did you read about the difference between compressions and rarefactions? you know, when i strike this thing, the waves--boom, boom-- compressed air comes out. the compressed air, compressed air, compressed air, followed by decompressed air? watch this. now, listen. [laughter] hear that? did you hear the absence of sound? - did you hear--was that neat? - - no. i never do it more than once because i don't wanna trust my luck, but you get the idea. but i'll tell you want. let me get these things so they're a little bit different in frequency and strike them both at the same time. can you hear the throbbing? - that is a result of inter-- - ference. --interference and the phenomenon that's called-- sound. this phenomenon of pulsating-- two sounds pulsating in and out, in and out of phase is called, by the way--scholars? - beats. - beats. all right. i thought you guys were putting me on there for a while. and that's a beat. ted, can we show beats up here? hopefully show beats. so you can see as well as hear what's going on. you can see the wave form. isn't that