1. A smoothing method for suppressing fluctuating artifacts during noise reduction, which comprises the following steps: providing short-term spectra for a series of signal frames, wherein a first forward transformation, using a signal from the time domain as input, generates the short-term spectra; transforming each short-term spectrum of the short-term spectra by a second forward transformation, the second forward transformation describing the short-term spectrum using transformation coefficients which describe the short-term spectrum divided into coarse structures and fine structures thereof; smoothing the transformation coefficients with the same coefficient indices in each case by combining at least two successive transformed short-term spectra, wherein different time constants are used for smoothing the respective transformation coefficients, wherein the time constants are chosen such that transformation coefficients describing spectral structures of fluctuating spectral magnitudes and of artifacts of noise reduction algorithms are smoothed to a greater extent than transformation coefficients typically describing spectral structures of speech; and transforming the smoothed transformation coefficients into smoothed short-term spectra by backward transformation.