Reliability of two infrared motion capture systems in a music performance setting

Abstract

This paper describes a comparative analysis of tracking quality in two infrared marker-based motion capture systems: one older but high-end (Qualisys, purchased in 2009) and the other newer and mid-range (OptiTrack, purchased in 2019). We recorded performances by a string quartet with both systems simultaneously, using the same frame rate. Our recording set-up included a combination of moving markers (affixed to musicians’ bodies) and stationary markers (affixed to music stands). Higher noise levels were observed in Qualisys recordings of stationary markers than in OptiTrack recordings, as well as a greater spatial range, though OptiTrack recordings had a higher rate of outliers (“spikes” in the signal). In moving markers, increased quantity of motion was associated with increased betweensystem error rates. Both systems showed minimal withintrial drift but a reduction in recording accuracy and precision over the duration of the experiment. Overall, our results show that the older/high-end system (Qualisys) produced slightly lower-quality recordings than the newer/midrange system (OptiTrack). We discuss how our findings may inform researchers’ interpretations of motion capture data, particularly when capturing the types of motion that are important for performing music.