So many drones move expectedly from whimper to rapture, modulating and growing at their own leisure, one half-life at a time. As a result, it’s rewarding from the start to experience “Blue” (MP3), off AO’s new two-track set, Endlessly, Sweetly and Slightly, from the netlabel that goes by the name test tube (at monocromatica.com/netlabel). The piece, a 12-plus-minute drone, goes loud and wide quite quickly, as if it is dropping into view suddenly from an overhead cloud. It’s a piercing work, like something U2 guitarist the Edge might play late at night when he’s alone in his studio. “Blue” is paired on Endlessly, Sweetly and Slightly with “Thyme” (MP3), which sounds like a tentative edit of “Blue.” It has the same sort of blissfully muted histrionics, packed into eight minutes, which after “Blue” sounds downright terse. AO is reportedly from Japan, though test tube’s site offers little more in the way of information.