How does modwpt details provide zero phase filtering ?
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I have used MODWPT for getting the wavelet coefficients for a given signal. But the resulting coefficients are shifted by some phase difference. Rather than that by using MODWPT details I am getting zero phase filtering. How does this result in zero phase difference? What are the changes in filter coefficients inorder to get this result?
Wayne King on 28 May 2018
MODWPTDETAILS actually projects the signal onto the various wavelet packet subspaces, that is what provides the zero-phase filtering because you are using not only the analysis filters but also the synthesis filters. MODWPT does have a time-aligned option that will provide an approximation to this using just the analysis filters (coefficients), but it is not exact like MODWPTDETAILS. The MODWPT with time-aligned does have the advantage of still conserving the signal energy though. The similarity between MODWPT and MODWPTDETAILS is analogous to MODWT and MODWTMRA.