Abstract: For the purpose of generating oscillations having a plurality of different frequencies, a read-only memory stores a plurality of binary words which are read cyclically. The individual pulse signals supplied by the read-only memory, each such signal representing a succession of corresponding bits read from the read-only memory, are used to control latches and the required oscillations are obtained by filtering pulse signals supplied by the latches. To guard against equipment failure, the read-only memory and latches are duplicated, the pulse signals supplied by the two sets of latches being combined by means of gates before filtering.