Frequency Reassignment Research Articles

Acoustic features for speech recognition based on Gammatone filterbank and instantaneous frequency

Most of the features used by modern automatic speech recognition systems, such as mel-frequency cepstral coefficients (MFCC) and perceptual linear predictive (PLP) coefficients, represent spectral envelope of the speech signal only. Nevertheless, phase or frequency modulation as represented in recent perceptual models of the peripheral auditory system might also contribute to speech decoding. Furthermore, such features can be complementary to the envelope features. This paper proposes a variety of features based on a linear auditory filterbank, the Gammatone filterbank. Envelope features are derived from the envelope of the subband filter outputs. Phase/frequency modulation is represented by the subband instantaneous frequency (IF) and is used explicitly by concatenating envelope-based and IF-based features or is used implicitly by IF-based frequency reassignment. Speech recognition experiments using a standard HMM-based recognizer under both clean training and multi-condition training are conducted on a Chinese mandarin digits corpus. The experimental results show that the proposed envelope and phase based features can improve recognition rates in clean and noisy conditions compared to the reference MFCC-based recognizer.

Detection of non-stationary sinusoids by using joint frequency reassignment and null-to-null bandwidth

We present a method that efficiently describes non-stationarities by parameterizing spectral peaks in terms of the frequency reassignment operator variation and null-to-null peak bandwidth. This kind of parameterization is designed in such a way to properly deal with situations of low signal-to-noise ratios. In addition, it provides for a strong separation between the sinusoidal and noise peak class in a two-dimensional (2D) feature space. Consequently, the percentage of misclassified spectral peaks is drastically reduced, which significantly simplifies the analysis/synthesis of audio signals in the following processing stages.

Frequency reassignment problem in mobile communication networks

In this paper, we present a new frequency reassignment problem (FP) arising from the installation of new base stations for capacity expansion of a mobile telecommunication network, and develop two mathematical formulations along with some valid inequalities. Also, we develop a novel decomposition based heuristic procedure for solving large size problems. Computational results show that the developed valid inequalities are quite strong, and the developed heuristic procedure finds an optimal solution to the most test problems within reasonable time bound.

Riding the US wave: spectrum auctions in the digital age

Given its significant technological advantages compared to analog broadcasting, digital television (DTV) will be the television system of the future. However, it requires a full replacement of analog television sets by digital receivers, as DTV can only be watched with special equipment. In order to make this transition happen smoothly without losing the analog television audience, both signals have to be simulcasted until a substantial coverage with DTV broadcasting has been achieved. Australia and the US meanwhile have established a regulatory framework to lead this transition towards the end of analog broadcasting, the so-called analog switch-off. Part of the US regime is the FCC's obligation to reassign analog frequencies after the switch-off has taken place by means of auction. Spectrum auctions, however, originate not from the US but from New Zealand, where they have been used since the end of 1989 and ever since been subject to legal and political criticism. The article outlines the principles of both the DTV and spectrum auctions regulation and shows the links between both areas of telecommunications regulation. It concludes by suggesting that the analog switch-off is a unique opportunity to reconsider current spectrum policies, as it frees large amounts of the radio spectrum that are today occupied by analog broadcasting and will soon be subject to one of the biggest frequency reassignment processes in the history of telecommunications regulation.