Volume 5, Issue 4, October 2004
5(2004); http://dx.doi.org/10.1121/1.1764452View Description Hide Description
Changes in formant frequency over time are important for vowel identification: listeners identify stimuli containing time-varying formants better than stimuli with steady-state formants. Statistically based pattern classifiers used as models for human perception have shown that very coarse representations of formant change over time result in accurate classification of American English vowels. In this study, using synthetic stimuli with five levels of formant contour detail, human listeners achieved maximum vowel identification for relatively coarse representations of formant movement containing information about onset, offset, and midpoint frequencies. More detailed representations of contour did not improve identification for most vowels.
5(2004); http://dx.doi.org/10.1121/1.1764472View Description Hide Description
Visual morphing and a high-quality vocoder were used to study the audio-visual contribution of talker gender to the identification of frequency-shifted vowels. Several acoustic continua from “bit” to “bet” were generated incorporating fundamental frequency and spectral envelope shifts. Visual continua were constructed from male or female faces, and corresponding steps along the audio/visual continua were synchronized. Boundary shifts emerged for both acoustic cues and spectral envelope shifts) and visual cues (visual gender) as predicted by the co-variation of these properties in natural speech. Results suggest that perceivers exploit learned relationships between acoustic and visual cues when judging vowel identity.
5(2004); http://dx.doi.org/10.1121/1.1771712View Description Hide Description
This work presents initial findings from an investigation into the use of otoacoustic emissions(OAEs) for identifying individuals. A data set of 2009 neonate transient otoacoustic emissions was quantified for uniqueness using the Euclidean distance separation of the power spectra. Each sample was compared to all the others and the minimum separation recorded. The percentage separation for 50%, 95%, and 99% of the sample set was calculated and the distribution of the minimum separation plotted. The minimum separation between samples was 1.84% while 99% of the samples had a separation of 3.68%. A simple technique was able to achieve a separation of 3.68% for 99% of the data set, indicating it is highly likely that otoacoustic emissions are unique to an individual and of potential use as a biometric variable in an identification system.
5(2004); http://dx.doi.org/10.1121/1.1771711View Description Hide Description
To help elucidate how distortion-product otoacoustic emissions propagate from their cochlear sites of origin to the middle ear, their group delays were compared with basilar-membrane and organ of Corti travel times measured in guinea pig, gerbil, and chinchilla.
5(2004); http://dx.doi.org/10.1121/1.1779673View Description Hide Description
Acoustic microcavitation is used to detect particles in liquids and suspensions. The observation that an acoustic cavitation threshold is characteristic of particle size is exploited to develop a solution for an important problem facing chemical mechanical planarization of silicon wafers. Specifically, it is established via experiments that a sparse presence of large particles in a nanofine slurry can be detected acoustically. Being able to detect such large particles prior to chemical mechanical planarization polishing is expected to save the wafers from being scratched during planarization. The acoustic method is entirely noninvasive.
5(2004); http://dx.doi.org/10.1121/1.1788071View Description Hide Description
Hearing aids with adaptive and fixed two-microphone processing are currently available. Although the noise reduction increase of adaptive over fixed aids can theoretically be tens of dB, it is unclear if this benefit can be found with realistic processing and conditions. Thus, a theoretical analysis of the ability of today’s aids to attenuate jammers in “everyday” conditions [direct-reverberant ratio is provided. Processing limitations restrict aids to wideband null steering through intermicrophone delay variation. Delay variation is predicted to provide maximally 2.0 dB more noise reduction than the best fixed system on average, and only at the highest direct-reverberant ratios.
5(2004); http://dx.doi.org/10.1121/1.1758239View Description Hide Description
The intent of this study is to examine the variations between current implementations of standard room acousticmeasures for impulse response measurements. An international round robin has been conducted using a single real measured impulse response, rather than a synthesized response. This offers a more rigorous test of analysis procedures. While there is good agreement at higher frequencies, large variations are found at lower frequencies in which the noise level within the measurement is greater. Some errors are attributed to the existence or robustness of noise-floor detection.
5(2004); http://dx.doi.org/10.1121/1.1795311View Description Hide Description
Ultrasound imaging of ultrasoundcontrast agent fragmentation in a water bath was performed with the color Doppler mode of the HDI 5000 (Phillips Ultrasound). A highly diluted suspension of ultrasoundcontrastmicrobubbles (Optison®) was injected into the water bath such that individual microbubbles passed through the image plane every few seconds. Decorrelation of the signal, along with the appearance of multiple signals, suggests that single microbubble fragmentation was observed, with daughter bubbles being formed from the original microbubbles, depending on the applied acoustic pressure.