Spectral Envelope Coding of Energy Attack Signal
AssigneeHuawei Technologies Co., Ltd.
InventorYang Gao
Life of this patent
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Abstract
MDCT or FFT-based audio coding algorithms often have the problem named here spectral pre-echoes when coding an energy attack signal. This invention presents several possibilities to avoid the spectral pre-echoes existing in decoded signal segment before the energy attack point. The spectral envelope before the attack point can be improved by performing spectrum smoothing, replacing the segment of having spectral pre-echoes or filtering the segment with a combined filter obtained by doing LPC analysis.
Claims18
A method of improving said spectral envelope shaping for said decoded energy attack signal in order to reduce said spectral pre-echo, comprising the following steps:
- detecting energy attack signal and make sure that current MDCT (or FFT) window covers significant energy portion of energy attack signal;
- detecting energy attack point location;
- smoothing said spectral envelope in Log domain or in Linear domain.
A method of improving said spectral envelope shaping for said decoded energy attack signal in order to reduce said spectral pre-echo, comprising the following steps:
- detecting energy attack signal and make sure that current MDCT (or FFT) window covers significant energy portion of energy attack signal;
- detecting energy attack point location;
- decoding the signal by Inverse-MDCT transforming received MDCT coefficients and keeping the good spectrum of signal segment after energy attack point;
- copying the signal segment without spectral pre-echoes from the signal history buffer to replace the signal segment with spectral pre-echoes before the attack point.
A method of improving said spectral envelope shaping for said decoded energy attack signal in order to reduce said spectral pre-echo, comprising the following steps of:
- detecting energy attack signal and make sure that current MDCT (or FFT) window covers significant energy portion of energy attack signal;
- detecting energy attack point location;
- performing LPC analysis on signal with spectral pre-echoes before energy attack point to have a LPC predictor A1(z);
- performing LPC analysis on signal without spectral pre-echoes covered by previous MDCT window to have a LPC predictor A2(z);
- filtering the signal segment before the attack point with the above combined filter A1(z)/A2(z).
Dependencies are inferred from the claim text.