The richness of the sound emanating from a stringed musical instrument can be improved by the making it linger for longer. It has traditionally been performed in Sitar and Sarod by modification of boundary conditions while introducing a jawari. We try to understand the effect of the jawari by assuming periodic modulation of boundary conditions of the string in a sonometer and find that the lobe-like effect can indeed be observed as an interference between the frequency-modulated sideband of one mode with the next higher order mode. The contributions from different modes can be added up. The size of the beat signal increases while increasing the depth of modulation.