Comparison of the different noise window size calculations for SPB star HD 48977. Left hand side: periodogram of the original signal (top) and residual signal (bottom) after frequency extraction using a significance criterion of S/N = 5 with the noise calculated in a window of 1 d⁻¹ around the frequency. Right hand side: same periodograms but with the noise calculated in a window of 5 d⁻¹ around the frequency. Green markers indicate singificant frequencies. The coloured solid lines represent the significance levels for each periodogram. The blue dashed line indicates the mean noise level over the whole periodogram.