Digital signal processing offers considerable advantages over analogue processing for video target extraction in moving target indication (m.t.i.) radars. These advantages include simplicity in the realization of delays, overall stability of the processor and the possibility of multiplexing. However, because of the finite resolution of the arithmetic unit, digital processing introduces a noise component which is a function of the resolution (register length), mode of arithmetic and filter configuration.A theoretical and experimental evaluation of six representative digital filters, suitable for m.t.i. systems, is presented which shows that the simple model of round-off noise is a good approximation of the round-off process and good agreement is obtained between the theoretical and experimental estimates. The model partially fails in the case of recursive filters, because these filters do not satisfy the basic assumptions of the model.