a system and method for determining from an arbitrary signal a characteristic signature or other characterizing feature and for distinguishing signals associated with one specific condition from those associated with one or more other conditions . the system uses dictionaries of plural sets of basis signal elements , for example , combinations of orthogonal bases with different characteristics . it optimizes the fit of part of an arbitrary signal to one or more elements of one class of basis signals from a dictionary and iteratively fits the remainder of the arbitrary signal to elements of an optimal class of basis signals , either the original or a different class depending on the goodness of match between the residual part of the signal and the subsequent basis class .