I understand that aliasing occurs in DWPT if the wavelet used is of low order since the "filters" are not perfect and the combination of down sampling and overlapping between bands causes aliasing. I am using low order wavelet as I aim to implement the process in real-time and I have limitations on the number of filter taps. Doing some simulations in matlab I saw aliasing in two cases:
- One case I saw it when I decomposed a signal to a tree and I plotted FFT of a certain node but when I reconstructed the tree I noticed that aliasing was canceled.(basically did not alter the coefficients only decomposed viewed and reconstructed).
- Doing the same thing as above but thresholding the node or compressing the coefficients to zero the aliasing was still present after reconstruction. I compressed level 22 coefficients to zero. So can I conclude that aliasing will always occur if I am using a low order wavelet say 'db4' and I manipulate the coefficients? If so how is wavelet such famous denoising tool and aliasing can be this bad?