The influence of the reference level on loudness and preference judgements for spectrally manipulated fan sounds.

Fan sounds are often quantified using A-weighted sound pressure levels, silently acknowledging their limitations to fully capture the perceived unpleasantness. To overcome this limitation, level adjustments are a way to quantify the subjective preference of spectrally different sounds in listening experiments by adjusting the level of a test sound until it is equally preferred to a fixed reference sound. Since equal loudness contours differ, depending on the overall level, level adjustments might vary for different levels of the reference sound. This study aims to quantify the effects of spectral manipulations on level adjustments for loudness and preference judgements at reference sound pressure levels of either 45, 60, or 75 dB(A). Level adjustments of up to 12 dB were measured to make the stimuli equally preferred to the reference, particularly for sounds with prominent high-frequency components. The loudness and preference judgements were closely linked with each other, but an offset of about 3.5 dB at a reference level of 45 dB(A) indicates that equal loudness is not synonymous with equal preference. A linear regression model to predict level adjustments based on the reference level and an index reflecting the ratio of mid- to high-frequency loudness explains 73% of the variance.

Spatial Resolution of Late Reverberation in Virtual Acoustic Environments.

Late reverberation involves the superposition of many sound reflections, approaching the properties of a diffuse sound field. Since the spatially resolved perception of individual late reflections is impossible, simplifications can potentially be made for modelling late reverberation in room acoustics simulations with reduced spatial resolution. Such simplifications are desired for interactive, real-time virtual acoustic environments with applications in hearing research and for the evaluation of hearing supportive devices. In this context, the number and spatial arrangement of loudspeakers used for playback additionally affect spatial resolution. The current study assessed the minimum number of spatially evenly distributed virtual late reverberation sources required to perceptually approximate spatially highly resolved isotropic and anisotropic late reverberation and to technically approximate a spherically isotropic sound field. The spatial resolution of the rendering was systematically reduced by using subsets of the loudspeakers of an 86-channel spherical loudspeaker array in an anechoic chamber, onto which virtual reverberation sources were mapped using vector base amplitude panning. It was tested whether listeners can distinguish lower spatial resolutions of reproduction of late reverberation from the highest achievable spatial resolution in different simulated rooms. The rendering of early reflections remained unchanged. The coherence of the sound field across a pair of microphones at ear and behind-the-ear hearing device distance was assessed to separate the effects of number of virtual sources and loudspeaker array geometry. Results show that between 12 and 24 reverberation sources are required for the rendering of late reverberation in virtual acoustic environments.

Tracking Musical Voices in Bach's The Art of the Fugue: Timbral Heterogeneity Differentially Affects Younger Normal-Hearing Listeners and Older Hearing-Aid Users.

Auditory scene analysis is an elementary aspect of music perception, yet only little research has scrutinized auditory scene analysis under realistic musical conditions with diverse samples of listeners. This study probed the ability of younger normal-hearing listeners and older hearing-aid users in tracking individual musical voices or lines in JS Bach's The Art of the Fugue. Five-second excerpts with homogeneous or heterogenous instrumentation of 2-4 musical voices were presented from spatially separated loudspeakers and preceded by a short cue for signaling the target voice. Listeners tracked the cued voice and detected whether an amplitude modulation was imposed on the cued voice or a distractor voice. Results indicated superior performance of young normal-hearing listeners compared to older hearing-aid users. Performance was generally better in conditions with fewer voices. For young normal-hearing listeners, there was interaction between the number of voices and the instrumentation: performance degraded less drastically with an increase in the number of voices for timbrally heterogeneous mixtures compared to homogeneous mixtures. Older hearing-aid users generally showed smaller effects of the number of voices and instrumentation, but no interaction between the two factors. Moreover, tracking performance of older hearing aid users did not differ when these participants did or did not wear hearing aids. These results shed light on the role of timbral differentiation in musical scene analysis and suggest reduced musical scene analysis abilities of older hearing-impaired listeners in a realistic musical scenario.

The role of early and late reflections on perception of source orientation.

Sound radiation of most natural sources, like human speakers or musical instruments, typically exhibits a spatial directivity pattern. This directivity contributes to the perception of sound sources in rooms, affecting the spatial energy distribution of early reflections and late diffuse reverberation. Thus, for convincing sound field reproduction and acoustics simulation, source directivity has to be considered. Whereas perceptual effects of directivity, such as source-orientation-dependent coloration, appear relevant for the direct sound and individual early reflections, it is unclear how spectral and spatial cues interact for later reflections. Better knowledge of the perceptual relevance of source orientation cues might help to simplify the acoustics simulation. Here, it is assessed as to what extent directivity of a human speaker should be simulated for early reflections and diffuse reverberation. The computationally efficient hybrid approach to simulate and auralize binaural room impulse responses [Wendt et al., J. Audio Eng. Soc. 62, 11 (2014)] was extended to simulate source directivity. Two psychoacoustic experiments assessed the listeners' ability to distinguish between different virtual source orientations when the frequency-dependent spatial directivity pattern of the source was approximated by a direction-independent average filter for different higher reflection orders. The results indicate that it is sufficient to simulate effects of source directivity in the first-order reflections.

Loudness and short-term annoyance of sonic boom signatures at low levels.

Supersonic aircraft produce a sonic boom when flying faster than the speed of sound. To rule out detrimental effects for inhabitants of overflown areas, civil supersonic flights (like the Concorde) were only allowed to fly at supersonic speed when over water. Due to the progress in aircraft design, the supersonic boom may be reduced considerably in the future. In this study, listening tests were carried out with a variety of low boom simulations and conventional sonic boom signatures in a similar level range. Participants rated the loudness and the short-term annoyance of 24 sonic boom signals, which differed in terms of the signature shape and maximum pressure but were confined to a range of A-weighted sound exposure levels around 60 dB(A). The results showed main effects of signature and relative level variation as well as an interaction of the two. Correlation coefficients between the ratings and sound exposure levels were highest for A-weighted sound exposure levels compared to other frequency weightings. Contrary to our expectations, the provision of background information about the nature of the presented sound sources had no statistically significant influence on the ratings.

The role of reliable interaural time difference cues in ambiguous binaural signals for the intelligibility of multitalker speech.

When listening to speech in the presence of concurrent talkers, listeners can benefit from glimpses that occur as a result of spectro-temporal modulations in the speech signals. These glimpses are characterized by a high local signal-to-noise ratio and allow listeners to collect relatively undistorted and reliable information on target speech features. A series of experiments was designed to measure the spatial advantage for binaurally presented speech when useful interaural time difference (ITD) information was provided only in glimpses of speech signals with otherwise ambiguous ITDs. For interaurally coherent signals, ITD information provided by target glimpses contributed substantially to the spatial advantage, but consistent target ITDs overall appeared to be of minor importance to speech intelligibility. For interaurally incoherent signals, a similarly large contribution of coherent ITD information in glimpses to the spatial advantage was not observed. Rather, target speech intelligibility depended on the interaural coherence of the interfering speech signals. While the previous observation conforms with models of auditory object formation, and the latter is consistent with equalization-cancellation theory modeling the spatial advantage, the two seem to be at odds for the presented set of experiments. A conceptual framework employing different strategies to process the perceptual foreground and background may solve this issue.

Contribution of binaural masking release to improved speech intelligibility for different masker types.

In situations with competing talkers or in the presence of masking noise, speech intelligibility can be improved by spatially separating the target speaker from the interferers. This advantage is generally referred to as spatial release from masking, and different mechanisms have been suggested to explain it. One proposed mechanism to benefit from spatial cues is the binaural masking release, which is purely stimulus-driven. According to this mechanism, the spatial benefit results from differences in the binaural cues of target and masker, which need to appear simultaneously in time and frequency to improve the signal detection. In an alternative proposed mechanism, the differences in the interaural cues improve the segregation of auditory streams, a process, which involves top-down processing rather than being purely stimulus-driven. Other than the cues that produce binaural masking release, the interaural cue differences between target and interferer required to improve stream segregation do not have to appear simultaneously in time and frequency. This study is concerned with the contribution of binaural masking release to spatial release from masking for three masker types that differ with respect to the amount of energetic masking they exert. Speech intelligibility was measured, employing a stimulus manipulation that inhibits binaural masking release and analysed with a metric to account for the number of better-ear glimpses. Results indicate that the contribution of the stimulus-driven binaural masking release plays a minor role while binaural stream segregation and the availability of glimpses in the better ear had a stronger influence on improving the speech intelligibility.

Sparse periodicity-based auditory features explain human performance in a spatial multitalker auditory scene analysis task.

Human listeners robustly decode speech information from a talker of interest that is embedded in a mixture of spatially distributed interferers. A relevant question is which time-frequency segments of the speech are predominantly used by a listener to solve such a complex Auditory Scene Analysis task. A recent psychoacoustic study investigated the relevance of low signal-to-noise ratio (SNR) components of a target signal on speech intelligibility in a spatial multitalker situation. For this, a three-talker stimulus was manipulated in the spectro-temporal domain such that target speech time-frequency units below a variable SNR threshold (SNRcrit ) were discarded while keeping the interferers unchanged. The psychoacoustic data indicate that only target components at and above a local SNR of about 0 dB contribute to intelligibility. This study applies an auditory scene analysis "glimpsing" model to the same manipulated stimuli. Model data are found to be similar to the human data, supporting the notion of "glimpsing," that is, that salient speech-related information is predominantly used by the auditory system to decode speech embedded in a mixture of sounds, at least for the tested conditions of three overlapping speech signals. This implies that perceptually relevant auditory information is sparse and may be processed with low computational effort, which is relevant for neurophysiological research of scene analysis and novelty processing in the auditory system.

Binaural frequency selectivity in humans.

Several behavioural studies in humans have shown that listening to sounds with two ears that is binaural hearing, provides the human auditory system with extra information on the sound source that is not available when sounds are only perceived through one ear that is monaurally. Binaural processing involves the analysis of phase and level differences between the two ear signals. As monaural cochlea processing (in each ear) precedes the neural stages responsible for binaural processing properties it is reasonable to assume that properties of the cochlea may also be observed in binaural processing. A main characteristic of cochlea processing is its frequency selectivity. In psychoacoustics, there is an ongoing discussion on the frequency selectivity of the binaural auditory system. While some psychoacoustic experiments seem to indicate poorer frequency selectivity of the binaural system than that of the monaural processing others seem to indicate the same frequency selectivity for monaural and binaural processing. This study provides an overview of these seemingly controversial results and the different explanations that were provided to account for the different results.

Determination of preference-equivalent levels for fan noise and their prediction by indices based on specific loudness patterns.

In a previous study by the authors, two indices were identified as appropriate descriptors for perceptual dimensions of fan noise. The index Nlow describes the amount of low-frequency loudness relative to the overall loudness. The index Nratio represents the ratio between the amount of loudness resulting from mid-frequency content and that from high frequencies. The aim of this study is to quantify how variations in these two indices affect subjects' preferences and loudness judgments. In listening experiments, fan noise signals were adjusted separately to equal loudness and equal preference compared to a common reference sound by varying their level in an adaptive procedure. The fan noises used in the listening tests consisted of 11 typical signals from three major groups of fan sounds from the earlier study and 18 signals that were parametrically varied in terms of the two indices. Reductions in A-weighted sound pressure level of up to 15 dB were necessary to make unpleasant fan sounds equally preferred as the fixed reference sound. A regression model based on the index Nratio explains 81% of the variation in the evaluation data with a root-mean-squared error of 2.53 dB.

Crispness, speech intelligibility, and coloration of reverberant recordings played back in another reverberant room (Room-In-Room).

This work examines the acoustical and perceptual consequences that can be found in a transfer chain consisting of a sound recorded in one room which is played back over a loudspeaker in another room. The total resulting "Room-In-Room" (RinR) response can be modelled as a convolution of the Room Impulse Response of the first and second room. Due to the convolution an increase in the reverberation time, pulse density, and a change of the temporal envelope of the early reflections can be observed, compared to a single room. In the spectral domain, the convolution results in an increase in spectral modulation strength, responsible for coloration. The listening test investigating the perceptual consequences of RinR found a decrease in perceived crispness due to reproduction in a playback room, especially for highly reverberant conditions. When within normal sized rooms the reverberation time and total source-receiver distance were kept constant, RinR and a single room condition showed no reduction in crispness. On the other hand, a strong increase in the perceived coloration was measured. Furthermore, a decrease in speech intelligibility has been found for RinR conditions, compared to single rooms (Speech Reception Threshold of 2-3 dB).

Better-ear rating based on glimpsing.

The better ear of a listener is the ear that benefits most from head shadow effects in a setting with spatially separated sources. Traditionally, the better ear is considered to be the ear that receives a signal at the best signal-to-noise ratio. For a speech target in interfering speech, the concept of rating the better ear based on glimpses was explored. The laterality of the expected better ear was shown to be well represented by metrics based on glimpsing. When employing better-ear glimpsing as a microscopic predictor for speech intelligibility, a strong relation was found between the amount of glimpsed target speech received by the better ear and the performance on a consonant recognition task. This relation was investigated for two spatial processing methods that included or excluded the possibility to use better-ear listening. It was shown that the amount of glimpses at the better ear plus an effect of angular separation of speech sources could account for a substantial part of the performance, but that a small, additional role of the contralateral ear may need to be considered.

Stimulus coherence influences sound-field localization and fusion/segregation of leading and lagging sounds.

The ability to localize sound sources in reverberant environments is dependent upon first-arriving information, an outcome commonly termed "the precedence effect." For example, in laboratory experiments, the combination of a leading (direct) sound followed by a lagging (reflected) sound is localized in the direction of the leading sound. This study was designed to measure the degree to which stimulus compactness/diffuseness (i.e., coherence as represented by interaural cross correlation) of leading and lagging sounds influences performance. The compactness/diffuseness of leading or lagging sounds was varied by either presenting a sound from a single loudspeaker or by presenting mutually uncorrelated versions of similar sounds from nine adjacent loudspeakers. In separate experiments, the listener's task was to point to the perceived location of leading and lagging 10-ms long low-pass filtered white noises or 2-s long tokens of speech. The leading and lagging stimuli were presented either from speakers located directly in front of the listeners or from speakers located ±45° to the right or left. The results indicate that leading compact (coherent) sounds influence perceived location more so than do leading diffuse (incoherent) sounds. This was true independent of whether the sounds were Gaussian noises or tokens of speech.

Just noticeable differences of spatial cues in echoic and anechoic acoustical environments.

The perceptual limits for detecting changes in binaural cues also define the boundaries for the perception of differences in spatial impression. This study reports just noticeable differences for interaural time delays (ITDs) and interaural level differences (ILDs) of the early part and for the interaural cross-correlation (IACC) of the early and diffuse part of binaural room impulse responses. The results show that ITDs only allow a high accuracy in localization in anechoic environments, whereas ILDs show a higher robustness against reverberation. Subjects are rather insensitive to changes in IACC, only changes that bring the IACC close to one are detectable.

The multiple contributions of interaural differences to improved speech intelligibility in multitalker scenarios.

Spatial separation of talkers is known to improve speech intelligibility in a multitalker scenario. A contribution of binaural unmasking, in addition to a better-ear effect, is usually considered to account for this advantage. Binaural unmasking is assumed to result from the spectro-temporally simultaneous presence of target and masker energy with different interaural properties. However, in the case of speech targets and speech interference, the spectro-temporal signal-to-noise ratio (SNR) fluctuates strongly, resulting in audible and localizable glimpses of target speech even at adverse global SNRs. The disparate interaural properties of target and masker may thus lead to improved segregation without requiring simultaneity. This study addresses the binaural contribution to spatial release from masking due to simultaneous disparities in interaural cues between target and interferers. For that purpose stimuli were designed that lacked simultaneously occurring disparities, but yielded a percept of spatially separated speech nearly indistinguishable from that of non-modified stimuli. A phoneme recognition experiment with either three collocated or spatially separated talkers showed a substantial spatial release from masking for the modified stimuli. The results suggest that binaural unmasking made a minor contribution to spatial release from masking, and that rather the interaural cues mediated by dominant speech components were essential.

Intelligibility for Binaural Speech with Discarded Low-SNR Speech Components.

Speech intelligibility in multitalker settings improves when the target speaker is spatially separated from the interfering speakers. A factor that may contribute to this improvement is the improved detectability of target-speech components due to binaural interaction in analogy to the Binaural Masking Level Difference (BMLD). This would allow listeners to hear target speech components within specific time-frequency intervals that have a negative SNR, similar to the improvement in the detectability of a tone in noise when these contain disparate interaural difference cues. To investigate whether these negative-SNR target-speech components indeed contribute to speech intelligibility, a stimulus manipulation was performed where all target components were removed when local SNRs were smaller than a certain criterion value. It can be expected that for sufficiently high criterion values target speech components will be removed that do contribute to speech intelligibility. For spatially separated speakers, assuming that a BMLD-like detection advantage contributes to intelligibility, degradation in intelligibility is expected already at criterion values below 0 dB SNR. However, for collocated speakers it is expected that higher criterion values can be applied without impairing speech intelligibility. Results show that degradation of intelligibility for separated speakers is only seen for criterion values of 0 dB and above, indicating a negligible contribution of a BMLD-like detection advantage in multitalker settings. These results show that the spatial benefit is related to a spatial separation of speech components at positive local SNRs rather than to a BMLD-like detection improvement for speech components at negative local SNRs.

Interaction of Object Binding Cues in Binaural Masking Pattern Experiments.

Object binding cues such as binaural and across-frequency modulation cues are likely to be used by the auditory system to separate sounds from different sources in complex auditory scenes. The present study investigates the interaction of these cues in a binaural masking pattern paradigm where a sinusoidal target is masked by a narrowband noise. It was hypothesised that beating between signal and masker may contribute to signal detection when signal and masker do not spectrally overlap but that this cue could not be used in combination with interaural cues. To test this hypothesis an additional sinusoidal interferer was added to the noise masker with a lower frequency than the noise whereas the target had a higher frequency than the noise. Thresholds increase when the interferer is added. This effect is largest when the spectral interferer-masker and masker-target distances are equal. The result supports the hypothesis that modulation cues contribute to signal detection in the classical masking paradigm and that these are analysed with modulation bandpass filters. A monaural model including an across-frequency modulation process is presented that account for this effect. Interestingly, the interferer also affects dichotic thresholds indicating that modulation cues also play a role in binaural processing.

Lateralization of stimuli with alternating interaural time differences: The role of monaural envelope cues.

A temporally acute binaural system can help to resolve inherent fluctuations in binaural information that are often present in complex auditory scenes. Using a broadband noise stimulus that rapidly alternates between two different values of interaural time difference (ITD), the ability of the binaural system to hear the lateral position resulting from one of the ITD values was investigated. Results show that listeners are able to accurately lateralize brief noise tokens of only 3-7 ms in duration. In two subsequent experiments, the role of an amplitude modulation (AM) imposed on the ITD-switching stimulus used in the first experiment was tested. For wideband stimuli, the temporal position of the ITD target relative to the phase of the AM did not influence absolute lateralization or detection performance. When the stimuli were narrowband, however, detection of the ITD target was best when temporally positioned in the rising portion of the AM. These experiments illustrate that the auditory system is capable of making accurate lateral estimates of very brief moments of ITD information. Furthermore, for these instantaneous changes in ITD information, the stimulus bandwidth can influence the role of envelope cues for the readout of binaural information.

Lateralization of noise bursts in interaurally correlated or uncorrelated background noise using interaural level differences.

The interaural level difference (ILD) of a lateralized target source may be effectively reduced when the target is presented together with background noise containing zero ILD. It is not certain whether listeners perceive a position congruent with the reduced ILD or the actual target ILD in a lateralization task. Two sets of behavioral experiments revealed that many listeners perceived a position at or even larger than that corresponding to the presented target ILD when a temporal onset/offset asynchrony between the broadband target and the broadband background noise was present. When no temporal asynchrony was present, however, the perceived lateral position indicated a dependency on the coherence of the background noise for several listeners. With interaurally correlated background noise, listeners reported a reduced ILD resulting from the combined target and background noise stimulus. In contrast, several of the listeners made a reasonable estimate of the position corresponding to the target ILD for interaurally uncorrelated, broadband, background noise. No obvious difference in performance was seen between low- or high-frequency stimuli. Extension of a weighting template to the output of a standard equalization-cancellation model was shown to remove a lateral bias on the predicted target ILD resulting from the presence of background noise. Provided that an appropriate weighting template is applied based on knowledge of the background noise coherence, good prediction of the behavioral data is possible.