21,024 research outputs found
Analyse des signaux AM-FM basée sur une version B-splines de l'EMD-ESA
In this paper a signal analysis framework for estimating time-varying amplitude and frequency functions of multicomponent amplitude and frequency modulated (AMâFM) signals is introduced. This framework is based on local and non-linear approaches, namely Energy Separation Algorithm (ESA) and Empirical Mode Decomposition (EMD). Conjunction of Discrete ESA (DESA) and EMD is called EMDâDESA. A new modified version of EMD where smoothing instead of an interpolation to construct the upper and lower envelopes of the signal is introduced. Since extracted IMFs are represented in terms of B-spline (BS) expansions, a closed formula of ESA robust against noise is used. Instantaneous Frequency (IF) and Instantaneous Amplitude (IA) estimates of a multi- component AMâFM signal, corrupted with additive white Gaussian noise of varying SNRs, are analyzed and results compared to ESA, DESA and Hilbert transform-based algorithms. SNR and MSE are used as figures of merit. Regularized BS version of EMDâ ESA performs reasonably better in separating IA and IF components compared to the other methods from low to high SNR. Overall, obtained results illustrate the effective- ness of the proposed approach in terms of accuracy and robustness against noise to track IF and IA features of a multicomponent AMâFM signal
Adjustment of interaural-time-difference analysis to sound level
To localize low-frequency sound sources in azimuth, the binaural system compares the timing of sound waves at the two ears with microsecond precision. A similarly high precision is also seen in the binaural processing of the envelopes of high-frequency complex sounds. Both for low- and high-frequency sounds, interaural time difference (ITD) acuity is to a large extent independent of sound level. The mechanisms underlying this level-invariant extraction of ITDs by the binaural system are, however, only poorly understood. We use high-frequency pip trains with asymmetric and dichotic pip envelopes in a combined psychophysical, electrophysiological, and modeling approach. Although the dichotic envelopes cannot be physically matched in terms of ITD, the match produced perceptually by humans is very reliable, and it depends systematically on the overall sound level. These data are reflected in neural responses from the gerbil lateral superior olive and lateral lemniscus. The results are predicted in an existing temporal-integration model extended with a level-dependent threshold criterion. These data provide a very sensitive quantification of how the peripheral temporal code is conditioned for binaural analysis
Time domain analysis of partial discharges envelope in medium voltage XLPE cables
Partial discharge (PD) analysis has been widely used to detect premature degradation of power cables. Although there are recognized techniques for PD analysis, there is still lack of knowledge about measuring and modeling this phenomenon.
This paper proposes a new model based on time domain parameters of the PD signal envelope. The proposed variables (time duration, and rising and falling slopes of the envelopes), together with conventional PD analyses focused on PD amplitude and phase resolved patterns, will provide a better understanding of this phenomenon. Based on this model, a new technique to reshape the PD signal envelope is also proposed that compensates the negative effect of dispersion in the location techniques that estimate the time of arrival (TOA).
Experimental results were obtained in the lab, where a power cable has been artificially damaged in order to produce PD. To this end, a specific PD on-line acquisition system has been developed. In the first set of experiments, we illustrate how the cable attenuates and disperses the PD signal envelope. In the second one, we show how the proposed variables are useful to distinguish among different types of PD sources. Finally, an accurate estimation of the PD source location is achieved by measuring the time of arrival of the PD signal envelopes at both cable ends, and reshaping one of the signals captured. This technique improves the accuracy of the estimated location of the PD sources, both in simulation and in experimental results
An evaluation of intrusive instrumental intelligibility metrics
Instrumental intelligibility metrics are commonly used as an alternative to
listening tests. This paper evaluates 12 monaural intrusive intelligibility
metrics: SII, HEGP, CSII, HASPI, NCM, QSTI, STOI, ESTOI, MIKNN, SIMI, SIIB, and
. In addition, this paper investigates the ability of
intelligibility metrics to generalize to new types of distortions and analyzes
why the top performing metrics have high performance. The intelligibility data
were obtained from 11 listening tests described in the literature. The stimuli
included Dutch, Danish, and English speech that was distorted by additive
noise, reverberation, competing talkers, pre-processing enhancement, and
post-processing enhancement. SIIB and HASPI had the highest performance
achieving a correlation with listening test scores on average of
and , respectively. The high performance of SIIB may, in part, be
the result of SIIBs developers having access to all the intelligibility data
considered in the evaluation. The results show that intelligibility metrics
tend to perform poorly on data sets that were not used during their
development. By modifying the original implementations of SIIB and STOI, the
advantage of reducing statistical dependencies between input features is
demonstrated. Additionally, the paper presents a new version of SIIB called
, which has similar performance to SIIB and HASPI,
but takes less time to compute by two orders of magnitude.Comment: Published in IEEE/ACM Transactions on Audio, Speech, and Language
Processing, 201
Self-Consistent Analysis of OH-Zeeman Observations: Too Much Noise about Noise
We had recently re-analyzed in a self-consistent way OH-Zeeman observations
in four molecular-cloud envelopes and we had shown that, contrary to claims by
Crutcher et al., there is no evidence that the mass-to-flux ratio decreases
from the envelopes to the cores of these clouds. The key difference between our
data analysis and the earlier one by Crutcher et al. is the relaxation of the
overly restrictive assumption made by Crutcher et al, that the magnetic field
strength is independent of position in each of the four envelopes. In a more
recent paper, Crutcher et al. (1) claim that our analysis is not
self-consistent, in that it misses a cosine factor, and (2) present new
arguments to support their contention that the magnetic-field strength is
indeed independent of position in each of the four envelopes. We show that the
claim of the missing cosine factor is false, that the new arguments contain
even more serious problems than the Crutcher et al. original data analysis, and
we present new observational evidence, independent of the OH-Zeeman data, that
suggests significant variations in the magnetic-field strength in the four
cloud envelopes.Comment: 8 pages, 3 figures, MNRAS in pres
Background derivation and image flattening: getimages
Modern high-resolution images obtained with space observatories display
extremely strong intensity variations across images on all spatial scales.
Source extraction in such images with methods based on global thresholding may
bring unacceptably large numbers of spurious sources in bright areas while
failing to detect sources in low-background or low-noise areas. It would be
highly beneficial to subtract background and equalize the levels of small-scale
fluctuations in the images before extracting sources or filaments. This paper
describes getimages, a new method of background derivation and image
flattening. It is based on median filtering with sliding windows that
correspond to a range of spatial scales from the observational beam size up to
a maximum structure width . The latter is a single free parameter
of getimages that can be evaluated manually from the observed image
. The median filtering algorithm provides a background
image for structures of all widths below
. The same median filtering procedure applied to an image of
standard deviations derived from a
background-subtracted image results in a
flattening image . Finally, a flattened
detection image
is computed, whose standard deviations are uniform outside sources and
filaments. Detecting sources in such greatly simplified images results in much
cleaner extractions that are more complete and reliable. As a bonus, getimages
reduces various observational and map-making artifacts and equalizes noise
levels between independent tiles of mosaicked images.Comment: 14 pages, 11 figures (main text + 3 appendices), accepted by
Astronomy & Astrophysics; fixed Metadata abstract (typesetting
The internal dynamical equilibrium of HII regions: a statistical study
We present an analysis of the integrated Halpha emission line profiles for
the HII region population of the spiral galaxies NGC 1530, NGC 6951 and NGC
3359. We show that 70% of the line profiles show two or three Gaussian
components. The relations between the Halpha luminosity and non-thermal line
width for the HII regions of the three galaxies are studied and compared with
the relation found taken all the HII regions of the three galaxies as a single
distribution. A clearer envelope in non-thermal line width is found when only
those HII regions with non-thermal line width bigger than 13kms are considered.
The linear fit for the envelope is logL=36.8+2.0*log(sigma). The masses of the
HII regions on the envelope using the virial theorem and the mass estimates
from the Halpha luminosity are comparable, which offers evidence that the HII
regions on the envelope are virialized systems, while the remaining regions,
the majority, are not in virial equilibrium.Comment: 19 pages, 10 figures,accepted for publication in A&
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