A new evenness evaluation method was developed in order to analyze short-termirregularity of spun yarns. The diameters of a spun yarn were measured at every 2 mm segments by using the G-580ulcorner tester produced by Zweigle Ltd. Simultaneously, the analog signals from the instrument were captured and then converted into the digital signals with the digital signal processing system specially developed for this study by using Lab-PC+ulcorner. In order to analyze the periodicity of the signals, Short-Time Fourier Transform(STFT) and Discrete Fourier Transform(DFT) were applied. The results from STFT were compared with those from DFT. It was found that STFT was more effective in analyzing the short-term irregularity of spun yarns than DFT and in detecting frequency content changes with time.