The technology of depth cameras has made designing gesture-based augmentation for existing instruments inexpensive. We explored the use of this technology to augment keyboard performance with 3-D continuous gesture controls. In a user study, we compared the control of one or two continuous parameters using gestures versus the traditional control using pitch and modulation wheels. We found that the choice of mapping depends on the choice of synthesis parameter in use, and that the gesture control under suitable mappings can outperform pitch-wheel performance when two parameters are controlled simultaneously.