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| == Constrained-Energy Fourier Transforms ==
| | #REDIRECT [[Constrained-Energy_Fourier_Transforms]] |
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| === Problems with current implementation and possible solutions ===
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| ==== Overlapped FFT not critically sampled ====
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| In the current implementation, we encode 4/3 times more samples than necessary because we use 256-point FFTs with 64 samples overlap.
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| Ideas:
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| * Use an MDCT instead of the FFT
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| * Do extrapolation on the input and use a wider FFT. Then optimise the search only for the "real" samples
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| ==== Non-harmonic signals (i.e. music) ====
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| CEFT only works on speech because most of its coding efficiency is provided by the pitch predictor.
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| Ideas:
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| * Sinusoidal prediction
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| * Use two (or more) pitch periods and choose one for each bin/band/whatever
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| * Use two (or more) pitch periods at the same time and use energy conservation to keep everything stable.
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| ==== Sparse spectrum ====
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| CEFT tends to have musical noise, especially at high frequency when there are very few bits/bin.
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| Ideas:
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| * Use a "rotation matrix"
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| * Prediction from lower frequencies
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| [[Category:Opus]]
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