When two sounds are played at the same loudness, pitch, and duration, what sets them apart are their timbres. This study documents the design and implementation of the Timbre Explorer, a synthesizer interface based on efforts to dimensionalize this perceptual concept. The resulting prototype controls four perceptually salient dimensions of timbre in real-time: attack time, brightness, spectral flux, and spectral density. A graphical user interface supports user understanding with live visualizations of the effects of each dimension. The applications of this interface are three-fold; further perceptual timbre studies, usage as a practical shortcut for synthesizers, and educating users about the frequency domain, sound synthesis, and the concept of timbre. The project has since been expanded to a standalone version independent of a computer and a purely online web-audio version.