Fifty Shades of Grey

Jamie Dornan as Christian Grey in Fifty Shades of Grey.

Courtesy of Universal Pictures

On the Billboard 200 albums chart dated April 4, Kendrick Lamar’s To Pimp a Butterfly debuted at No. 1, while the previous week’s leader, the soundtrack to the TV series Empire slipped to No. 2.

The Billboard 200 chart ranks the week’s most popular albums based on their overall consumption. That overall unit figure combines pure album sales, track equivalent albums (TEA) and streaming equivalent albums (SEA).

Let’s take a closer look at some of the action on the chart:

- Soundtrack, Fifty Shades of Grey - No. 6: After only six weeks on the chart, the Fifty Shades of Grey soundtrack has sold more than a half-million copies, according to Nielsen Music. The multi-artist set sold another 28,000 in the week ending March 29, bringing its to-date total to 516,000. It’s the fourth-largest selling album of 2015, behind Taylor Swift’s 1989 (916,000), Drake’s If You’re Reading This, It’s Too Late (774,000) and Sam Smith’s In the Lonely Hour (525,000).

- Mark Knopfler, Tracker - No. 14: The veteran artist (and front man for Dire Straits) nets his highest charting solo album yet, as Tracker debuts at No. 14 with 36,000 units. That surpasses the No. 17 peak of both 2006's All the Roadrunning and 2009's Get Lucky.

- Madonna, Rebel Heart - No. 21: Madonna’s Rebel Heart slips from No. 2 to No. 21 with 26,000 units (down 78 percent) in its second week. It fell by 80 percent in album sales, to 24,000 (down from 116,000). The 80 percent erosion is steep, but not terribly out-of-the-ordinary for a title that likely had a lot of pre-order sales that made it difficult to sustain a strong second week. High-debuting albums from big-named stars regularly see second-week declines of more than 75 percent in sales. For example, in the tracking week ending March 8, Big Sean’s Dark Sky Paradise, Kid Rock’s First Kiss and Chris Brown & Tyga’s Fan of a Fan all dropped by 75 or more in their second frame. In the past year, albums that fell sharper than Rebel Heart include: Fall Out Boy’s American Beauty/American Psycho (82 percent), Foo FightersSonic Highways (81 percent) and 5 Seconds of Summer’s She Looks So Perfect EP (82 percent).

- Echosmith, Talking Dreams: No. 38: The still-rising band finally graduates from the Heatseekers Albums chart, as the 2013 release breaks into the top 100 of the Billboard 200 chart, zooming from No. 101 to No. 38 -- a new peak. (Titles are removed from Heatseekers once the act reaches the top 100 of the Billboard 200.)

- Soundtrack, Annie - No. 55: The musical's March 17 home video release prompts a surge for its companion soundtrack: it's up 143 percent in units (to 9,000 for the week), pushing the set to a re-entry at No. 55. Pure album sales accounted for 7,000 of that overall unit total.

- Elle King, Love Stuff - No. 84: After a month's absence from the list, the album returns courtesy of promotion and discounting in the iTunes store. The set earned a 248 percent download gain, assisting its overall 6,000 unit total for the week (up 94 percent)

- Soundtrack, The Sound of Music - No. 148 — Following the ABC TV special The Untold Story of The Sound of Music (which aired March 18), the soundtrack returns (up 15 percent in units and 8 percent in sales) nearly almost exactly 50 years after its chart debut (March 20, 1965). The former No. 1 -- it topped the list for two weeks in 1965 -- was recently reissued with bonus tracks.

- Rush, 2112 - No. 149 — A hologram vinyl edition of the 1976 album was released on March 17, prompting the set's debut at No. 2 on Vinyl Albums (4,000 sold) and it's 649 percent sales gain (basically all from the LP release).