Properties Of Acoustic Signals Research Articles

Cardiac Activity Based on Acoustic Signal Properties

The in uence of sleeping conditions on human health and well-being is now fully understood, but still underestimated. Sleep disorders e.g. snoring, wheezing or sleep apnea are widespread among people of all ages, although prevalent amidst the male population, obese people with a high value of BMI, people who su ered a stroke, have hypertension or other heart diseases. Medical support is needed in order to ensure a good night's sleep for patients su ering from sleep disorders. Sleep monitoring is also very important in case of emergencies. This research was aimed at nding a correlation between sleep disorders represented by acoustic signals and heart activity parameters. The measurement of breathing through simultaneously acquired acoustic and ECG signals is used to quantify the respiratory obstruction during sleep. The information collected by synchronized recording of acoustic e ects and the ECG signal partly overlaps, giving an opportunity to improve accuracy of measurement. Results indicate that the aspect of sleep analysis can be extended using this method. The information collected by simultaneous recording of acoustic e ects and the ECG signal is provided and the results are described.

Mode-2 internal waves impact on acoustic signal properties.

The properties of mode-2 internal waves repeatedly observed on the New Jersey Shelf (USA) with high-frequency acoustic flow visualization systems will be overviewed. The impact of the mode-2 internal waves on the range/depth distribution of acoustic signal properties will be discussed.

Acoustic spectral preferences in two cryptic species of grey treefrogs: implications for mate choice and sensory mechanisms

Females are expected to use spectral properties of acoustic signals for mate choice because dominant frequency often provides reliable information about male size. The advertisement calls of grey treefrogs ( Hyla chrysoscelis and H. versicolor ) have two main frequency bands: the amplitude of the dominant, high-frequency band averages 7–10 dB greater than that of the low-frequency band. The frequencies of these peaks were negatively correlated with male body size in both species. I used two-speaker playbacks of synthetic calls to generate preference functions for both species based on simultaneous variation in the frequencies of the two bands and, for H. versicolor , on variation in single-component calls; frequencies of most of these stimuli fell within the range of the dominant, high-frequency band. When two-component sounds were used, preference functions were bimodal and broad, with peaks close to ( H. versicolor ) or slightly higher than ( H. chrysoscelis ) mean frequencies in conspecific calls. Because preferences were not strong, I predict that females exert only weak stabilizing or directional selection on male call frequencies. When single-component calls were used in tests of H. versicolor , the preference-function peak was shifted to a lower-than-average frequency within the high-frequency range. I hypothesize that such a frequency may better stimulate both of the inner ear organs, whose tuning roughly matches frequencies in the two bands in conspecific calls, than a single component of average or much lower-than-average frequency. Females of both species preferred calls with both spectral peaks to calls with a single, high-frequency peak, even when the low-frequency peak was attenuated by 24–30 dB. This result serves to emphasize that typically subdominant frequency components can have seemingly disproportionate effects on signal attractiveness.

Matched-field processing gain degradation caused by tidal flow over continental shelf bathymetry.

Temporally variable, range dependent sound-speed profiles measured during ebb flow and estimated for slack flow are used to quantify the variability of matched-field signal-processing gain degradation in shallow water propagation channels controlled by tidally driven stratified flow over variable bathymetry. Calculations along a 9.3 km range establish phase changes in the acoustic signal as the primary cause of a 3-9 dB degradation in the coherent matched-field processing output of a full water column vertical array. The work indicates that over a tidal cycle acoustic signal properties and matched-field processing gain can be expected to change continuously in a shallow water stratified channel that has bathymetry variability. Acoustic signals propagating in such tidal flow-controlled environments may be expected to display repeatable (over successive tidal cycles) and predictable changes in their phase coherent properties. These results suggest that matched-field processor replica fields used in the shelf/slope propagation environment will have to be updated regularly during a tidal cycle to maintain maximum processor gain.

Impact of depression to elevation internal soliton wave conversion on upslope acoustic propagation—A simulation

Depression to elevation soliton wave conversion has been observed at the South China Sea shelf break during the recent AsiaEX experiment. Numerical simulation of the internal soliton conversion process for a two-layer fluid has been used to generate a range/time-dependent sound speed profile for upslope propagation along a 20-km propagation path. Acoustic signal properties during various stages of soliton conversion are compared. [Work supported by the ONR Ocean Acoustic Program and ONRs NRL base funding.]

Frequency analysis of broadband acoustic signals propagating through nonlinear internal waves

Nonlinear internal waves along the ocean thermocline are known to affect modal compositions and other properties of acoustic signals. Such nonlinear waves were observed during the SWARM 95 Orthogonal Propagation Experiment, where extensive data were collected from two broadband sources. One source was a 30-s linear frequency modulated sweep signal, and the other was a 0.1-s airgun shot. Both sources were repeated every minute and received by two vertical linear arrays several kilometers away. Sound speed profiles were measured near the source and the receiver arrays simultaneously. The influences of internal waves on the broadband frequency behavior of received and simulated signals are described. Features of energy spectral density and of transmission loss versus frequency plots are used to detect resonant frequencies where anomalous loss occurs. A time-frequency analysis of received signals at several ranges is performed to determine modal propagation characteristics, including modal transitions of the signals passing through the internal waves. An objective of this study is to link acoustic signal behavior to internal wave properties such as wavelength, packet length, and amplitude. [Work supported by ONR.]

Frequency Content of Randomly Scattered Signals

The statistical properties of acoustic signals reflected by a randomly layered medium are analyzed when a pulsed spherical wave issuing from a point source is incident upon it. The asymptotic analysis of stochastic equations and geometrical acoustics is used to arrive at a set of transport equations that characterize multiply scattered signals observed at the surface of the layered medium. The results of extensive numerical simulations are presented, illustrating the scope of the theory. A number of inverse problems for randomly layered media are also formulated where we recover large-scale properties of the sound speed profile from the statistics of reflected signals.

Source characteristics: A study of hand clapping

The present research evaluated the capabilities of listeners to determine source characteristics from acoustic signal properties. Repp [J. Acoust. Soc. Am. 81, 1100–1110 (1987)] demonstrated that naive listeners have some ability to determine the source characteristic of hand position given the acoustic signal of a clap. The purpose of this hand clapping experiment was (1) to more directly assess the capabilities of naive listeners to determine source characteristics, (2) to determine the physical aspects of the acoustic signal that are highly correlated with the source, and (3) to train subjects so that performance could be improved. The production phase of the experiment consisted of recording claps in five different hand positions. The perceptual phase consisted of a within clapper same/different task with listeners asked to judge whether the hand position was the same (never physically identical) or different. Half of the listeners tested received feedback. Preliminary results indicate that naive listeners could distinguish hand position from only a few clappers. Furthermore, training over 360 trials was only marginally beneficial in improving performance. Results will be discussed in terms of different methods of assessing and improving listener performance. [Work supported by BRSG program grant.]