The use of creaky voice, or vocal fry in speech has been extensively studied for its linguistic, paralinguistic, and sociolinguistic functions. However, much of the existing research on this topic is fragmented and often contradictory. In order to gain a deeper understanding of the communicative functions of creaky voice, we propose the use of comparative perceptual studies with natural sounding speech synthesis. We present a neural speech synthesizer that produces highly naturalsounding synthetic speech with controllable creaky voice styles. In a subjective listening experiment, speech experts were able to identify the presence and intensity of creaky voice produced by the synthesizer. Our results suggest that neural speech synthesis can be a valuable tool in furthering our understanding of the communicative functions of creaky voice.