Φ THE PULSE

Two tones a few hertz apart drift in and out of step, and you hear the difference as a pulse. Both sit near 210.1 Hz, the pitch of the (3,5) pattern on the plate.

off

With headphones, each ear hears its own tone, and the pulse forms in your hearing rather than in the air. On speakers, choose "speakers": one tone switches on and off, and "circle around me" moves it slowly from side to side. The picture moves slowly and never flashes at the pulse rate. This is a listening experiment, not a therapy. Keep the volume low, and stop if it isn't pleasant.