The flow field generated by the diffraction of a shock wave from the open end of a shock tube is studied using the Particle Image Velocimetry (PJV). In particular, we examine the evolution of the compressible vortex ring as it travels from the tube exit. The shock Mach number was varied from about 1. 2 to 1. 5. The vorticity field associated with the vortex ring and its core are calculated from the measured velocity field. During initial formation and propagation, a jet like flow exists behind the vortex ring. The vortex ring detachment from the tailing jet, commonly referred to" pinch-off" is described in terms of a non-dimensional parameter. Far field microphone measurements show that the pressure signal consists of two pressure pulses of significant intensity corresponding to the spherically expanding shock wave and the incipient formation of the vortex ring at the tube exit Vortex generated sound is also identified in the signal with high frequency pressure fluctuations.