A fundamental aspect of music is its ability to express emotions. To develop and extend the potential of music in computer entertainment, a deeper understanding of music's emotional aspects is essential. An experiment was designed to explore the suitability of a specially designed interface (REMUPP) as a means to investigate how musical parameters can contribute to expressing the emotions of 'happiness' and 'sadness'. In the experiment, a number of subjects listened to music examples where the musical performance was governed by a set of musical parameters that were controlled by the subject. The subjects adjusted the parameter settings to best express a given emotion. These settings were recorded and analyzed. The experiment verifies the REMUPP tool as a valid means for the investigation of musical parameters and emotion. Issues of importance for realization of music in the computer entertainment context are also addressed.