Norman McLaren began experimenting with hand-drawn sound in the late 1930s. The first two films made using this technique are Dots and Loops (both 1940). In Pen Point Percussion (1951), the hand-drawn sound method is explained. Optical sound makes it possible to transform visual information into sounds. McLaren made use of the possibilities offered by this optical sound recording system by drawing serial, graphic patterns on the soundtrack at the edge of the filmstrip with brush and ink. The size of the figures determined the volume, their shape the quality of sound, and the distance between them the pitch. For example, widely separated, large, round shapes produced a loud, mellow and deep sound. Hand-drawn sound also made it possible to perfectly synchronize image and sound.