Discovery of DDJ within measured Total Jitter (TJ) begins with a suitably long digital Test Pattern, from which an Acquisition Record is made. A Time Interval Error/Voltage Error Record is made of the Acquisition Record. A Template defines a collection of associated bit value or transitions that are nearby or otherwise related to a bit location of interest, and through the applied test pattern produces a sequence of Data Symbols. The TIE/VLE Record is examined, and a parameter is measured for each Data Symbol as it occurs in the Test Pattern. A regression technique may be use to find coefficients for a DDJ Calculator whose inputs are the Data Symbols and whose output is respective values of DDJ. Subsequent separation of DDJ from TJ is possible because DDJ is correlated with the Data Symbols, while Periodic Jitter (PJ) and Random Jitter (RJ) can be expected to average to near zero over a sufficient number of instances of a given Data Symbol.