The acousto-optical dual frequency shifter DFD-40/80 is a device for shifting the frequency of laser light. It is based on the acousto-optical effect. The DFD-40/80 has two channels driven by the same master clock oscillator, hence they are phase-locked but the frequency and amplitude can be individually adjusted. This makes the DFD-40/80 the ideal source for heterodyne experiments. It consists of the RF-driver electronics and two acousto-optical modulator elements.