52,306 research outputs found
Signal Reconstruction from Mel-spectrogram Based on Bi-level Consistency of Full-band Magnitude and Phase
We propose an optimization-based method for reconstructing a time-domain
signal from a low-dimensional spectral representation such as a
mel-spectrogram. Phase reconstruction has been studied to reconstruct a
time-domain signal from the full-band short-time Fourier transform (STFT)
magnitude. The Griffin-Lim algorithm (GLA) has been widely used because it
relies only on the redundancy of STFT and is applicable to various audio
signals. In this paper, we jointly reconstruct the full-band magnitude and
phase by considering the bi-level relationships among the time-domain signal,
its STFT coefficients, and its mel-spectrogram. The proposed method is
formulated as a rigorous optimization problem and estimates the full-band
magnitude based on the criterion used in GLA. Our experiments demonstrate the
effectiveness of the proposed method on speech, music, and environmental
signals.Comment: Accepted to IEEE WASPAA 202
Speckle interferometry
We have presented the basic mathematical treatment of interferometry in the
optical domain. Its applications in astronomical observations using both the
single aperture, as well as the diluted apertures are described in detail. We
have also described about the shortcomings of this technique in the presence of
Earth's atmosphere. A short descriptions of the atmospheric turbulence and its
effect on the flat wavefront from a stellar source is given. The formation of
speckle which acts as carrier of information is defined. Laboratory experiments
with phase modulation screens, as well as the resultant intensity distributions
due to point source are demonstrated. The experimental method to freeze the
speckles, as well as data processing techniques for both Fourier modulus and
Fourier phase are described. We have also discussed the technique of the
aperture synthesis using non-redundant aperture masks at the pupil plane of the
telescope, emphasizing set on the comparison with speckle interferometry. The
various methods of image restoration and their comparisons are also discussed.
Finally, we have touched upon certain astrophysical problems which can be
tackled with the newly developed speckle interferometer using the 2.34 meter
Vainu Bappu Telescope (VBT), situated at the Vainu Bappu Observatory (VBO),
Kavalur, India.Comment: 32 pages tex files including figure
Discrete structure of the brain rhythms
Neuronal activity in the brain generates synchronous oscillations of the
Local Field Potential (LFP). The traditional analyses of the LFPs are based on
decomposing the signal into simpler components, such as sinusoidal harmonics.
However, a common drawback of such methods is that the decomposition primitives
are usually presumed from the onset, which may bias our understanding of the
signal's structure. Here, we introduce an alternative approach that allows an
impartial, high resolution, hands-off decomposition of the brain waves into a
small number of discrete, frequency-modulated oscillatory processes, which we
call oscillons. In particular, we demonstrate that mouse hippocampal LFP
contain a single oscillon that occupies the -frequency band and a
couple of -oscillons that correspond, respectively, to slow and fast
-waves. Since the oscillons were identified empirically, they may
represent the actual, physical structure of synchronous oscillations in
neuronal ensembles, whereas Fourier-defined "brain waves" are nothing but
poorly resolved oscillons.Comment: 17 pages, 9 figure
Speckle from phase ordering systems
The statistical properties of coherent radiation scattered from
phase-ordering materials are studied in detail using large-scale computer
simulations and analytic arguments. Specifically, we consider a two-dimensional
model with a nonconserved, scalar order parameter (Model A), quenched through
an order-disorder transition into the two-phase regime. For such systems it is
well established that the standard scaling hypothesis applies, consequently the
average scattering intensity at wavevector _k and time t' is proportional to a
scaling function which depends only on a rescaled time, t ~ |_k|^2 t'. We find
that the simulated intensities are exponentially distributed, with the
time-dependent average well approximated using a scaling function due to Ohta,
Jasnow, and Kawasaki. Considering fluctuations around the average behavior, we
find that the covariance of the scattering intensity for a single wavevector at
two different times is proportional to a scaling function with natural
variables mt = |t_1 - t_2| and pt = (t_1 + t_2)/2. In the asymptotic large-pt
limit this scaling function depends only on z = mt / pt^(1/2). For small values
of z, the scaling function is quadratic, corresponding to highly persistent
behavior of the intensity fluctuations. We empirically establish a connection
between the intensity covariance and the two-time, two-point correlation
function of the order parameter. This connection allows sensitive testing,
either experimental or numerical, of existing theories for two-time
correlations in systems undergoing order-disorder phase transitions. Comparison
between theory and our numerical results requires no adjustable parameters.Comment: 18 pgs RevTeX, to appear in PR
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