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A Kohlrausch

Publications and source records attributed to A Kohlrausch.

At least 37 records · Page 2Linked to original sources
PubMed1996

A quantitative model of the "effective" signal processing in the auditory system. II. Simulations and measurements.

This and the accompanying paper [Dau et al., J. Acoust. Soc. Am. 99, 3615-3622 (1996)] describe a quantitative model for signal processing in the auditory system. The model combines several stages of preprocessing with a decision device that has the properties of an optimal detector. The present paper compares model predictions for a variety of experimental conditions with the performance of human observers. Simulated and psychophysically determined thresholds were estimated with a three-interval forced-choice adaptive procedure. All model parameters were kept constant for all simulations discussed in this paper. For frozen-noise maskers, the effects of the following stimulus parameters were examined: signal frequency, signal phase, temporal position and duration of the signal within the masker under conditions of simultaneous masking, masker level, and masker duration under conditions of forward masking, and backward masking. The influence of signal phase and the temporal position of the signal, including positions at masker onset, was determined for a random-noise masker and compared with corresponding results obtained for a frozen noise. The model describes all the experimental data with an accuracy of a few dB with the following exceptions: forward-masked thresholds obtained with brief maskers are too high and the change in threshold with a change in signal duration is too small. Both discrepancies have their origin in the adaptation stages in the preprocessing part of the model. On the basis of the wide range of simulated conditions we conclude that the present model is a successful approach to describing the detection process in the human auditory system.

Adult↗
PubMed1995

The role of envelope fluctuations in spectral masking.

Two experiments are reported in this study. In the first experiment the masking effect of five different types of narrow-band maskers was compared. The masker was either a tone, a narrow-band Gaussian noise, or a multiplication noise obtained by multiplying a sinusoid with a low-pass Gaussian noise. The noise maskers had a bandwidth of either 20 or 100 Hz. In all cases the masker had a center frequency of 1.3 kHz and a duration of 500 ms. Five-point growth-of-masking functions were measured using a 2-kHz tonal target with a duration of 400 ms, temporally centered in the masker. Six subjects participated in the experiment. Although considerable intersubject differences were observed, the data of all subjects showed several common trends. First, the tonal maskers produced more masking than the noise maskers. Second, Gaussian noise maskers produced more masking than multiplication noise maskers of the same bandwidth. Finally, 100-Hz-wide noise maskers produced more masking than 20-Hz-wide maskers of the same type. Differences in masked thresholds between the various masker types generally increased with masker level, and exceeded 25 dB in some conditions. The results are discussed in terms of masker envelope fluctuations. In the second experiment the masking effect was investigated for a bandpass noise at 1.3 kHz, with regular zero crossings, but with the envelope characteristics of a 100-Hz-wide Gaussian noise. Five-point growth-of-masking functions were measured using a tonal target of 2 kHz.(ABSTRACT TRUNCATED AT 250 WORDS)

Auditory Perception↗
PubMed1995

Comparison of auditory filter shapes obtained with notched-noise and noise-tone maskers.

The notched-noise method has been widely used to estimate the shape of the auditory filter. Results obtained using this method may be influenced by combination bands produced by the interaction of components within the upper band of noise in the notched-noise masker. To assess the possible effect of such combination bands, results were compared for two types of masker: A notched noise, as used in previous experiments; and a masker in which the upper band of noise was replaced by a sinusoid with a frequency corresponding to the lower edge frequency of that band. This is referred to as the noise-tone masker. The signal frequency was 2 kHz, and measurements were obtained for two different spectrum levels of the noise masker, 30 and 45 dB. Auditory filter shapes derived using the two maskers were similar on their low-frequency sides, as expected. The low-frequency sides were less steep at the higher masker level. The high-frequency sides of the auditory filters derived using the noise-tone masker were sometimes slightly steeper than those obtained using the notched-noise masker, but the effect was generally small. Changes with level on the high-frequency sides were not consistent across subjects. An analysis of the notched-noise data taking into account the effects of the combination bands suggests that the maximal spectrum level of the combination bands, in the region just below the lower spectral edge of the primary noise band, is about 20 to 30 dB below the spectrum level of the primary band.(ABSTRACT TRUNCATED AT 250 WORDS)

Auditory Perception↗
PubMed1995

Phase effects in masking related to dispersion in the inner ear. II. Masking period patterns of short targets.

This article investigates how the amplitude and phase characteristics of the inner ear influence the spectrotemporal representation of harmonic complex sounds. Five experiments are reported, in each of which three sets of maskers are compared that differ only in their phase spectra. The amplitude spectra of the complexes were flat and the phase choices were (a) zero phase, (b) Schroeder phases with a positive sign, and (c) Schroeder phases with a negative sign. In the first four experiments, the spectra contained all harmonics between 200 and 2000 Hz. In experiments 1 and 2, the signal frequency was fixed at 1100 Hz and the fundamental frequency of the maskers was varied. In experiments 3 and 4, the fundamental frequency of the maskers was fixed and the signal frequency varied between 200 and 2000 Hz. In experiments 1 and 3, the signal duration was long compared to the period of the maskers. In experiments 2 and 4, the signal duration was only 5 ms and thresholds were determined for different time points within the masker's period. The results show a strong correlation between the minima of the short signal's thresholds and the threshold of the long signal. In experiment 5, the spectral extent of the masker was shifted to values one octave lower (100 to 1000 Hz) or one or two octaves higher (400 to 4000 Hz and 800 to 8000 Hz, respectively). For each spectral region, masked thresholds of a long signal were obtained for three values of the fundamental frequency. In all five experiments the thresholds depended very much on the specific phase choices with differences of up to 25 dB. The masker with a negative Schroeder phase always led to the highest thresholds. The thresholds of the masker with a positive Schroeder phase, on the other hand, were for a wide range of parameters lower than the thresholds for the zero-phase masker. These phase effects are most likely caused by the phase characteristic of the basilar-membrane filter, which affects the flat envelopes of the two Schroeder-phase maskers in a very different way. For an appropriate choice of parameters, one of the two becomes even more strongly modulated than the zero-phase complex. This latter observation imposes some restrictions on the second derivative (curvature) of the phase-versus-frequency relation for the auditory filters.

Adult↗
PubMed1994

Using an excitation-pattern model to predict auditory masking.

This paper evaluates the extent to which auditory masking can be reliably predicted from excitation patterns. For this purpose a quantitative model proposed by Glasberg and Moore [Hear. Res. 47, 103-138 (1990)] was used to calculate excitation patterns evoked by stationary sounds. Model simulations were performed for a number of masking experiments, reported in the literature, by calculating excitation patterns for the masker-alone as well as for the masker-plus-target conditions. As a threshold criterion, a difference between the two patterns of 1 dB at any frequency was imposed. For narrow-band-noise masking patterns, the method yields a fairly precise prediction of experimental data. For other conditions, however, systematic deviations between model predictions and data are observed. For instance, the model does not reproduce the typical tip-tail shape of psychophysical tuning curves. Furthermore, the nonlinearities in level dependence are not correctly described, and the model fails to reproduce a realistic two-tone masking curve.

Acoustic Stimulation↗
PubMed1994

Effect of masker level on overshoot in running- and frozen-noise maskers.

Masked thresholds were measured with running- and frozen-noise maskers. The 5-kHz signal was 2 ms in duration. The masker was low-pass noise (20 Hz-10 kHz); its total duration was 300 ms. The overall level of the masker was 30, 50, or 70 dB SPL. The onset of the signal was delayed by 0, 3, 8, 18, 198, or 278 ms relative to the onset of the masker. In all frozen-noise measurements, the signal was added to the same fine structure of the noise. Overshoot in frozen noise was measured for two starting phases of the signal that led to a 10-dB difference for large signal-onset delays. In all three configurations (running noise and frozen noise with two different signal phases) masker level had a similar influence on overshoot. At the intermediate masker level (50 dB SPL), a significant amount of overshoot (up to 15 dB) was observed in all three conditions. At the low and the high masker levels, overshoot was very much reduced, and even became negative in most conditions for the 30-dB-SPL masker. For the 50-dB frozen-noise masker, the total variation of thresholds with signal phase was 8 to 11 dB for long signal-onset delays, but only 3 to 6 dB for short delays. For the low- and high-level maskers, where only a small overshoot was observed, the threshold variation with phase for a signal at masker onset was the same as that for the long-delay condition. An explanation for the variation of signal detectability with masker level is proposed that refers explicitly to the compressive input-output characteristic of the basilar membrane at intermediate levels.

Adult↗
PubMed1992

Pitch related to spectral edges of broadband signals.

A complex tone often evokes a pitch sensation associated with its extreme spectral components, besides the holistic pitch associated with its fundamental frequency. We studied the edge pitch created at the upper spectral edge of complexes with a low-pass spectrum by asking subjects to adjust the frequency of a sinusoidal comparison tone to the perceived pitch. Measurements were performed for different values of the fundamental frequency and of the upper frequency of the complex as well as for three different phase relations of the harmonic components. For a wide range of these parameters the subjects could adjust the comparison tone with a high accuracy, measured as the standard deviation of repeated adjustments, to a frequency close to the nominal edge frequency. The detailed dependence of the matching accuracy on temporal parameters of the harmonic complexes suggests that the perception of the edge pitch in harmonic signals is related to the temporal resolution of the hearing system. This resolution depends primarily on the time constants of basilar-membrane filters and on additional limitations due to neuronal processes.

Acoustic Stimulation↗
PubMed1992

Spectral integration of broadband signals in diotic and dichotic masking experiments.

The method of Gässler [Acustica 4, 408-414 (1954)] was used to measure the audibility of multicomponent signals as a function of their bandwidth against a broadband, white-noise masker. Test signals were composed of 1 to 41 sinusoids with a spectral spacing of 10 Hz and were always spectrally centered around 400 Hz. Masker duration was 400 ms and the 300-ms signals were centered within the noise intervals. A three-interval forced-choice procedure with adaptive level adjustment was applied. NoSo, NoSm, NoS pi, and N pi So masked thresholds were obtained for four subjects. A comparison of the diotic and the three dichotic conditions yields no significant difference in the bandwidth dependence and suggests equal integration bandwidths for all conditions. However, the original results of Gässler could not be replicated: Neither were the overall levels of signals with a bandwidth below the critical bandwidth constant nor were the results for broadband signals in accordance with a single-band model of detection. The narrow-band data are much better described by calculating the overall signal level at the output of a rounded exponential filter [Patterson et al., J. Acoust. Soc. Am. 72, 1788-1803 (1982)] with an equivalent rectangular bandwidth of 65 Hz. For broader signal bandwidths, the signal level at threshold increases as predicted by a multiband model.

Acoustics↗
PubMed1992

Differences in auditory performance between monaural and dichotic conditions. I: masking thresholds in frozen noise.

Thresholds of a 5-ms, 1-kHz signal were determined in the presence of a frozen-noise masker. The noise had a flat power spectrum between 20 Hz and 5 kHz and was presented with a duration of 300 ms. The following interaural conditions were tested with four listeners: Noise and signal monaural at the same ear (monaural condition, NmSm), noise and signal identical at both ears (diotic condition, NoSo), noise identical at both ears and signal monaural (dichotic condition, NoSm) and uncorrelated noise at the two ears and signal monaural (NuSm). The signal was presented at a fixed temporal position with respect to the frozen noise in all measurements and thresholds were determined for different starting phases of the carrier frequency of the signal. Variation of the carrier phase strongly influenced the detection in the diotic condition and the masked thresholds varied by more than 10 dB. The pattern of thresholds for the monaural condition was less variable and the thresholds were generally higher than for the diotic condition. The monaural-diotic difference for specific starting phases amounted to as much as 8 dB. Comparison measurements using running noise maskers revealed no such difference. This relation between monaural and diotic thresholds was further investigated with eight additional subjects. Again, monaural and diotic thresholds in running noise were identical, while in frozen noise, diotic thresholds were consistently lower than monaural thresholds, even when the ear with the lower NmSm threshold was compared. For the starting phase showing the largest monaural-diotic difference, the thresholds for NoSm lay between the monaural and the diotic values. At other starting phases, the NoSm threshold was clearly lower than both the NmSm and the NoSo threshold. One possible explanation of the observed monaural-diotic differences relates to contralateral efferent interaction between the right and the left hearing pathway. A prediction based on this explanation was verified in a final experiment, where frozen-noise performance for NmSm was improved by simultaneously presenting an uncorrelated running noise to the opposite ear.

Acoustic Stimulation↗
PubMed1990

Binaural masking experiments using noise maskers with frequency-dependent interaural phase differences. I: Influence of signal and masker duration.

In this paper previous experiments on auditory filter shapes in binaural masking experiments [A. Kohlrausch, J. Acoust. Soc. Am. 84, 573-583 (1988)] are extended to a wider range of masker and signal durations. The masker was a dichotic broadband noise with frequency-dependent interaural parameters. The interaural phase difference of the masker was 0 below 500 Hz and pi above 500 Hz. Signal frequency varied between 200 and 800 Hz, and the signal was presented either monaurally (Sm) or binaurally in antiphase (S pi). In the first experiment, the masker duration was fixed at 500 ms and signals of 250 and 20 ms were used. In the second experiment, the signal duration was fixed at 20 ms, and the masker duration was reduced to 25 ms. The results from both experiments are consistent with studies using No or N pi maskers: The binaural masking level difference (BMLD) increases slightly for shorter test signals and decreases strongly for short maskers. The BMLD patterns of the first experiment are well described by the auditory-filter model derived for stationary test signals, if the additional influence of "off-frequency listening" for the short test signal is taken into account. The BMLDs resulting from the second experiment (25-ms masker), however, are much lower than predicted by this filter model This outcome supports previous observations that binaural unmasking becomes less effective for very short masker durations and indicates that this effect is even stronger for maskers with a complex structure of interaural parameters.

Attention↗
PubMed1990

Binaural masking experiments using noise maskers with frequency-dependent interaural phase differences. II: Influence of frequency and interaural-phase uncertainty.

This study investigates whether binaural signal detection is improved by the listener's previous knowledge about the interaural phase relations of masker and test signal. Binaural masked thresholds were measured for a 500-ms dichotic noise masker that had an interaural phase difference of 0 below 500 Hz and of pi above 500 Hz. The thresholds for two difference 20-ms test signals were determined within the same measurement using an interleaved adaptive 3-interval forced-choice (3IFC) procedure. In each 3IFC trial, both signals could occur with equal probability (uncertainty). The two signals differed in frequency and interaural phase in such a way that one signal always had a frequency above the masker edge frequency (500 Hz) and no interaural phase difference (So), whereas the other signal frequency was below 500 Hz and the interaural phase difference was pi (S pi). The frequencies of a signal pair remained fixed during the whole 3IFC track. These two signals thus lead to two different binaural conditions, i.e., NoS pi for the low-frequency signal and N pi So for the high-frequency signal. For comparison, binaural masked thresholds were measured with the same masker for fixed signal frequency and phase. The binaural masking level differences (BMLDs) resulting from the two experimental conditions show no significant difference. This indicates that the binaural system is able to apply different internal transformations or processing strategies simultaneously in different critical bands and even within the same critical band.

Attention↗
PubMed1988

Auditory filter shape derived from binaural masking experiments.

The shape of the auditory filter was calculated from binaural masking experiments. Two different types of maskers were used in the study, a masker that was interaurally in phase at all frequencies (No), and a masker with an interaural phase difference of 0 below 500 Hz and of pi above 500 Hz. The test-signal frequency varied between 200 and 800 Hz, and the test signal was presented either monaurally (Sm) or binaurally in antiphase (S pi). By comparing the masked thresholds from the two experimental conditions, the following conclusion can be drawn: The threshold of the test signal is only affected by the masker phase within a narrow frequency range around the test frequency. Thus, for test-signal frequencies well above or below 500 Hz, no influence of the phase transition on the BMLD is observed, and normal masked thresholds for No and N pi maskers are obtained. For test frequencies around 500 Hz, the step in interaural phase difference leads to a decrease in the interaural correlation of the masker within the critical band around the test-signal frequency. This results in strong threshold changes for both monaural and binaural signals. A calculation of the auditory filter shape from the masked threshold values was performed under the assumption that the masked threshold is only dependent on the interaural cross correlation of the masker within the filter band. Using the formula of the EC theory for the relation between masker correlation and BMLD, the experimental data are well described by a trapezoidal filter with an equivalent rectangular bandwidth of 80 to 84 Hz.

Adult↗
PubMed1986

The influence of signal duration, signal frequency and masker duration on binaural masking level differences.

Binaural masked thresholds were measured to study the influence of masker and test signal duration on binaural unmasking for three different interaural phase relations (N0S0, N0S pi and N pi S0) and for test signal frequencies ranging from 200 to 800 Hz. Six observers participated in this study. An adaptive 3 Interval Forced Choice paradigm was employed. Reducing the signal duration from 250 to 20 ms results in an average binaural masking level difference (BMLD) increase of 2.5 dB for all frequencies and both dichotic conditions. Masker duration, however, has a more distinct influence on BMLD: a decrease from 500 to 25 ms reduces the BMLD in the N0S pi condition by 7 dB and in the N pi S0 condition up to 11 dB at low frequencies. These results reveal further evidence for different detection mechanisms in monaural and binaural masking experiments.

Adult↗
PubMed1986

Phase effects in masking related to dispersion in the inner ear.

Phase effects in masking experiments using multitone maskers are usually associated with strong variations in the masker envelope. In this article, psychoacoustic experiments with such maskers that lead to phase-dependent threshold variations of up to 20 dB, although the phase transformation leaves the envelope unchanged, are described. However, after filtering the maskers with a realistic basilar membrane model, the envelopes are different owing to the models phase-dispersive properties. Comparison of model outputs with the experimental results reveals a strong correlation between the two for a wide range of parameters, provided one makes the additional assumption that the ear has a minimum integration time of a few milliseconds.

Auditory Threshold↗