Frequency changing over time. A: A time series with a changing frequency, simulated from with ω1 = 0.25 rad/s. B: The posterior probability distribution for the estimated frequency using a local BSA, BSAL, with a window size of 20. The distribution is so narrow that it resembles a sharp line in the plot. C: The wavelet power spectrum using a Morlet mother wavelet , with a lower cut-off at ω = 0.1 rad/s in the spectrum. The wavelet reproduces the correct result but with a broad distribution of frequencies. D: The STFT result with a window size of 50, and an overlap of 40, is similar to the wavelet results.