Read: RIAA CEO Mitch Bainwol's Farewell Letter to Music Execs
Read: RIAA CEO Mitch Bainwol's Farewell Letter to Music Execs

Bucking a years-long trend of decline, U.S. music sales continued this year's upward swing, rising 1.6% through May 8, according to Billboard analysis of Nielsen SoundScan data. The gain is measured in track-equivalent albums (TEA), which combines the unit sales of albums and digital tracks into a single, comparable number.

The small gain occurred after gains in digital sales more than offset the decline in physical sales. Album sales dropped 1.5% and track sales increased 9.6%. The TEA metric converts track sales into albums (at the rate of 10 tracks per album), thus a 1.7 million-unit decline in album sales was more than outweighed by a 40.4 million-unit increase in track sales.

Physical sales have fared comparatively well this year: CD sales dropped 8.8% to 72.3 million units through May 8, a relatively small decline for a format that has routinely dropped 20% in recent years. Combined with a 37% increase in vinyl LP sales and negligible gains in cassettes and DVDs, total physical sales were down 6.6 million units.

Album sales were down 1.5%, as the increase in digital album sales nearly offset the drop in physical sales. Digital albums rose 16.7%, or 4.9 million units, though May 8, a better improvement than digital albums posted in 2010 (13%) and at this same point last year (15.2%).

However, catalog titles, not current releases, are driving the strength in album sales. Current albums are down 7% while catalog (titles more than 18 months old) is up 5.4% and deep catalog (titles more than 36 months old) is up 8.3%. To emphasize the fact that this year's revival is not hit-driven: In spite of the breakout performance of Adele's "21," this year's 10 top sellers have sold 26.9% fewer units than the top 10 titles of the same period in 2010. "21" has sold 1.55 million units, #2 "Sigh No More" by Mumford and Sons has sold 783,000 units, and #3 "Now That's What I Call Music 37" has sold 565,000. At this time last year, Lady Antebellum's "Need You Now" had sold 2.03 million units, Sade's "Soldier of Love" had sold 1.15 million units and Justin Bieber's "My World" was at 983,000 units.

Digital tracks have also gained momentum lately. Through May 8, track sales were up 9.6% to 462.4 million units. The year-to-date gain is better than tracks' improvement in 2010 (1.1%) and at this point in May 2010 (-0.6%). The year's top-selling tracks are led by Lady Gaga's "Born This Way" (2.48 million), Katy Perry's "E.T." (2.29 million) and Adele's "Rolling in the Deep" (2.19 million).

Sony gained the top TEA market share through May 8 with 29.4%, up from 28.1% last year. Universal Music Group dropped to #2 with 29.1%, down from 30%. Warner Music Group remained at #3 with 19.2%, down slightly from 19.4% last year. EMI remained at #4 with 9%, down from 10.4%. And the independents increased their share to 12.8% from 12%.