You could always get a second degree after you get the first one.
After I saw a group of high schoolers who wanted to "triple major" I started thinking more about why a "major" is called "major" -- It's major work. It's a full-time amount of work. Triple majors though... quite amusing. I suppose there are geniuses but... it makes me wonder what type of quality it would be to have a triple major in 4 years.
If I were you, I would decide on my career choice and then see how music fits into that.
If you're unsure, you might be able to plan classes that meet many requirement areas -- like a gen ed that covers an area of math, economics, or music. Then you can postpone for-sure decisions.
You could always stretch it out possibly -- Do some of both. I guess that would be the double major idea though. It would just take longer -- if they will let you do that.
On the math/economic side, music will probably look like gold. On the music side, they might wonder what's up with the math/economics thing. If you double majored or did one degree after the other, someone might be wondering where your loyalities lie. And, you might find people consider you less dedicated -- the math/economic people think you're a music person, the music people think your a math/economic person. They might take you less seriously.
The trouble of course will be when to have time and energy to practice. If you're a music major, it's part of the day. If you're something else -- math/ec, or working full-time -- then music has to fit in on top of the rest. Quite challenging.
I have heard of a double major in math and music. Music and chemistry, music and engineering, music and business too. Music and economics is new to me, but who's to say you can't?