Evaluating a distortion-weighted glimpsing metric for predicting binaural speech intelligibility in rooms

A distortion-weighted glimpse proportion metric (BiDWGP) for predicting binaural speech intelligibility were evaluated in simulated anechoic and reverberant conditions, with and without a noise masker. The predictive performance of BiDWGP was compared to four reference binaural intelligibility metrics, which were extended from the Speech Intelligibility Index (SII) and the Speech Transmission Index (STI). In the anechoic sound field, BiDWGP demonstrated high accuracy in predicting binaural intelligibility for individual maskers (ρ ≥ 0.95) and across maskers (ρ ≥ 0.94). The reference metrics however performed less well in across-masker prediction (0.54 ≤ ρ ≤ 0.86) despite reasonable accuracy for individual maskers. In reverberant rooms, BiDWGP was more stable in all test conditions (ρ ≥ 0.87) than the reference metrics, which showed different predictive patterns: the binaural STIs were more robust for the stationary than for the fluctuating noise masker, whilst the binaural SII displayed the opposite behaviour. The study shows that the new BiDWGP metric can provide similar or even more robust predictive power than the current standard metric

Messung und Bewertung von Lärm in Kindertagesstätten

Noise is one of the main factors for stress and discomfort at working places in child care facilities, and it is also one major reason for job changes and early retirements. This study investigated noise at a kindergarten site comprising several groups of children of the two typical age groups 0 to 3 years (German "Krippe") and 3 to 6 years (German ,.Kindergarten"). Noise was assessed subjectively by means of a questionnaire, as well as objectively by means of long-Term level measurements in 12 different rooms. The subjective evaluation indicated that playing children and toy noise were the most dominant noise sources. It also showed a strong influence of day time, week day, and season on perceived noise. This was also reflected in the long-Term level measurement in the group rooms, where median values of sound pressure level distributions showed similar trends. Peak sound pressure levels measured for blocks of 125 ms exceeded 90 dBA for the majority of days in the meas urement period of more than 30 weeks. In addition to the noise assessment, a collection of simple noise reduction measures was collected from interviews and previous literature. This catalog of measures was presented to and partly implemented by child care workers in the facility under investigation. A subjective assessment of the implemented measures one year later showed a large satisfaction, indicating that subjective noise reduction can be achieved by relatively simple low-price measures

Masking versus cognition during speech recognition in noise and reverberation: Can different sentence tests provide a quantitative estimate?

This study investigates the effect of noise and reverberation on speech recognition for an open- and a closed-set sentence test. While both tests yield approximately the same recognition threshold in trained normal hearing listeners, their performance may differ due to cognitive factors, i.e., the closed-set test is more sensitive to training effects while the open-set test is more affected by language familiarity. The experimental data were compared to predictions of the speech transmission index as a measure of pure acoustic effects. The largest differences between the open- and closed-set speech tests were measured in reverberation indicating a considerable influence of non-acoustic, cognitive factors. The recognition scores were on average 50% higher for the closed-set test with syntactically fixed and semantically unpredictable sentences than for the open-set test consisting of everyday sentences. To examine the underlying reasons, the closed-set test was presented to naïve listeners, with no training prior the measurements and no information about the test’s structure. Removing this information, the differences between the tests were not present indicating that the degree of familiarity with the speech material has a major impact on speech recognition. This indicates a strong cognitive factor which cannot be predicted by the speech transmission index

Prediction of the influence of reverberation on binaural speech intelligibility in noise and in quiet

Reverberation usually degrades speech intelligibility for spatially separated speech and noise sources since spatial unmasking is reduced and late reflections decrease the fidelity of the received speech signal. The latter effect could not satisfactorily be predicted by a recently presented binaural speech intelligibility model [Beutelmann et al. (2010). J. Acoust. Soc. Am. 127, 2479-2497]. This study therefore evaluated three extensions of the model to improve its predictions: (1) an extension of the speech intelligibility index based on modulation transfer functions, (2) a correction factor based on the room acoustical quantity "definition," and (3) a separation of the speech signal into useful and detrimental parts. The predictions were compared to results of two experiments in which speech reception thresholds were measured in a reverberant room in quiet and in the presence of a noise source for listeners with normal hearing. All extensions yielded better predictions than the original model when the influence of reverberation was strong, while predictions were similar for conditions with less reverberation. Although model (3) differed substantially in the assumed interaction of binaural processing and early reflections, its predictions were very similar to model (2) that achieved the best fit to the data

Spectral loudness summation of nonsimultaneous tone pulses

The level of broadband signals is usually lower than that of equally loud narrow-band signals. This effect, referred to as spectral loudness summation, is commonly measured for broadband signals where all frequency components are presented simultaneously. The present study investigated to what extent spectral loudness summation also occurs for nonsimultaneously presented frequency components. Spectral loudness summation was measured in normal-hearing listeners with an adaptive forced-choice procedure for sequences of short tone pulses with varying frequencies, randomly chosen from a set of five frequencies. In addition, spectral loudness summation was measured for the simultaneous presentation of all five frequencies. The comparison stimulus consisted of tone pulses with the same frequency for all tone pulses of the sequence and the same repetition rate and overall duration as the test signal. The pulse duration was 10, 20, 50, or 100 ms and the inter-pulse interval ranged from 0 to 390 ms. In general, a considerable nonsimultaneous spectral loudness summation was found for short pulse durations and inter-pulse intervals, but a residual effect was also observed for the largest inter-pulse interval. The data are discussed in the light of repetition-rate dependent spectral loudness summation and effects of persistence of specific loudness after tone-pulse offset

Loudness of complex time-varying sounds? A challenge for current loudness models

The calculation of perceived loudness is an important factor in many applications such as the assessment of noise emissions. Generally, loudness of stationary sounds can be accurately predicted by existing models. For sounds with time-varying characteristics, however, there are still discrepancies between experimental data and model predictions, even with the most recent loudness models. This contribution presents a series of experiments in which loudness was measured in normal-hearing subjects with different types of realistic signals using an adaptive loudness matching procedure and categorical loudness scaling. The results of both methods indicate that loudness of speech-like signals is largely determined by the long-term spectrum, while other speech-related properties (particularly temporal modulations) play only a minor role. Loudness of speech appears to be quite robust towards even severe signal modifications, as long as the long-term spectrum is similar. In contrast, loudness of technical, strongly impulsive signals is considerably influenced by temporal modulations. For some of the signals, loudness could not be predicted by current models. Since the perceived loudness was underestimated by the models for some signals, but overestimated for other signals, a simple adjustment of the employed time constants in the temporal integration stage could not eliminate the discrepancies

Spectro-temporal weighting of loudness

Real-world sounds like speech or traffic noise typically exhibit spectro-temporal variability because the energy in different spectral regions evolves differently as a sound unfolds in time. However, it is currently not well understood how the energy in different spectral and temporal portions contributes to loudness. This study investigated how listeners weight different temporal and spectral components of a sound when judging its overall loudness. Spectral weights were measured for the combination of three loudness-matched narrowband noises with different center frequencies. To measure temporal weights, 1,020-ms stimuli were presented, which randomly changed in level every 100 ms. Temporal weights were measured for each narrowband noise separately, and for a broadband noise containing the combination of the three noise bands. Finally, spectro-temporal weights were measured with stimuli where the level of the three narrowband noises randomly and independently changed every 100 ms. The data consistently showed that (i) the first 300 ms of the sounds had a greater influence on overall loudness perception than later temporal portions (primacy effect), and (ii) the lowest noise band contributed significantly more to overall loudness than the higher bands. The temporal weights did not differ between the three frequency bands. Notably, the spectral weights and temporal weights estimated from the conditions with only spectral or only temporal variability were very similar to the corresponding weights estimated in the spectro-temporal condition. The results indicate that the temporal and the spectral weighting of the loudness of a time-varying sound are independent processes. The spectral weights remain constant across time, and the temporal weights do not change across frequency. The results are discussed in the context of current loudness models

ASR-based, single-ended modeling of listening effort - a tool for TV sound engineers

This paper reviews our research approaches towards a listening effort model and its applications as a tool to automatically measure and display the perceived listening effort required to understand speech in a variety of different background sounds. It is single-ended, i.e. it does not require a clean speech reference, and is based on an automatic speech recognition (ASR) system. Speech distortions and interfering background sounds increase the uncertainty of the ASR system, which can be quantified and mapped to a perceptually interpretable scale using a psychoacoustic modeling approach. This performance measure correlates well with mean subjective listening effort ratings for a variety of distortions and acoustic backgrounds typical for TV broadcast material (r > 0.9). In principle, the tool is applicable to be integrated as a software plugin for digital audio workstations (DAWs) to support the work of sound engineers, or in other applications such as speech quality monitoring of communication channels or real-time control of signal-enhancement algorithms

Listening effort and speech intelligibility in listening situations affected by noise and reverberation

This study compared the combined effect of noise and reverberation on listening effort and speech intelligibility to predictions of the speech transmission index (STI). Listening effort was measured in normal-hearing subjects using a scaling procedure. Speech intelligibility scores were measured in the same subjects and conditions: (a) Speech-shaped noise as the only interfering factor, (b) + (c) fixed signal-to-noise ratios (SNRs) of 0 or 7 dB and reverberation as detrimental factors, and (d) reverberation as the only detrimental factor. In each condition, SNR and reverberation were combined to produce STI values of 0.17, 0.30, 0.43, 0.57, and 0.70, respectively. Listening effort always decreased with increasing STI, thus enabling a rough prediction, but a significant bias was observed indicating that listening effort was lower in reverberation only than in noise only at the same STI for one type of impulse responses. Accordingly, speech intelligibility increased with increasing STI and was significantly better in reverberation only than in noise only at the same STI. Further analyses showed that the broadband reverberation time is not always a good estimate of speech degradation in reverberation and that different speech materials may differ in their robustness toward detrimental effects of reverberation