The can be filters that either block or pass low frequencies, high frequencies or a band of frequencies. (In that one sentence I have covered six separate scenarios.)
A simple, rat's-tail, microfilter will just have a low-pass filter before the telephony port and nothing before the xDSL modem port. All modems (modem/routers) have a high-pass filter internally just before their analogue front-end.
Centralised filters (service specific face plates (SSFPs) in Openreach talk) will contain a combination of low-pass, high-pass and band-pass filters depending upon the service for which they have been optimised.
Those old ADSLnation centralised filters were designed for ADSL/ADSL2+ as that was only what existed "back then".