4,681 research outputs found
Robust Speech Detection for Noisy Environments
This paper presents a robust voice activity detector (VAD) based on hidden Markov models (HMM) to improve speech recognition systems in stationary and non-stationary noise environments: inside motor vehicles (like cars or planes) or inside buildings close to high traffic places (like in a control tower for air traffic control (ATC)). In these environments, there is a high stationary noise level caused by vehicle motors and additionally, there could be people speaking at certain distance from the main speaker producing non-stationary noise. The VAD presented in this paper is characterized by a new front-end and a noise level adaptation process that increases significantly the VAD robustness for different signal to noise ratios (SNRs). The feature vector used by the VAD includes the most relevant Mel Frequency Cepstral Coefficients (MFCC), normalized log energy and delta log energy. The proposed VAD has been evaluated and compared to other well-known VADs using three databases containing different noise conditions: speech in clean environments (SNRs mayor que 20 dB), speech recorded in stationary noise environments (inside or close to motor vehicles), and finally, speech in non stationary environments (including noise from bars, television and far-field speakers). In the three cases, the detection error obtained with the proposed VAD is the lowest for all SNRs compared to Acero¿s VAD (reference of this work) and other well-known VADs like AMR, AURORA or G729 annex b
Nearest-Neighbor Distributions and Tunneling Splittings in Interacting Many-Body Two-Level Boson Systems
We study the nearest-neighbor distributions of the -body embedded
ensembles of random matrices for bosons distributed over two-degenerate
single-particle states. This ensemble, as a function of , displays a
transition from harmonic oscillator behavior () to random matrix type
behavior (). We show that a large and robust quasi-degeneracy is present
for a wide interval of values of when the ensemble is time-reversal
invariant. These quasi-degenerate levels are Shnirelman doublets which appear
due to the integrability and time-reversal invariance of the underlying
classical systems. We present results related to the frequency in the spectrum
of these degenerate levels in terms of , and discuss the statistical
properties of the splittings of these doublets.Comment: 13 pages (double column), 7 figures some in color. The movies can be
obtained at http://link.aps.org/supplemental/10.1103/PhysRevE.81.03621
Fidelity decay in interacting two-level boson systems: Freezing and revivals
We study the fidelity decay in the -body embedded ensembles of random
matrices for bosons distributed in two single-particle states, considering the
reference or unperturbed Hamiltonian as the one-body terms and the diagonal
part of the -body embedded ensemble of random matrices, and the perturbation
as the residual off-diagonal part of the interaction. We calculate the
ensemble-averaged fidelity with respect to an initial random state within
linear response theory to second order on the perturbation strength, and
demonstrate that it displays the freeze of the fidelity. During the freeze, the
average fidelity exhibits periodic revivals at integer values of the Heisenberg
time . By selecting specific -body terms of the residual interaction,
we find that the periodicity of the revivals during the freeze of fidelity is
an integer fraction of , thus relating the period of the revivals with the
range of the interaction of the perturbing terms. Numerical calculations
confirm the analytical results
QCD equation of state at finite isospin density from the linear sigma model with quarks: The cold case
We use the two-flavor linear sigma model with quarks to study the phase
structure of isospin asymmetric matter at zero temperature. The meson degrees
of freedom provide the mean field chiral- and isospin-condensates on top of
which we compute the effective potential accounting for constituent quark
fluctuations at one-loop order. Using the renormalizability of the model, we
absorb the ultraviolet divergences into suitable counter-terms that are added
respecting the original structure of the theory. These counter-terms are
determined from the stability conditions which require the effective potential
to have minima in the condensates directions at the classical values, as well
as the transition from the non-condensed to the condensed phase to be smooth as
a function of the isospin chemical potential. We use the model to study the
evolution of the condensates as well as the pressure, energy and isospin
densities and the sound velocity as functions of the isospin chemical
potential. The approach does a good average description up to isospin chemical
potentials values not too large as compared to the vacuum pion mass.Comment: 11 pages and 7 figures. Expanded discussion, references and graphs
added, conclusions unchange
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