Bridge that moves about quietly close to Soho (4)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

CA (abbreviation for Latin circa = about = approximately) + P (p, in musical notation = abbreviation for Italian piano = quietly) + last letter (close) of [soh] O . Short for Italian capotasto : a movable device that can be attached across the neck of a guitar in different positions, to change the pitch of all the strings at once. It’s not the same as the “bridge” of a guitar, which supports the strings, but it spans the gaps between the strings like a bridge.