What is the difference between signal before wavelet decomposition and after reconstruction?

Question

napp.alexandra 2016-6-16

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https://ww2.mathworks.cn/matlabcentral/answers/290323-what-is-the-difference-between-signal-before-wavelet-decomposition-and-after-reconstruction

回答： Good mind 2017-12-9

Hello, I am working on a program where I am trying to filter the noise out of a volume scan signal- (3D Matrix). I use for that the functions wavedec and then waverec but here is what I do not understand: [C,L]=wavedec(ascan,3,'sym3'); rec=waverec(C,L,'sym3'); So wavedec decomposes my Signal called ascan in 3 Levels thanks to the wavelet sym3. But then, for the reconstruction, the Signal called rec is the reconstructed Signal coming from the C and L values with sym3. How does the reconstruction work ? Which levels/scales are used ? Because I would expect that my reconstructed Signal is actually my Signal without the undesired noise, but it seems like the reconstructed Signal is the same as the original one. What is the difference then between those two? Also, when I do : ascan-rec and plot the resulting Signal, i obtain what I actually expected, which does not make sense to me. This Signal difference is a residual, isn't it? I hope someone can help me answering those questions. Thanks by advance.