Masked Thresholds Research Articles

Psychoacoustic Requirements for Warning Sounds of Quiet Cars

According to upcoming legislative regulations in certain countries, electric and hybrid-electric vehicles (EVs and HEVs) will have to be equipped with devices to compensate for the lack of engine noise needed to warn pedestrians against the vehicles. This leads to the question of appropriate sound design which has to meet specific psychoacoustic requirements. The present paper focuses on auditory features of warning sounds to enhance pedestrians' safety with a major focus on the detectability of the exterior noise of the vehicle in an ambient noise. For the evaluation of detectability, the psychoacoustic model developed by Kerber and Fastl will be introduced allowing for the prediction of masked thresholds of the approaching vehicle. The instrumental assessment yields estimates of the distance of an approaching vehicle at the point it becomes audible to the pedestrians. This way the risk of collision can be assessed assuming that only auditory cues are used by pedestrians to identify vehicles before crossing a street. The corresponding algorithm was applied in a field study to assess the detectability of selected EVs and HEVs as opposed to conventional vehicles. A second focus of this paper will be on the issue of recognisability. It is suggested to design sounds which both are perceptually indicative of the vehicle behaviour and inform about the specific type of propulsion and vehicle make. As a result, the concept of a sound signature specific for vehicles with electric propulsion is proposed which may enhance detectability considerably while recognisability is retained to a large extent. Language: en

Hearing impairment and self-masking: Listening during vocalization

Objectives: To describe the masking effect of a vocalized [a:] on noise bands and speech in persons with mild-to-moderate hearing impairment (HI). Design: The masked threshold of noise bands (250–8000 Hz), continuous discourse, and the amount of masking produced were determined. The maximal vocalization level was determined, that still allowed the subject to just follow the continuous discourse. Study sample: Twenty persons with sensory-neural HI, twelve with a high-frequency (HF) loss and eight with low-, mid-frequency or flat (LMF) loss. Results: The [a:] gave a significantly higher masked threshold at 70 and 80 dBA vocalization for subjects with HF loss than for normal-hearing (NH) subjects, and somewhat higher thresholds than for those with LMF loss. The amount of masking produced was significantly smaller for subjects with HI than NH. Conclusions: It is important to consider masking effects of self-produced sounds in auditory rehabilitation, and in the future design of hearing aids.

A voxel based morphometry (VBM) analysis of gray matter volume (GMV) loss in patients with refractory mesial temporal lobe epilepsy (MTLE) with and without depression

Objective: Study GMV differences in patients with depression, and mesial temporal lobe epilepsy (MTLE) with and without depression, compared to normal controls, by applying VBM technique. Method:We included 24 adults with MTLE without depression (17 women, 38.7 mean age), 24 adults with MTLE with depression (13 women, 39.6 mean age), and 96 healthy controls (75 women, 35.1 mean age). All MTLE patients were diagnosed by clinical, eletro and image features. Depression was diagnosed by a structured clinical interview (SCID I) and its sympomatology was checked by the Beck Depression Inventory. All patients underwent highresolution MRI scan. We performed VBM analysis on SPM5 and MATLAB7, comparing groups of patients with control group. The statistical analysis for all comparisons was performed with grand mean scaling, proportional threshold masking and implicit masking. The results were corrected for multiple comparisons using a false discovery rate of 5%. We also investigated the regional correlation between GMV in MTLE with depression, checking their performance on the BDI. This form of VBM was performed on the whole brain, using the general linear model protocols built into SPM5. Results: Half of the patients with MTLE also had depression. There wasno significative difference in termsof sex (p=0.371), epilepsyonset (p=0.495), epilepsy duration (p=0.129) and frequency of seizures (p=0.285) in thegroups ofMTLEwithorwithout depression.We found no significant difference between groups when the group of MTLE with depression was divided in right and left MTLE with depression (p=0.147). Besides the fact that the laterality was not a significant factor for depression in MTLE, the group of left MTLE with depression had a more severe depression than the group of right MTLE with depression (p=0.014). Therewasno regional correlation betweenGMV in MTLE with depression and their performance on the BDI. Patients with MTLE with depression had more areas of reduced volume. Conclusions: The neuropathologic changes of MTLE seem to be magnified in the presence of a chronic untreated depression disorder. The evidence of GMV loss in patients with MTLE with depression calls our attention to the importance of timely recognition and treatment of depression in patients with MTLE and also to the bidirectional relation between the two disorders and their frequent comorbid occurrence.

Effects of Age and Hearing Impairment on the Ability to Benefit From Temporal and Spectral Modulation

At poor signal-to-noise ratios, speech understanding may depend on the ability to combine speech fragments that are distributed across time and frequency. The goal of this study was to determine the effects of development and hearing impairment on this ability. Listeners in the present study included adults and children with normal hearing and with hearing impairment. The children with normal hearing included a younger group (aged 4.6-6.9 yr, N = 10) and an older group (aged 7.3-11.1 yr, N = 11). The adults with normal hearing were aged 19 to 27 yr (N = 10). Adults (aged 19-54 yr, N = 9) and children (aged 7.2-10.7 yr, N = 8) with hearing impairment were also tested. The two groups with hearing impairment had comparable mild/moderate bilateral sensorineural hearing impairment. Masked speech reception thresholds for sentences were determined in a baseline condition of steady speech-shaped noise and in noise that was temporally modulated, spectrally modulated, or both temporally and spectrally modulated. The results of normal-hearing listeners indicated higher masked speech reception thresholds for children than adults in steady noise. Adults and children showed the same magnitude of masking release for spectral modulation. Adults showed more masking release than the younger children for temporal modulation and showed more masking release than both the younger and older children for combined temporal/spectral modulation. Comparing normal-hearing and hearing-impaired listeners, the hearing-impaired listeners had higher masked speech reception thresholds in the steady noise condition and reduced masking release in the modulated noise conditions. Neither the two-way interaction between age and hearing impairment nor the three-way interaction between age, hearing impairment, and masking configuration was significant. Although the reduced masking release for temporal modulation shown by the younger children with normal hearing could be a result of poor temporal resolution, it more likely reflects inefficient use of speech cues in temporal gaps or factors stemming from higher signal-to-noise ratios required by children in the baseline condition. The reduced masking release for combined temporal/spectral modulation demonstrated by both the younger and older children with normal hearing may indicate that children in the age range tested here have some difficulty in combining speech information that is distributed across temporal and spectral gaps. Hearing impairment was associated with higher thresholds and reduced masking release in all modulation conditions. Children with hearing impairment showed the poorest performance of any group, consistent with additive effects of hearing loss and development.

Suprathreshold Perception of Tonal Components in Noise Under Conditions of Masking Release

Many technical sounds contain tonal components in a noise background. The present study investigates how such tonal components embedded in noise are perceived under conditions of enhanced detectability of the tone due to (i) amplitude modulation of the noise background or (ii) interaural disparities in the signal's phase. To quantify the sensation elicited by a tonal component in these masking-release conditions, the listeners are asked to adjust the level of the tone to have the same magnitude of tonal content (German “Tonhaltigkeit”) or to be perceived as equally loud as a tone which is masked by an unmodulated noise and presented diotically (baseline condition). For both sensations the signal-to-noise ratio at equal magnitude of the sensation is lower for the tone in the masking-release conditions than for the baseline condition. This is mainly due to the lower masked threshold of the tone in masking-release conditions. The eff ect is most prominent at low levels and decreases towards higher levels. A high correlation is observed between the data for the magnitude of tonal content and the partial loudness of the tone, demonstrating the similarity between these two sensations.

Understanding concurrent speech is not impaired by removal of spectro-temporal overlap

Removal of spectro-temporal overlap is the operation performed on acoustic signals in the time-frequency domain. It can be seen as extreme energetic masking, where the masking threshold is equal to the level of the masker. In Experiment 1 the triplets of words were presented concurrently with reversed speech of four speakers. The recognition of words with and without spectro-temporal overlap was compared. In Experiment 2, understanding of five words spoken simultaneously, with and without spectro-temporal overlap was compared. Over 50 subjects took part in both experiments. The joint results showed no significant difference between unprocessed presentation and the processed one, where spectro-temporal overlap was removed. This is rather surprising, as the amount of information provided to the ear was considerably reduced in the processed case.

Parallelization of Speech Compression Algorithm Based on Human Auditory System on Multicore System

Human auditory system has been successfully employed in speech compression to reduce bit rate requirement. Previous researches on speech compression stated that the use of simultaneous masking and/or temporal masking reduced the bit rate requirement while maintained perceptual quality. However, the benefit of using auditory masking in speech coding was outweighed by the amount of computation required to calculate masking threshold. Nevertheless, the current advances in microprocessor technology shows that to overcome heat generation and power cap, a multicore processor integrates two or more independent cores into a single package become popular. The objective of this research is to develop and implement a novel parallel speech compression algorithm based on human auditory system on a multicore system. To achieve a scalable parallel speech coding algorithm, single program multiple data (SPMD) programming model was used, in which a single program was written for all cores. Matlab parallel computing toolbox was used in the implementation. Finally, the performance of the developed parallel algorithm was evaluated using Perceptual Evaluation of Speech Quality (PESQ) and parallel execution time. Results show that the average PESQ score and pulse reduction for all 30 files when both auditory masking models were used is around 4.00 (transparent quality) and 41.12%, respectively. Moreover, the maximum speed achievable on our parallel experiment was around 2.45 if four cores were fully utilized.

A Low-Complexity Spectro-Temporal Distortion Measure for Audio Processing Applications

Perceptual models exploiting auditory masking are frequently used in audio and speech processing applications like coding and watermarking. In most cases, these models only take into account spectral masking in short-time frames. As a consequence, undesired audible artifacts in the temporal domain may be introduced (e.g., pre-echoes). In this article we present a new low-complexity spectro-temporal distortion measure. The model facilitates the computation of analytic expressions for masking thresholds, while advanced spectro-temporal models typically need computationally demanding adaptive procedures to find an estimate of these masking thresholds. We show that the proposed method gives similar masking predictions as an advanced spectro-temporal model with only a fraction of its computational power. The proposed method is also compared with a spectral-only model by means of a listening test. From this test it can be concluded that for non-stationary frames the spectral model underestimates the audibility of introduced errors and therefore overestimates the masking curve. As a consequence, the system of interest incorrectly assumes that errors are masked in a particular frame, which leads to audible artifacts. This is not the case with the proposed method which correctly detects the errors made in the temporal structure of the signal.

A NEW SPEECH ENHANCEMENT TECHNIQUE USING PERCEPTUAL CONSTRAINED SPECTRAL WEIGHTING FACTORS

This paper deals with musical noise result from perceptual speech enhancement type algorithms and especially wiener filtering. Although perceptual speech enhancement methods perform better than the non perceptual methods, most of them still return annoying residual musical noise. This is due to the fact that if only noise above the noise masking threshold is filtered then noise below the noise masking threshold can become audible if its maskers are filtered. It can affect the performance of perceptual speech enhancement method that process audible noise only. In order to overcome this drawback here proposed a new speech enhancement technique. It aims to improve the quality of the enhanced speech signal provided by perceptual wiener filtering by controlling the latter via a second filter regarded as a psychoacoustically motivated weighting factor. The simulation results shows that the performance is improved compared to other perceptual speech enhancement methods

MASKING THRESHOLD DIFFERENTIAL (MLD): PILOT STUDY

MASKING THRESHOLD DIFFERENTIAL (MLD): PILOT STUDY

The effect of carrier level on tuning in amplitude-modulation masking

The effect of carrier level on tuning in modulation masking was investigated for noise and tonal carriers. Bandwidths of the modulation filters, estimated from the masked detection thresholds using an envelope power spectrum model, were independent of level for the noise carrier but seemed to decrease with increasing level for the tonal carrier. However, the apparently sharper tuning could be explained by increased modulation sensitivity and modulation dynamic range with increasing level rather than improved modulation-frequency selectivity. Consistent with this interpretation, the addition of a high-pass noise with a level adjusted to maintain the same threshold for the detection of the signal modulation for each carrier level used eliminated the effect of level on tuning. Overall, modulation filters estimated from psychophysical data do not depend on level in contrast to the modulation transfer functions obtained from neural recordings in the inferior colliculus in physiological studies. The results highlight differences between the characteristics of modulation processing obtained from neural data and perception. The discrepancies indicate the need for further investigation into physiological correlates of tuning in modulation processing.

The Effect of Gabapentin on Gap Detection and Forward Masking in Young and Old Gerbils

Auditory temporal processing frequently appears more affected in old subjects than would be predicted by the degree of peripheral hearing loss, pointing to an age-dependent central processing deficit. In parallel, an age-dependent decline of inhibitory function has been demonstrated in the auditory pathway, suggesting a causal relationship between temporal processing and inhibition. Gabapentin has been specifically synthesized as a potential gamma-amino-butyric-acid (GABA) mimetic with the capability to cross the blood-brain barrier. Gabapentin treatment ameliorated tinnitus in a rat model and improved tinnitus annoyance in humans with acoustic trauma. Consequently, the present study evaluated the effect of gabapentin on auditory temporal processing in the gerbil model. Psychometric functions were collected for different test paradigms. (A) "Gap detection": The detection of a gap in the middle of a 800 msec broadband noise pulse was determined either at 15 or at 30 dB SL. (B) "Forward masking": The detection of a 20 msec probe stimulus following 2.5 msec after a 400 msec 40 dB SPL masker was determined with masker and probe frequency at 2.85 kHz. The effect of gabapentin was evaluated by collecting gap detection and forward masking functions before, during, and after treating gerbils with gabapentin doses of 115 or 350 mg/kg/day administered via drinking water. Data under different experimental conditions were collected for groups of 3 to 5 young (<2 years) and 6 to 10 old (>2 years) gerbils. Two-way analyses of variance for the factors age groups and treatment groups with subsequent pairwise comparisons for significant effects were used for the statistical evaluation of the data. For gap detection, mean thresholds were significantly increased in the group of old as compared with the young gerbils at 30 dB SL (young 2.0 msec; old 3.2 msec) and at 15 dB SL (young 2.9 msec; old 9.1 msec). Gabapentin had no significant effect on gap detection, and there was no significant interaction between age group and gabapentin treatment. Mean thresholds in the forward masking paradigm were significantly elevated in old (45.5 dB SPL) as compared with young (35.0 dB SPL) gerbils. Overall, gabapentin had no significant effect on masked thresholds; however, there was a significant interaction between treatment and age. Subsequent pairwise comparisons revealed no significant effect on masked thresholds in old gerbils but showed significantly elevated thresholds of young gerbils during 350 mg/kg gabapentin (38.3 dB SPL) compared with thresholds obtained in young gerbils before (32.3 dB SPL) and after (33.5 dB SPL) treatment. Gabapentin did not exert a therapeutic effect on impaired gap detection and forward masking in old gerbils. The lack of an effect of gabapentin on impaired auditory temporal processing in old gerbils and the finding of elevated masked thresholds in young gerbils can be reconciled with reports of only moderate GABAergic effects compared with other drugs (e.g., comparing elevation of GABA levels in the brain by gabapentin and vigabatrin) and effects due to binding of gabapentin to alpha-2-delta units of voltage-gated calcium channels.

Effect of Harmonicity on the Detection of a Signal in a Complex Masker and on Spatial Release from Masking

The amount of masking of sounds from one source (signals) by sounds from a competing source (maskers) heavily depends on the sound characteristics of the masker and the signal and on their relative spatial location. Numerous studies investigated the ability to detect a signal in a speech or a noise masker or the effect of spatial separation of signal and masker on the amount of masking, but there is a lack of studies investigating the combined effects of many cues on the masking as is typical for natural listening situations. The current study using free-field listening systematically evaluates the combined effects of harmonicity and inharmonicity cues in multi-tone maskers and cues resulting from spatial separation of target signal and masker on the detection of a pure tone in a multi-tone or a noise masker. A linear binaural processing model was implemented to predict the masked thresholds in order to estimate whether the observed thresholds can be accounted for by energetic masking in the auditory periphery or whether other effects are involved. Thresholds were determined for combinations of two target frequencies (1 and 8 kHz), two spatial configurations (masker and target either co-located or spatially separated by 90 degrees azimuth), and five different masker types (four complex multi-tone stimuli, one noise masker). A spatial separation of target and masker resulted in a release from masking for all masker types. The amount of masking significantly depended on the masker type and frequency range. The various harmonic and inharmonic relations between target and masker or between components of the masker resulted in a complex pattern of increased or decreased masked thresholds in comparison to the predicted energetic masking. The results indicate that harmonicity cues affect the detectability of a tonal target in a complex masker.

Drift Correction Modulation scheme for digital signal processing

The article describes a new method of embedding and extracting the digital watermark in an acoustic signal, which operates in the frequency domain and uses a drift correction modulator of the watermark’s phase angle, as well as a precise correction procedure of the watermark signal to the minimum masking threshold. The Drift Correction Modulation (DCM) has been worked out for the needs of the watermarking system with a large data payload and robustness against degrading factors which occur during signal processing. The digital watermark embedded in the original signal using the DCM method is inaudible and robust against the majority of degrading factors. The DCM method may be used in Digital Signal Processing applications, e.g. for a hidden authentication of subscribers in telecommunication channels or for determining the output phase mistuning of devices. DCM is characterized by a high normalized data payload of the watermark signal and may be implemented in applications of hidden and secure data transmission. The paper presents the results of auditory tests according to the ITU-R 1116-1 standard; moreover, results of the watermark extraction tests in a VHF radio link, with the use of military tactical radio stations have been presented.

지각 특성 및 라우드니스를 이용한 입체음향의 성능 개선

인간의 청각기관은 소리의 방향과 거리인지에 있어서 양 귀에 들어오는 소리세기의 차이, 위상의 차이, 그리고 주파수 스펙트럼의 차이 등의 정보들을 복합적으로 이용한다. 이런 정보를 종합적으로 포함하고 있는 것을 머리전달함수라 하며, 이를 이용하여 실질적으로 존재하지 않는 음원을 근사적으로 생성할 수 있는 입체음향 시스템을 구현할 수 있다. 그러나 비개인화 된 머리전달함수는 음상정위 성능을 떨어뜨리는 주된 원인이 된다. 이에 본 논문에서는 이 머리전달함수를 이용한 3차원 음상정위를 위해 사람의 청각 특성을 이용한 알고리즘을 제안한다. 청자가 정확한 방향을 인지하기 위해 1차로 측정된 머리전달함수의 청각 자극 에너지를, 2차로 전역 마스킹 임계치와 라우드니스를 이용하여 방향감을 강조하였다. 제안된 알고리즘의 성능 평가를 위해 청감 테스트를 수행하였으며 실험결과 기존의 알고리즘에 비해 입체음향의 전체적인 인지도가 50% 이상 증가하였음을 확인할 수 있었다. The binaural auditory system of human has ability to differentiate the direction and the distance of the sound sources by using the information which are inter-aural intensity difference(IID), inter-aural time difference(ITD) and/or the spectral shape difference(SSD). These information is generated from the acoustical transfer of a sound source to pinna, the outer ears. We can create a virtual sound system using the information which is called Head related transfer function(HRTF). However the performance of 3D sound is not always satisfactory because of non-individual characteristics of the HRTF. In this paper, we propose the algorithm that uses human's auditory characteristics for accurate perception. To achieve this, excitation energy of HRTF, global masking threshold and loudness are applied to the proposed algorithm. Informal listening test shows that the proposed method improves the sound localization characteristics much better than conventional methods.

The relationship between MOC reflex and masked threshold

Otoacoustic emission (OAE) amplitude can be reduced by acoustic stimulation. This effect is produced by the medial olivocochlear (MOC) reflex. Past studies have shown that the MOC reflex is related to listening in noise and attention. In the present study, the relationship between strength of the contralateral MOC reflex and masked threshold was investigated in 19 adults. Detection thresholds were determined for 1000-Hz, 300-ms tone presented simultaneously with one repetition of a 300-ms masker in an ongoing train of masker bursts. Three masking conditions were tested: 1) broadband noise 2) a fixed-frequency 4-tone complex masker and 3) a random-frequency 4-tone complex masker. Broadband noise was expected to produce energetic masking and the tonal maskers were expected to produce informational masking in some listeners. DPOAEs were recorded at fine frequency intervals from 500 to 4000 Hz, with and without contralateral acoustic stimulation. MOC reflex strength was estimated as a reduction in baseline level and a shift in frequency of DPOAE fine-structure maxima near 1000-Hz. MOC reflex and psychophysical testing were completed in separate sessions. Individuals with poorer thresholds in broadband noise and in random-frequency maskers were found to have stronger MOC reflexes.

인간의 청각 특성을 이용한 입체음향의 방향감 개선

The Head Related Transfer Function (HRTF) means a process related to acoustic transmission from 3d space to the listener`s ear. In other words, it contains the information that human can perceive locations of sound sources. So, we make virtual 3d sound using HRTF, despite it doesn`t actually exist. But, it can deteriorate some three-dimensional effect by the confusion between front and back directions due to the non-individual HRTF depending on each listener. In this paper, we proposed the new algorithm to reduce the confusion of sound image localization using human`s acoustic characteristics. The frequency spectrum and global masking threshold of 3d sounds using HRTF are used to calculate the psychoacoustical differences among each directions. And perceptible cues in each critical band are boosted to create effective 3d sound. As a result, we can make the improved 3d sound, and the performances are much better than conventional methods.

Narrow noise band detection in a complex masker: Masking level difference due to harmonicity

Three experiments investigated listeners' ability to detect a narrow band of noise, centered on one partial of a random-phase complex tone, as a function of inharmonicity. Inharmonicity was generated by randomly mistuning the partial frequencies from a 100-Hz fundamental frequency (F0). In experiment 1, masked detection thresholds were lower when the masker was harmonic than when it was inharmonic for target bands in the range 0.5–2.5 kHz. The presence of this masking level difference due to harmonicity (HMLD) in regions of resolved partials and the reduction of the HMLD with increasing center frequency did not support the idea that HMLD was primarily caused by the envelope modulations produced by the beating of unresolved partials within an auditory filter. In experiment 2, masker mistunings ranging beyond 12% of the F0 disrupted the HMLD while smaller mistunings gave thresholds similar to a harmonic masker. In experiment 3, all partials contributed to some extent to the HMLD, but the harmonicity of partials neighboring the target had a greater influence than distant partials. The observed HMLDs can best be accounted for by a mechanism of harmonic cancellation.

Masking level difference in an adaptive procedure for clinical investigation

Objective: Masking level difference (MLD) tests are an established component of auditory processing test batteries; however, normative data for these tests vary according to procedure. The purpose of this study was to establish a standardized procedure for clinical use in the measurement of the MLD Design: A newly developed computer software program using both an adaptive procedure (MLDA) and a Békésy procedure (MLDB) was evaluated in this study. Study sample: Forty normal-hearing, native-English speaking adults between the ages of 18 and 26 years were included in the study. Results: Both the MLDA and MLDB procedures showed statistically significant sex differences in the masked thresholds used to obtain the MLD, but not for the calculated MLD value; hence, normative data need not be reported separately by sex. Furthermore, statistically significant differences between procedures were observed, with the MLDA procedure producing higher MLDs. The MLDA procedure permitted a d’ analysis, which could not be determined using the MLDB procedure. For MLDA, d’ = 1.4, test sensitivity = 96.4%, and test specificity = 60.3%. Conclusions: The results of this study indicate that MLDA is a more efficient testing procedure due to MLDA's higher MLD average and the statistical data available (d’, and measures of sensitivity and specificity).SumarioObjetivo: Las pruebas de Diferencia en el Nivel de Enmascaramiento (MLD) son un componente establecido de las baterías de pruebas de procesamiento auditivo; sin embargo, los datos normativos para estas pruebas varían de acuerdo al procedimiento. Diseño: Se evaluó en este estudio un programa de computadora recientemente desarrollado que utiliza un procedimiento adaptativo (MLDA) y un procedimiento de Békésy (MLDB). Muestra del Estudio: Se incluyeron cuarenta adultos normales, hablantes naturales del inglés, en edades entre los 18 y los 26 años. Resultados: Tanto el procedimiento MLDA, como el MLDB mostraron diferencias estadísticamente significativas en cuanto a género en los umbrales enmascarados usados para obtener la MLD, pero no para el valor calculado de MLD por tanto, los datos normativos no tiene que se reportados separadamente por sexo. Más aún, se observaron diferencias estadísticamente significativas entre los procedimientos, produciendo el MLDA niveles más altos de MLD. El procedimiento de MLDA permitió un análsis d’, que no pudo ser determinado usando el procedimiento MLDB. Para MLDA, d’ = 1.4, sensibilidad de la prueba = 96.4%, y especificidad de la prueba = 60.3%. Conclusiones: Los resultados de este estudio indican que el MLDA es un procedimiento de evaluación más eficiente debido a su MLD promedio más alto y a los datos estadísticos disponibles (d’y las medidas de sensibilidad y especificidad).

Spectrum Resolving Power of Hearing: Measurements, Baselines, and Influence of Maskers.

Contemporary methods of measurement of frequency resolving power in the auditory system are reviewed. Majority of classical methods are based on the frequency-selective masking paradigm and require multi-point measurements (a number of masked thresholds should be measured to obtain a single frequency-tuning estimate). Therefore, they are rarely used for practical needs. As an alternative approach, frequency-selective properties of the auditory system may be investigated using probes with complex frequency spectrum patterns, in particular, rippled noise that is characterized by a spectrum with periodically alternating maxima and minima. The maximal ripple density discriminated by the auditory system is a convenient measure of the spectrum resolving power (SRP). To find the highest resolvable ripple density, a phase-reversal test has been suggested. Using this technique, normal SRP, its dependence on probe center frequency, spectrum contrast, and probe level were measured. The results were not entirely predictable by frequency-tuning data obtained by masking methods. SRP is influenced by maskers, with on- and off-frequency maskers influencing SRP very differently. Dichotic separation of the probe and masker results in almost complete release of SRP from influence of maskers.