Sorry as it might be a silly question since I am a beginner in wavelets. I have been using the matlab wavelet toolbox for denoising purposes and saw that thresholding is only applied on the detail (high pass) coefficients. Is there a different method that can be used where thresholding is applied on the approximation coefficients rather than the detail coefficients ? I am interested in this because I want to implement the denoising in real time and would like the least amount of levels for decomposition for low computational power, and most of my noises fall in the low frequency range so thresholding on approximation coefficients would be helpful.

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    $\begingroup$ You can directly apply thresholding on all coefficients. The fact to apply it on high pass coefficients only is based on the assumption that the useful signal is predominent in low index coefficients. However, thresholding would have no effect if applied on a region where useful signal is predominent $\endgroup$ – Damien Jun 17 at 14:34

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