showed associations with age and reading span score. CONCLUSIONS This new dynamic speech comprehension test appears to be valid and suitable for experimental purposes. Further work will explore its utility as a tool for predicting real-world communication ability and hearing aid benefit.

The effect of spatial separation in distance on the intelligibility of speech in rooms

The influence of spatial separation in source distance on speech reception thresholds (SRTs) is investigated. In one scenario, the target was presented at 0.5 m distance, and the masker varied from 0.5 m distance up to 10 m. In a second scenario, the masker was presented at 0.5 m distance and the target distance varied. The stimuli were synthesized using convolution with binaural room impulse responses (BRIRs) measured on a dummy head in a reverberant auditorium, and were equalized to compensate for distance-dependent spectral and intensity changes. All sources were simulated directly in front of the listener. SRTs decreased monotonically when the target was at 0.5 m and the speech-masker was moved further away, resulting in a SRT improvement of up to 10 dB. When the speech masker was at 0.5 m and the target was moved away, a large variation across subjects was observed. Neither short-term signal-to-noise ratio (SNR) improvements nor cross-ear glimpsing could account for the observed improvement in intelligibility. However, the effect might be explained by an improvement in the SNR in the modulation domain and a decrease in informational masking. This study demonstrates that distance-related cues can play a significant role when listening in complex environments.

Characterizing the monaural and binaural processes underlying reflection masking

Reflection masked thresholds (RMTs) for the simple scenario of a test reflection masked by the direct sound (200 ms long broadband noise) were measured as a function of reflection delay for diotic and dichotic stimulus presentations. In order to discriminate between contributions to reflection masking from simultaneous versus forward masking, the simultaneous RMT was measured in addition to the traditional RMT. Simultaneous RM was realized by truncating the offset of the test reflection such that the test reflection and the direct sound had a common offset. By comparing the experimental results for the two RMTs, it is shown that forward masking effects only have a significant effect on reflection masking for delays above 7-10 ms. Moreover, binaural mechanisms were revealed which deteriorate auditory detection of test reflections for delays below 7-10 ms and enhance detection for larger delays. The monaural and binaural processes that may underlie reflection masking are discussed in terms of auditory-modelling concepts.

An examination of speech reception thresholds measured in a simulated reverberant cafeteria environment

Abstract Objective: There is increasing demand in the hearing research community for the creation of laboratory environments that better simulate challenging real-world listening environments. The hope is that the use of such environments for testing will lead to more meaningful assessments of listening ability, and better predictions about the performance of hearing devices. Here we present one approach for simulating a complex acoustic environment in the laboratory, and investigate the effect of transplanting a speech test into such an environment. Design: Speech reception thresholds were measured in a simulated reverberant cafeteria, and in a more typical anechoic laboratory environment containing background speech babble. Study sample: The participants were 46 listeners varying in age and hearing levels, including 25 hearing-aid wearers who were tested with and without their hearing aids. Results: Reliable SRTs were obtained in the complex environment, but led to different estimates of performance and hearing-aid benefit from those measured in the standard environment. Conclusions: The findings provide a starting point for future efforts to increase the real-world relevance of laboratory-based speech tests.