Some pieces of gear become legendary because everyone used them. Others become legendary because one person used them, relentlessly, until the sound became inseparable from the player. The original MXR Flanger/Doubler—the M-126 rack unit, a fixture of studios and touring rigs throughout the ’70s and ’80s—belongs mostly to the second category. Yes, it swept through countless studio sessions in its heyday, doing the jet-engine swoosh work flangers are built for.