Commercial tools for measurement and analysis of vibration signals have traditionally been very expensive. In the last decade, however, multi-channel measurement systems have become relatively inexpensive. The analysis functionality in most inexpensive instruments is limited. Therefore, many companies are using alternatives for post processing of measurement results. MATLAB is a platform that is popular for this purpose and which offers many advantages over dedicated menu driven systems. The open functions in MATLAB assure flexibility and the possibility to modify functions for specific needs. In this paper, the presentation and numerical applications of an interactive and comparative digital signal processing software developed in MATLAB by writers is described. The software is named as SignalCAD. For developing SignalCAD, about 120 new functions have been created and are used with MATLAB Signal Processing Toolbox functions. The SignalCAD program is a powerful tool that deals with processing raw measured data obtained from forced and ambient vibration testing of engineering structures. SignalCAD offers extensive functionalities for the visualization and processing of the measurement data and the determination and visualization of the spectral analysis results. The program disposes of a graphical user interface, which what makes it very intuitive and easy to handle. The most common spectral analysis techniques have been used in SignalCAD. The possibilities of the program are demonstrated with a three dimensional steel frame model vibration test and some results are compared with commercial PULSE signal analysis software.