The power spectrum
is the Fourier transform of the effective learning window *W*_{0}, which in turn is the convolution of the learning window *W* and the EPSP *ε*. The figure shows the learning windows required for SFA for three different EPSP durations (*τ* = 4, 40, 400 ms). The maximal input frequency *ν*_{max} was 1 / (40 ms) in all plots.