Metallica drummer Lars Ulrich has revealed that the band is "deep into the songwriting" of its next album. 

It has been almost six years since Metallica released its latest studio album, the return-to-form thrash gem "Death Magnetic." Yet while Metallica gear up for European summer festivals, the group is also coming up with new songs for its next full-length record, and heavily focused on the process.

"We're going through the grind," Ulrich told Rolling Stone. "We're in there doing riffs and putting them into songs. We don't really write one song and then show up the next day and do another one. We just work on riffs and sections, connecting riffs and tempos and moods."

The drummer told RS that Metallica has been working on the record "off and on" for nearly a year and will regroup in the studio at the beginning of May. "We're going to start talking about who is going to produce the album. We haven't started recording yet. But we are deep into the songwriting part of it."

While that's happening, Metallica is planning its summer tour of Europe. "We haven't done the festival run in Europe in two summers," Ulrich said to Rolling stone. "We had our own festival [Orion] for the past couple of years, but because of scheduling issues and so on we decided to sit this year out." 

During the European tour, Metallica enthusiasts will have total control over the quartet's setlist. "We're calling it 'Metallica by Request,'" Ulrich points out. "Ticket holders can go on a website and vote for any song Metallica ever recorded. There's 145 or something. We play the top 17 vote getters. It's really fun."

A trial run of the "Metallica by Request" proceedings took place in South America in March. Fans chose Metallica classics like "Nothing Else Matters," "Enter Sandman" and "One" while also selecting a few rarities. "To be totally honest with you," Ulrich told RS, "sometimes I wish they would vote on some of the really obscure songs. We love playing crazy stuff."

The voting process is fully transparent, and fans can observe a constantly updated list of winner songs in every city, Rolling Stone reported.

"It looks like when we play Helsinki in May we'll be playing a song called 'The Frayed Ends of Sanity' from '…And Justice For All,'" says Ulrich about the expansive, technically dazzling speed-metal piece. "We're really excited about that. Also, 'St. Anger' was really big in Germany, so we'll get to play some of the songs there. That's going to be really fun. We want to mix it up as much as possible."

According to Rolling Stone, voting ends about one week week prior to , allowing Metallica the opportunity to familiarize itself with any tune fans might ask for. "We've never played 'The Frayed Ends of Sanity' before," the drummer said to the online version of the rock magazine. "We're going to have sit down and spin that one around for an hour or two. We carry a rehearsal room with us wherever we go. Give us an hour and we can learn any song in our catalog. We like to make the setlist real wacky and change it up as much as possible, but in 2014 the fans are picking the songs." 

When Rolling Stone asked whether U.S. audiences will get the chance to attend a "Live by Request" show in the near future, Ulrich responded:

"The main thing this year after Europe is just trying to make a record. Then we can come home and do a bunch of stuff in America. If that's not next year, then in 2016."

Bookmakers Paddy Power has made Metallica joint favorites with Prince to headline the Saturday night of the Glastonbury Festival, NME reported. There's also speculation that the metal titans will headline the Pyramid Stage on June 28, after Glastonbury organizer Emily Eavis said that long-time favorite Prince "wasn't happening this year."

As for Metallica's upcoming studio album, Ulrich said there is no timeline for its release. But he said plenty of progess has been made thus far: "We've been doing this, off and on, for the better part of a year. We're going to do these dates this summer and then really hone down. I'd say that right now, we're in the fourth inning."