The definition of Crest Factor is: true peak value of time waveform / rms value of time waveform.
At the beginning stage of bearing damage, the bearing's inner race, outter race, rolling elements and the cage may
generate periodical spike signals (numerator). That would cause the Crest Factor value to increase. However,
as the damage gets worse, the rms value (denominator) will increase as well, and that would cause Crest Factor value
to decrease. Because of this drawback, the true peak value would be a better parameter for monitoring the bearing