Time variable spectral analysis based on interpolation for speech coding
AssigneeTelefonaktiebolaget L M Ericsson
InventorTorbjorn K. Wigren
Life of this patent
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Abstract
A time variable spectral analysis for speech coding based upon interpolation between speech frames. A speech signal is modeled by a linear filter which is obtained by a time variable linear predictive coding analysis algorithm. Interpolation between adjacent speech frames is used in order to express a time variation of the speech signal. In addition, interpolation between adjacent frames secures a continuous track of filter parameters across different speech frames.
Claims71
A method of linear predictive coding analysis and interpolation of uninterpolated input signal frames using time variable spectral models, the method comprising the steps of:
- sampling a signal to obtain a series of discrete samples and constructing therefrom a series of frames;
- modeling the spectrum of said signal using a filter model utilizing interpolation of parameter signals between a previous, present and next frame for forming estimated parameters;
- calculating regressor signals from said estimated parameters;
- smoothing the spectrum by combining the regressor signals with a smoothing parameter to obtain smoothed regressor signals;
- combining said smoothed regressor signals with weighting factors to produce a first set of signals;
- combining parameter signals from the previous frame with said smoothed regressor signals, a signal sample and a weighting factor to produce a second set of signals;
- calculating parameter signals for the present frame and the next frame from the first and second set of signals;
- determining whether the filter model is stable after each frame;
- and
- stabilizing the filter model if the filter model is determined to be unstable.
A method of linear predictive coding analysis and interpolation of uninterpolated input signal frames using time variable spectral models, the method comprising:
- sampling a signal to obtain a series of discrete samples and constructing therefrom a series of frames;
- modeling the spectrum of said signal using a filter model utilizing interpolation of parameters between a previous, present and next frame for forming estimated parameters;
- calculating regressor signals from said estimated parameters;
- smoothing the spectrum by combining the regressor signals with a smoothing parameter to obtain smoothed regressor signals;
- combining said smoothed regressor signals with a weighting factor to produce a first set of signals;
- combining parameter signals from the previous frame with said smoothed regressor signals, a signal sample and a weighting factor to produce a second set of signals;
- calculating parameter signals for the present frame from the first and second set of signals;
- determining whether the filter model is stable after each frame;
- stabilizing the filter model if the filter model is determined to be unstable.
A method of signal coding, the method comprising:
- determining a first spectral analysis of signal frames using time variable spectral models and utilizing interpolation of spectral parameters between frames;
- determining a second spectral analysis using time invariant spectral models;
- comparing the first analysis to the second spectral analyses to determine which spectral analysis has the highest quality;
- and
- selecting the spectral analysis with the highest quality to code the signal.
Dependencies are inferred from the claim text.