Abstract: The present invention relates to a method and a device for compensating undesirable side bands in nuclear magnetic resonance spectrometers. The frequency (.omega..sub.m) and the phase of rotation of the sample (10) are detected by means of a light sensor (12) and supplied to a compensation generator (18). The latter generates modulation signals (44 and 43) for modulating the amplitude and the phase of the detected nuclear magnetic signal of the sample, using an amplitude modulator (13) and a phase modulator (14), the modulation frequency being equal to an integral multiple, including the simple value, of the frequency of rotation (.omega..sub.m) of the sample. The additional frequency components heterodyne with the side bands provoked by the rotation of the sample (10) in the static magnetic field (B.sub.O), whereby the said side bands are eliminated.