The new semi-active variable stiffness tuned mass damper (SAIVS-TMD) system, developed by the authors, is capable of continuously varying its stiffness and retuning its frequency in real time. The tuned mass damper (TMD) system can only be tuned to a fixed frequency, which is the first mode frequency of the building. The SAIVS-TMD system is robust to changes in building stiffness and damping.The short time Fourier transform (STFT) is the most widely used method for studying non-stationary signals. The basic idea of short time Fourier transform is to break up the signal into small time segments and Fourier analyze each time segment to ascertain the frequencies that exist in it. For each different time a different spectrum is obtained and the totality of these spectra is the time–frequency distribution. The new idea proposed in this study is to use STFT to identify the dominant frequency of response, and track its variation as a function of time to retune the SAIVS-TMD.The effectiveness of a SAIVS-TMD controlled by the new STFT algorithm for response reduction of a wind excited tall building is investigated in this study. An analytical model of the tall building with time varying stiffness of SAIVS-TMD is developed. The frequency tuning of the SAIVS-TMD is achieved by a new time frequency algorithm based on STFT. It is shown that the SAIVS-TMD can reduce the structural response, when compared to the uncontrolled case and the case with TMD. SAIVS-TMD is particularly effective in reducing the response when the building stiffness changes; the TMD loses its effectiveness under building stiffness variations. The response reductions due to an active tuned mass damper can also be achieved by SAIVS-TMD—with an order of magnitude less power consumption—with the STFT algorithm.