Two of NPR’s top technologists recently back from the NAB Show share the microphone to weigh the pros and cons for stations that might boost their digital signals to improve listeners’ reception of HD Radio. Dennis: Digital radio broadcasting is a reality now in most American communities, though adoption is still modest. About 2.5 million receivers have been sold, but assuming multiple receivers for early adopters and counting methodologies, household penetration might be roughly 2 percent — about as many households as in a market the size of Washington. Public radio has aggressively invested in digital radio transmission. Some stations, such as WAMU in Washington, have also made significant programming investments in new channels.