Subjective loudness level measurements and equal loudness contours in a bottlenose dolphin (Tursiops truncatus)

Loudness level measurements in human listeners are straightforward; however, it is difficult to convey the concepts of loudness matching or loudness comparison to (non-human) animals. For this reason, prior studies have relied upon objective measurements, such as response latency, to estimate equal loudness contours in animals. In this study, a bottlenose dolphin was trained to perform a loudness comparison test, where the listener indicates which of two sequential tones is louder. To enable reward of the dolphin, most trials featured tones with identical or similar frequencies, but relatively large sound pressure level differences, so that the loudness relationship was known. A relatively small percentage of trials were "probe" trials, with tone pairs whose loudness relationship was not known. Responses to the probe trials were used to construct psychometric functions describing the loudness relationship between a tone at a particular frequency and sound pressure level and that of a reference tone at 10 kHz with a sound pressure level of 90, 105, or 115 dB re 1 μPa. The loudness relationships were then used to construct equal loudness contours and auditory weighting functions that can be used to predict the frequency-dependent effects of noise on odontocetes.     

The role of fundamental frequency contours in the perception of speech against interfering speech

Four experiments investigated the effect of the fundamental frequency (F0) contour on speech intelligibility against interfering sounds. Speech reception thresholds (SRTs) were measured for sentences with different manipulations of their F0 contours. These manipulations involved either reductions in F0 variation, or complete inversion of the F0 contour. Against speech-shaped noise, a flattened F0 contour had no significant impact on SRTs compared to a normal F0 contour; the mean SRT for the flattened contour was only 0.4 dB higher. The mean SRT for the inverted contour, however, was 1.3 dB higher than for the normal F0 contour. When the sentences were played against a single-talker interferer, the overall effect was greater, with a 2.0 dB difference between normal and flattened conditions, and 3.8 dB between normal and inverted. There was no effect of altering the F0 contour of the interferer, indicating that any abnormality of the F0 contour serves to reduce intelligibility of the target speech, but does not alter the masking produced by interfering speech. Low-pass filtering the F0 contour increased SRTs; elimination of frequencies between 2 and 4 Hz had the greatest effect. Filtering sentences with inverted contours did not have a significant effect on SRTs.     

Voice frequency change in singers and nonsingers

Trained singers and nonsingers vocally shadowed sequences of rapidly changing tones. Tone changes within the sequences were unpredictable in terms of direction and extent of frequency change. Subjects' responses to the shadowing task could be evaluated for accuracy of frequency matching, and for time and speed of voice frequency change. In addition, subjects' transitions between tones could be classified as hit, overshoot, undershoot, or oscillate. The two groups were equally accurate in matching the pitches of tones comprising the sequences. Similarly, pitch lowering was faster than pitch raising for both groups of subjects, while speeds for both lowering and raising increased with increases in size of the interval between tones. However, singers required less time than nonsingers in effecting transitions, apparently because they achieved faster peak speeds and took more direct paths between tones. Implications of the data for physiological and mechanical aspects of voice frequency control are discussed.     

Detection of quasitrapezoidal frequency and amplitude modulation

It has been proposed that the detection of frequency modulation (FM) of sinusoidal carriers can be mediated by two mechanisms; a place mechanism based on FM-induced amplitude modulation (AM) in the excitation pattern, and a temporal mechanism based on phase locking in the auditory nerve. The temporal mechanism appears to be "sluggish" and does not play a role for FM rates above about 10 Hz. It also does not play a role for high carrier frequencies (above about 5 kHz). This experiment provided a further test of the hypothesis that the effectiveness of the temporal mechanism depends upon the time spent close to frequency extremes during the modulation cycle. Psychometric functions for the detection of AM and FM were measured for two carrier frequencies, 1 and 6 kHz. The modulation waveform was quasitrapezoidal. Within each modulation period, P, a time Tss was spent at each extreme of frequency or amplitude. The transitions between the extremes, with duration Ttrans had the form of a half-cycle of a cosine function. The modulation rate was 2, 5, 10, or 20 Hz, giving values of P of 500, 200, 100, and 50 ms. TSS varied from 0 ms (sinusoidal modulation) up to 160, 80, 40, or 20 ms, for rates of 2, 5, 10, and 20 Hz, respectively. The detectability of AM was not greatly affected by modulation rate or by the value of TSS, except for a slight improvement with increasing TSS for the lowest modulation rates; this was true for both carrier frequencies. For FM of the 6-kHz carrier, the pattern of results was similar to that found for AM, which is consistent with an excitation-pattern model of FM detection. For FM of the 1-kHz carrier, performance improved markedly with increasing TSS, especially for the lower FM rates; there was no change in performance with TSS for the 20-Hz modulation rate. The results are consistent with the idea that detection of FM of a 1-kHz carrier is partly mediated by a sluggish temporal mechanism. That mechanism benefits from greater time spent at frequency extremes of the modulation cycle for rates up to 10 Hz.     

Detection of combined frequency and amplitude modulation.

This article is concerned with the detection of mixed modulation (MM), i.e., simultaneously occurring amplitude modulation (AM) and frequency modulation (FM). In experiment 1, an adaptive two-alternative forced-choice task was used to determine thresholds for detecting AM alone. Then, thresholds for detecting FM were determined for stimuli which had a fixed amount of AM in the signal interval only. The amount of AM was always less than the threshold for detecting AM alone. The FM thresholds depended significantly on the magnitude of the coexisting AM. For low modulation rates (4, 16, and 64 Hz), the FM thresholds did not depend significantly on the relative phase of modulation for the FM and AM. For a high modulation rate (256 Hz) strong effects of modulator phase were observed. These phase effects are as predicted by the model proposed by Hartmann and Hnath [Acustica 50, 297-312 (1982)], which assumes that detection of modulation at modulation frequencies higher than the critical modulation frequency is based on detection of the lower sideband in the modulated signal's spectrum. In the second experiment, psychometric functions were measured for the detection of AM alone and FM alone, using modulation rates of 4 and 16 Hz. Results showed that, for each type of modulation, d' is approximately a linear function of the square of the modulation index. Application of this finding to the results of experiment 1 suggested that, at low modulation rates, FM and AM are not detected by completely independent mechanisms. In the third experiment, psychometric functions were again measured for the detection of AM alone and FM alone, using a 10-Hz modulation rate. Detectability was then measured for combined AM and FM, with modulation depths selected so that each type of modulation would be equally detectable if presented alone. Significant effects of relative modulator phase were found when detectability was relatively high. These effects were not correctly predicted by either a single-band excitation-pattern model or a multiple-band excitation-pattern model. However, the detectability of the combined AM and FM was better than would be predicted if the two types of modulation were coded completely independently.     

Statistical damage identification of structures with frequency changes

Model updating methods based on structural vibration data have being rapidly developed and applied to detect structural damage in civil engineering. But uncertainties existing in the structural model and measured vibration data might lead to unreliable damage detection. In this paper a statistical damage identification algorithm based on frequency changes is developed to account for the effects of random noise in both the vibration data and finite element model. The structural stiffness parameters in the intact state and damaged state are, respectively, derived with a two-stage model updating process. The statistics of the parameters are estimated by the perturbation method and verified by Monte Carlo technique. The probability of damage existence is then estimated based on the probability density functions of the parameters in the two states. A higher probability statistically implies a more likelihood of damage occurrence. The presented technique is applied to detect damages in a numerical cantilever beam and a laboratory tested steel cantilever plate. The effects of using different number of modal frequencies, noise level and damage level on damage identification results are also discussed.     

Detection and discrimination of frequency modulation of complex signals

Detection and discrimination of frequency modulation were studied for harmonic signals with triangular spectral envelopes. The center frequency of the stimuli was near 2 kHz; the fundamental frequency was near 100 Hz. To prevent the possibility that the discrimination was based on differences of initial or final frequencies, these frequencies were equal within and across modulations in each individual experiment. Differences between modulations consisted of differences in the trajectories between the initial and final frequencies. Performance worsened as the slopes of the spectral envelopes decreased. Addition of noise also impaired modulation discrimination. The dependence on the signal-to-noise ratio was similar to what is found for stationary stimuli: Discrimination of frequency modulation deteriorated more rapidly with decreasing signal-to-noise ratio when stimuli had shallow spectral slopes than when they had steep spectral slopes. In spite of the precautions taken (i.e., initial and final frequency the same), the discrimination of these stimuli was more likely based on quasistationary frequency discrimination than on discrimination of modulation rate. This conclusion is consistent with previous findings for pure tones presented in quiet that frequency discrimination is more acute than modulation-rate discrimination.     

Nonlinear standing waves,resonance phenomena,and frequency characteristics of distributed systems

This review is dedicated to resonator oscillations under conditions of a strongly expressed nonlinearity under which steep shock fronts emerge in the wave profiles. Models and approximated methods for their analysis for quadratic and cubic nonlinear media are examined, as well as for nonlinearity when taking into account the mobility of boundaries. The forms of the profiles are calculated both for a steady-state oscillation regime and during the establishment of the profiles. Dissipative losses and selective losses at specially chosen frequencies are considered. An analysis of nonlinear Q-factor is given. The possibility of increasing the acoustic energy accumulated in the cavity of the resonator is discussed. Special attention is given to various physical phenomena that are exhibited only in nonlinear acoustic fields.     

Low frequency flows through an array of airfoils

The linearized flow through a finite array of airfoils undergoing arbitrary motion is investigated analytically. The key assumptions are that motion is at low frequencies and that the interference between the airfoils is weak; both of these assumptions are defined precisely in the main body of the paper. An important ingredient of the analysis is the enforcement of the Kutta condition and the treatment of the unsteady wakes. It is shown that the effective induced velocity at each airfoil also depends on the shed vorticity and not only on the interference created by the neighboring airfoils. Two examples are treated at the end of the paper in order to illustrate the power of the present approach.     

Detection of chemical damage in concrete using ultrasound

This research deals with a non-destructive method for characterizing the degraded cover of concrete structures using high-frequency ultrasound (0.5-1 MHz). Although such a frequency range is unusual in civil engineering, it is well suited to the kind of defect to be detected, as it corresponds to a thin near-to-surface layer with increased porosity and density of microcracks. In order to assess the feasibility of detecting concrete cover degradation, velocity and attenuation measurements were made on both halves of a concrete slab. One half was immersed into an acid solution for 15-45 days, while the other half remained sound. These measurements were made for longitudinal, transverse and surface waves. The results obtained show a 23% decrease of ultrasonic pulse velocity and a 1000% increase of attenuation in the degraded material relative to the sound material. It is thus possible to detect and characterize concrete cover degradation using high-frequency ultrasound. Although attenuation measurements in heterogeneous media are difficult, their sensitivity to degradation is very high.     

Line narrowing of a distributed feedback dye laser using external frequency selective feedback

Frequency selective feedback, employing a mirror and etalon, applied to a distributed feedback dye laser has reduced the linewidth of the emitted radiation by a factor of up to twenty. Criteria used for choosing suitable etalons are discussed.     

Electron irradiation-induced change of structure and damage mechanisms in multi-walled carbon nanotubes

Owing to their unique structure and excellent electrical property, carbon nanotubes(CNTs) as an ideal candidate for making future electronic components have great application potentiality. In order to meet the requirements for space application in electronic components, it is necessary to study structural changes and damage mechanisms of multi-walled carbon nanotubes(MWCNTs), caused by the irradiations of 70 and 110 ke V electrons. In the paper, the changes of structure and damage mechanisms in the irradiated MWCNTs, induced by the irradiations of 70 and 110 ke V electrons, are investigated.The changes in surface morphology and structure of the irradiated MWCNT film are characterized using scanning electron microscopy(SEM), x-ray photoelectron spectroscopy(XPS), Raman spectroscopy, x-ray diffraction analysis(XRD), and electron paramagnetic resonance(EPR) spectroscopy. It is found that the MWCNTs show different behaviors in structural changes after 70 and 110 ke V electron irradiation due to different damage mechanisms. SEM results reveal that the irradiation of 70 ke V electrons does not change surface morphology of the MWCNT film, while the irradiation of 110 ke V electrons with a high fluence of 5 × 1015cm-2leads to evident morphological changes, such as the formation of a rough surface, the entanglement of nanotubes and the shrinkage of nanotubes. Based on Raman spectroscopy, XPS, and XRD analyses, it is confirmed that the irradiation of 70 ke V electrons increases the interlayer spacing of the MWCNTs and disorders their structure through electronic excitations and ionization effects, while the irradiation of 110 ke V electrons obviously reduces the interlayer spacing of the MWCNTs and improves their graphitic order through knock-on atom displacements. The improvement of the irradiated MWCNTs by 110 ke V electrons is attributed to the restructuring of defect sites induced by knock-on atom displacements. EPR spectroscopic analyses reveal that the MWCNTs exposed to both70 ke V electrons and 110 ke V electrons suffer ionization damage to some extent.     

Comparative analysis of the frequency noise in two distributed circuits of semiconductor self-excited oscillators

Kuibyshev State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 32, No. 2, pp. 242–245, February, 1989.     

Structural damage detection of controlled building structures using frequency response functions

If a building structure requires both a vibration control system and a health monitoring system, the integration of the two systems will be cost-effective and beneficial. One of the key problems of this integrated system is how to use control devices to enhance system identification and damage detection. This paper presents a new method for system identification and damage detection of controlled building structures equipped with semi-active friction dampers through model updating based on frequency response functions. The two states of the building are first created by adding a known stiffness using semi-active friction dampers. A scheme based on the frequency response functions of the two states of the building is then presented to identify stiffness parameters of structural members in consideration of structural connectivity and transformation information. By applying the proposed model updating scheme to the damaged building, a damage detection scheme is proposed based on the identified stiffness parameters of structural members of both the original and damaged buildings. The feasibility of the proposed schemes is finally demonstrated through a detailed numerical investigation in terms of an example building, in which the effects of measurement noise and excitation conditions are discussed. The numerical results clearly show that the proposed method can locate and quantify damage satisfactorily even though measurement noise is taken into consideration.     

Detection of electron paramagnetic resonance absorption using frequency modulation

A frequency modulation (FM) method was developed to measure electron paramagnetic resonance (EPR) absorption. The first-derivative spectrum of 1,1-diphenyl-2-picrylhydrazyl (DPPH) powder was measured with this FM method. Frequency modulation of up to 1.6 MHz (peak-to-peak) was achieved at a microwave carrier frequency of 1.1 GHz. This corresponds to a magnetic field modulation of 57microT (peak-to-peak) at 40.3 mT. By using a tunable microwave resonator and automatic control systems, we achieved a practical continuous-wave (CW) EPR spectrometer that incorporates the FM method. In the present experiments, the EPR signal intensity was proportional to the magnitude of frequency modulation. The background signal at the modulation frequency (1 kHz) for EPR detection was also proportional to the magnitude of frequency modulation. An automatic matching control (AMC) system reduced the amplitude of noise in microwave detection and improved the baseline stability. Distortion of the spectral lineshape was seen when the spectrometer settings were not appropriate, e.g., with a lack of the open-loop gain in automatic tuning control (ATC). FM is an alternative to field modulation when the side-effect of field modulation is detrimental for EPR detection. The present spectroscopic technique based on the FM scheme is useful for measuring the first derivative with respect to the microwave frequency in investigations of electron-spin-related phenomena.