broadband vs baseband

DSL is digital service.  It is provided over an analog signal.  It uses higher frequencies than voice, fax, and traditional dial-up MoDem traffic.  But, you need filters or splitter to isolate the audio frequencies for the DSL signal.

DSL traffic is above 20KHz (shouldn't be heard by humans).  Voice signals should be below 5Khz.

That's one reason why some areas cannot get DSL service, even if they are close to a CO.  I know a location that has limited copper going up a hill to service an area with 10 times as many residences as when the lines were put in in the 1970s.  To extend service, fiber was run.  Voice lines were compressed and consolidated to run up the hill to new customers.  So, many customers cannot run DSL over their copper to the house because the analog signal is being modified (compressed/decompressed) to get it up the hill.

Limited DSL service is subscribed, but it requires that that line is migrated off the fiber and moved to a real copper pair.  There may be none available...so you have to wait until somebody gets service disconnected.  Good news for the incumbent cable company.