Segregation of concurrent sounds. II: Effects of spectral envelope tracing, frequency modulation coherence, and frequency modulation width

The research presented here concerns the simultaneous grouping of the components of a vocal sound source. McAdams [J. Acoust. Soc. Am. 86, 2148-2159 (1989)] found that when three simultaneous vowels at different pitches were presented with subaudio frequency modulation, subjects judged them as being more prominent than when no vibrato was present. In a normal voice, when the harmonics of a vowel undergo frequency modulation they also undergo an amplitude modulation that traces the spectral envelope. Hypothetically, this spectral tracing could be one of the criteria used by the ear to group components of each vowel, which may help explain the lack of effect of frequency modulation coherence among different vowels in the previous study. In this experiment, two types of vowel synthesis were used in which the component amplitudes of each vowel either remained constant with frequency modulation or traced the spectral envelope. The stimuli for the experiment were chords of three different vowels at pitch intervals of five semitones (ratio 1.33). All the vowels of a given stimulus were produced by the same synthesis method. The subjects' task involved rating the prominence of each vowel in the stimulus. It was assumed that subjects would judge this prominence to be lower when they were not able to distinguish the vowel from the background sound. Also included as stimulus parameters were the different permutations of the three vowels at three pitches and a number of modulation conditions in which vowels were unmodulated, modulated alone, and modulated either coherently with, or independently of, the other vowels. Spectral tracing did not result in increased ratings of vowel prominence compared to stimuli where no spectral tracing was present. It would therefore seem that it has no effect on grouping components of sound sources. Modulated vowels received higher prominence ratings than unmodulated vowels. Vowels modulated alone were judged to be more prominent than vowels modulated with other vowels. There was, however, no significant difference between coherent and independent modulation of the three vowels. Differences among modulation conditions were more marked when the modulation width was 6% than when it was 3%.     

Thin film platinum cuff electrodes for neurostimulation: in vitro approach of safe neurostimulation parameters

Thin film technology takes more and more importance in the development of biomedical devices dedicated to functional neurostimulation. Our research about the design of implant neurostimulating electrode is oriented toward thin film cuff electrodes based on a polyimide substrate covered by a chromium/gold/Pt film. The chromium/gold sputtered film serves as adhesion layer and current collector whereas platinum acts as an electrochemical actuator. The electrode surface has been designed to obey safe stimulation criteria (i.e. chemically inert noble metal, low electrode-electrolyte impedance, high electrochemical reversibility, high corrosion stability). The electrochemical behaviour of such platinum electrodes has been assessed and compared to a foil of platinum. Extensive in vitro characterisations of the both electrode types were carried out using AFM, SEM and electrochemical techniques. The role of enhanced surface roughness enabling high double layer capacitances to be achieved was clearly highlighted. The obtained results are discussed, with particular reference to thin film electrodes stability under in vitro electrical stimulation in NaCl 0.9% (physiological serum). Therefore, these thin film devices showed reversible PtOH formation and decomposition making them potentially attractive for the fabrication of implant stimulation cuff electrodes.     

A comparison of amperometric screen-printed, carbon electrodes and their application to the analysis of phenolic compounds present in beers

In this paper a comparison between three commercially-available, screen-printable graphite inks for the construction of phenolic biosensors is made. The enzyme tyrosinase was immobilised within a polymer matrix and the substrate catechol was used to characterise the bio-electroanalytical response of each electrode. Biosensors fabricated from Gwent graphite inks exhibited the greatest sensitivity (5740 mA mol cm(-2)) compared to Dupont and Acheson graphite-based inks. This difference in sensitivity was attributed to a combination of a larger electroactive surface area, and thus a greater number of immobilised enzyme molecules. However, the dynamic range was considerably smaller (0.025-14 muM) indicating that the enzyme molecules were easily accessible to the substrate catechol. The surface properties of the biosensors were characterised using ac impedance, which indicated that the presence of the polymer on the electrode surface not only increased the charge-transfer kinetics of the three biosensors, but also increased the surface roughness of biosensors fabricated from Gwent inks. On the basis of these results Gwent graphite-based inks were used for analysis of phenolic compounds in lager beers by flow-injection analysis. The biosensor displayed favourable response characteristics, but cannot differentiate between the various phenolic compounds present in the samples. Nevertheless, the biosensor maybe suitable for indicating the phenolic status of beer or brew samples compared to time-consuming traditional methods, e.g. colorimetric or chromatographic methods.     

Segregation of concurrent sounds. I: Effects of frequency modulation coherence

Frequency modulation coherence was investigated as a possible cue for the perceptual segregation of concurrent sound sources. Synthesized chords of 2-s duration and comprising six permutations of three sung vowels (/a/, /i/, /o/) at three fundamental frequencies (130.8, 174.6, and 233.1 Hz) were constructed. In one condition, no vowels were modulated, and, in a second, all three were modulated coherently such that the ratio relations among all frequency components were maintained. In a third group of conditions, one vowel was modulated, while the other two remained steady. In a fourth group, one vowel was modulated independently of the two other vowels, which were modulated coherently with one another. Subjects were asked to judge the perceived prominence of each of the three vowels in each chord. Judged prominence increased significantly when the target vowel was modulated compared to when it was not, with the greatest increase being found for higher fundamental frequencies. The increase in prominence with modulation was unaffected by whether the target was modulated coherently or not with nontarget vowels. The modulation and pitch position of nontarget vowels had no effect on target vowel prominence. These results are discussed in terms of possible concurrent auditory grouping principles.     

Amperometric detection of phenolic compounds by polypyrrole-based composite carbon paste electrodes

This contribution describes new composite carbon paste electrodes (CPEs) for the determination of phenolic compounds. The composite CPEs were prepared by in situ generation of polypyrrole (PPy) within a paste containing the enzyme polyphenol oxidase (PPO). The best paste composition (enzyme/pyrrole monomer/carbon particles/Nujol) was determined for a model enzyme, glucose oxidase (GOx) according to the enzymatic activity of the resulting electrodes and to the enzyme leakage from the paste during storage in phosphate buffer. The in situ electrogenerated PPy improves the enzyme immobilisation within the paste since practically no enzyme was lost in solution after 72 h of immersion. Moreover, the enzyme activity remains particularly stable under storage since the biocomposite structure conserves 80% of its activity after 1 month of storage. Following the optimisation of the paste composition, PPO-based carbon paste biosensors were prepared and presented excellent analytical properties toward catechol detection with a sensitivity of 4.7 A M(-1) cm(-2) and a response time lower than 20 s. The resulting biosensors were applied to the determination of polyphenolic compounds (e.g., epicatechin and ferulic acid).     

Characterizing the sound quality of air-conditioning noise

The aim of the psychoacoustic study presented here was to characterize listeners' preferences for a set of sounds produced by different brands and models of indoor air-conditioning units. In addition, some synthetic sounds, created by interpolation between recorded sound samples, were integrated into the set. The multidimensional perceptual space and the corresponding physical space representative of the sound set were determined with multidimensional scaling (MDS). Then the preferences for different classes of listeners were related to the physical space. The best spatial model yielded by the MDS had three common dimensions and specificities. The three dimensions are correlated with the ratio of the noisy part of the spectrum to the harmonic part (NHR), with the spectral center of gravity (SC) and with loudness (N). Two classes of listeners can be distinguished in terms of preference. For one, preference varied primarily with loudness, whereas for the other it varied more with SC and NHR. However, for one class the preference grew with the parameter NHR, while it decreased for the other class. The results replicate under different laboratory conditions and indicate the usefulness of this sound quality assessment approach for characterizing appliance noises.     

The vacuum ultraviolet spectra of fluorine chlorine substituted trivalent phosphorus

The vapor phase absorption spectra of PF₃, PF₂Cl, PFCl₂, and PCl₃ are reported in the vacuum ultraviolet spectral region 2400—1200 A. These results are compared with information obtained from photoelectron spectra. A brief discussion of the spectra in terms of analogous absorption regions and results from CNDO/2 calculations are given.     

Monotonicity in asymmetric first-price auctions with affiliation

I study monotonicity of equilibrium strategies in first-price auctions with asymmetric bidders, risk aversion, affiliated types, and interdependent values. Every mixed-strategy equilibrium is shown to be outcome-equivalent to a monotone pure-strategy equilibrium under the “priority rule” for breaking ties. This provides a missing link to establish uniqueness in the “general symmetric model” of Milgrom and Weber (Econometrica 50:1089–1122, 1982). Non-monotone equilibria can exist under the “coin-flip rule” but they are distinguishable: all non-monotone equilibria have positive probability of ties whereas all monotone equilibria have zero probability of ties. This provides a justification for the standard empirical practice of restricting attention to monotone strategies. Hendricks et al. (2003) provide an overview of recent empirical work. For a survey of experimental work, see Kagel and Levin (2002).     

The auditory continuity phenomenon: role of temporal sequence structure

The auditory continuity phenomenon occurs when listening to a series of alternating high- and low-level tones: instead of perceiving this intermittence, listeners often report hearing a continuous tone upon which is superimposed a series of intermittent tones. The temporal limits to the perception of this phenomenon are investigated, as well as effects of task instructions on it. A loudness-matching paradigm developed previously [McAdams et al., J. Acoust. Soc. Am. 130, 1580-1591 (1998)] provided both an objective indication of this phenomenon and an indication of its strength. In the studies reported here, the phenomenon was observed reliably when the low-level tones were at least half the duration of the high-level tones: the greater the duration ratio between low-level and high-level tones, the stronger the phenomenon. Duty-cycle duration did not affect the strength of this phenomenon. It proved to be particularly robust as its strength was unaffected by task instructions, level of expertise, and repetition. A model is proposed in which adjusted levels depend on the relative levels of the high- and low-level tones weighted by relative duration and attentional focusing.