A comparison of time-domain time-scale modification algorithms

Time-domain approaches to time-scale modification are popular due to their ability to produce high quality results at a relatively low computational cost. Within the category of time-domain implementations quite a number of alternatives exist, each with their own computational requirements and associated output quality. This paper provides a computational and objective output quality assessment of a number of popular time-domain time-scaling implementations; thus providing a means for developers to identify a suitable algorithm for their application of interest. In addition, the issues that should be considered in developing time-domain algorithms are outlined, purely in the context of a waveform editing procedure

A comparison of time-domain time-scale modification algorithms

Time-domain approaches to time-scale modification are popular due to their ability to produce high quality results at a relatively low computational cost. Within the category of time-domain implementations quite a number of alternatives exist, each with their own computational requirements and associated output quality. This paper provides a computational and objective output quality assessment of a number of popular time-domain time-scaling implementations; thus providing a means for developers to identify a suitable algorithm for their application of interest. In addition, the issues that should be considered in developing time-domain algorithms are outlined, purely in the context of a waveform editing procedure

Time Scale Modification of Music using a Subband Approach Based on the Bark Scale

Time-domain time-scaling algorithms are efficient in comparison to their frequency-domain counterparts, but they rely upon the existence of a quasi-periodic signal to produce a high quality output. This requirement makes them unsuitable for use on multi-pitched signals such as polyphonic music. However, time-domain techniques applied on a subband basis can resolve the multi-pitch problem. The authors propose an improved subband implementation based upon the bark scale for the time scale modification of music. The new subband approach is supported by psychoacoustic and music theory and subjectively through informal listening tests

A Phase Vocoder based on Nonstationary Gabor Frames

We propose a new algorithm for time stretching music signals based on the theory of nonstationary Gabor frames (NSGFs). The algorithm extends the techniques of the classical phase vocoder (PV) by incorporating adaptive time-frequency (TF) representations and adaptive phase locking. The adaptive TF representations imply good time resolution for the onsets of attack transients and good frequency resolution for the sinusoidal components. We estimate the phase values only at peak channels and the remaining phases are then locked to the values of the peaks in an adaptive manner. During attack transients we keep the stretch factor equal to one and we propose a new strategy for determining which channels are relevant for reinitializing the corresponding phase values. In contrast to previously published algorithms we use a non-uniform NSGF to obtain a low redundancy of the corresponding TF representation. We show that with just three times as many TF coefficients as signal samples, artifacts such as phasiness and transient smearing can be greatly reduced compared to the classical PV. The proposed algorithm is tested on both synthetic and real world signals and compared with state of the art algorithms in a reproducible manner.Comment: 10 pages, 6 figure

A Linear Hybrid Sound Generation of Musical Instruments using Temporal and Spectral Shape Features

The generation of a hybrid musical instrument sound using morphing has always been an area of great interest to the music world. The proposed method exploits the temporal and spectral shape features of the sound for this purpose. For an effective morphing the temporal and spectral features are found as they can capture the most perceptually salient dimensions of timbre perception, namely, the attack time and the distribution of spectral energy. A wide variety of sound synthesis algorithms is currently available. Sound synthesis methods have become more computationally efficient. Wave table synthesis is widely adopted by digital sampling instruments or samplers. The Over Lap Add method (OLA) refers to a family of algorithms that produce a signal by properly assembling a number of signal segments. In granular synthesis sound is considered as a sequence with overlaps of elementary acoustic elements called grains. The simplest morph is a cross-fade of amplitudes in the time domain which can be obtained through cross synthesis. A hybrid sound is generated with all these methods to find out which method gives the most linear morph. The result will be evaluated as an error measure which is the difference between the calculated and interpolated features. The extraction of morph in a perceptually pleasant manner is the ultimate requirement of the work. DOI: 10.17762/ijritcc2321-8169.16045

Study of laser-plasma interaction with particle-in-cell simulations: attosecond pulse generation and proton acceleration

The advancement of lasers over the last decades has allowed researchers to explore new regimes of physics and their applications. High power lasers interacting with plasmas have provided with the tools to create high frequency ultrashort pulsed radiation, near the X-ray regime and with temporal lengths on the attosecond scale, and has allowed to create compact and cheap particle accelerators. Numerical simulations are a fundamental tool in the advancement of this scientific area, since they provide with insights into the physical processes involved and they can be used to design experiments. In this thesis we present the results of numerical simulations for ultrashort pulse production, ion acceleration and other laser-plasma applications

Generation and Characterization of Isolated Attosecond Pulse in the Soft X-ray Regime

The observation of any atomic and molecular dynamics requires a probe that has a timescale comparable to the dynamics itself. Ever since the invention of laser, the temporal duration of the laser pulse has been incrementally reduced from several nanoseconds to just attoseconds. Picosecond and femtosecond laser pulses have been widely used to study molecular rotation and vibration. In 2001, the first single isolated attosecond pulse (1 attosecond = 10^-18 seconds.) was demonstrated. Since this breakthrough, attoscience has become a hot topic in ultrafast physics. Attosecond pulses typically have span between EUV to X-ray photon energies and sub-femtosecond pulse duration. It becomes an ideal tool for experimentalists to study ultrafast electron dynamics in atoms, molecules and condensed matter. The conventional scheme for generating attosecond pulses is focusing an intense femtosecond laser pulse into inert gases. The bound electrons are ionized into continuum through tunneling ionization under the strong electrical field. After ionization, the free electron will be accelerated by the laser field away from the parent ion and then recombined with its parent ion and releases its kinetic energy as a photon burst that lasts for a few hundred attoseconds. According to the classical three-step model , high order harmonic will have a higher cutoff photon energy when driven by a longer wavelength laser field. Compared to Ti:sapphire lasers center at a wavelength of 800 nm, an optical parametric amplifier could offer a broad bandwidth at infrared range, which could support few cycle pulses for driving high harmonic generation in the X-ray spectrum range. In this work, an optical parametric chirped-pulse amplification system was developed to deliver CEP-stable 3-mJ, 12-fs pulses centered at 1.7 micron. We implement a chirped-pump technique to phase match the board parametric amplification bandwidth with high conversion efficiency. Using such a laser source, isolated attosecond pulses with photon exceeding 300 eV are achieved by applying the polarization gating technique at 1.7 micron. The intrinsic positive chirp of the attosecond pulses is measured by the attosecond streak camera and retrieved with our PROOF technique. Sn metal filters with negative dispersion were chosen to compensate the intrinsic attochirp. As a result, isolated 53-attosecond soft x-ray pulses are achieved. Such water window attosecond source will be a powerful tool for studying charge distribution/migration in bio-molecules and will bring opportunities to study high field physics or attochemistry

Attosecond Wave Packet Metrology

Attosecond pulses allow the study of electrons on their natural timescale. They are created from the interaction of atoms with ultrashort, intense laser pulses whose electric field approaches the strength of inner-atomic electric fields. This thesis presents experiments around the generation, characterization and application of attosecond pulses. First, we study the influence of the atomic generation medium on the temporal properties of attosecond pulses. Their central photon energy can be controlled by using a two-color generation field and by thin-foil filtering techniques tailored to specific spectral bands. With these techniques, broadband attosecond pulses with durations down to 130 as have been measured. To characterize attosecond pulse trains at their birth, we introduce a new method that perturbs the generation laser field with its weak second harmonic. This allows us to assess the influence of the medium in the generation process. We then test the limits of a well-established pulse train characterization method with regard to probe intensity and demonstrate a way to circumvent these limitations. A second set of experiments uses attosecond pulses to excite atoms and molecules for the creation of ultrashort wave packets. Free electron wave packets can be controlled by an external laser field and driven to scatter off their parent ions. They also carry information on the atomic structure, which enables the phase-resolved characterization of unknown bound wave packets. Exposing molecules to attosecond pulses can trigger dissociation reactions that can be controlled by a delayed probe laser pulse. We present a study of different probe pulse properties and report the observation of attosecond electron dynamics inside a hydrogen molecule