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How do capos affect tuning stability?

A capo does one job — clamp strings down at a fret — and somehow manages to generate a shocking number of tuning complaints anyway. Almost all of it comes down to pressure and placement, not some inherent flaw in "clamping a bar onto some strings."

Too much clamping force

A capo that clamps harder than it needs to pulls the string sharp, same as pressing too hard with your finger. Cheap capos, or capos with zero adjustable tension, are frequent offenders. If your guitar sounds noticeably sharp the second you clamp a capo on, that's almost always excess pressure talking, not your guitar betraying you.

Placement and pressure matter

A capo parked too far from the fret (instead of snug right up against it, like your finger would be) increases your odds of pulling strings out of tune or causing buzz. That's also why the same capo can behave differently use to use — you're just not being consistent about where you clamp it.

Some capo designs spread pressure across all six strings more evenly than others. Curved capos matched to your fretboard radius perform more consistently than a flat bar jammed onto a curved board, especially on acoustics with a pronounced radius.

What actually helps

My favorite capo is called the Shubb, because it allows you to vary pressure based on the thickness of the neck at any given point. Also, it’s incredible low profile so it doesn’t get in the way so much.

Use an adjustable-tension capo if you can, dial it to the minimum pressure that kills buzzing, and place it right against the fret instead of floating in the middle of the space behind it. Re-tune (or at least spot-check) after clamping — a capo on top of an already-imperfect setup can expose small intonation issues that were hiding just fine open.