Comparison of the ranges around the value of Δν of the autocorrelation of the periodogram (solid black line) and the corresponding section of the envelope spectrum (dashed red line) for the time series without added noise (top left panel), with S/N = 1 (top right panel), with S/N = 1/4 (bottom left panel), and with S/N = 1/16 (bottom right panel). All data is boxcar smoothed over 0.5 μHz.