Tony Bennett, left, and Lady Gaga perform during a concert at the Umbria Jazz Festival in Perugia, Italy. (Gian Matteo Crocchioni/ANSA/AP)

There’s a lesson to be learned from the bevy of outsiders, usually pop musicians, who have tried their hands at releasing jazz records, and it’s a simple one: Not everyone is Lady Gaga.

In fact, if you ask jazz historian Ted Gioia, author of “Jazz Standards: A Guide to the Repertoire,” Lady Gaga is a unicorn. She’s the rare pop artist who can not only comfortably sing jazz, but who excels at it.

“There is a cynical feeling in the jazz community that when a major star in popular music embraces jazz, it’s because they’re on the downside of their career and they’re reaching for some gimmick to reestablish themselves,” Gioia said. “That’s definitely not true with this Lady Gaga album, and it’s definitely not true with the Bob Dylan album [“Shadows in the Night"]. Those are great artistic works. But probably more often than not, when you see a pop star embracing jazz, you should run for the hills.”

It’s not as though the conduit between pop and jazz is a one-way street; John Coltrane and Miles Davis recorded takes on “My Favorite Things” and “Bye Bye Blackbird,” respectively.

Still, something about leaving their mark — via the standards or the 12-bar blues — keeps drawing in jazz neophytes who’ve become household names by releasing rock, pop, folk and even rap albums. So why do so many artists take this route? Well, it allows them to reassert their musical bona fides, and even when critics find said bona fides wanting, these efforts tend to net tremendous commercial success. These albums tend to fall into three basic categories: Legitimate, Enh … Passable, and — how to put it? — This is Not Your Best Work.

Let’s start with the brightest before we begin our descent into secondhand embarrassment, shall we?

Legitimate

Lady Gaga

Lady Gaga benefited from the imprimatur of Tony Bennett, who has basically fashioned his own cottage industry from recording songs with pop artists who fancy themselves jazz vocalists, if only for one track. Indeed, that’s how his relationship with Gaga began; they recorded “The Lady is A Tramp” together for Bennett’s “Duets II” album. But he took a shine to Gaga and they became close friends. Annie Leibovitz even shot Bennett sketching a nude Gaga for the January 2012 issue of Vanity Fair. (The sketch later sold on eBay for $30,000.)

They teased fans with surprise appearances at the Montreal Jazz Festival and the Frank Sinatra School of the Arts before releasing their joint album “Cheek to Cheek” in September 2014. Their “Great American Songbook” concert, taped at New York’s Lincoln Center, aired on the PBS series “Great Performances” in October. The popularity of “Cheek to Cheek” made Bennett, now 88, the oldest act to reach No. 1 on the Billboard chart.

“It’s a test of musicianship, because when you sing these old songs, you invite comparison with people who sang them in the past,” Gioia said. “So if Lady Gaga sings a standard, she’s immediately compared to Frank Sinatra or Billie Holiday or Ella Fitzgerald and that brings with it great risk. It brings with with it tremendous risk. I commend Lady Gaga for taking on that risk and I also praise her for pulling it off. I think she shows considerable talent as a jazz singer. I don’t think many pop megastars of her generation could withstand the scrutiny of singing these songs live in concert, without Auto-Tune, sharing a stage with Tony Bennett and pull it off. Quite extraordinary.”

Bob Dylan

Dylan’s 36th album, “Shadows in the Night,” earned the grudging respect of unrepentant jazz snob Geoff Dwyer, author of “But Beautiful: A Book About Jazz.”

“For me, jazz is so much kind of instrumental music, and then there’s this thing called jazz vocal, which to me, is already a kind of pop music,” Dwyer said. “And I know there’s all sorts of people that would cry out and complain about that and say, ‘oooh, Billie Holiday, Ella Fitzgerald,’ or whatever, but … that was as much pop music as it was jazz. It’s already getting toward pop once you have a voice in it.”

But Dwyer’s endorsement wasn’t just rooted in “Shadows in the Night” alone. It was mostly because Dylan had long established his chops as a skilled improvisationalist before he ever thought about releasing an album of Frank Sinatra songs. Just listen to his many different iterations of “Tangled Up In Blue” or the nearly 12-minute meditation that takes place on “Sad Eyed Lady of the Lowlands.”

“The myth, if not the reality of jazz, is that you could go and hear the same person many nights running and it would be different every time,” Dwyer said. “I think it tends to be in a jazz style, a lot of this stuff, rather than being inherently jazz with that inherent core of it being improvised.”

Queen Latifah/Dana Owens

Those who remember that Queen Latifah began her entertainment career as a rapper will always associate her with 1993’s “U.N.I.T.Y.” And while Latifah was recently nominated for an Emmy for her performance as the empress of the blues in “Bessie,” a project she’d been nursing for 20 years, her interest in jazz and the blues didn’t come at the end of her career. If anything, her Oscar-nominated turn playing Mama Morton in the 2002 movie-musical “Chicago,” or the 2004 release of “The Dana Owens Album” (which, titled after her birth name, received a Grammy nod for best jazz vocal album) likely boosted Latifah’s credibility for “Bessie.”

Enh … Passable

Joni Mitchell

Usually, non-jazz artists will ease themselves and their fans into the genre with standards — songs that carry with them an aura of the highbrow while still remaining familiar to most. This was not the route Joni Mitchell took, and she paid for it. Before she released “Mingus” in 1979, Mitchell was known as a folk singer-songwriter. She began dabbling a bit with jazz, and then collaborated with Charlie Mingus to create something that just wasn’t “Embraceable You.”

“If you look back at her history, you’ll find she never had another huge hit record after that. Before she embraced jazz, her albums were all … toward the top of the Billboard charts. After she did this switch to jazz, her albums never had quite the same sales,” Gioia said. “Is there cause and effect? I fear that by embracing the artistry of jazz, Joni Mitchell may have alienated some of her core fans.”

Linda Ronstadt

Like Mitchell before her, Linda Rondstadt marked her foray into jazz with some help from an established and respected name, Nelson Riddle. She never quite veered completely into the genre, and instead established a reputation as a solid cabaret singer.

“I almost don’t want to pass verdict on that,” Gioia said. “She’s in between cabaret and jazz. I think she did a credible job of performing those songs. I’m not 100 percent sure I’d call them jazz renditions.”

But Ronstadt clearly found it appealing; she recorded a trilogy of jazz albums, all arranged by Riddle: “What’s New,” “Lush Life” and “For Sentimental Reasons.”

Annie Lennox

In recent years, Annie Lennox has taken some heat for her comments about whether or not she thinks Beyoncé is a feminist. “Twerking is not feminism,” Lennox said in a September 2014 interview when she was promoting “Nostalgia,” her album of great American songbook covers. Lennox didn’t choose easy songs, something that worked to her advantage critically, but she also found herself in the midst of a tempest of controversy when she did an interview with Tavis Smiley and basically decoupled “Strange Fruit” from its origins as a protest song about lynching.

This is Not Your Best Work

Rod Stewart

One of the ways to capture some of the gravitas of jazz without treading full bore into the shark-infested depths of improvisation is to record an album of cuts that amount to Jazz Lite™.

“Jazz purists would distinguish between ‘real jazz’ and formulaic delivery of an old jazz song,” Gioia said. “And a lot of the old pop musicians who are trying to reinvent themselves — they’re able to sing the song. They’re able to pull it off and it even sounds good, but it doesn’t capture that kind of risk-taking that jazz fans want to see in their music.”

Rod Stewart has found tremendous success with this model by plumbing the great American songbook for five discs of standards. His first effort, “It Had to Be You: The Great American Songbook” went multi-platinum. The big question is who exactly is listening to this stuff? It’s about as far away as you can get from “The First Cut is the Deepest” and “Do Ya Think I’m Sexy” as one can get, and the world’s relatively tiny contingent of jazz snobs aren’t rushing to hand over their money, so who is it?

Robbie Williams

One of the commendable aspects of “Shadows in the Night” was that even though the album was a clear homage to Sinatra, Dylan managed to retain his own style instead of aping Ol’ Blue Eyes. Not so for Robbie Williams, formerly of the pop group “Take That.”

“Almost anyone … who would try to tackle a Sinatra song would find themselves drawing on the mannerisms or phraseology of Sinatra,” Gioia said.

But the commercial reception to “Swing When You’re Winning” was enthusiastic enough that Williams followed it with “Swing Both Ways,” which is half standards and half original compositions. Both topped the U.K. charts.

Barry Manilow

Manilow’s 1985 dalliance with jazz was a full-bore departure from his repertoire. All the songs on “2:00 AM Paradise Cafe” were original and penned by Manilow — it was clear he wanted to insulate himself from some of the pitfalls and clichés of his peers. He enlisted the help of respected musicians such as baritone saxophonist Gerry Mulligan and drummer Shelly Manne. He recorded duets with Sarah Vaughan and Mel Tormé. It wasn’t a hit with jazz aficionados or critics, but it went platinum, and reached No. 28 on the Billboard chart.

Never underestimate the purchasing power of the Fanilows.