The polyphase decomposition of into channels in (11.11) may be termed a ``type I'' polyphase decomposition. In the ``type II'', or reverse polyphase decomposition, the powers of progress in the opposite direction:
We will see that we need type I for analysis filter banks and type II for synthesis filter banks in a general ``perfect reconstruction filter bank'' analysis/synthesis system.
Filtering and Downsampling, Revisited
N-Channel Polyphase Decomposition