Among musicians, flat is a word you don't want to hear. But to the industry, flat is truly music to everyone's ears.

Soundscan's sales year doesn't end until January 1, but current year-to-year comparisons have album sales for 2011 ahead of comparable 2010 business.

OK, it's only by a whisker of 1 percent. But it is welcome news in an industry where album sales for 2010 were down 13 percent from 2009. And prior to that they'd been down an average of 8 percent every year through the 2000s, suggesting an incredible shrinking music business.

This year reversed the trend, but there is a cloud buried in the silver lining: the success stories of 2011 will not be easy to replicate.

The year's two biggest albums were Adele's 21 and Michael Buble's Christmas -- and even the most copycat-prone execs aren't foolish enough to start looking for pleasingly plump Englishwomen or Sinatra-bred carolers to sign.

Regardless of how applicable the lessons might be, here's our look back at what worked and what didn't in 2011:

RETRO ROCKS -- IF YOU DON'T CALL IT RETRO

Artists from Adele to the Black Keys thrived by recalling good old days for oldsters while seeming utterly contemporary to kids who'd rebel at the word throwback.

At last tally, Adele's 21 had sold 5,281,000; with two sales weeks yet to be reported, the blockbuster should finish out the year a little shy of 6 million. (The only release in the past few years to cross the 6 million mark was Taylor Swift's Fearless.) Moreover, she sold an additional 750,000 copies this year of her previous album, 19.

Adele is a singles artist, too. Rolling in the Deep has sold 5,665,000 downloads, followed by Someone Like You with 3,352,000, Set Fire to the Rain with 963,000, and Rumour Has It with 551,000.

On a smaller but louder end of the spectrum, the Black Keys put the lie to rock is dead theories -- again -- by moving 426,000 copies this year of their two-year-old Brothers. Their brand new El Camino, whose nostalgic aspects lean more toward glam-rock than neo-blues, has sold an impressive 293,000 units in two weeks.

BET ON THE RIGHT CAROLER

Everyone guessed there'd be a big Christmas album this year. Almost everyone guessed it'd be Justin Bieber's. But Buble's sold 1,964,000 of his holiday CD, versus Bieber's 1,003,000.

We should have seen it coming, since Buble's previous album quietly sold 2 million-plus. Despite his crooner image, Buble's holiday set wisely had something for everyone, whereas Bieber's had something to annoy just about everyone outside his core.

Christmas currently stands at No. 3 on the list of 2011's bestsellers, and will surpass Lady Gaga to land at No. 2 by January 1.

Again, maybe not a surprise to anyone who recalled how Josh Groban's Noel became 2008's surprise bestseller.

FORGET WHAT WE SAID ABOUT ROCK NOT BEING DEAD

The news wasn't so great if you weren't the Black Keys. One of the biggest bands of the 2000s, Evanescence, belly flopped with their self-titled third album, which has sold an anemic 284,000 units in 10 weeks and currently sits at No. 101.

Some other big rock names did just OK. Coldplay sold 877,000 copies of Mylo Xyloto in eight weeks -- impressive, until you remember their last album sold 721,000 in one week.

Don't call Blink-182's Neighborhoods a comeback. The dormant superstars' return moved 259,000 units in 10 weeks. Their current neighborhood (No. 200 on the Billboard 200)? The chart ghetto.

Daughtry looked to be one of the big sellers of this holiday season, on paper, but their new album sits at No. 27, having sold 241,000 in a month.

The Red Hot Chili Peppers sold 458,000 of their latest, leaving a long road to catch up with the two and a half million their last effort managed. The term red hot just doesn't seem to apply to anything related to rock ...

Unless, of course, it's U2's 360 tour, officially the highest grossing ever. Their lengthy worldwide trek brought in $293 million, playing to 2.8 million patrons.

SINGLES ARTISTS VS. ALBUM ARTISTS

Adele and Taylor Swift sometimes appear to be the only acts who can move millions of long-players and singles. Swift's 2010 release Speak Now sold another 902,000 copies this year, upping its total to 3.9 million.

But the trend is toward acts like LMFAO, who had far and away the year's biggest single with Party Rock Anthem -- a 4,579,000 seller as of mid-month.

The dance duo also have the current top-selling single with Sexy and I Know It, with 2,544,000 downloads. Another song, Shots, has moved 1,540,000. Fans clearly prefer the a la carte approach. The act with the year's top-selling song can only lay claim to the 56th best-selling album, as Sorry for Party Rocking has sold 401,000 copies.

The ultimate example of a singles-only act: Hot Chelle Rae. The pop group won best new artist at the American Music Awards, after their Tonight Tonight single sold an astonishing 2,382,000 singles. The subsequent album has moved 31,000 copies in three weeks.

Britney Spears may also fall into this category now. Her Femme Fatale did better than expected, given a run of bad pre-release publicity, but its 725,000-copy total wasn't good enough to push it into the top 20 sellers of the year.

NEW COUNTRY VS. OLD(ER) COUNTRY:

It used to be that country was the genre most hospitable to mid-career artists. Tell that to Martina McBride, who's sold a mere 119,000 in 10 weeks. Toby Keith is down to No. 28 after just eight weeks, with an OK 266,000 tally, the kind of number he used to do in just his opening week.

So who's barnstorming down the dirt road? Country's new guard of guys. Jason Aldean's My Kinda Party, a late 2010 release, has racked up a 2.2 million total, and it moved back up to No. 16 in the week prior to Christmas. No other album that's been out more than a year has anywhere near that ongoing momentum.

For second-tier success stories, check out Eric Church at 504,000 units, Luke Bryan at 580,000 with his latest, the Zac Brown Band adding 720,000 to their 2010 album's total -- and Scotty McCreery, putting an end to the recent Idol curse with 748,000 and counting.

One female-fronted group broke through the wall of dudes: the Band Perry added 666,000 to the 998,000 total for their debut album, which will be well over a million by year's end -- capitalizing on their 3.5 million-selling single, If I Die Young, the funeral song of the millennium.

DID HIP-HOP FAIL TO WATCH ITS THRONE?

Eminem had the top-selling album last year, but there were no such contenders in 2011. Lil Wayne had the best first-week tally, selling over a million -- but he has yet to double that. Still, his Tha Carter IV is the year's fourth-best seller, with 1,826,000 so far.

Jay-Z's and Kanye West's Watch the Throne is up to 1,116,000, but was expected to have done better. Drake's sophomore Take Care will soon surpass it. As for the old guard, you only have to look to The Game to see who's lost his game, with a braggadocio-defying 222,000 units.

LOSS LEADERS TAKE A LOSS

Lady Gaga should end up with the third best-selling album of the year, after Adele and Buble -- but it'll always have a steroid-sized asterisk, since first-week sales were goosed by a controversial 99-cent sale on Amazon.com. Billboard allowed the sub-dollar sales when they celebrated a million-plus opening week for Born This Way, but later announced they wouldn't include virtual giveaways in the future.

That's not to say Gaga's fans aren't willing to shell out where it counts: at the box office. Her concert trek grossed $72 million -- even without putting any tickets on sale at the Dollar Store. She was the only performer under 30 besides Swift to land among Billboard Boxscore's top 10 money-making tours, a realm otherwise largely populated by the veteran likes of U2, Bon Jovi and Roger Waters.

With music shelf space still shrinking at big-box stores, which of course helped kill dedicated music outlets during the flush years, it's doubtful whether music can manage another up or flat year in 2012.

That might take Adele breaking her every-other-year release pattern and giving us a surprise 22 on the inevitable path to 23.

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