A method of processing signal data comprises receiving signal data, calculating a first k-th moment from the signal data based on a first number of samples N1, calculating a second k-th moment from the signal data based on a second number of samples N2, the first number N1 being different than the second number N2, calculating a combined error, the combined error being a function of the first and second k-th moments, classifying a data region of the signal data as flat if the combined error is below or equal to a threshold curve in the data region, and classifying a data region of the signal data as non-flat if the combined error is higher than the threshold curve in the data region.