I think low-pass/high-pass is sort of a misleading simplification. When they say "chronic" pain they're referring to inflammatory pain, which is distinguished from "acute" pain by its source, not its time course. (I think. Not a biologist.)
Different sources might use different time codes. Anyway, inflammation likely attacks all kinds of sensors and perhaps nerves directly, so the signal is noisy, and the high frequency constituents very unstable. Whereas functioning receptor networks likely fire in ensemble, so that signal should be kind of clear. The functionally intact rim of an inflammation is a comparably large area, so that would correspond to a low frequency signal. Although, it's much more complicated, surely, I wouldn't know.
Also, hunger after a long time becomes a dull feeling, too. Less energy -> longer time to light a synapse.
