Hi Zhuang,
While it is true that for TR=5s, it means bandpassing would
take out basically nothing, what it also means is that all
of the higher frequencies are aliased, so you just cannot
see them. On the flip side, a TR of 2s throws away 60% of
the dof just for bandpassing. So I certainly would not
consider going faster than that.
My feeling is that something in the 2-3s range is good,
though I am far from an expert on this. If TR=4s gives you
full coverage, that might be worth using.
If no one else chimes in, you might ask this again as a new
thread. This one is long so maybe people would not read it.
- rick