A new method is proposed with which it is possible to find a delta-modulated signal of the half sum of two analogue signals through a direct operation on their delta-modulated form. With a direct operation it is also possible to form a delta-modulated signal of the product of an analogue signal by a constant. The resulting modulated signal includes an error which is generally considered negligible. The hardware implementation of the method is both, simple and modular employing only conventional full adders and D-flip-flops. This leads to the possibility of realization of digital filters with straight delta-modulated input and output signals which are not intermediately transformed. Multiplexing for changing coefficients is also possible.