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PubMed2001

A measure for predicting audibility discrimination thresholds for spectral envelope distortions in vowel sounds.

Both in speech synthesis and in sound coding it is often beneficial to have a measure that predicts whether, and to what extent, two sounds are different. This paper addresses the problem of estimating the perceptual effects of small modifications to the spectral envelope of a harmonic sound. A recently proposed auditory model is investigated that transforms the physical spectrum into a pattern of specific loudness as a function of critical band rate. A distance measure based on the concept of partial loudness is presented, which treats detectability in terms of a partial loudness threshold. This approach is adapted to the problem of estimating discrimination thresholds related to modifications of the spectral envelope of synthetic vowels. Data obtained from subjective listening tests using a representative set of stimuli in a 3IFC adaptive procedure show that the model makes reasonably good predictions of the discrimination threshold. Systematic deviations from the predicted thresholds may be related to individual differences in auditory filter selectivity. The partial loudness measure is compared with previously proposed distance measures such as the Euclidean distance between excitation patterns and between specific loudness applied to the same experimental data. An objective test measure shows that the partial loudness measure and the Euclidean distance of the excitation patterns are equally appropriate as distance measures for predicting audibility thresholds. The Euclidean distance between specific loudness is worse in performance compared with the other two.

Auditory Threshold↗
PubMed2001

Revisiting relations between loudness and intensity discrimination.

A comparison is made between the variation of delta Ljnd with L (loudness), based on the beat-detection data of Riesz at 1 kHz [Phys. Rev. 31, 867-875 (1928)], and analogous relations obtained from a cross section of studies. Data analysis shows that only beat detection exhibits the degree of level-dependent variation in slope relating log (delta Ljnd) to log (L) described in a recent paper by Allen and Neely [J. Acoust. Soc. Am. 102, 3628-3646 (1997)]. Moreover, the slope variation determined from beat detection is not dependent on the detailed shape of the loudness function. The results imply that Allen and Neely's strong conclusions about the dependence of delta Ljnd on L are too tightly coupled to Riesz's methodology to be generally applicable.

Audiometry↗
PubMed2001

Intracochlear pressure measurements related to cochlear tuning.

Pressure in turn one of the scala tympani (s.t.) was measured close to the basilar membrane (b.m.) and at additional positions as the pressure sensor approached and/or withdrew from the b.m. The s.t. pressure measured within about 100 microm of the b.m. varied rapidly in space at frequencies around the region's best frequency. Very close to the b.m. the s.t. pressure was tuned and scaled nonlinearly with sound level. The scala vestibuli (s.v.) pressure was measured at one position close to the stapes within seconds of the s.t. pressure and served primarily as a reference pressure. The driving pressure across the organ of Corti and the b.m. velocity were derived from the pressure data. Both were tuned and nonlinear. Therefore, their ratio, the specific acoustic impedance of the organ of Corti complex, was relatively untuned, and only subtly nonlinear. The impedance was inspected specifically for negative resistance (amplification) and resonance. Both were detected in some instances; taken as a whole, the current results constrain the possibilities for these qualities.

Acoustic Impedance Tests↗
PubMed2002

Summary of recent NASA studies of human response to sonic booms.

NASA Langley Research Center has conducted three groups of studies on human response to sonic booms: laboratory, "inhome," and field. The laboratory studies were designed to: (1) quantify loudness and annoyance response to a wide range of shaped sonic boom signatures and (2) assess several noise descriptors as estimators of sonic boom subjective effects. The studies were conducted using a sonic boom simulator capable of generating and playing, with high fidelity, both user-prescribed and recorded boom waveforms to test subjects. Results showed that sonic boom waveform shaping provided substantial reductions in loudness and annoyance and that perceived level was the best estimator of subjective effects. Booms having asymmetrical waveforms were found to be less loud than symmetrical waveforms of equivalent perceived level. Subjective responses to simulated ground-reflected waveforms were fully accounted for by perceived level. The inhome study presented participants with simulated sonic booms played within their normal home environment. The results showed that the equal energy theory of annoyance applied to a variety of multiple sonic boom exposures. The field studies concluded that sonic boom annoyance is greater than that in a conventional aircraft noise environment with the same continuous equivalent noise exposure.

Aircraft↗
PubMed2001

Evidence for a behavioral significance of saccular acoustic sensitivity in humans.

In this article the results are reported of an experiment to provide direct evidence for a perceptual and behavioral significance of human saccular acoustic sensitivity. Ten human subjects were stimulated monaurally with 100-ms trains of 10-ms tone pulses with pulse repetition rate of 40 Hz, and were required to rate the pleasantness of the stimuli on a nine-point scale. The design included three within-subject factors: carrier frequency (two levels, 200 and 4,000 Hz), intensity [13 levels from 55 to 115 dB(A) in 5-dB steps] and ear (left and right). For intensities above 90 dB myogenic vestibular evoked potentials (MVEP) were also obtained from the ipsilateral sternocleidomastoid muscle from which it was possible to obtain thresholds by linear regression of MVEP amplitudes against intensity. A further between-subjects factor was added which assessed subjects' attitude to vestibular sensations. The results indicate that across subjects there is a general trend of decreasing pleasantness with increasing intensity, but for the 200-Hz condition there is a significant positive departure from monotonicity in pleasantness (p<0.05) above the mean saccular threshold. However, when split by the between-subjects factor, the positive departure was only evident for those subjects who have a positive attitude to vestibular sensations (p < 0.01). Implications of these results for human responses to loud sound and the possible evolutionary significance of saccular acoustic sensitivity are discussed.

Attitude↗
PubMed2001

Auditory nerve fiber responses to electric stimulation: modulated and unmodulated pulse trains.

Many modern cochlear implants use sound processing strategies that stimulate the cochlea with modulated pulse trains. Rubinstein et al. [Hear. Res. 127, 108 (1999)] suggested that representation of the modulator in auditory nerve responses might be improved by the addition of a sustained, high-rate, desynchronizing pulse train (DPT). In addition, activity in response to the DPT may mimic the spontaneous activity (SA) in a healthy ear. The goals of this study were to compare responses of auditory nerve fibers in acutely deafened, anesthetized cats elicited by high-rate electric pulse trains delivered through an intracochlear electrode with SA, and to measure responses of these fibers to amplitude-modulated pulse trains superimposed upon a DPT. Responses to pulse trains showed variability from presentation to presentation, but differed from SA in the shape of the envelope of the interval histogram (IH) for pulse rates above 4.8 kpps (kilo pulses per second). These IHs had a prominent mode near 5 ms that was followed by a long tail. Responses to modulated biphasic pulse trains resembled responses to tones in intact ears for small (<10%) modulation depths, suggesting that acousticlike responses to sinusoidal stimuli might be obtained with a DPT. However, realistic responses were only observed over a narrow range of levels and modulation depths. Improved coding of complex stimulus waveforms may be achieved by signal processing strategies for cochlear implants that properly incorporate a DPT.

Acoustic Stimulation↗
PubMed2001

Melody lead in piano performance: expressive device or artifact?

As reported in the recent literature on piano performance, an emphasized voice (the melody) tends to be played not only louder than the other voices, but also about 30 ms earlier (melody lead). It remains unclear whether pianists deliberately apply melody lead to separate different voices, or whether it occurs because the melody is played louder (velocity artifact). The velocity artifact explanation implies that pianists initially strike the keys simultaneously; it is only different velocities that make the hammers arrive at different points in time. The measured note onsets in these studies, mostly derived from computer-monitored pianos, represent the hammer-string impact times. In the present study, the finger-key contact times are calculated and analyzed as well. If the velocity artifact hypothesis is correct, the melody lead phenomenon should disappear at the finger-key level. Chopin's Ballade op. 38 (45 measures) and Etude op. 10/3 (21 measures) were performed on a Bösendorfer computer-monitored grand piano by 22 skilled pianists. The hammer-string asynchronies among voices closely resemble the results reported in the literature. However, the melody lead decreases almost to zero at the finger-key level, which supports the velocity artifact hypothesis. In addition to this, expected onset asynchronies are predicted from differences in hammer velocity, if finger-key asynchronies are assumed to be zero. They correlate highly with the observed melody lead.

Artifacts↗
PubMed2001

Basilar-membrane response to multicomponent stimuli in chinchilla.

The response of chinchilla basilar membrane in the basal region of the cochlea to multicomponent (1, 3, 5, 6, or 7) stimuli was studied using a laser interferometer. Three-component stimuli were amplitude-modulated signals with modulation depths that varied from 25% to 200% and the modulation frequency varied from 100 to 2000 Hz while the carrier frequency was set to the characteristic frequency of the region under study (approximately 6.3 to 9 kHz). Results indicate that, for certain modulation frequencies and depths, there is enhancement of the response. Responses to five equal-amplitude sine wave stimuli indicated the occurrence of nonlinear phenomena such as spectral edge enhancement, present when the frequency spacing was less than 200 Hz, and mutual suppression. For five-component stimuli, the first, third, or fifth component was placed at the characteristic frequency and the component frequency separation was varied over a 2-kHz range. Responses to seven component stimuli were similar to those of five-component stimuli. Six-component stimuli were generated by leaving out the center component of the seven-component stimuli. In the latter case, the center component was restored in the basilar-membrane response as a result of distortion-product generation in the nonlinear cochlea.

Animals↗
PubMed2002

Relative rates of growth of annoyance of impulsive and non-impulsive noises.

Twenty-nine people judged the relative annoyance of five variable level signals and 29 impulsive and non-impulsive fixed-level signals in an adaptive paired comparison study. Signals were presented for judgment as heard indoors in a facility capable of accurately reproducing the very low-frequency content of sonic booms. When the annoyance of sonic booms unaccompanied by rattle was compared with that of sounds containing more higher-frequency energy (an aircraft flyover and an octave band of noise centered at 1 kHz), the relative rate of growth of annoyance, as expressed in C-weighted SEL units, was nearly 2:1. In other words, to maintain subjective equality of annoyance, each increase in level of sonic booms had to be matched by nearly twice the increase in level of an aircraft flyover or an octave band of noise centered at 1 kHz. Relative rates of growth of annoyance of sonic booms accompanied by rattle and of non-impulsive sounds, including both low- (63-Hz octave band of noise) and high-frequency energy (1-kHz octave band of noise and an aircraft flyover), were closer to 1:1. Relative rates of growth of annoyance for sonic booms unaccompanied by rattle and low-frequency sounds (63 Hz) were also about 1:1. These differences in relative rates of growth of annoyance of impulsive and non-impulsive sounds are as plausibly attributed to their relative low-frequency content as to impulsiveness per se. It may therefore be more useful for some purposes to express the annoyance of impulsive signals and other environmental noises containing substantial low-frequency energy in terms of effective (duration-corrected) loudness level rather than commonplace ASEL or CSEL.

Aircraft↗
PubMed2001

Intensity-invariance of fine time structure in basilar-membrane click responses: implications for cochlear mechanics.

Basilar-membrane and auditory-nerve responses to impulsive acoustic stimuli, whether measured directly in response to clicks or obtained indirectly using cross- or reverse-correlation and/or Fourier analysis, manifest a striking symmetry: near-invariance with stimulus intensity of the fine time structure of the response over almost the entire dynamic range of hearing. This paper explores the origin and implications of this symmetry for cochlear mechanics. Intensity-invariance is investigated by applying the EQ-NL theorem [de Boer, Aud. Neurosci. 3, 377-388 (1997)] to define a family of linear cochlear models in which the strength of the active force generators is controlled by a real-valued, intensity-dependent parameter, gamma (with 0 < or = gamma < or = 1). The invariance of fine time structure is conjectured to imply that as gamma is varied the poles of the admittance of the cochlear partition remain within relatively narrow bands of the complex plane oriented perpendicular to the real frequency axis. Physically, the conjecture implies that the local resonant frequencies of the cochlear partition are nearly independent of intensity. Cochlear-model responses, computed by extending the model obtained by solution of the inverse problem in squirrel monkey at low sound levels [Zweig, J. Acoust. Soc. Am. 89, 1229-1254 (1991)] with three different forms of the intensity dependence of the partition admittance, support the conjecture. Intensity-invariance of cochlear resonant frequencies is shown to be consistent with the well-known "half-octave shift," describing the shift with intensity in the peak (or best) frequency of the basilar-membrane frequency response. Shifts in best frequency do not arise locally, via changes in the underlying resonant frequencies of the partition, but globally through the intensity dependence of the driving pressure. Near-invariance of fine time structure places strong constraints on the mechanical effects of force generation by outer hair cells. In particular, the symmetry requires that the feedback forces generated by outer hair cells (OHCs) not significantly affect the natural resonant frequencies of the cochlear partition. These results contradict many, if not most, cochlear models, in which OHC forces produce significant changes in the reactance and resonant frequencies of the partition.

Acoustic Impedance Tests↗
PubMed2001

Loudness summation for pulsatile electrical stimulation of the cochlea: effects of rate, electrode separation, level, and mode of stimulation.

The aim of these two experiments was to gain systematic data on the amount of loudness summation measured for dual-electrode stimuli with varying temporal and spatial separation of current pulses. Loudness summation is important in the implementation of speech processing strategies for implantees. However, the loudness mapping functions used in current speech processors utilize psychophysical data (thresholds and comfortable loudness levels) derived using single-electrode stimuli, and do not take into account the temporal and spatial patterns of the speech processor output. In the first experiment, the current reduction required to equalize the loudness of a dual-electrode stimulus to that of its component (and equally loud) single-electrode stimuli was measured for three electrode separations (0.75, 2.25, and 7.5 mm), three repetition rates (250, 500, and 1000 Hz), and two loudness levels (comfortably loud, and mid-dynamic range). It was found that electrode separation had little effect on loudness summation, except for interactions with level and rate effects at the smallest separation. More current adjustment (in dB) was required for higher rates and lower levels of stimulation. The second experiment investigated the effects of mode (monopolar versus bipolar) and pulse duration on loudness summation. More current adjustment was required in bipolar mode than in monopolar mode at the lower level only. The main effects in both experiments, and their interactions, are consistent with a loudness model in which the neural excitation density is first obtained by temporal integration of excitation at each cochlear place, then converted to specific loudness via a nonlinear relationship, and finally integrated over cochlear place to obtain the loudness. The two important features which affect the loudness relationships in dual-electrode stimulation in this model are the shape of the excitation density function and the amount by which the neural spike probability per pulse is reduced in areas of overlapping excitation due to refractory effects.

Adult↗
PubMed2001

Evaluation of loudness-level weightings for assessing the annoyance of environmental noise.

Assessment of the annoyance of combined noise environments has been the subject of much research and debate. Currently, most countries use some form of the A-weighted equivalent level (ALEQ) to assess the annoyance of most noises. It provides a constant filter that is independent of sound level. Schomer [Acust. Acta Acust. 86(1), 49-61 (2000)] suggested the use of the equal loudness-level contours (ISO 226, 1987) as a dynamic filter that changes with both sound level and frequency. He showed that loudness-level-weighted sound-exposure level (LLSEL) and loudness-level-weighted equivalent level (LL-LEQ) can be used to assess the annoyance of environmental noise. Compared with A-weighting, loudness-level weighting better orders and assesses transportation noise sources, sounds with strong low-frequency content and, with the addition of a 12-dB adjustment, it better orders and assesses highly impulsive sounds vis-a-vis transportation sounds. This paper compares the LLSEL method with two methods based on loudness calculations using ISO 532b (1975). It shows that in terms of correlation with subjective judgments of annoyance-not loudness-the LLSEL formulation performs much better than do the loudness calculations. This result is true across a range of sources that includes aircraft, helicopters, motor vehicles, trains, and impulsive sources. It also is true within several of the sources separately.

Humans↗
PubMed2002

Propagation of finite amplitude sound through turbulence: modeling with geometrical acoustics and the parabolic approximation.

Sonic boom propagation can be affected by atmospheric turbulence. It has been shown that turbulence affects the perceived loudness of sonic booms, mainly by changing its peak pressure and rise time. The models reported here describe the nonlinear propagation of sound through turbulence. Turbulence is modeled as a set of individual realizations of a random temperature or velocity field. In the first model, linear geometrical acoustics is used to trace rays through each realization of the turbulent field. A nonlinear transport equation is then derived along each eigenray connecting the source and receiver. The transport equation is solved by a Pestorius algorithm. In the second model, the KZK equation is modified to account for the effect of a random temperature field and it is then solved numerically. Results from numerical experiments that simulate the propagation of spark-produced N waves through turbulence are presented. It is observed that turbulence decreases, on average, the peak pressure of the N waves and increases the rise time. Nonlinear distortion is less when turbulence is present than without it. The effects of random vector fields are stronger than those of random temperature fields. The location of the caustics and the deformation of the wave front are also presented. These observations confirm the results from the model experiment in which spark-produced N waves are used to simulate sonic boom propagation through a turbulent atmosphere.

Acoustics↗
PubMed2001

Auditory brainstem response recovery in the dolphin as revealed by double sound pulses of different frequencies.

Recovery of auditory brainstem responses (ABR) in a bottlenose dolphin was studied in conditions of double-pip stimulation when two stimuli in a pair differed in frequency and intensity. When the conditioning and test stimuli were of equal frequencies, the test response was markedly suppressed at short interstimulus intervals; complete recovery appeared at intervals from about 2 ms (when two stimuli were of equal intensity) to 10-20 ms (when the conditioning stimulus exceeded the test by up to 40 dB). When the two stimuli were of different frequencies, the suppression diminished and was almost absent at a half-octave difference even if the conditioning stimulus exceeded the test one by 40 dB. Frequency-dependence curves (ABR amplitude dependence on frequency difference between the two stimuli) had equivalent rectangular bandwidth from +/-0.2 oct at test stimuli of 20 dB above threshold to +/-0.5 oct at test stimuli of 50 dB above threshold.

Acoustic Stimulation↗
PubMed2001

A new procedure for measuring peripheral compression in normal-hearing and hearing-impaired listeners.

Forward-masking growth functions for on-frequency (6-kHz) and off-frequency (3-kHz) sinusoidal maskers were measured in quiet and in a high-pass noise just above the 6-kHz probe frequency. The data show that estimates of response-growth rates obtained from those functions in quiet, which have been used to infer cochlear compression, are strongly dependent on the spread of probe excitation toward higher frequency regions. Therefore, an alternative procedure for measuring response-growth rates was proposed, one that employs a fixed low-level probe and avoids level-dependent spread of probe excitation. Fixed-probe-level temporal masking curves (TMCs) were obtained from normal-hearing listeners at a test frequency of 1 kHz, where the short 1-kHz probe was fixed in level at about 10 dB SL. The level of the preceding forward masker was adjusted to obtain masked threshold as a function of the time delay between masker and probe. The TMCs were obtained for an on-frequency masker (1 kHz) and for other maskers with frequencies both below and above the probe frequency. From these measurements, input/output response-growth curves were derived for individual ears. Response-growth slopes varied from >1.0 at low masker levels to <0.2 at mid masker levels. In three subjects, response growth increased again at high masker levels (>80 dB SPL). For the fixed-level probe, the TMC slopes changed very little in the presence of a high-pass noise masking upward spread of probe excitation. A greater effect on the TMCs was observed when a high-frequency cueing tone was used with the masking tone. In both cases, however, the net effects on the estimated rate of response growth were minimal.

Audiometry, Pure-Tone↗
PubMed2001

Rate and timing cues associated with the cochlear amplifier: level discrimination based on monaural cross-frequency coincidence detection.

The perceptual significance of the cochlear amplifier was evaluated by predicting level-discrimination performance based on stochastic auditory-nerve (AN) activity. Performance was calculated for three models of processing: the optimal all-information processor (based on discharge times), the optimal rate-place processor (based on discharge counts), and a monaural coincidence-based processor that uses a non-optimal combination of rate and temporal information. An analytical AN model included compressive magnitude and level-dependent-phase responses associated with the cochlear amplifier, and high-, medium-, and low-spontaneous-rate (SR) fibers with characteristic frequencies (CFs) spanning the AN population. The relative contributions of nonlinear magnitude and nonlinear phase responses to level encoding were compared by using four versions of the model, which included and excluded the nonlinear gain and phase responses in all possible combinations. Nonlinear basilar-membrane (BM) phase responses are robustly encoded in near-CF AN fibers at low frequencies. Strongly compressive BM responses at high frequencies near CF interact with the high thresholds of low-SR AN fibers to produce large dynamic ranges. Coincidence performance based on a narrow range of AN CFs was robust across a wide dynamic range at both low and high frequencies, and matched human performance levels. Coincidence performance based on all CFs demonstrated the "near-miss" to Weber's law at low frequencies and the high-frequency "mid-level bump." Monaural coincidence detection is a physiologically realistic mechanism that is extremely general in that it can utilize AN information (average-rate, synchrony, and nonlinear-phase cues) from all SR groups.

Audiometry, Pure-Tone↗
PubMed2001

Sources of variation in profile analysis. I. Individual differences and extended training.

This study investigated two sources of variance in the ability to discriminate auditory profiles: individual differences and extended training. The goals of the study were (1) to determine the range and origins of individual differences in profile analysis and (2) to determine whether those who initially had poor sensitivity to changes in spectral shape could eventually acquire finer sensitivity. Profile stimuli had 11 components with equal-log spacing from 200-2200 Hz. Thresholds ranged from - 1 to -25 dB (signal level relative to the context level) across 46 listeners. The correlation between spectral-shape discrimination thresholds after 2000 trials and pure-tone intensity-discrimination thresholds was 0.36. The range of individual differences for pure-tone intensity discrimination and spectral-shape discrimination was about the same. Two groups of listeners were given extended practice on the profile task, one group that showed low thresholds after an initial 2000 trials of practice and another that showed much higher initial thresholds. All listeners improved during the course of the first 2000 trials of training. Most of the poor listeners continued to improve during 9000 trials of training. Individual differences in the listeners' sensitivity to changes in spectral shape still existed after the extended practice.

Adult↗
PubMed2001

The intensity-difference limen for Gaussian-enveloped stimuli as a function of level: tones and broadband noise.

Van Schijndel et al. [J. Acoust. Soc. Am. 105, 3425-3435 (1999)] have proposed that the internal excitation evoked by an auditory stimulus is segmented into "windows" according to the stimulus spectrum and stimulus length. This "multiple looks" model accounts for the mid-duration hump they observed in plots of intensity-difference limens (DLs) versus pip duration for Gaussian-shaped 1- and 4-kHz tones, an effect replicated by Baer et al. [J. Acoust. Soc. Am. 106, 1907-1916 (1999)]. However, van Schijndel et al. and Baer et al. used few levels. A greater number of levels were used by Nizami (1999) for Gaussian-shaped 2-kHz tone-pips whose equivalent rectangular duration (D) was 1.25 ms. The DLs show the mid-level hump known for clicks [Raab and Taub, J. Acoust. Soc. Am. 46, 965-968 (1969)]. At some duration this pattern must become the "near-miss to Weber's law." To determine this duration, as well as the level-dependence of the mid-duration hump, DLs were established for Gaussian-shaped 2-kHz tone-pips of D = 1.25, 2.51, and 10.03 ms at levels of 30-90 dB SPL. The across-subject average DLs for the tone-pips rise up at mid-levels for D= 1.25 and D = 2.51 ms. The DLs for D=2.51 ms are larger, creating the mid-duration hump. At all durations, the new DLs are smaller at high levels than at low levels, consistent with the near-miss to Weber's law. DLs were also obtained here for Gaussian-shaped broadband-noise pips of D=0.63, 1.25, 2.51, 5.02, and 10.03 ms. The DLs for the noise-pip show a mid-level hump for all pip durations. The noise-pip DLs decrease as the pip lengthens, such that the plot of DL versus log duration shows a linear decline, with no mid-duration hump. Analysis of variance reveals that the mid-level hump coexists with the classical patterns of level-dependence, perhaps reflecting the existence of two level-encoding mechanisms, one that depends on firing-rates counted over single neurons and which is responsible for the classical patterns, and one that depends on the initial coordinated burst of neuronal spikes caused by rapid ramping, and which presumably causes the mid-level hump.

Adult↗