Time-frequency spectral estimation of speech

In recent years there has been a growing interest amongst the speech research community into the use of spectral estimators which circumvent the traditional quasi-stationary assumption and provide greater time-frequency (t-f) resolution than conventional spectral estimators, such as the short time Fourier power spectrum (STFPS). One distribution in particular, the Wigner distribution (WD), has attracted considerable interest. However, experimental studies have indicated that, despite its improved t-f resolution, employing the WD as the front end of speech recognition system actually reduces recognition performance; only by explicitly re-introducing t-f smoothing into the WD are recognition rates improved. In this paper we provide an explanation for these findings. By treating the spectral estimation problem as one of optimization of a bias variance trade off, we show why additional t-f smoothing improves recognition rates, despite reducing the t-f resolution of the spectral estimator. A practical adaptive smoothing algorithm is presented, whicy attempts to match the degree of smoothing introduced into the WD with the time varying quasi-stationary regions within the speech waveform. The recognition performance of the resulting adaptively smoothed estimator is found to be comparable to that of conventional filterbank estimators, yet the average temporal sampling rate of the resulting spectral vectors is reduced by around a factor of 10. © 1992.

Frequency-based interpolation of sampled signals with applications in audio restoration

A new interpolation technique has been developed for replacing missing samples in a sampled waveform drawn from a stationary stochastic process, given the power spectrum for the process. The method works with a finite block of data and is based on the assumption that components of the block DFT are Gaussian zero-mean independent random variables with variance proportional to the power spectrum at each frequency value. These assumptions make the interpolator particularly suitable for signals with a sharply-defined harmonic structure, such as audio waveforms recorded from music or voiced speech. Some results are presented and comparisons are made with existing techniques.

HVIC switch for high-frequency power converters

A high voltage integrated circuit (HVIC) switch designed as a building block for power converters operating up to 13.56 MHz from off-line voltages is presented. A CMOS-compatible, 500 V power device process is used to integrate control circuitry with a high-speed MOS gate driver and high voltage lateral power MOSFET. Fabrication of the HVIC switches has proceeded in two stages. The first batch of devices showed switching times of less than 5 ns for the power switch and good high frequency performance of a level-shifter for driving half bridge converters. In the second phase, a switch that monolithically integrates all the elements required to form a complete high-frequency converter has been designed.

CACSD, GUI's, and the multivariable frequency domain toolbox

This talk describes a new version of the Multivariable Frequency Domain Toolbox for Matlab. The intellectual issue which arises here is whether there is a role for Matlab-4 GUI facilities in a Toolbox which provides relatively low-level functionality, with a correspondingly random pattern of user interaction. My belief is that there is a role, but it is very restricted: in effect only for providing convenient 'viewing' facilities for low-level objects (which are multivariable frequency responses in the case of the MFD Toolbox). There is a more obvious role for a GUI with higher-level functions, such as frequency domain identification or parametric controller optimisation.

Recent progress in high-bit-rate applications of four-wave-mixing in SOAs

Non-linearities in semiconductor optical amplifiers have been used to demonstrate a wide range of functions applicable to future optical networks such as wavelength conversion and optical switching. Four-wave-mixing effects in SOAs have been studied extensively in many laboratories with respect to the underlying physical processes and system applications. At BT Labs an optimization of SOAs for FWM has been achieved by altering the device active layer composition and by increasing the device length. We will review recent progress at BT Labs in dispersion compensation, wavelength conversion and demultiplexing at bit-rates of 40 Gbit/s using these devices.

High-frequency acousto-electric single-photon source

We propose a single optical photon source for quantum cryptography based on the acoustoelectric effect. Surface acoustic waves (SAWs) propagating through a quasi-one-dimensional channel have been shown to produce packets of electrons that reside in the SAW minima and travel at the velocity of sound. In our scheme, the electron packets are injected into a p-type region, resulting in photon emission. Since the number of electrons in each packet can be controlled down to a single electron, a stream of single- (or N-) photon states, with a creation time strongly correlated with the driving acoustic field, should be generated. ©2000 The American Physical Society.

Blind frequency synchronisation for OFDM systems with pulse shaping

In multi-carrier systems, small carrier frequency offsets result in significant degradation of performance and this offset should be compensated before demodulation can be performed. In this paper, we consider a generic multi-carrier system with pulse shaping and estimate the frequency offset by exploiting the cyclostationarity of the received signal. By transforming the time domain signal to the cyclic correlation domain we are able to estimate the frequency offset without the aid of pilot symbols or the cyclic prefix. The Bayesian framework is used to obtain the estimate and we show how we can simplify the estimation process. © 1999 IEEE.

Recent progress in high-bit-rate applications of four-wave-mixing in SOAs

Non-linearities in semiconductor optical amplifiers have been used to demonstrate a wide range of functions applicable to future optical networks such as wavelength conversion and optical switching. Four-wave-mixing effects in SOAs have been studied extensively in many laboratories with respect to the underlying physical processes and system applications. At BT Labs an optimisation of SOAs for FWM has been achieved by altering the device active layer composition and by increasing the device length. We will review recent progress at BT Labs in dispersion compensation, wavelength conversion and demultiplexing at bit-rates of 40Gbit/s using these devices.

An efficient frequency-domain algorithm for wave scattering problems with application to jet noise

This paper presents a pseudo-time-step method to calculate a (vector) Green function for the adjoint linearised Euler equations as a scattering problem in the frequency domain, for use as a jet-noise propagation prediction tool. A method of selecting the acoustics-related solution in a truncated spatial domain while suppressing any possible shear-layer-type instability is presented. Numerical tests for 3-D axisymmetrical parallel mean flows against semi-analytical reference solutions indicate that the new iterative algorithm is capable of producing accurate solutions with modest computational requirements.

Adjoint linearised Euler solver in the frequency domain for jet noise modelling

The paper is devoted to extending the new efficient frequency-domain method of adjoint Green's function calculation to curvilinear multi-block RANS domains for middle and farfield sound computations. Numerical details of the method such as grids, boundary conditions and convergence acceleration are discussed. Two acoustic source models are considered in conjunction with the method and acoustic modelling results are presented for a benchmark low-Reynolds-number jet case.

Influence of voltage and frequency dimming on power losses in HF electronic ballasts for compact fluorescent lamps

Compact Fluorescent Lamps (CFL) incorporating electronic ballasts are widely used in lighting. In many cases the ability to dim the lamp is a requirement Dimming can be achieved by varying the voltage supplied to the inverter or by changing the switching frequency of the inverter. The effect of dimming by both approaches on the power losses in the inverter is studied in this work. The lamp and associated inverter has been modeled in PSPICE, using a behavioral model for the CFL. Predicted losses are in good agreement with experimental data obtained from calorimetry. The model was then used to determine the distribution of losses within the inverter, enabling a comparison of the effects of the two dimming methods to be made. © 2006 IEEE.

Bayesian estimation of simultaneous musical notes based on frequency domain modelling

This paper proposes a Bayesian method for polyphonic music description. The method first divides an input audio signal into a series of sections called snapshots, and then estimates parameters such as fundamental frequencies and amplitudes of the notes contained in each snapshot. The parameter estimation process is based on a frequency domain modelling and Gibbs sampling. Experimental results obtained from audio signals of test note patterns are encouraging; the accuracy is better than 80% for the estimation of fundamental frequencies in terms of semitones and instrument names when the number of simultaneous notes is two.

A single all-optical processor for multiple spectral amplitude code label recognition using four wave mixing

We propose a novel label processor which can recognize multiple spectral-amplitude-code labels using four-wave-mixing sidebands and selective optical filtering. Ten code-labels x 10 Gbps variable-length packets are transmitted over a 200 km single-hop switched network.

Carbon nanotube based photocathodes for high frequency amplifiers

The combination of high frequency, high power, high efficiency capabilities is a feature of vacuum tube technology. For most of applications, large bandwidths are required, and therefore the modulation method should also allow large bandwidth operation. Optically modulated cold cathodes, avoiding the use of resonant cavities, should satisfy this requirement. This is the reason why we have developed carbon nanotube based photocathode.© 2009 IEEE.

Minimize frequency fluctuations of isolated power system with wind farm by using superconducting magnetic energy storage

Wind power generation as one of the most popular renewable energy applications is absorbing more and more attention all over the world. However, output power fluctuations of wind farm due to random variations of wind speed can cause network frequency and voltage flicker in power systems. The power quality consequently declines, particularly in an isolated power system such as the power system in a remote community or a small island. This paper proposes an application of superconducting magnetic energy storage (SMES) to minimize output fluctuations of an isolated power system with wind farm. The isolated power system is fed by a diesel generator and a wind generator consisting of a wind turbine and squirrel cage induction machine. The control strategy is detailed and the proposed system is evaluated by simulation in Matlab/Simulink.