High-accuracy, low-distortion time-frequency analysis of signals using rotated-window spectrograms

摘要

A speech processing and analysis apparatus and method (18) for generating a time-frequency distribution of a speech signal which combines a set of spectrograms with varying window lengths and orientations to provide a parameter-less time-frequency distribution having good joint time and frequency resolution at all angular orientations are disclosed. The analysis window of a spectrogram is rotated relative to the frequency components of the signal by preprocessing using a Fractional Fourier Transform to form rotated window spectrograms. In particular, to form the rotated window spectrogram, the signal 24 is initially pre-processed (1) using a Fractional Fourier Transform of angle alpha . The spectrogram time-frequency distribution of the pre-processed signal is then computed (2) using analysis window h(t) and then rotated (3) by angle - alpha . The geometric mean of a set of rotated window spectrograms, which are indexed by both the analysis window length and the angular orientation of the window relative to the signal's time-frequency features, may then be computed to form a combination of rotated window spectrograms.