How does modwpt details provide zero phase filtering ?

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?

Answer 1

[Wayne King]

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.