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W M Hartmann

Publications and source records attributed to W M Hartmann.

35 records · Page 2Linked to original sources
PubMed1991

Turning on a tone.

It is possible to choose the starting phase of a pure tone in a way that minimizes the onset noise when the tone is turned on abruptly. A spectral model shows that when the tone has a low frequency, minimum onset noise is expected for a starting phase of zero (turning on a sine tone) but when the tone has a high frequency, minimum onset noise is expected for a starting phase of +/- 90 deg (turning on a cosine tone). Listening experiments confirm the above expectations and show that the transition between low- and high-frequency domains is sharp and depends upon both the electroacoustical transducer and the individual listener.

Adult↗
PubMed1990

Hearing a mistuned harmonic in an otherwise periodic complex tone.

The ability of a listener to detect a mistuned harmonic in an otherwise periodic tone is representative of the capacity to segregate auditory entities on the basis of steady-state signal cues. By use of a task in which listeners matched the pitch of a mistuned harmonic, this ability has been studied, in order to find dependences on mistuned harmonic number, fundamental frequency, signal level, and signal duration. The results considerably augment the data previously obtained from discrimination experiments and from experiments in which listeners counted apparent sources. Although previous work has emphasized the role of spectral resolution in the segregation process, the present work suggests that neural synchrony is an important consideration; our data show that listeners lose the ability to segregate mistuned harmonics at high frequencies where synchronous neural firing vanishes. The functional form of this loss is insensitive to the spacing of the harmonics. The matching experiment also permits the measurement of the pitches of mistuned harmonics. The data exhibit shifts of a form that argues against models of pitch shifts that are based entirely upon partial masking.

Adult↗
PubMed1989

On the minimum audible angle--a decision theory approach.

The minimum audible angle (MAA) technique is a well-known psychoacoustical paradigm often used in the study of localization of sound. A difficulty with this paradigm, however, is that, in terms of decision theory, it is subject to two quite different interpretations. Although it is normally regarded as involving a discrimination task, the present work suggests that it is more likely to be an absolute identification task. Because of this difference in interpretation, it appears that previous work has overestimated the ability of listeners to localize sources of sound.

Acoustic Stimulation↗
PubMed1989

Localization of sound in rooms. IV: The Franssen effect.

The Franssen effect is an illusion that causes human listeners to make large errors in localizing a sound source. This paper describes steps taken to convert the illusion into an experiment in order to study the localization precedence effect as it operates in rooms. The results of the experiment suggest that there are two components to the illusion: The first is the inability of listeners to localize a sine tone in a room in the absence of an onset; the second is the obscuring of modulation cues by the irregular transient response of a room. Experiments show that the Franssen effect fails completely in an anechoic environment, as expected if the effect depends upon the implausibility of steady-state cues in a room. The Franssen effect also fails when the spectrum of the sound is dense.

Auditory Perception↗
PubMed1988

Noise power fluctuations and the masking of sine signals.

This article is concerned with fluctuations in noise power and with the role that such fluctuations play in the masking of sine signals by noise. Several measures of noise fluctuations are discussed: the fourth moment of the waveform, the fourth moment of the envelope, and the crest factor. Relationships among these quantities are found for cases of equal-amplitude random-phase noise and Rayleigh-distributed-amplitude noise. Of particular interest is a special non-Gaussian noise called low-noise noise in which the fluctuations are small by any of our measures. The results of frozen-noise masking experiments are reported, where the noise waveform was fixed for all stimulus presentations. In separate experiments, equal-amplitude random-phase Gaussian noise, with typical fluctuations, and low-noise noise, with almost no fluctuations were used. The data show that for a noise bandwidth less than the critical bandwidth, the masked threshold is about 5 dB lower for low-noise noise than for Gaussian noise. When the noise bandwidth is larger than the critical bandwidth, the masked threshold is the same for both kinds of noise. It is concluded that noise power fluctuations increase masked threshold by about 5 dB and that filtering by the auditory system reintroduces fluctuations into broadband low-noise noise.

Acoustic Stimulation↗
PubMed1987

Digital waveform generation by fractional addressing.

This article concerns the generation of waveforms by a digital oscillator in which sampled data in a memory buffer are recycled. The buffer contains a fixed waveform and the output sample rate is also fixed. Despite these constraints, the oscillator is capable of arbitrarily high frequency resolution if the technique of fractional addressing is used. However, fractional addressing introduces distortion. This article gives a theory of fractional addressing, resembling the theory of diffraction in crystal lattices with a basis. The theory shows how the spectrum of the distortion components can be calculated and how the distortion can be minimized. Attention is called to numerous symmetries in the distortion spectrum. These symmetries are especially interesting if the purpose of the system is to make use of the distortion components to create inharmonic signals. Of particular importance is the gamma p symmetry theorem, which makes it possible to derive simple formulas for the level of the largest distortion component and for the total distortion power.

Acoustics↗
PubMed1986

Discrimination of spectral density.

Experiments were performed to determine the ability of human listeners to discriminate between a sound with a large number of spectral components in a band, of given characteristic frequency and bandwidth, and a sound with a smaller number of components in that band. A pseudorandom placement of the components within the band ensured that no two sounds were identical. The data suggested that discrimination is primarily based upon the perception of temporal fluctuations in the intensity of the sound and secondarily upon resolved structure in the spectrum, perceived as tone color. Experiments using clusters of complex harmonic sounds showed that listeners are able to use the information in upper harmonic bands to discriminate spectral density.

Acoustic Stimulation↗
PubMed1986

Localization of sound in rooms, III: Onset and duration effects.

The steady-state sound field of a sine tone does not provide useful localization information in a room. Nevertheless, listeners can localize a sine tone in a room if it has an onset transient which allows the precedence effect to operate. In the present study, we made a quantitative assessment of onsets and the precedence effect by systematically varying onset duration from 0 s (impulsive), where the precedence effect is maximal, to 5 s, where there is no precedence effect at all. We also assessed listeners' sensitivity to the steady-state sound field under impulsive conditions by varying the total duration of tone pulses. Our experiments were conducted in a room with a single acoustical reflection having various directions and delays, and in an anechoic room. The results for tones of various frequencies (500 and 2000 Hz) and sound-pressure levels (65 and 40 dBA) indicate the following: Localization in rooms is facilitated by onsets even if the onsets are as long as 100 ms. The facilitation depends upon the peak intensity of the tone, as well as the onset duration, suggesting that onset rate is critical for the precedence effect; our results are most consistent with rate expressed as an increase in sound pressure per unit time. The facilitation also depends upon the reflection delay time for a room; gradual onsets take on much more importance for the precedence effect in rooms with long delays. As onsets begin to lose their effectiveness listeners become increasingly "misdirected" by invalid cues in the steady-state sound field. The pattern of misdirection suggests a perceptual averaging of cues over an interval more than an order of magnitude longer than previous estimates of the summation window for the precedence effect. The pattern of misdirection varies with the frequency of a tone, due to frequency-dependent interference effects in a room, but it is independent of signal level. Localization of an impulsive sine tone in rooms is very insensitive to the pulse duration; this suggests that binaural inhibition models of the precedence effect must be supplemented by an evaluative component that we term the "plausibility hypothesis."

Acoustic Stimulation↗
PubMed1985

Localization of sound in rooms, II: The effects of a single reflecting surface.

Auditory localization was studied in a room bounded by a single acoustically reflective surface. The position of that surface was varied so as to stimulate a floor, a ceiling, and left and right side walls. The surface was eliminated in one condition so that we could examine localization in free field for purposes of comparison. Using a source identification method we assessed the influences of these various room configurations on the localization of both slow-onset and impulsive sine tones of low frequency (500 Hz). We also measured the steady-state interaural-time-difference (ITD) and interaural-intensity-difference (IID) cues available to subjects in the different room configurations and compared these data with the perceptual judgments. Our results indicate the following: (1) A sound must include transients if the precedence effect is to operate as an aid to its localization in rooms. (2) Even if transients are present the precedence effect does not eliminate all influences of room reflections. (3) Due to the interference of reflections large interaural intensity differences may occur in a room and these have a considerable influence on localization; this is true even at low frequencies for which IID cues do not exist in a free field. (4) Listeners appear to have certain expectations about the reliability and plausibility of various directional cues and perceptually weight the cues accordingly; we suggest that this may explain, in part, the large variation in time-intensity trading ratios reported in the literature and also the differing reports regarding the importance of onsets for localization. (5) In this study we find that onset cues are of some importance to localization even in free field.

Acoustic Stimulation↗
PubMed1984

A search for central lateral inhibition.

A central spectrum explanation of the existence of the binaural edge pitch [Klein and Hartmann, J. Acoust. Soc. Am. 70, 51-61 (1981)] appears to require central lateral inhibition in the human auditory system. We have looked for this effect in central masking experiments. Using the binaural-edge noise, which creates the binaural edge pitch, as a masker (in standard notation: No below and N pi above a phase boundary frequency), we measured pulsation thresholds for sine tones in two frequency ranges where the binaural edge pitch exists. We also obtained reference data, using the same pulsation threshold technique, for standard binaural conditions NoSo, NoS pi, N pi So, and N pi S pi. These data revealed masking level differences. Theoretically the difference between the binaural-edge thresholds and the reference data should show the peak and valley signature of lateral inhibition. No such structure was found. We suggest that this negative result does not exclude the possibility of central lateral inhibition, but that the time course of central lateral inhibition makes the pulsation threshold technique an inappropriate means for observing the effect.

Auditory Threshold↗
PubMed1983

Localization of sound in rooms.

This paper is concerned with the localization of sources of sounds by human listeners in rooms. It presents the results of source-identification experiments designed to determine whether the ability to localize sound in a room depends upon the room acoustics, and how it depends upon the nature of the source signal. The experiments indicate that the localization of impulsive sounds, with strong attack transients, is independent of the room reverberation time, though it may depend upon the room geometry. For sounds without attack transients, localization improves monotonically with the spectral density of the source. Localization of continuous broadband noise does depend upon room reverberation time, and we propose the concept of direct signal to reverberant noise ratio to study that effect. Source identification experiments reveal certain localization biases, invisible to minimum-audible-angle experiments, and of uncertain origin. Appendices to this paper develop the statistics of the source-identification paradigm and show how they relate to the minimum audible angle.

Acoustics↗
PubMed1982

On the detection of a tone masked by two tones.

We reopen the question of an appropriate representation to describe the masking of a site midway in frequency between two sine maskers. We suggest that when the maskers are closely spaced in frequency signal detection is mediated by differences in the stimulus envelope caused by the target signal. We show that in previous two-masker experiments detection threshold was limited by stimulus duration. Our experiments for long stimulus durations find thresholds that are approximately independent of the phase angle between the target and the maskers. Because the different phase angles correspond to very different stimulus envelopes the observed invariance is not easy to understand. For a general phase angle the presence of the signal cause both periodic changes in the envelope and periodic frequency modulation. The experimental detection data do not allow one to distinguish between these two effects.

Acoustic Stimulation↗
PubMed1981

Binaural edge pitch.

The Huggins pitch effect is created by dichotic broadband noise with interaural phase varying from 0 to 2 pi over a narrow frequency region. The sensation of pitch, corresponding to the frequency of the phase shift region, is usually understood as the result of a binaural differencing operation. We report here a pitch effect created by dichotic broadband noise with interaural phase varying from 0 to pi over a narrow boundary region, creating an edge in a difference channel. We call this effect Binaural Edge Pitch. For experienced listeners the effect is similar in nature and strength to the Huggins pitch. It is strongest for boundary frequencies in the 350--800 Hz range. Pitch matching experiments in this range find that the spread of matches in 1%--2% of the boundary frequency and that the pitch is 4% higher or lower than the boundary frequency. This shift is identical to the shifts which we find for the pitch of high-pass and low-pass noise bands. The correspondence argues strongly for an explanation of the Binaural Edge Pitch in terms of the Equalization--Cancellation Model of binaural processing, and pitch derived from central spectrum.

Acoustic Stimulation↗
PubMed1980

Theory of frequency modulation detection for low modulation frequencies.

There is general agreement that the frequency difference limen measured in a two-sine-tone frequency discrimination experiment is smaller than that measured in a frequency modulation (FM) experiment. We present a model of frequency modulation detection for low modulation frequencies, within the framework of signal detection theory, which accounts well for the observed difference between frequency discrimination experiments and FM detection experiments. The FM detection model also predicts psychometric functions for detection of FM with different modulation waveforms. FM detection experiments with square, sine, trapezoid, and triangle FM are in reasonable agreement with the model predictions.

Acoustic Stimulation↗
PubMed1978

The effect of amplitude envelope on the pitch of sine wave tones.

Psychophysical experiments show that the pitch of a short sine wave tone depends upon the amplitude envelope of the tone. Subjects find that the pitch of an exponentially decaying tone (1dB/ms) is higher than the pitch of a (20-ms) rectangularly gated tone of equal frequency. The percentage difference in frequency required to produce equal pitches with the two envelopes depends upon frequency fo: 2.6% at fo = 412 Hz, 1.4% at fo = 825 Hz, 1% at fo = 1650 Hz, and 0.7% at fo = 3300 Hz. The pitch change is insensitive to the relative intensities of the two tones. The spectra of tones with the two different envelopes suggest no obvious explanation for the pitch change. However, the weighted time-varying spectra for tones with two different envelopes evolve differently with time. Alternatively the pitch change can be derived from a modified version of the auditory phase theory of Huggins.

Humans↗