Volume 4, Issue 3, July 2003
4(2003); http://dx.doi.org/10.1121/1.1573131View Description Hide Description
Digital implementations of linear gammatone filters are regularly part of auditory models and can be used in the sound processing in cochlear implants. How close digital impulse, magnitude, and phase responses match the corresponding properties of the analog gammatone filter is evaluated for one, finite-impulse response filter design, and for five, infinite-impulse response filter designs: base-band impulse invariant transformation, impulse invariant transformation, matched z transformation, bilinear transformation, and mapping of differentials with backward differences. Filter properties and computational cost are compared as a function of the filter’s order and center frequency, and sampling frequency. Results show that filters designed with the base-band impulse invariant transformation give the best overall approximation of the analog properties with reasonable computational cost.
4(2003); http://dx.doi.org/10.1121/1.1578951View Description Hide Description
An experiment addressed perceptual assumptions that have formed the basis of models for auditory feature integration. Musicians searched stimuli containing two lateralized tones for a target timbre and its pitch. Errors representing potential illusory conjunctions exceeded feature misperception errors. Responses were submitted to multinomial models to evaluate the contribution of guessing, illusory conjunctions, and intertone distance. Illusory conjunction models provided the most accurate data fits. Illusory conjunction rates exceeded zero, and were not affected by distance. Implications for feature binding models are discussed.
Analysis and effectiveness of deer whistles for motor vehicles: frequencies, levels, and animal threshold responses4(2003); http://dx.doi.org/10.1121/1.1582071View Description Hide Description
Whitetail deer (Odocileus virginianus) are common across much of the United States. In areas where deer populations are prevalent, there is a propensity for interactions with automobiles. Various methods have been suggested for reducing the number of automobile-deer collisions, including acoustic devices such as deer whistles. Six different whistles were tested in the laboratory and on motor vehicles. Frequencies and intensities generated by the devices when mounted on vehicles at speeds from 30–45 miles per hour were determined. The primary frequency of operation of the closed end whistles on vehicles was determined to be approximately 3.3 kHz with little variation with changes in air pressure. Open-end whistles had a primary frequency of about 12 kHz, with significant variation with changes in air pressure. The best frequency range of hearing for whitetail deer appears to be between 2 and 6 kHz. The effectiveness of these devices was concluded based on the comparison of the acoustical attributes of the devices to deer hearing thresholds and acoustic behavior.
4(2003); http://dx.doi.org/10.1121/1.1582072View Description Hide Description
Systematic errors in the high frequency predictions of geometrical acoustics software can result from the use of seat absorption coefficients derived by traditional measurement methods based on diffuse-field assumptions. This analysis treats in-situmeasurement methods in which seat absorption coefficients are calculated by a diffuse-field model from reverberation time measurements made in auditoria.Computermodels illustrate that the nonuniform distributions of absorption in auditoria result in significant differences between the absorption coefficients derived by an in-situmeasurement method and the true random-incidence absorption coefficients. Proposals are made for methods to be used when measuring seat absorption coefficients for use in geometrical acoustics software.
4(2003); http://dx.doi.org/10.1121/1.1588271View Description Hide Description
There are only 200 to 300 Sumatran rhinos (Dicermoceros sumatrensis) left in the world. Sumatran rhinos are solitary, and their native habitat is dense tropical forest and mountain moss forest. Three Sumatran rhinos, housed at the Cincinnati Zoo, were recorded using Statham Radio microphones and Sony TCD-D8 DAT recorders. Sumatran rhinos produce sounds described as eeps, 70 Hz–4 kHz (57–92 dB); whales, 100 Hz–3.2 kHz (87 dB); and whistle-blows, 17 Hz–8 kHz (100 dB). The whistle-blows contain high level infrasound that would be advantageous for use in the rhino’s forest habitat. Some Sumatran rhino vocalizations resemble humpback whale signals.
4(2003); http://dx.doi.org/10.1121/1.1590936View Description Hide Description
A novel method for the simultaneous acquisition of optical absorption and ultrasonic attenuationspectra is described. The technique is based on the photoacoustic generation of bi-directional ultrasonic pulses by a thin optical absorber that is remote from the sample. A single piezoelectric transducer ultimately detects the two pulses of ultrasound, and the captured signals are used to determine both the optical absorption and ultrasonic attenuationproperties of the sample. Measurements on a polycarbonate resin sample using the simultaneous photoacoustic method and conventional techniques show good agreement, indicating the validity of the method.
Delay of the propagation time of an optoacoustic pulse at the vaporization threshold of liquid carbon disulfide4(2003); http://dx.doi.org/10.1121/1.1591711View Description Hide Description
The propagation time of an acoustic pulse generated via an optoacoustic technique is analyzed. The propagation time is delayed by approximately 225 ns once a stable bubble is produced due to vaporization of the liquid. Although there is little change in the general spatial and temporal profile of the acoustic wave, it is observed that the time duration is increased near the vaporization threshold of the liquid.
4(2003); http://dx.doi.org/10.1121/1.1591712View Description Hide Description
Three experiments examined whether the Clarion 1.2 S-Series cochlear implant could be safely and effectively used within a Carstens Medizinelektronik EMA (electromagnetic articulography) system. Experiment 1 indicated no measurable effects of EMA magnetic fields on implant function. Experiment 2 showed no influence of the implant on the accuracy of EMA measurements. Experiment 3 found no indication of reduced sentence repetition abilities when EMA fields were present. The results suggest experiments with the Clarion 1.2 cochlear implant and the Carstens AG100 articulograph are safe and feasible.
4(2003); http://dx.doi.org/10.1121/1.1591713View Description Hide Description
Observations of multipath on the western shelf area of the Florida Straits have consistently revealed an intense arrival associated with refracted bottom reflected (RBR) rays/modes. The ‘late’ or ‘focused’ arrival is 15 to 20 dB higher than other arrivals. Parabolic Equation and Normal Mode propagation models and the shallow water invariant, beta, are used to explain the focusing. The sound speed profile that produces the focusing comes about from a combination of a strong downward refracting layer resulting from the geostrophic equilibrium of the Florida current on top of a well mixed turbulent bottom boundary layer. The resulting c(z) resembles cosh(g(1−z/D)), which produce perfect focusing at every range, that is, all RBR modes have the exact same group velocity.