Fourier harmonics in the form of Young’s interference fringes, may be added together by successive exposures on a photographic plate. In the synthesizer to be described, an optical system using a Wollaston prism generates the Young’s fringes with adjustable spacing, position, and intensity. This provides the necessary variations of frequency, phase, and amplitude of the harmonics simply by setting dials. The apparatus is potentially capable of adding a few hundred harmonics, as can be shown by preliminary experimental results. Spherical aberration in the optical system merely remains to be corrected.