The present invention relates to an input system for feeding sheets from a paper web to a high speed mass mailing inserter system. Sheets of paper are separated from the paper web and are fed to a stacking module configured to receive the separated sheets, to stack the sheets, and to individually feed sheets from the stack. The rate of feeding sheets into the stacking module is adjusted as a function of the rate at which individual sheets are fed out of the stack, and as a function of the deviation of the stack height from a pre-selected nominal stack height.