Sometime in 2001, I was at a party in San Francisco when someone introduced me to Jason Hammel, one-half of the keyboards-drums duo Mates of State, which had recently moved to the Bay Area and was gathering buzz on the local scene. He told me that he and his bandmate, Kori Gardner, were about to get married. He seemed like such a nice guy and so genuinely happy that I felt caught up in his good fortune. I went to see the band soon after that and watched this young couple, obviously in love, harmonizing together on songs that were almost comically upbeat and exuberant. Much of the audience seemed to be going through what I went through at the party. They were caught up in Hammel and Gardner’s happiness.

More than ten years later, Hammel and Gardner are indie-rock veterans. They moved to Connecticut long ago, and they’re still married, and when you follow Mates of State, you’re still caught up in their relationship. For years, Gardner wrote the blog Band on the Diaper Run on the parenting site Babble.com, where she would document the joys and absurdities of touring around the world with the couple’s two little girls. Gardner now runs a business that provides nannies for the children of touring artists.

But from a listener’s point of view, the biggest change can be heard in the music. Compare 2011’s Mountaintops to the band’s early releases and you’ll find that both Hammel and Gardner’s voices sound deeper, their songwriting much richer. Final track “Mistakes” has them harmonizing on the line “I need you,” and maybe they’re singing about themselves, maybe not. I don’t know. I’m caught up in the music alone.

MATES OF STATE: House of Blues, Friday, July 6, 8 p.m. 619-299-2583. $16 advance/ $18 door.