This paper is devoted to the selection of an appropriate model for a time- series. It is a complex problem which requires both types of processing: numerical and symbolic. The idea was to develop a coupled expert system FILTEX which upgrades a professional digital signal processing software package SIG by symbolic knowledge representing expert knowledge used for time-series modeling. FTLTEX blackboard architecture enables opportunistic problem-solving. The appropriateness of using frames for the blackboard implementation is briefly discussed.