Digital Filter Design in electronics/electrical engineering involves complicated mathematical equations and dynamic waveform variations. It is a consensus among educators that using simulation tools helps improve students' learning experience. However, very few studies provided scientific evidence to support this notion. In a Digital Signal Processing (DSP) course, students received three different types of instructional messages (online text only, text plus static illustrations, and text plus simulations). An experimental study was designed to investigate potential main effects of the independent variables: instructional message on students' post-test scores. Multivariate Analysis of Variance (MANOVA) was performed to analyze collected data. Results from 132 students showed significant differences among students in a post-test learning achievement (F(2,130)=13.590, p<.05). A follow-up test indicated that students who used a simulation tool performed significant better scores on their learning achievement test than those who only received online text materials and than those who received text plus static illustrations (p<.05).