Speech sinusoidal modeling has been successfully applied to a broad range of speech analysis, synthesis and modification tasks. At most, it reproduces a high quality speech, however for speech transients (e.g. plosives, glottal stops) it suffers from reduced fidelity due to lack of intra-frame modeling of irregularities. Various extensions had been proposed for the stationary sinusoidal model to cope with this problem. One of simple and well-known in the art approaches is incorporating of an intra-frame magnitude envelope into the sinusoidal model. It used to be done by iterative analysis-by-synthesis procedure. In this paper we derive an optimal analytic solution for this problem. We will show that this solution yields significantly better model fit than the known-in-the-art analysis-by-synthesis approach. © 2013 IEEE.