The instantaneous pressure distribution around the azimuth of a cylinder undergoing forced oscillations is measured using an array of 18 miniature microphones. The microphones were placed at the midspan of the cylinder with 20 degree increments between each sensor. The Reynolds number for the experiments was 13,800. The cylinder is driven in a sinusoidal motion by a printed circuit motor with an amplitude A/D = 0.18 and with bare winding numbers (Ω = f/fn) of 0 ≤ Ω ≤ 1.1. Regions of lock-in between the cylinder motion and the lift coefficient were observed at dressed winding numbers of ω = 2:3, 1:2 and 1:1. Phase diagrams show two distinctly different synchronization mechanisms, one fundamental and the other a subharmonic type, which supports the findings of Ongoren and Rockwell (1988).