Each of the twelve black celluloid disks has a pattern of slits or holes cut into it in concentric circles, representing seven octaves of a note, e.g. all Cs. Since the instrument is fitted with twenty-four disks, two rows of twelve, each encoded with different wave patterns, it is possible to produce harsher as well as softer tones. The graphic representation of the waveform is read by small lamps and selenium cells, and the signal is amplified. The brightness of the light sources is regulated by variable resistors, one for each key, with the effect that volume is controlled by the degree of pressure applied to the key.