  We address the long standing problem of the origin of acoustic emission
commonly observed during plastic deformation. We propose a frame-work to deal
with the widely separated time scales of collective dislocation dynamics and
elastic degrees of freedom to explain the nature of acoustic emission observed
during the Portevin-Le Chatelier effect. The Ananthakrishna model is used as it
explains most generic features of the phenomenon. Our results show that while
acoustic emission bursts correlated with stress drops are well separated for
the type C serrations, these bursts merge to form nearly continuous acoustic
signals with overriding bursts for the propagating type A bands.
