Four-note chords — tetrads — connected by the smallest possible moves. Set the key center and scale, choose the bottom note of the starting tetrad, then pick a cycle and press play: at every step the voices that must move slide one scale step and recolor as their function changes, while the others hold still. The same pitches light up on the neck and on the keyboard. Click a string name on the neck to choose which four strings carry the voicing.