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With 15.66 million digital songs sold in the U.S. in the week ending Aug. 27, according to Nielsen Music, the industry saw its lowest weekly song volume in nearly eight years.

It's the smallest weekly sum for song downloads since the week ending Dec. 9, 2007, when 15.64 million were sold.

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Conversely -- and unsurprisingly -- as sales plummet, streaming continues its ascent, with the same frame marking the highest week of total U.S. on-demand audio and video streams: 6.6 billion. The streaming surge follows as consumers adapt to free and low-cost streaming services (like Spotify, YouTube and Apple Music) and shift away from the pay-to-own model. (More on streaming's big gains in a moment.)

Digital Song Sales Slide: The top-selling song of the Aug. 27 tracking week was R. City’s “Locked Away,” featuring Adam Levine, which sold 92,000. That’s the smallest sum for the week’s top-selling download in almost nine years, since the frame ending Dec. 17, 2006, when Beyonce’s “Irreplaceable” shifted 88,000. “Locked Away” also marks the first time that the week’s top seller fell below 100,000 downloads since the week ending Jan. 14, 2007 (when, again, “Irreplaceable” was tops, with 98,000).

Overall song sales for 2015 total 678.3 million -- a decline of 10 percent compared to the same point a year ago (through the frame ending Aug. 24, 2014). If song volume doesn’t pick up before the end of the year, 2015 will become the third straight year that song sales have declined. In 2014, song sales volume dropped by 12 percent.

Streaming On the Rise: The week ending Aug. 27 was the largest week for combined on-demand audio and video streams ever, with 6.6 billion. The most-streamed song of that week was Silento's "Watch Me," with 22.3 million. 

And, year-to-date, total on-demand streams stand at 191.4 billion -- up 100 percent compared to the same time frame a year ago (95.8 billion through the week ending Aug. 242014). 

Album Sales Update: The digital song dip (and streaming high) comes four weeks after weekly album sales volume fell to a new low: 3.71 million in the week ending July 30. A week later, another woeful distinction was claimed: the top album of the week -- the soundtrack to Disney Channel’s Descendants -- sold just 42,000 copies. That’s the lowest sales figure for a No. 1 album on the Billboard 200, or Top Album Sales, since Nielsen Music began powering the charts' rankings in 1991.

Year-to-date album sales stand at 149.1 million, down 3 percent compared to the same point a year ago.