Masked Thresholds Research Articles

Time and frequency metrics related to auditory masking of a 10 kHz tone in bottlenose dolphins (Tursiops truncatus).

Metrics related to the frequency spectrum of noise (e.g., critical ratios) are often used to describe and predict auditory masking. In this study, detection thresholds for a 10 kHz tone were measured in the presence of anthropogenic, natural, and synthesized noise. Time-domain and frequency-domain metrics were calculated for the different noise types, and regression models were used to determine the relationship between noise metrics and masked tonal thresholds. Statistical models suggested that detection thresholds, masked by a variety of noise types at a variety of noise levels, can be explained with metrics related to the spectral density of noise and the degree to which amplitude modulation is correlated across frequency regions of the noise. The results demonstrate the need to include time-domain metrics when describing and predicting auditory masking.

A Study on the Performance of Watermarking Algorithm Based on DCT

Based on DCT domain, this paper presents a digital watermarking algorithm, which combines luminance masking threshold characteristics of Watson and controls the watermark embedding position through transforming the chaotic sequence so that the watermark has better robustness and imperception. For watermark algorithm of the same kind, the values assigned to some factors could bring substantial influence to the watermarking system. This article primarily analyzes these factors which affect the performance of the watermarking system through the quality of image perception and robustness, provides specific experimental data, and explains the importance of the assignment of these values in algorithm design. This article employs two kinds of watermark information carriers which can precisely explain the problem and evaluate the performance of the watermarking system.

Improved Spectral Subtraction Speech Enhancement Algorithm

The paper addresses the problems of speech distortion and residual musical noise introduced by conventional spectral subtraction (SS) method for speech enhancement. In this paper, we propose a modified SS algorithm for speech enhancement based on the masking properties of human auditory system. The algorithm computes the parameters α and β dynamically according to the masking thresholds of the critical frequency segments for each speech frame. Simulation results show that the proposed algorithm is superior to the conventional SS method, not only in the improvement of output SNR, but in the reduction of the speech distortion and residual musical noise.

Transmission of bone conducted sound – Correlation between hearing perception and cochlear vibration

The vibration velocity of the lateral semicircular canal and the cochlear promontory was measured on 16 subjects with a unilateral middle ear common cavity, using a laser Doppler vibrometer, when the stimulation was by bone conduction (BC). Four stimulation positions were used: three ipsilateral positions and one contralateral position. Masked BC pure tone thresholds were measured with the stimulation at the same four positions. Valid vibration data were obtained at frequencies between 0.3 and 5.0 kHz. Large intersubject variation of the results was found with both methods. The difference in cochlear velocity with BC stimulation at the four positions varied as a function of frequency while the tone thresholds showed a tendency of lower thresholds with stimulation at positions close to the cochlea. The correlation between the vibration velocities of the two measuring sites of the otic capsule was high. Also, relative median data showed similar trends for both vibration and threshold measurements. However, due to the high variability for both vibration and perceptual data, low correlation between the two methods was found at the individual level. The results from this study indicated that human hearing perception from BC sound can be estimated from the measure of cochlear vibrations of the otic capsule. It also showed that vibration measurements of the cochlea in cadaver heads are similar to that measured in live humans.

Bayesian adaptive estimation of the auditory filter

A Bayesian adaptive procedure for estimating the auditory-filter shape was proposed and evaluated using young, normal-hearing listeners at moderate stimulus levels. The resulting quick-auditory-filter (qAF) procedure assumed the power spectrum model of masking with the auditory-filter shape being modeled using a spectrally symmetric, two-parameter rounded-exponential (roex) function. During data collection using the qAF procedure, listeners detected the presence of a pure-tone signal presented in the spectral notch of a noise masker. Dependent on the listener's response on each trial, the posterior probability distributions of the model parameters were updated, and the resulting parameter estimates were then used to optimize the choice of stimulus parameters for the subsequent trials. Results showed that the qAF procedure gave similar parameter estimates to the traditional threshold-based procedure in many cases and was able to reasonably predict the masked signal thresholds. Additional measurements suggested that occasional failures of the qAF procedure to reliably converge could be a consequence of incorrect responses early in a qAF track. The addition of a parameter describing lapses of attention reduced the likelihood of such failures.

Speech enhancement based on soft audible noise masking and noise power estimation

This paper presents a perceptual model based speech enhancement algorithm. The proposed algorithm measures the amount of the audible noise in the input noisy speech based on estimation of short-time spectral power of noise signal, and masking threshold calculated from the estimated spectrum of clean speech. An appropriate amount of noise reduction is chosen based on the result to achieve good noise suppression without introducing significant distortion to the clean speech. To mitigate the problem of “musical noise”, the amount of noise reduction is linked directly to the estimation of short-term noise spectral amplitude instead of noise variance so that the spectral peaks of noise can be better suppressed. Good performance of the proposed speech enhancement system is confirmed through objective and subjective tests.

The computational prediction of masking thresholds for ecologically valid interference scenarios

Auditory interference scenarios, where a listener wishes to attend to some target audio while being presented with interfering audio, are prevalent in daily life. The goal of developing an accurate computational model which can predict masking thresholds for such scenarios is still incomplete. While some sophisticated, physiologically inspired, masking prediction models exist, they are rarely tested with ecologically valid programs (such as music and speech). In order to test the accuracy of model predictions human listener data is required. To that end a masking threshold experiment was conducted for a variety of target and interferer programs. The results were analyzed alongside predictions made by the computational auditory signal processing and prediction model described by Jepsen et al. (2008). Masking thresholds were predicted to within 3 dB root mean squared error with the greatest prediction inaccuracies occurring in the presence of speech. These results are comparable to those of the model by Glasberg and Moore (2005) for predicting the audibility of time-varying sounds in the presence of background sounds, which otherwise represent the most accurate predictions of this type in the literature.

Glenis Long's contribution to animal psychoacoustics

Glenis and I were psychology graduate students together in 1970-1971. She was interested in auditory psychophysics, but soon developed an interest in comparative psychophysics which she pursued in a post-doc and a faculty position in Germany, where she obtained a behavioral audiogram for the horseshoe bat and later studied masking in the same species. This audiogram was one of the very first psychophysical investigations of hearing in any bat and the very first for the horseshoe bat. It confirmed a rather complex frequency response function with sensitivity peaks at about 20 kHz and 60 kHz, and a very sharp peak at about 80 kHz. The masked thresholds indicated rather normal critical masking ratios (CR) except in a narrow region at about 80 kHz where the CRs are up to 15 dB lower than expected, suggesting a critical band of about 300 Hz at 80 kHz that is presumably used in Doppler-shift compensation. In 1981-1983, Glenis went on to investigate frequency and rate modulation discrimination in the chinchilla, for the first time, and to study tone-on-tone masking in the chinchilla. Since these early works, Glenis has maintained her comparative interests with studies on birds, kangaroo rats, frogs, and fleas on cats.

Extending Schroeder-phase masking: Influence of direction and shape of masker instantaneous frequency

Schroeder (1970) devised an algorithm to produce low peak factor signals. Schroeder signals with equal amplitude spectra, but reversed phase spectra, reveal large differences in masker effectiveness for listeners with normal hearing [Smith et al. (1986)]. Results reported here extend previous work to include detection of multiple bursts of the same frequency, and multiple bursts that increase or decrease in frequency. Signal frequencies were selected to correspond with harmonics in the maskers. Results indicate that changing the frequency of the signal amplifies the difference between the Schroeder-phase maskers, but the direction of the change does not. When a frequency modulated tone is substituted for the Schroeder maskers, masked threshold depends on the shape of the instantaneous frequency (IF) function, as well as the direction of change. For linear FM (with IF similar to the Schroeder maskers), masked thresholds are comparable to the Schroeder-phase maskers. However, for logarithmic FM, IF changes at a constant ERB/s and directional differences are much smaller. A modified channel model [Oh (2012)] shows substantial differences in the basilar membrane response to these different maskers. [Research supported by a grant from the Office of Naval Research #N000140911017.]

Effect of talker sex on infants’ detection of spondee words in a two-talker or a speech-shaped noise masker

Speech recognition performance in the presence of competing speech is typically better for adults when the target and masker talkers are different sexes than when the target and masker talkers are the same sex. One explanation for this result is that the acoustic differences between male and female speech productions promote segregation of the two streams of speech, thus leading to a reduction in informational masking. In this study, an observer-based psychophysical procedure was used to compare infants’ (7–13 months) masked speech detection thresholds for spondee words produced by a male or a female talker in either a two-female-talker or a speech-shaped noise masker. Infants were assigned to a single testing condition. Maskers were presented continuously throughout testing at an overall level of 50 dB SPL, fixed throughout testing. Following training to an 80%-correct criterion, thresholds for the target word were measured adaptively using a 2-down, 1-up procedure. Infants’ thresholds in the two-female-talker masker were higher for the female compared to the male target word. In contrast, infants’ thresholds were similar for the female and male target words in the speech-shaped noise masker. These results suggest that introducing a different sex between the target and masker aids in the segregation of sounds for infants, as has previously been shown for adults. [Work supported by the NIH.]

Study on effects of presence of cue-tone on psychophysical tuning curves

Our previous study indicated that tunings of the auditory filter were sharpened by the presence of a cue-tone [Kidani et al. (2012), ISH2012]. It is unclear, however, whether the variation of the auditory filter due to the cue-tone is caused by excitation or suppression, because tip of the filter is normalized at 0 dB. Psychophysical tuning curves (PTCs) can show that the detection threshold is decreased at the probe frequency or increased around the probe by the presence of cue-tone, indicating excitation and suppression respectively. PTCs, because, are measured as masked threshold of probe by narrow-band noise. This study aims to consider the effect of the presence of cue-tone by measuring of PTCs. In present study, PTCs were measured in simultaneous masking in the absence and presence of cue-tone for four probe frequencies. The probes were presented at 10 dB above each absolute threshold. The frequency and level of the cue-tone were same as the probe. The result revealed that filter-Q, regarded as the sharpness of tuning, was increased by the presence of cue-tone when the probe frequencies were 1.0 and 2.0 kHz, while the filter-Q was not changed when the probe frequencies were 0.5 and 4.0 kHz.

Relationship of distortion product otoacoustic emission components to psychoacoustic measures of noise induced hearing loss

Distortion product otoacoustic emissions (DPOAEs) have promise as a tool to detect and monitor cochlear hair cell damage in noise-induced hearing loss (NIHL). However, variability in OAE amplitudes and thresholds across individuals limits their potential for detecting the early impact of NIHL. The DPOAE has two components, one generated at the point of interaction between the primaries (generator), the second reflected from the characteristic place of the DPOAE frequency (reflected). This study investigated the components of the DPOAE and how they correlate with injury. A total of 109 men, including 54 with varying degrees of occupational noise exposure, were tested. We recorded DPOAEs using logarithmically swept pure-tones and extracted the components of the DPOAE using a least-squares fit approach. Audiometry was conducted at 1.5 and 4kHz with 1dB resolution. Compressive nonlinearity was evaluated psychoacoustically with 1.5 and 4kHz pure-tones using Schroeder-phase maskers. Overall there were associations between the generator component and the psychoacoustic measures: stronger DPOAE amplitudes were associated with better thresholds and greater difference in Schroeder-phase masking threshold. Associations were stronger at 4kHz than 1.5kHz. Similar, but weaker effects were observed for the reflected component. Findings suggest that separation of DPOAE components enhances the assessment of cochlear noise-induced injury.

The effect of the medial olivocochlear reflex on click-evoked otoacoustic emissions during psychoacoustic forward-masking tasks

Measurements of otoacoustic emissions in animals have shown that the effects of efferent activation are greater in attentive than in anesthetized animals suggesting that the medial olivocochlear reflex (MOCR) effects can be modulated by attention. In this study, the effect of efferent activation was measured in humans using click-evoked otoacoustic emissions while listeners were performing a psychoacoustic forward-masking task. Each trial within a block started with a sequence of 50-dB pSPL clicks presented at a rate of 40 Hz that were followed by a 200-ms harmonic-complex masker. The masker was immediately followed by a 10-ms tonal probe and another click train. The listeners’ task was to detect the probe. A constant stimuli method was used to measure performance in the forward-masking task, with the probe presented at seven randomized levels around the predetermined masked threshold. Catch trials were dispersed randomly throughout the block. Click trains before and after the masker-signal segments were recorded from the ear canal and analyzed to extract effects of efferent activation at different levels of difficulty of the psychoacoustic task. The results will be discussed with respect to the role of attention and the role of the MOCR in forward masking. [Work supported by NIH grant R01DC010374.]

Rapid measurement of auditory filter shape in mice using the auditory brainstem response and notched noise

The notched noise method is an effective procedure for measuring frequency resolution and auditory filter shapes in both human and animal models of hearing. Briefly, auditory filter shape and bandwidth estimates are derived from masked thresholds for tones presented in noise containing widening spectral notches. As the spectral notch widens, increasingly less of the noise falls within the auditory filter and the tone becomes more detectible until the notch width exceeds the filter bandwidth. Behavioral procedures have been used for the derivation of notched noise auditory filter shapes in mice; however, the time and effort needed to train and test animals on these tasks renders a constraint on the widespread application of this testing method. As an alternative procedure, we combined relatively non-invasive auditory brainstem response (ABR) measurements and the notched noise method to estimate auditory filters in normal-hearing mice at center frequencies of 8, 11.2, and 16 kHz. A complete set of simultaneous masked thresholds for a particular tone frequency were obtained in about an hour. ABR-derived filter bandwidths broadened with increasing frequency, consistent with previous studies. The ABR notched noise procedure provides a fast alternative to estimating frequency selectivity in mice that is well-suited to high through-put or time-sensitive screening.

Masking patterns for monopolar and phantom electrode stimulation in cochlear implants

Phantom electrode (PE) stimulation consists of out-of-phase stimulation of two electrodes. When presented at the apex of the electrode array, phantom stimulation is known to produce a lower pitch sensation than monopolar (MP) stimulation on the most apical electrode. The ratio of the current between the primary electrode (PEL) and the compensating electrode (CEL) is represented by the coefficient σ, which ranges from 0 (monopolar) to 1 (full bipolar). The exact mechanism by which PE stimulation produces a lower pitch sensation is unclear. In the present study, unmasked and masked thresholds were obtained using a forward masking paradigm to estimate the spread of current for MP and PE stimulation. Masked thresholds were measured for two phantom electrode configurations (1) PEL = 4, CEL = 5 (lower pitch phantom) and (2) PEL = 4, CEL = 3 (higher pitch phantom). The unmasked thresholds were subtracted from the masked thresholds to obtain masking patterns which were normalized to their peak. The masking patterns reveal (1) differences in the spread of excitation that are consistent with the direction of pitch shift produced by PE stimulation, and (2) narrower spread of electrical excitation for PE stimulation relative to MP stimulation.

A New Speech Enhancement Technique to Reduce Residual Noise Using Perceptual Constrained Spectral Weighted Factors

This paper deals with residual musical noise which results from the perceptual speech enhancement type algorithms and especially using wiener filtering approach. Perceptual speech enhancement techniques perform better than the non perceptual techniques, most of them still return a trouble residual musical noise. This is due to that only noise above the noise masking threshold (NMT) is filtered out then noise below the noise masking threshold (NMT) can become audible if its maskers are filtered. It can affect the performance of perceptual speech enhancement method that process the audible noise only (Residual noise is still present). In order to overcome this drawback a new speech enhancement technique is proposed here.The main aim here is to improve the enhanced speech signal quality provided by perceptual wiener filtering and by controlling the latter via a second filter regarded as a psychoacoustically motivated weighting factor. The simulation results gives the information that the performance is improved compared to other perceptual speech enhancement methods.

Effect of Mistuning on the Detection of a Tone Masked by a Harmonic Tone Complex

The human auditory system is sensitive in detecting “mistuned” components in a harmonic complex, which do not match the frequency pattern defined by the fundamental frequency of the complex. Depending on the frequency configuration, the mistuned component may be perceptually segregated from the complex and may be heard as a separate tone. In the context of a masking experiment, mistuning a single component decreases its masked threshold. In this study we propose to quantify the ability to detect a single component for fixed amounts of mistuning by adaptively varying its level. This method produces masking release by mistuning that can be compared to other masking release effects. Detection thresholds were obtained for various frequency configurations where the target component was resolved or unresolved in the auditory system. The results from 6 normal-hearing listeners show a significant decrease of masked thresholds between harmonic and mistuned conditions in all configurations and provide evidence for the employment of different detection strategies for resolved and unresolved components. The data suggest that across-frequency processing is involved in the release from masking. The results emphasize the ability of this method to assess integrative aspects of pitch and harmonicity perception.

High-frequency auditory filter shape for the Atlantic bottlenose dolphin

High-frequency auditory filter shapes of an Atlantic bottlenose dolphin (Tursiops truncatus) were measured using a notched noise masking source centered on pure tone signals at frequencies of 40, 60, 80 and 100 kHz. A dolphin was trained to swim into a hoop station facing the noise/signal transducer located at a distance of 2 m. The dolphin's masked threshold was determined using an up-down staircase method as the width of the notched noise was randomly varied from 0, 0.2, 04, 0.6, and 0.8 times the test tone frequency. The masked threshold decreased as the width of the notched increased and less noise fell within the auditory filter associated with the test tone. The auditory filter shapes were approximated by fitting a roex (p,r(r)) function to the masked threshold results. A constant-Q value of 8.4 modeled the results within the frequency range of 40 to 100 kHz relatively well. However, between 60 and 100 kHz, the 3 dB bandwidth was relatively similar between 9.5 and 10 kHz, indicating a constant-bandwidth system in this frequency range The mean equivalent rectangular bandwidth calculated from the filter shape was approximately 16.0%, 17.0%, 13.6% and 11.3% of the tone frequencies of 40, 60, 80, and 100 kHz.

A Version of the TEN Test for Use With ER-3A Insert Earphones

The aim of this study was to develop a version of the threshold-equalizing noise (TEN) test for the diagnosis of dead regions for use with Etymotic ER-3A insert earphones. The use of such earphones is helpful when testing clients with asymmetric hearing loss or clients whose ear canals tend to collapse under the pressure of supra-aural headphones. It can also be useful when ambient noise levels are problematic. The spectral shape of the noise required to give equal masked thresholds at all frequencies, when expressed in dB HL, was derived by empirical measurements of the electrical output of audiometers using ER-3A earphones. To reduce the loudness of the noise and to minimize distortion generated in the audiometer or earphone, the noise was band-limited between 354 and 6500 Hz. In addition, the noise was synthesized using a method that leads to a low crest factor (ratio of peak to root mean square value). This further reduced audiometer/earphone distortion, and allowed higher levels per ERBN; ERBN is the equivalent rectangular bandwidth of the auditory filter at 1 kHz, as determined using young normally hearing subjects. The test tone frequencies were limited to the range 500 to 4000 Hz. Subjects with normal or near-normal hearing were tested using a noise level of 60 dB HL/ERBN, to assess whether the noise did lead to equal masked thresholds in dB HL for all audiometric frequencies from 500 to 4000 Hz. Thresholds in the TEN were measured using manual audiometry with a 2 dB final step size. The mean-masked thresholds varied by 1.3 dB across frequency when expressed in dB HL, and were close to the noise level per ERBN. This version of the TEN test can be used with ER-3A insert earphones.

Acceptable Noise Level and Psychophysical Masking

Individuals with low acceptable noise levels (ANLs) accept more noise than individuals with high ANLs. To determine whether ANL is influenced more by afferent or efferent cortical responsiveness, the authors measured differences in temporal masking responses between individuals with low versus high ANLs. If listeners with low ANLs have masked thresholds similar to those of listeners with high ANLs, low ANLs may be due to reduced afferent responsiveness affecting both the masker and signal. If, however, listeners with low ANLs have masked thresholds better than that of listeners with high ANLs, there may be a physiological basis for improved selective attention via stronger efferent inhibition of the "unwanted" sound. Participants were 19 listeners with normal hearing between the ages of 19 and 35. Ten listeners had low ANLs and 9 had high ANLs. All participants were compared using tone-in-noise simultaneous, forward, and backward masking tasks. Results revealed no observed differences in masked thresholds between the low versus high ANL group. The low ANL group, however, required significantly more threshold runs to achieve criterion necessary for threshold determinations. Findings suggest that low ANLs are associated with reduced afferent cortical responsiveness and, possibly, decreased sustained attention.