Paul McCartney is "looking at some lyric ideas" for a studio follow-up to 2013's New as his latest round of live dates continues. "I can write all over the place," he told Rolling Stone. "I've got a lot of ideas on the go."

New, which followed McCartney's marriage to third wife Nancy Shevell, was marked by a return to upbeat music making – a sharp departure from darker efforts like 2005's Chaos and Creation in the Backyard. McCartney suggested his next album might be a more a balanced blend of both moods.

"Music is like a psychiatrist," he said. "You can tell your guitar things that you can't tell people. And it will answer you with things people can't tell you. But there's a value to sad songs. Something bad happens, you don't want to repress it. So you unload it on yourself, with a guitar. I've got a couple on my next album which are a bit – [makes a shocked look]. But it works, because with songs, you can do that."

There isn't any timeline yet for the album. Whenever it arrives, however, McCartney has resigned himself to a current climate in which physical sales will never match the hey day of his old band Wings, much less the Beatles.

"I'll put out my next album, but I won't think I'm gonna sell a lot," he said. "I'm putting it out because I have songs that I like. And I will do my best job. The scene has changed, but it doesn't disturb me, because I had the best of it – selling 100,000 a day on something like 'Mull of Kintyre.' I've had the joy of that. If I don't have it now, it's not just about me. All of my contemporaries, who are still pretty cool, don't have it, because things have moved on. And you know what? We had it. And it was great."

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