The time-scale of a digital signal is efficiently modified. A system suitable for embedded or stand-alone processing includes a module that can transform the time-scale of the signal according to a user's preference. An improved method for time-scale modification is based on envelope-matching but introduces a new function that is very fast to compute, the use of which avoids the computation of correlation coefficients where they are not needed. The invention is demonstrably faster than other methods related to SOLA (synchronized-overlap-and-add) with envelope matching, yet with no sacrifice in quality of the processed output.