A signal generator is described that provides two oscillations of “almost” incommensurate frequencies, along with their sum and difference frequency. There is no phase drift between the outputs since all signals are generated from a single master clock. The concept is based on Fibonacci approximands to the golden mean. Technical implementation requires ordinary digital frequency dividers and a single phase-locked-loop frequency multiplier. Applications are measurements of weak nonlinearities in “almost linear” transfer functions. ©1997 American Institute of Physics.