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PubMed1978

Loudness of complex sounds as a function of the standard stimulus and the number of components.

The purpose of this study was twofold: to determine if the measured loudness level of a signal depends on the standard stimulus used and to measure loudness as a function of the number of components in a wide-band signal. The stimuli were a pure tone, tone complexes with frequency separations of 231 and 1592 Hz, and noise bands with widths of 220 and 1592 Hz. The center frequency was 1 kHz and the loudness level was approximately 65 phons. Loudness matches between all combinations of stimuli showed that the measured loudness of the sounds did not depend on the standard stimulus used and the measured loudness level of a wide-band sound increased as a function of the number of components. Individual observers were consistent in their loudness estimations; the greatest source of variability was among subjects. Additional measurements indicated that the rate at which loudness increased beyond the critical band appeared to be greater for noise bands that for two-tone complexes.

Acoustic Stimulation↗
PubMed1978

Subjective loudness of "minimized" sonic boom waveforms.

For very long supersonic aircraft the "midfield" sonic boom signature may not have evolved fully into an N wave at ground level. Thus in current boom minimization techniques the shape of the aircraft may be tailored to optimize this midfield wave form for reduced subjective loudness. The present investigation tests a family of "flat-top" waveforms cited by Darden: all but one have a front shock height (deltapSH) less than the peak amplitude (deltapMAX). For equal subjective loudness, "flat top" vs N wave (peak overpressure deltapN), the peak amplitude of the "flat top" signature was found to be substantially higher than that of the N wave; thus for equal peak amplitude the "flat-top" signature was quieter. The results for equal loudness were well fitted by an emperical law deltapSH + 0.11deltapMAX = deltapN; the equivalence shows how the front shock amplitude (deltapSH) dominates the loudness. All this was found compatible with predictions by the method of Johnson and Robinson.

Humans↗
PubMed1978

Growth function for human response to large-amplitude impulse noise.

The U. S. Environmental Protection Agency has proposed the use of C-weighted day/night level for the assessment of impulse noise such as the noise resulting from sonic boom, blast noise (artillery, armor, demolition, etc.) and other large-amplitude impulse sources. One remaining question pertaining to the use of C-weighting has been the growth function for human response to impulse noise. This question arises because work by Kryter and by Young using peak values and/or small amplitudes exhibited growth functions of 6--7dB for a doubling of annoyance, while the growth function for human response to common sources (planes, vehicles, etc.) increases by about 10 dB for a doubling of annoyance. Kyter's and Young's data are reanalyzed herein by using C-weighting and by including only large-amplitude data. This reanalysis results in a growth function for human response to impulse noise which increases by about 10 dB for a doubling of annoyance. This equality of growth function between common A-weighted noise and C-weighted impulse noise further supports the use of C-weighted day/night level for assessment of sonic boom, blast noise, or other large-amplitude impulse noises having similar spectral content.

Humans↗
PubMed1978

Subjective loudness of N-wave sonic booms.

A loudspeaker-driven simulation booth with extended rise-time capability (down to 0.22 ms) has been used for subjective loudness tests of N-wave sonic booms. The test series compared signatures over a range of 0.22--10 ms in rise time, 100--250 ms in duration and 0.5--2.5 psf (24--120 Pa) in peak overpressure. In one sequence, the tradeoff between rise time and overpressure was measured for equal loudness; in another, the tradeoff between duration and overpressure. For equal loudness 10-ms rise time required 8-dB higher overpressure than for 1-ms rise time. Duration had little effect in the range 100--200 ms, but at 250 ms noticeably enhanced the loudness. These results confirm those measured by Shepherd and Sutherland made at 1-ms rise time and above (except for the anomalous enhancement at 250-ms duration), and extend the measurements down to 0.22 ms. There is also good agreement with theoretical predictions (Johnson-Robinson, Zepler-Harel methods) except for the 10-ms rise time and 250-ms duration cases.

Humans↗
PubMed1979

Automatic speech recognition using psychoacoustic models.

An approach to automatic speech recognition is described, which, in a straightforward way, follows the concept of (1) preprocessing in terms of auditory parameters and (2) subsequent classification and recognition. The preprocessing system has been realized in analog hardware, while recognition is carried out on a digital computer. In the preprocessing system, the essential psychoacoustic principles of the perception of loudness, pitch, roughness, and subjective duration are implemented with some approximation. The system essentially consists of 24 bandpass filters, nonlinear transformation of each filter output into specific loudness and specific roughness, and final transformation of these parameters into total loudness, total roughness, and three spectral momenta. As a means to further reduce the information flow, continuous selection of dominant parameters is also considered on the basis of psychoacoustic data. The subsequent recognition process is mainly characterized by (1) discrimination between speech and silent periods, (2) detection of syllable peaks and classification of syllable nuclei, and (3) assumption of syllable boundaries and classification of consonant clusters. Though the entire system as yet is far from being complete and perfect, the present results indicate that the concept provides a systematic and promising way towards automatic recognition of continuous speech.

Computers↗
PubMed1979

Subjective loudness and annoyance of filtered N-wave sonic booms.

The contribution of the "infrasonic" low-frequency content of sonic boom N waves to subjective loudness and annoyance has been investigated. An extended low-frequency response loudspeaker-driven simulation booth was employed, with computer-generated input test signals. For test N waves of 1 ms rise time and 150 ms duration, frequencies below 25 and 50 Hz, respectively, were cut off by digital filters simulating simple RC circuits. The filtered signal amplitude was adjusted versus the amplitude (48 Pa) of a reference unfiltered N wave (effective low-frequency cutoff approximately 0.1 Hz) until the two sounded equally loud (first experiment) or equally annoying (second experiment). The amplitude differences for equality were very slight: less than 0.6 dB at most. Surprisingly, while loss of the low frequencies slightly decreased the loudness, it slightly increased the annoyance.

Humans↗
PubMed1979

Subjective loudness of simulated quarry blast waves, with implications for the transition from impulsive to continuous sound.

The tradeoff between amplitude and duration for equal loudness was explored for idealized quarry blast waves. An extended low-frequency response loudspeaker-driven simulation booth was employed with computer-generated imput test signals. In place of actual irregular blast waves, the simulated signatures were composed of sequences of identical shock-decay impulses of 25 ms duration and 0.2 ms rise time. Sequences of 1--16 impulses yielded overall durations of 25--400 ms. At the short durations the loudness was found to increase 2 dB for each doubling of duration; above 100 ms the increase was progressively lower, approaching as an asymptote the level for continuous sound. The results were compared with theoretical predictions: for this purpose the spectral method of Johnson and Robinson, well varified in our earlier studies of sonic boom impulses, was used. The shorter quarry blast judgments (T less than or equal to 100 ms) were found to be in very good agreement in terms of relative loudness levels. With an ad hoc--but physically plausible--modification (including adjustment of the critical integration time of the ear) the predictive method was extended to encompass the long duration signals as well. Thus the applicability of the method has been demonstrated for other types of transient sounds than the N wave; and the extension of the method tentatively appears to bridge the range between impulsive and continuous sounds of similar spectral content.

Humans↗
PubMed1979

Bimodal cues for speech loudness.

This paper presents a bimodal (audio-visual) study of speech loudness. The same acoustic stimuli (three sustained vowels of the articulatory qualities "effort" and "noneffort") are first presented in isolation, and then simultaneously together with an appropriate optical stimulus (the speaker's face on a video screen, synchronously producing the vowels). By the method of paired comparisons (law of comparative judgment) subjective loudness differences could be represented by different intervals between scale values. By this method previous results of effort-dependent speech loudness could be verified. In the bimodal study the optical cues have a measurable effect, but the acoustic cues are still dominant. Visual cues act most effectively if they are presented naturally, i.e., if acoustic and optical effort cues vary in the same direction. The experiments provide some evidence that speech loudness can be influenced by other than acoustic variables.

Acoustic Stimulation↗
PubMed1980

Some effects of different maskers on psychophysical performance in discrimination and detection tasks.

Psychophysical performance was measured in a number of different tasks in order to compare performance under different masking conditions. With the noise masker set to provide a given amount of masking, frequency discrimination of a 4-kHz tone was shown to be worse in a lowpass noise than in a wideband noise. Discrimination of the intensity of the tone under these two masking conditions was comparable except at the lowest level of tone. Finally, the growth of detectability with level was measured in a detection task, with a greater slope being found in lowpass noise than in wideband noise. The results are discussed in light of the differences in physiological responses observed under similar masking conditions.

Adult↗
PubMed1980

Loudness enhancement and decrement in four paradigms.

When one tone burst (the conditioner) preceeds another (the target) by 100 ms, target loudness is enhanced if the conditioner is more intense and decreased if it is less intense. We show here that similar loudness enhancements and decrements occur when the conditioner follows the target. In all instances, monaural loudness enhancements (in which the conditioner and target are delivered to the same ear) are greater than the dichotic enhancements (in which the conditioner is presented contralaterally), but the decrements, which are smaller than the enhancements, are similar in magnitude. Loudness enhancements and decrements are similar to sequential loudness effects and central tendency effects; the major difference is the relatively very large increases in loudness obtainable in loudness enhancement experiments. We outline a mechanism to account for these loudness phenomena and suggest that this mechanism is responsible for similar perceptual effects that occur in other stimulus dimensions and modalities.

Acoustic Stimulation↗
PubMed1981

A neural-counting model incorporating refractoriness and spread of excitation. II. Application to loudness estimation.

In previous paper [Teich and Lachs, J. Acoust. Soc. Am 66, 1738--1749 (1979)] we demonstrated that an energy-based neural counting model incorporating refractoriness and spread of excitation satisfactorily described the results of pure-tone intensity discrimination experiments. In this paper, we show that the identical linear filter refractoriness model (LFRM) also provides proper results for pure-tone loudness estimation experiments at all stimulus levels. In particular, as the stimulus intensity increases from very low to moderate values, the model predicts that the slope of the intensity discrimination curve will climb from 1/2 toward 1, whereas the slope of the loudness function will gradually decline below 1 in this same region. For sufficiently high values of the stimulus intensity, the slopes calculated from a simplified (crude saturation) version of the model are found to be 1--1/4N for the intensity discrimination curve and 1/2N for the loudness function. The quantity N is the number of poles associated with the tuned-filter characteristic of the individual neural channels; it is the only important free parameter in the model. Appropriate values for N appear to lie between 2 and 4, providing an asymptotic slope for the intensity discrimination curve bounded by 7/8 and 15/16 (the near miss to Weber's Law), and an asymptotic slope for the loudness function bounded by 1/4 and 1/8. The results follow from the assumption that the neural concomitant of loudness is the number of impulses observed on a collection of parallel neural channels during a fixed observation time. Our calculations are supported by Hellman and Zwislocki's [J. Acoust. Soc. Am. 33, 687--694 (1961)] observation of unit slope for the loudness function at low intensities and provide a theoretical foundation, based on spread of excitation, for Stevens' power law at high intensities.

Differential Threshold↗
PubMed1981

Determining individual loudness scales from binary comparisons of loudness intervals.

A method is described in which individual loudness scales can be derived without resorting to numerical judgments on the part of the subject. Loudness scales constructed via this method differed significantly from subject to subject. Since a non-numerical scaling procedure was employed, the individual differences could not be attributed to biases in the way in which observers use numbers or numerical concepts to describe the loudnesses of tones.

Humans↗
PubMed1981

Invariant characteristics of partial masking: implications for mathematical models.

The loudness of a tone in a noisy background increases very rapidly above its threshold with increasing intensity of the tone. The particular curve describing loudness growth as measured by a loudness matching paradigm depends on the level of the background noise. We introduce the hypothesis that an increment in masking noise induces a shift of the loudness matching curve in a diagonal direction (the matching curve being plotted in conventional log--log coordinates). This shift invariance is shown here to hold empirically for individual subjects within a monaural loudness matching task, based on a 2IFC paradigm using 1000-Hz tones and a wide band Gaussian noise. Shift invariance places considerable restrictions on models feasible for such data. In conjunction with a very general class of models involving the notion of gain control, the shift invariance property determines all parametric forms possible for the loudness matching functions. The fit of such parametric expressions to the data reported here yields very satisfying results. The resulting model is also found to be consistent with relevant results in the literature.

Humans↗
PubMed1981

Loudness of tone pulses in a free field.

Investigations of temporal loudness summation of tone pulses have been performed. The investigations comprised equal loudness determinations between pairs of tone pulses with a duration ratio of 1:2, and threshold determinations of the same tone pulses. Pulse duration ranged from 5 to 640 ms. The frequencies were 500, 1000, and 4000 Hz. All pulses were shaped by means of 1/3 octave filters. For 25 normal hearing observers the investigations were performed at the observer's threshold, and at 35 and 55 dB SPL. Fitting of the experimental data to a single exponential function yields a time constant (tau) of about 200 ms near and at the threshold, whereas tau is about 100 ms at levels well above threshold. Discrepancies exist, nevertheless, between this single-time-constant model and the experimental data obtained for the pulses of shortest duration. To account for this, a model is proposed comprising a combination of two exponential functions. This yields a short time constant of 5 to 10 ms combined with the longer constant mentioned above.

Acoustics↗
PubMed1982

Some effects of spectral shaping on recognition of speech by hearing-impaired listeners.

The effects of spectral shaping on speech recognition were investigated for hearing-impaired listeners with flat and steep audiometric configuration. Three frequency responses were tested: uniform frequency gain, high pass filtering, and a response shaped relative to each subject's loudness discomfort level curve. Speech-recognition performance was measured at four levels (from 80 to 95 dB SPL) using nonsense syllable (NST) and synthetic sentence (SSI) tests, presented against a background of "cafeteria noise." No significant differences in performance on the NST were observed between the two subject groups across all spectral shapes (frequency response) and presentation levels. On the SSI, performance of subjects with flat audiometric configuration was highest using the uniform frequency response, while performance of listeners with steep configuration was poorest for the uniform response. The recognition data were compared with predictions of relative performance using a modification of the Articulation index (AI). The AIs provided accurate estimates of relative performance across spectral shapes but were not consistent with relative performance as a function of presentation level. The results indicate that the selection of spectral shape for optimal performance is influenced by the particular speech task used to test recognition and also suggest that, with further validation, the AI may provide an objective technique for selecting optimal spectral shape.

Aged↗
PubMed1982

Loudness, annoyance, and noisiness produced by single-tone-noise complexes.

Single tones centered within the noise spectrum were added to three different broadband spectra: flat, low pass, and high pass. Judgments of overall loudness, annoyance, and noisiness (perceived magnitude) were obtained by absolute magnitude estimation (AME) supplemented by loudness matching. The data were evaluated to determine how the overall SPL of the noise-tone complex, and tone-to-noise ratio effect judged perceived magnitude. In addition, the relationship among the tree judged attributes was assessed. Results obtained with the different noise spectra show that the growth of perceived magnitude is a nonmonotonic function of the overall SPL of the noise-tone complex. More summation between tone and noise was found for relatively small tone-to-noise ratios (+5, +10, +15 dB), as measured in 1/3-octave bands, than for relatively large tone-to-noise ratios (+20 dV and greater). Data analysis suggests that the extent of the increments and decrements in perceived magnitude depends on the absolute loudness of the component stimuli, the interaction between a specific tone frequency and noise spectrum, and the attribute judged. An attempt is made to quantify the observed effects and to relate them to the published results of other investigators.

Acoustics↗
PubMed1982

A computer program for fitting a master hearing aid to the residual hearing characteristics of individual patients.

The electroacoustic characteristics of an experimental master hearing aid are determined by the choice of transducers and settings of 26 controls which include a preamplifier, the gains and limiting levels in each of 12 channels as well as the gain of a final power amplifier. Here, a computer program which aids in the fitting of the electroacoustic characteristics of this aid to the characteristics of a patient's residual hearing is described. The patient's audiologic data and the hearing-aid parameters are entered into the computer and the gain and limiting level of each channel of the hearing aid are adjusted until an appropriate fit is achieved. The results of the fitting procedure are displayed on a graphics terminal. Permanent copies of the results can be produced on a printer-plotter. Included in the results for each of 12 channels are (1) the discomfort level, most comfortable listening level, and hearing threshold of the patient, and (2) the maximum output and noise floor of the hearing aid as well as the aided speech level. This approach has simplified the problem of fitting a complicated hearing aid to a patient's residual hearing and seems to offer attractive possibilities for fitting commercial hearing aids in the future.

Acoustics↗
PubMed1982

Loudness adaptation induced by an intermittent tone.

The loudness of a continuous 1000-Hz tone at 60 dB SPL was measured in the presence of an intermittent tone in the contralateral ear. Over 70 observers participated in a series of eight experiments. The method of successive magnitude estimation showed that the intermittent tone causes the steady tone to diminish in loudness within 2 or 3 min by 40% to 60%. The amount of this induced loudness adaptation depends weakly upon the presentation rate, frequency, and level of the contralateral tone. Loudness reduction of the steady tone is coupled with loudness enhancement of the intermittent tone in the opposite ear. Induced loudness adaptation was also revealed by interaural and cross-modality matching. Induced loudness adaptation depends strongly on interaural interaction and is probably related to lateralization and interaural funneling of loudness. Adaptation induced by an intermittent tone stands in marked contrast to the near absence of loudness adaptation, except near threshold, when a continuous sound is presented alone.

Acoustic Stimulation↗