A new research report from eMarketer projects U.S. online listening to grow incrementally through 2018, from 148-million listeners in 2013 to 183-million listeners in 2018. iMarketer characterizes the audience as “mass market” now, totaling over half the U.S. population, and two-thirds of the online U.S. population.

Unusual terminology creates some confusion in the report’s headline and footnotes. eMarketer calls online listening “digital radio,” which normally refers to digital terrestrial broadcasting, both in the U.S. and other countries. Thus, a quick glance would imply a status update for HD Radio in the U.S. A note in the report attempts to clarify what the study means: “Digital broadcasts of terrestrial radio stations, digital-only radio stations, or audio podcasts via any device at least once per month.” That would seem to be a mix of HD Radio and online listening, but eMarketer tells us the report refers only to Internet-delivered listening, desktop and mobile.

eMarketer cites a parallel report from AccuStream which predicts growth in listening hours, in addition to eMarketer’s projection of expanded reach.

All this generally coincides with Edison Research data indicating a large U.S. audience for online audio, and an expansion of listening hours due to new mobile listening environments. Edison’s “The New MainStream” research from last fall indiciates just over half the online U.S. population listens to online audio, roughly coinciding with eMarketer data. See our latest Edison coverage here.