Unless you're a musician, or particularly observant, you don't notice The Sound Guy.

But if he weren't there, you'd notice his absence. A good soundman balances the volume levels and adjusts the equalization (basically, treble and bass) of every instrument's amplification. He is also responsible for something you don't hear, but which makes a huge difference in the quality of a performance: He adjusts the same things on the monitor mix, or the sound that the musicians hear on stage. A band on stage without good monitors can't hear each other, can't even, often, hear themselves. Which means they can't tell how they're playing. And at that point, you don't want to hear it, either.

A bad soundman - and there are many - does just the opposite. You can hate him without even knowing he exists.

Donny Boyer is a GOOD soundman. He's been around town forever, it seems, and in recent years he's made a whole lot of bands playing Marilyn's On K sound good, including yours truly. Accomodating and knowledgeable, Donny is one of those soundmen who acts like he's a member of the band - and not because he wants the glory. He wants it to sound good.

And now Donny is in some medical trouble, and like most musicians who aren't married to someone with a "real" job, he doesn't have health insurance.

So, tomorrow night (Friday March 13), a handful of the bands who Donny has made sound good over the years are trying to give him a hand back: They're playing a benefit performance, with all of the ticket price of $10 going to help Donny pay medical bills. They've dubbed it Donnaroo.

$10 buys you quite a bit: In addition to members of popular party band Mercy Me, there will be performances by Richard March and Tyler Ragle, Rowdy Kate, Tattooed Love Dogs and Seventy, Boulevard Park and Jay Swanigan, perhaps with a few surprises in store.

I don't know if Donny is doing the sound, but even if he isn't, that's one show that already sounds pretty good. Downbeat is 7 p.m.