“…A wide variety of techniques have been developed and used for rolling element bearing diagnostics [5], such as envelope analysis which has been extended by [6,7] for variable speed applications, cyclostationary analysis [8,9] which can be seen as a generalisation of envelope analysis [8], regression analysis for variable loads [10], empirical mode decomposition and its extensions [11,12], wavelet analysis [13][14][15][16], the spectral kurtosis [17], the kurtogram and its variants [18,19], the sparsogram [20] and the infogram [21]. Varying rotational speeds complicate the condition monitoring process due to its influence on the properties of the vibration signal [7,22,23] and the rotational speed information of the shaft is also required. The rotational speed information can be difficult and impractical to measure for some machines; this makes tacholess order tracking methods very important for condition monitoring under varying speed conditions [24][25][26][27].…”