This paper presents an experiment testing which sound parameters, in a survival horror game context, most warrant further investigation as a means to control the level of fear in such games. The experiment is part of a long-term study ultimately designed to support the development of a biofeedback procedural audio engine for computer games. By this means, it is hoped to provide an enhanced gaming experience whereby sound synthesis and audio processing is conducted in real-time according to the player's affect responses and emotional state. Results indicate that coarse manipulation of audio parameters has the potential to influence the intensity of the player's fear response whilst playing a survival horror game. Evidence is also presented that supports the integration of event logging and realtime participant vocal response into an experimental design to gather unbiased, quantitative data that can be associated with qualitative emotional response.