Based on a deep understanding of all-phase digital filter (APDF) design and all-phase biorthogonal transform (APBT). this paper will further study the windowed all-phase digital filter (WAPDF) and windowed all-phase biorthogonal transform (WAPBT). discuss the principle of the WAPBT. and provide a unified construction method of the all-phase transform (APT). https://www.knowall.blog/