An Internet-based online laboratory for educational investigations of both FIR and IIR digital filters is presented. The online laboratory includes facilities for simulations of one- and two-dimensional, separable and non-separable filters. The software is written as a Java applet that can be accessed over the Internet. Object oriented programming allows users to construct and simulate a variety of systems. The system offers users a library of objects for many operations, including one- and two-dimensional input generation, as well as one- and two-dimensional IIR and FIR filtering. Moreover, J-DSP contains objects for processing of sound files. The program uses a graphical user interface that is easy to learn and provides a visualization of the system and signal flow. The software is currently being used at Arizona State University to support an online software laboratory for senior and first-year graduate level courses on digital signal processing. Additionally, the paper summarizes experiences in a classroom setting, and discusses new laboratory exercises which were developed with the simulation tool.