This is a circuit that uses a dekatron as an analog readout. Ironic, since a dekatron is a digital (though ancient) device. Its rigged with a microphone input to sample audio and convert it to a glowing arc. In reality, only one dot, of the dekatron's 30, is glowing at any one time. The AVR Tiny44 circuit steps the dot, back and forth, at a high rate, to form the glowing arc.