Buddy Holly has been dead for 60 years now, Roy Orbison for 31. However, the Rock Hall of Famers will share a concert bill Thursday at Mystic Lake Casino as life-size holograms, accompanied by a live band.

"When it first happened, the audience had a bit of a gasp. But after like 10 seconds, they're totally into it," said Martyn Axe, keyboardist for the Holly/Orbison tour.

The star's voice is taken from actual recordings. Flanking the holograms, Axe and the other musicians stand in darkness "so the hologram can be as sharp as possible," while in-ear monitors provide a "click track" keeping them in sync with the spectral image throughout the 90-minute show.

Holograms of deceased stars have been creeping onto the stage since the late rapper Tupac Skakur appeared briefly during Snoop Dogg's set at the Coachella fest in 2012. Two years later, a hologram of Michael Jackson performed a number on the Billboard Music Awards.

But hologram concert tours, first launched last year, are a burgeoning new trend.

Heavy-metal hero Ronnie James Dio posthumously rocked the Myth in Maplewood last June. Opera diva Maria Callas is on tour with a 50-piece orchestra. Frank Zappa is freaking out fans as a ghostly guitarist.

A Whitney Houston hologram tour, with 18 singers, dancers and musicians, is slated for 2020. The families of Amy Winehouse and Prince have had discussions about similar tours.

It's a whole new frontier, with a host of legal, technological and ethical issues. Yet, holograms have captured the attention of the music industry as a potentially significant revenue source — and a legacy preserver, especially for late greats with passionate fan bases.

Here's how a hologram tour comes together.

A year to develop hologram

Legal issues come first, starting with permission from the artist's heirs.

Song publishers and record labels — which provide the recorded voices — also have to sign off, but they're invariably looking for new revenue.

There's plenty more work for lawyers, too, addressing rights of publicity (i.e. use of name and likeness), with policies sometimes varying from state to state.

As for the technology, there are two processes right now. Neither, strictly speaking, involves an actual hologram.

For the Dio and Zappa tours, a company called Eyellusion Live uses an old magician's technique called Pepper's Ghost that dates back to the 1800s. Basically, a reflective screen bounces a two-dimensional image of the performer onto a see-through screen.

For Holly, Orbison and Callas, Base Hologram Entertainment employs a new technology similar to the CGI process used in the movies.

"It's exactly the way they created Carrie Fisher and Peter Cushing [posthumously] for the 'Star Wars' movies," said Marty Tudor, CEO of Base Hologram. "You start with a body double and learn the intricate movements of the character. We use old footage [of the stars] as reference material. I could make Roy Orbison do back flips onstage if I wanted to, but Roy just stood there and played. Then you build from there, and you add CGI."

With an image generated by a digital laser projector, the performer appears 3-D onstage but it's really only 2-D, Tudor explained.

Once a project is greenlighted, it takes about a year to develop a show, at a cost of about $1 million. Base Hologram scripts it just like a Broadway musical; in fact, it hired Broadway director Eric Schaeffer ("Million Dollar Quartet") to help stage the Holly/Orbison show, which is running simultaneously in the United States and Europe.

Like a rock-band tour in a theater, the show takes about four hours to set up. The tour has an entourage of 12, including five musicians and two backup singers. The musicians' credits include both musical theater ("Rock of Ages," "Mamma Mia") and live concerts (Aretha Franklin, Liz Phair).

Believers and skeptics

Not all music lovers warm to the idea of hologram concerts.

"I think it's silly. It's fake," said avid live-music fan Bonnie Dickel Hoffman of Golden Valley, who this year has seen everyone from Lizzo to Van Morrison. "I'd rather watch a movie or concert footage in real time, not dead time."

Star Tribune critic Chris Riemenschneider had reservations about Dio's hologram show at the Myth.

"The novelty of the show never gave way to a more authentic rock-concert experience," he wrote, "and the weirdness of seeing a 3-D Dio back from the Great Beyond never went away."

Morris Day of the Time is uncertain if he'd go see his "Purple Rain" co-star Prince as a hologram.

"It's gonna be nothing like seeing Prince in concert," Day said. "It might be fun for big fans. It might be creepy to see."

However, some people in the music industry are big believers in the potential for holograms, especially as the biz has seen revenue from recordings and streaming dwindle in the past few years.

"To me, it is the next billion-dollar music business," Minneapolis entertainment lawyer Ken Abdo wrote this summer in the trade journal Variety. "Holograms can protect — and perhaps immortalize — artists' legacies, keep audiences in venues, introduce younger generations to the artists, provide continued protection of artists' intellectual property and create revenue for artists' estates."

He even sees a potential for living artists, such as megastars Taylor Swift and Ed Sheeran, to do hologram tours of modest-sized markets they might not otherwise play. Or a star with a perfume line could make holographic appearances at stores.

Abdo is encouraging one of his clients — Hanson, the band of brothers known for the 1997 smash "MMMBop" — to film a concert to preserve for future hologram use.

He'd like to see a hologram of 1950s rocker Bill Haley, whose estate is one of his clients, open for the Holly/Orbison tour. His firm also handles the estates of Muddy Waters and Pete Seeger and such clients as Roberta Flack, Erik B & Rakim, Jonny Lang and Toto.

Abdo said entertainment lawyers are now encouraging clients to include clauses in their wills regarding digital exploitation of their images.

Some stars feel strongly about their careers after death. The late comedian/actor Robin Williams specified in his will that his image not be used in any commercials, holograms or other forms for 25 years after his death.

Even though Abdo knows that hologram technology is in its infancy, he is bullish about its future.

"There is enough momentum and money in this movement that the rights will get figured out," he said. "The music business needs this. The possibilities are endless."

Twitter: @JonBream • 612-673-1719