MetaSynth is a sound design and music production tool developed by U&I Software for the Macintosh operating system, that allows the creation of sound from images. It was most notably used on The Matrix (for bullet-speed special effects), but has also appeared on the electronic artist Aphex Twin's single "Windowlicker" in the title track and the B-side track "ÃÂM<sub>i</sub><sup>âÂÂ1</sup> = −ñã<sub>n=1</sub><sup>N</sup>D<sub>i</sub>[n][ã<sub>jâÂÂC[i]</sub>F<sub>ji</sub>[n − 1] + Fext<sub>i</sub>[n<sup>âÂÂ1</sup>]]".