Fourier analysis with data windows (Tukey tapers). Compare standard series with a series with a taper (select Fejer, Lanczos, Hamming...) for a given number of terms of the series expansion. Several signals are available: square wave, rectified sine wave, full rectified sine wave, linear ramp-sawtooth, etc. http://www2.ee.ufpe.br/codec/tapers.html
Download apps, toolboxes, and other File Exchange content using Add-On Explorer in MATLAB.