Articles de revista
http://hdl.handle.net/2117/3924
Fri, 09 Dec 2016 02:29:10 GMT
20161209T02:29:10Z

Filtering the time sequences of spectral parameters for speech recognition
http://hdl.handle.net/2117/97902
Filtering the time sequences of spectral parameters for speech recognition
Nadeu Camprubí, Climent; Paches, Pau; BiingHwang, Juang
In automatic speech recognition, the signal is usually represented by a set of time sequences of spectral parameters (TSSPs) that model the temporal evolution of the spectral envelope frametoframe. Those sequences are then filtered either to make them more robust to environmental conditions or to compute differential parameters (dynamic features) which enhance discrimination. In this paper, we apply frequency analysis to TSSPs in order to provide an interpretation framework for the various types of parameter filters used so far. Thus, the analysis of the average longterm spectrum of the successfully filtered sequences reveals a combined effect of equalization and band selection that provides insights into TSSP filtering. Also, we show in the paper that, when supplementary differential parameters are not used, the recognition rate can be improved even for clean speech, just by properly filtering the TSSPs. To support this claim, a number of experimental results are presented, both using wholeword and subword based models. The empirically optimum filters attenuate the lowpass band and emphasize a higher band so that the peak of the average longterm spectrum of the output of these filters lies at around the average syllable rate of the employed database (˜3 Hz).
Wed, 07 Dec 2016 17:04:13 GMT
http://hdl.handle.net/2117/97902
20161207T17:04:13Z
Nadeu Camprubí, Climent
Paches, Pau
BiingHwang, Juang
In automatic speech recognition, the signal is usually represented by a set of time sequences of spectral parameters (TSSPs) that model the temporal evolution of the spectral envelope frametoframe. Those sequences are then filtered either to make them more robust to environmental conditions or to compute differential parameters (dynamic features) which enhance discrimination. In this paper, we apply frequency analysis to TSSPs in order to provide an interpretation framework for the various types of parameter filters used so far. Thus, the analysis of the average longterm spectrum of the successfully filtered sequences reveals a combined effect of equalization and band selection that provides insights into TSSP filtering. Also, we show in the paper that, when supplementary differential parameters are not used, the recognition rate can be improved even for clean speech, just by properly filtering the TSSPs. To support this claim, a number of experimental results are presented, both using wholeword and subword based models. The empirically optimum filters attenuate the lowpass band and emphasize a higher band so that the peak of the average longterm spectrum of the output of these filters lies at around the average syllable rate of the employed database (˜3 Hz).

Selfsplitting of beams into spatial solitons in planar waveguides made of quadratic nonlinear media
http://hdl.handle.net/2117/97901
Selfsplitting of beams into spatial solitons in planar waveguides made of quadratic nonlinear media
Perez, J; Torner Sabata, Lluís
The propagation of intense light beams in planar optical waveguides made of quadratic nonlinear media under conditions for secondharmonic generation is investigated. It is shown numerically that under appropriate conditions, input light beams break up into several spatial solitons that separate from each other and exit the waveguide at different positions. This paper reports the results of a series of numerical experiments and analytical investigations that were performed to elucidate the dynamics of the selfsplitting process and discusses the implications of the results to the implementation of an eigenvalue switching device.
Wed, 07 Dec 2016 16:59:46 GMT
http://hdl.handle.net/2117/97901
20161207T16:59:46Z
Perez, J
Torner Sabata, Lluís
The propagation of intense light beams in planar optical waveguides made of quadratic nonlinear media under conditions for secondharmonic generation is investigated. It is shown numerically that under appropriate conditions, input light beams break up into several spatial solitons that separate from each other and exit the waveguide at different positions. This paper reports the results of a series of numerical experiments and analytical investigations that were performed to elucidate the dynamics of the selfsplitting process and discusses the implications of the results to the implementation of an eigenvalue switching device.

Crosscoupled doa trackers
http://hdl.handle.net/2117/97899
Crosscoupled doa trackers
Pérez Neira, Ana Isabel; Lagunas Hernandez, Miguel A.; Kirlin, R L
A new robust, low complexity algorithm for multiuser tracking is proposed, modifying the twostage parallel architecture of the estimatemaximize (EM) algorithm. The algorithm copes with spatially colored noise, large differences in source powers, multipath, and crossing trajectories. Following a discussion on stability, the simulations demonstrate an asymptotic and tracking behavior that neither the EM nor a nonparallelized tracker can emulate.
Wed, 07 Dec 2016 16:55:25 GMT
http://hdl.handle.net/2117/97899
20161207T16:55:25Z
Pérez Neira, Ana Isabel
Lagunas Hernandez, Miguel A.
Kirlin, R L
A new robust, low complexity algorithm for multiuser tracking is proposed, modifying the twostage parallel architecture of the estimatemaximize (EM) algorithm. The algorithm copes with spatially colored noise, large differences in source powers, multipath, and crossing trajectories. Following a discussion on stability, the simulations demonstrate an asymptotic and tracking behavior that neither the EM nor a nonparallelized tracker can emulate.

Integral equation mei applied to threedimensional arbitrary surfaces
http://hdl.handle.net/2117/97898
Integral equation mei applied to threedimensional arbitrary surfaces
Rius Casals, Juan Manuel; Parrón Granados, Josep; Úbeda Farré, Eduard; Mosig, J R
The authors present a new formulation of the integral equation of the measured equation of invariance (MEI) as a confined field integral equation discretised by the method of moments, in which the use of numerically derived testing functions results in an approximately sparse linear system with storage memory requirements and a CPU time for computing the matrix coefficients proportional to the number of unknowns.
Wed, 07 Dec 2016 16:46:43 GMT
http://hdl.handle.net/2117/97898
20161207T16:46:43Z
Rius Casals, Juan Manuel
Parrón Granados, Josep
Úbeda Farré, Eduard
Mosig, J R
The authors present a new formulation of the integral equation of the measured equation of invariance (MEI) as a confined field integral equation discretised by the method of moments, in which the use of numerically derived testing functions results in an approximately sparse linear system with storage memory requirements and a CPU time for computing the matrix coefficients proportional to the number of unknowns.

Soliton evolution in quasiphasematched secondharmonic generation
http://hdl.handle.net/2117/97897
Soliton evolution in quasiphasematched secondharmonic generation
Torner Sabata, Lluís; Stegeman, G I
We investigate the formation and evolution of spatial solitons with light beams propagating in quadratic nonlinear media under conditions for secondharmonic generation in quasiphasematched samples. We study the properties of the solitons as a function of the periodicity of the domainreversal process involved in the quasiphasematching techniques, and we show the effects introduced by random shifts of the nominal domain length.
© 1997 Optical Society of America
Wed, 07 Dec 2016 16:41:51 GMT
http://hdl.handle.net/2117/97897
20161207T16:41:51Z
Torner Sabata, Lluís
Stegeman, G I
We investigate the formation and evolution of spatial solitons with light beams propagating in quadratic nonlinear media under conditions for secondharmonic generation in quasiphasematched samples. We study the properties of the solitons as a function of the periodicity of the domainreversal process involved in the quasiphasematching techniques, and we show the effects introduced by random shifts of the nominal domain length.
© 1997 Optical Society of America

Asymmetrical splitting of higherorder optical solitons induced by quintic nonlinearity
http://hdl.handle.net/2117/97895
Asymmetrical splitting of higherorder optical solitons induced by quintic nonlinearity
Artigas García, David; Torner Sabata, Lluís; Pérez Torres, Juan; Akhmediev, Juan P Torres I Nail N
We address the effect of quintic nonlinearities in the propagation of optical solitons in cubic nonlinear media. Our focus is on the decay of higherorder solitons in the presence of selfdefocusing quintic perturbations. We show that, in spite of the fact that the governing evolution equations are symmetric, the quintic nonlinearity produces the asymmetrical selfsplitting of the solitons. We study in detail the selfsplitting process and compare the results with the soliton evolution with selffocusing quintic perturbations.
Wed, 07 Dec 2016 16:37:01 GMT
http://hdl.handle.net/2117/97895
20161207T16:37:01Z
Artigas García, David
Torner Sabata, Lluís
Pérez Torres, Juan
Akhmediev, Juan P Torres I Nail N
We address the effect of quintic nonlinearities in the propagation of optical solitons in cubic nonlinear media. Our focus is on the decay of higherorder solitons in the presence of selfdefocusing quintic perturbations. We show that, in spite of the fact that the governing evolution equations are symmetric, the quintic nonlinearity produces the asymmetrical selfsplitting of the solitons. We study in detail the selfsplitting process and compare the results with the soliton evolution with selffocusing quintic perturbations.

Stochastic vector quantization of images
http://hdl.handle.net/2117/97894
Stochastic vector quantization of images
Torres Urgell, Lluís; Casas Pla, Josep Ramon; Arias, E
One of the most important steps in the vector quantization of images is the design of the codebook. The codebook is generally designed using the LBG algorithm, that is in essence a clustering algorithm which uses a large training set of empirical data that is statistically representative of the image to be quantized. The LBG algorithm, although quite effective for practical applications, is computationally very expensive and the resulting codebook has to be recalculated each time the type of image to be encoded changes. One alternative to the generation of the codebook, called stochastic vector quantization, is presented in this paper. Stochastic vector quantization (SVQ) is based on the generation of the codebook according to some previous model defined for the image to be encoded. The wellknown AR model has been used to model the image in the current implementations of the technique, and has shown good performance in the overall scheme. To show the merit of the technique in different contexts, stochastic vector quantization is discussed and applied to both pixelbased and segmentationbased image coding schemes.
Wed, 07 Dec 2016 16:28:13 GMT
http://hdl.handle.net/2117/97894
20161207T16:28:13Z
Torres Urgell, Lluís
Casas Pla, Josep Ramon
Arias, E
One of the most important steps in the vector quantization of images is the design of the codebook. The codebook is generally designed using the LBG algorithm, that is in essence a clustering algorithm which uses a large training set of empirical data that is statistically representative of the image to be quantized. The LBG algorithm, although quite effective for practical applications, is computationally very expensive and the resulting codebook has to be recalculated each time the type of image to be encoded changes. One alternative to the generation of the codebook, called stochastic vector quantization, is presented in this paper. Stochastic vector quantization (SVQ) is based on the generation of the codebook according to some previous model defined for the image to be encoded. The wellknown AR model has been used to model the image in the current implementations of the technique, and has shown good performance in the overall scheme. To show the merit of the technique in different contexts, stochastic vector quantization is discussed and applied to both pixelbased and segmentationbased image coding schemes.

Secondharmonic generation by intense beams containing phase dislocations:selfbreaking into sets of solitons
http://hdl.handle.net/2117/97893
Secondharmonic generation by intense beams containing phase dislocations:selfbreaking into sets of solitons
Petrov, D V; Torner Sabata, Lluís
Secondharmonic generation of light in bulk quadratic nonlinear media with intense input beams containing phase dislocations is studied numerically under conditions for TypeI phasematching. We investigate how, above a threshold light intensity, the input beams selfsplit along the azimuthal direction into a pattern of separate beams which then form a set of spatial solitons. The mechanism of such a behaviour is the azimuthal modulational instability of the ringshaped, mutually trapped fundamental and secondharmonic beams containing the phase dislocations.
Wed, 07 Dec 2016 16:12:47 GMT
http://hdl.handle.net/2117/97893
20161207T16:12:47Z
Petrov, D V
Torner Sabata, Lluís
Secondharmonic generation of light in bulk quadratic nonlinear media with intense input beams containing phase dislocations is studied numerically under conditions for TypeI phasematching. We investigate how, above a threshold light intensity, the input beams selfsplit along the azimuthal direction into a pattern of separate beams which then form a set of spatial solitons. The mechanism of such a behaviour is the azimuthal modulational instability of the ringshaped, mutually trapped fundamental and secondharmonic beams containing the phase dislocations.

Walking solitons in type II secondharmonic generation
http://hdl.handle.net/2117/97892
Walking solitons in type II secondharmonic generation
Mihalache, Dumitru; Mazilu, D; Crasovan, L C; Torner Sabata, Lluís
We find the families of spatial walking solitons propagating in quadratic nonlinear media under conditions for type II secondharmonic generation in the presence of Poynting vector walkoff between the interacting beams. The analytical stability criterion for these threeparameter vector solitons is established. We study the shape and general properties of the solitons and their stability on propagation. It is found that the stationary solutions are stable at moderate positive phase mismatch. At phase matching and negative phase mismatch there are some unstable solutions near the cutoff.
Wed, 07 Dec 2016 16:08:13 GMT
http://hdl.handle.net/2117/97892
20161207T16:08:13Z
Mihalache, Dumitru
Mazilu, D
Crasovan, L C
Torner Sabata, Lluís
We find the families of spatial walking solitons propagating in quadratic nonlinear media under conditions for type II secondharmonic generation in the presence of Poynting vector walkoff between the interacting beams. The analytical stability criterion for these threeparameter vector solitons is established. We study the shape and general properties of the solitons and their stability on propagation. It is found that the stationary solutions are stable at moderate positive phase mismatch. At phase matching and negative phase mismatch there are some unstable solutions near the cutoff.

Walking solitons
http://hdl.handle.net/2117/97891
Walking solitons
Torner Sabata, Lluís; Santos Blanco, M. Concepción; Mihalache, Dumitru; Mazilu, D; Crasovan, L C
By and large, optical
Wed, 07 Dec 2016 16:04:24 GMT
http://hdl.handle.net/2117/97891
20161207T16:04:24Z
Torner Sabata, Lluís
Santos Blanco, M. Concepción
Mihalache, Dumitru
Mazilu, D
Crasovan, L C
By and large, optical