The word “timbre” has been rattling around my brain for the past week or so. Z’that ever happen to you? Songs getting stuck up there is more common, but single words get lodged from time to time, bubbling to the surface at seemingly random and uncomfortably frequent moments. I can source the start of this particular affliction to the fact that I’m making my way through This Is Your Brain on Music, by psychologist Daniel J. Levitin. The book starts by defining some familiar terms — “sound,” “melody” and “scale,” to name a few — and my reactions have ranged from “Yeah, that’s pretty much what I thought that meant” to “Whoa. I’ve been using that word inappropriately for years.” Timbre fell somewhere in between.

I had a vague understanding of what it meant, one that’s suffered because it seems to be one of the harder musical concepts to explain, but Levitin’s definition is as clear as it gets: “Timbre (rhymes with amber) distinguishes one instrument from another when both are playing the same written note.” Our brains decode the distinctive frequencies that different instruments produce, so we can tell a guitar from a piano, a saxophone from a flute, etc. Some like to call it sound’s “tonal color.” It’s one reason rock music and classical sound vastly dissimilar, especially when the two are juxtaposed. It’s also the reason Goldrush’s We Don’t Have To Worry EP is one of the most intriguing recordings I’ve heard in a while.

Led by Prabir Mehta, who contributes lead vocals and guitar, Goldrush has a lineup that can best be described (for the purposes of this conversation) as timbre-expansive. The first couple times I saw the band, what stuck out most was Treesa Gold’s outstanding violin playing, in part because, well, it’s outstanding, but also because hers is an instrument you expect to hear in genres like classical, bluegrass and country. And while Goldrush does incorporate these styles to varying degrees (“Tonight I’m Not Going Anywhere” is probably the closest the EP gets to a straightforward country song), you wouldn’t use any one of those names alone to sum up their music — there’s just too much rawk going on, with Mehta’s searing electric guitar and Gregg Brooks’ drumming. Because of the instrument’s strong personality and traditional associations, Gold’s violin feels both familiar and foreign, like that time when you were a kid and you ran into your elementary school teacher at the grocery store.

But violin isn’t the only timbre-forward force in Goldrush, as her husband Matt slings a whopper of a bass sound via his standup. Far from the sedate walking bass that you’d find holding down the low end in a dark and smoky jazz club, songs like “Touch” find him bowing his strings, bringing to the table a timbre that you almost never hear accompanying an electric guitar (thinking about these two next to one another calls to mind those charts that compare the size of whales to people and cars). The bowed double bass is one aspect that comes through even more clearly on We Don’t Have To Worry than it has in the live shows I’ve seen. It’s a daring choice, aggressive-sounding and uncommon, and I would love to see more bands go in this direction.

What’s truly remarkable isn’t that these distinctive sounds are simply there, it’s how well they work together and the way they leave room for each other to be heard. The violin and double bass operate at opposite ends of the tonal spectrum, meaning that there is an amazing, wide-open middle space, where clever lyrics can shine and Mehta’s guitar sounds beautifully crisp, whether he’s playing chords or single notes. This much space is hard to find in rock music, and songs like “God” and “Atomic Bomb Blue” show that you can generate boatloads of momentum and energy without packing the mix with every instrument imaginable.

Of the EP’s 6 tunes, my favorite timbre-spotting one has to be “Touch.” Have a listen below to experience a one-of-a-kind blend of textures, and click here to buy We Don’t Have To Worry on iTunes.

Goldrush — “Touch” [Soundcloud/iTunes]