1. A method of operating an optical motion-capture system in low-light situations, the method including: monitoring at least two contact microphones coupled to the optical motion-capture system, wherein the contact microphones are in contact with a surface; and in response to detection of audio signals generated by contact of an object with the surface determining a surface location by: measuring a time difference of arrival (TDOA) of the audio signals at the contact microphones and mapping a curve, including a plurality of possible surface locations of the contact, using the measured time difference of arrival; analyzing at least one image, captured by a camera of the optical motion-capture system, of the object in contact with the surface; and using the image analysis, selecting one of the plurality of possible surface locations included in the mapped curve, as the surface location of the contact; repeatedly measuring time difference of arrival of the audio signals at the contact microphones responsive to successive contacts of the object with the surface; and analyzing a sequence of images of the successive contacts of the object with the surface; thereby calculating a path of the object traveling across and in contact with the surface.