摘要:

The time‐domain description of musical and other nonlinear oscillators complements the more commonly used frequency‐domain description, and is advantageous for some purposes. It is especially advantageous when studying large‐amplitude oscillations, for which nonlinearity may be severe. It gives direct insight into the physical reasons for the variation of waveform as playing conditions vary, and into certain phenomena which may seem counter‐intuitive from the frequency‐domain viewpoint, such as the musically undesirable flattening in the pitch of a bowed string when the bow is pressed too hard onto the string. It is easy to set up efficient time‐domain simulations on a small computer, a fact that has been surprisingly little exploited in musical acoustics. The simplest relevant model is described here. It demonstrates some of the basic nonlinear behavior of the clarinet, violin, and flute families with very little programming effort. Remarkably, a single set of model equations has relevance to all three cases, at a certain level of idealization, with appropriate choices of parameter values and of linear and nonlinear characteristics. For the flute family, this simplest model gives waveforms and phase relations closely resembling those observed at resonance in the organ‐pipe experiments of Coltman [J. Acoust. Soc. Am.60, 725–733 (1976)], including the triangular pressure and velocity waveforms. It can be shown (again using a time‐domain approach) that the triangular waveform is a universal limiting form, independent of detailed acoustic loss mechanisms provided losses are small.

ISSN:0001-4966    

DOI:10.1121/1.390157

出版商:Acoustical Society of America    

年代:1983

数据来源: AIP

摘要:

Determinations of shear wave speeds of sound and attenuation coefficients are reported for soft tissues, a silicone rubber reference material, and a gel used in manufacturing ultrasonically tissue‐mimicking materials. Fresh bovine tissues were investigated, including calfskin, liver, cardiac muscle, and striated muscle. Because of the very large shear wave attenuation coefficients, reasonably accurate determinations of shear wave properties are difficult to make. The quantity measured directly was the complex reflection coefficient for shear waves at a planar interface between the sample and fused silica. Measurements were made at frequencies spanning the range 2–14 MHz. The shear wave attenuation coefficients increase with frequency and are of the order of 104times the longitudinal wave attenuation coefficients. The shear wave speeds of sound also increase with frequency but are only a few percent of the longitudinal wave speeds of sound. The results are accurate enough to allow frequency dependencies to be proposed.

ISSN:0001-4966    

DOI:10.1121/1.390158

出版商:Acoustical Society of America    

年代:1983

数据来源: AIP

摘要:

The classic method for measuring absorption coefficients of materials requires a determination of the temperature rise within a medium during ultrasonic irradiation. Serious errors may result from a viscous heating effect around the required thermocouple probe, and from heat lost by conduction to surrounding, cooler regions. A thermal pulse‐decay technique is proposed and evaluated which allows for the separation, in time and space, of the viscous heating artifact and the true absorptive heating of a medium. In addition, the pulse‐decay method explicitly accounts for heat conduction and the ultrasonic beam patterns used in experiments. The inherent advantages of the new technique allow for an extension of absorption measurements to smaller beamwidths and higher frequencies and intensities than were previously possible.

ISSN:0001-4966    

DOI:10.1121/1.390159

出版商:Acoustical Society of America    

年代:1983

数据来源: AIP

摘要:

A miniature recessed (i.e., cup) surface EMG electrode intended for use in the perioral region during speech has been constructed and tested. In addition to its small size and low mass, a custom acrylic electrode housing features an extruded design to yield secure attachment to the skin with skin cement rather than with conventional double adhesive collars. A durable, commercially manufactured disk of homogeneous silver and silver chloride was utilized to optimize bioelectric characteristics and durability. In relation to the commonly used fine‐wire intramuscular electrode composed of platinum–iridium, this surface electrode demonstrates comparable bioelectric performance in perioral applications including low, stable, and well‐matched skin‐electrode impedance, a low noise floor, a surprisingly wide bandwidth, and good signal‐to‐noise ratios.

ISSN:0001-4966    

DOI:10.1121/1.390160

出版商:Acoustical Society of America    

年代:1983

数据来源: AIP

摘要:

Observers performed several different detection tasks using both the PEST adaptive psychophysical procedure and a fixed‐level (method of constant stimuli) psychophysical procedure. In two experiments, PEST runs targeted atP(C)=0.80 were immediately followed by fixed‐level detection runs presented at the difficulty level resulting from the PEST run. The fixed‐level runs yieldedP(C) about 0.75. During the fixed‐level runs, the probability of a correct response was greater when the preceding response was correct than when it was wrong. Observers, even highly trained ones, perform in a nonstationary manner. The sequential dependency data can be used to determine a lower bound for the observer’s ‘‘true’’ capability when performing optimally; this lower bound is close to the PEST target, and well above the forced choiceP(C). The observer’s ‘‘true’’ capability is the measure used by most theories of detection performance. A further experiment compared psychometric functions obtained from a set of PEST runs using different targets with those obtained from blocks of fixed‐level trials at different levels. PEST results were more stable across observers, performance at all but the highest signal levels was better with PEST, and the PEST psychometric functions had shallower slopes. We hypothesize that PEST permits the observer to keep track of what he is trying to detect, whereas in the fixed‐level method performance is disrupted by memory failure. Some recently suggested ‘‘more virulent’’ versions of PEST may be subject to biases similar to those of the fixed‐level procedures. Experimenters are advised to use the original version of PEST rather than fixed‐level psychophysics or ‘‘improved’’ versions of PEST when accuracy as well as speed of psychophysical measurement is important.

ISSN:0001-4966    

DOI:10.1121/1.390161

出版商:Acoustical Society of America    

年代:1983

数据来源: AIP

摘要:

This paper examines how intensity discrimination depends on the test frequency, the level, and the subjects’s high‐frequency hearing. Three experiments were performed. In the first experiment, intensity discrimination of pulsed tones was measured as a function of level at 1 and 14 kHz in five listeners. Results show less deviation from Weber’s law at 14 kHz than at 1 kHz. In the second experiment, intensity discrimination was measured for a 1‐kHz tone at 90‐dB SPL as a function of the cutoff frequency of a high‐pass masking noise in two listeners. Results show that the audibility of very high frequencies is important for frequency discrimination at 1 kHz. The DL increased by a factor between 1.5 and 2.0 as the cutoff frequency of the noise was lowered from 19 to 6 kHz. In the third experiment, thresholds from 6 to 20 kHz and intensity discrimination for a 1‐kHz tone was measured in 12 listeners. Results show that the DLs at 80‐dB SPL are correlated with the ability to hear very high frequencies. Results of all three experiments are consistent with the multiband version of the excitation‐pattern model for intensity discrimination [Florentine and Buus, J. Acoust. Soc. Am.70, 1646–1654 (1981)].

ISSN:0001-4966    

DOI:10.1121/1.390162

出版商:Acoustical Society of America    

年代:1983

数据来源: AIP

摘要:

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, isindependentof 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 noisedoesdepend 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.

ISSN:0001-4966    

DOI:10.1121/1.390163

出版商:Acoustical Society of America    

年代:1983

数据来源: AIP

摘要:

The probability that a cochlear nerve fiber spike discharge occurs during a time interval Δtdepends on both the acoustic stimulus and on aftereffects from earlier spike discharges. We have examined the influence of discharge‐history on post‐stimulus time (PST) histogram responses to acoustic click and tone‐burst stimuli. Discharge‐history effects were found to include the modification of observed interpeak times of PST responses to clicks, a loss of distinct peaks in the click response of high characteristic frequency (CF > 5 kHz) fibers, and changes in the ratio of initial to steady‐state response portions of tone‐burst responses. The method used to separate discharge‐history from stimulus‐related factors is based on a model developed in Gaumondetal. [J. Neurophysiol.48, 856–873 (1982)]. The results are in general agreement with those obtained by the method of Peter Gray [Biophys. J.7, 759–777 (1967)], which discards from consideration those portions of the response record not preceded by a silent interval of 20 or 25 ms or more. Our method requires more assumptions about the spike train, but produces less variable results by utilizing more of the spike train data.

ISSN:0001-4966    

DOI:10.1121/1.390164

出版商:Acoustical Society of America    

年代:1983

数据来源: AIP

摘要:

The problem of detecting a constant signal in nearly Gaussian skewed noise is studied in this paper. Sensitivity of both the linear detector and the sign detector are examined. It is shown that the performance of the linear detector deteriorates when the noise distribution becomes skewed. On the other hand, the sign detector appears to be less sensitive to the noise skewness. Furthermore, a modification of the linear detector is proposed. This modified scheme, when the noise skewness measure is small, will behave almost like the linear detector in Gaussian noise.

ISSN:0001-4966    

DOI:10.1121/1.390165

出版商:Acoustical Society of America    

年代:1983

数据来源: AIP

摘要:

It is shown that one can perform mode separation and source location using a focused horizontal array by utilizing the fact that the system response is greatest to a source located at or near the focal point. This mode separation/source location scheme is discussed for four different physical situations (1) a motionless point cw source in a range invariant environment, (2) a motionless point cw source in a range varying environment, (3) a motionless point broadband source in a range invariant environment, and (4) a moving cw source in a range invariant waveguide environment. Two types of (horizontal) arrays are treated, the line array and the convex circularly curved array. To illustrate the theory, preliminary numerical modeling results are displayed for a line array focused on a motionless point cw source in a range invariant environment.

ISSN:0001-4966    

DOI:10.1121/1.390142

出版商:Acoustical Society of America    

年代:1983

数据来源: AIP