fill harmonics is a crossword-themed music machine created by Parker Higgins and Natan Last. Parker is an artist and activist. Natan is a policy researcher and writer, whose book on the history of crosswords, Across the Universe, comes out November 2025. Both of them have published crosswords in outlets like The New York Times and The New Yorker.
It was built for inclusion in the 10,000 Drum Machines project.
In block entry mode, clicking creates or removes a block in that square, as well as one in the square that is radially symmetrical with it. Changing the size of the grid changes the radial symmetry.
In text entry mode, the keyboard enters letters in the grid—“fill” in crossword parlance. Entering a period will create a block in the highlighted square as well as its symmetrical counterpart.
In either mode, holding the shift key while changing a block affects the current square but not its symmetrical counterpart.
In grid play mode, the beat steps through each column to determine which sounds are played. Blocks trigger notes whose pitch is based on their row number. Letters in the grid are ignored except for K, S, and H, which trigger kick drum, snare, and hi-hat sounds, respectively.
In word play mode, the beat proceeds polymetrically through every across entry simultaneously. In other words, blocks are now inactive musically, except for defining the length of each pattern. The letters K, S, and H again trigger kicks, snares, and hi-hats, but now, other letters trigger notes based on their row number.