A microphone and a speaker in the same air. The tone leaves the cone, enters the mic, comes back louder, comes back again. Below gain one every echo returns smaller; cross the cinnabar ring and the loop catches its own tail — the howl chooses the pitch the delay loves most and holds it with no hand at all.
Move the microphone (pointer, drag, or the slider) toward the speaker to raise the gain. Clap puts a sound into the loop; still cuts it. Inside the ring, the loop lights itself.
the loop is open — every echo returns smaller.