In setting threshold to determine the arrival time in mechanical vibration signals which are collected by sensors and contain noise, five methods based on MATLAB have been proposed. Direct observation of the figure, powering operation to data, variance theory, reverse search and MATLAB programming has been used. Each method’s merits and demerits will be discussed so that it can be varied according to different situations. Consistent results have been achieved by those methods. MATLAB code has also been presented for better understanding of the algorithm and reproduction. After this analysis, a systematic way of setting threshold (determining the arrival time) has been formed and these methods could actually be used in all similar data separation.