 So here's my guitar. Again I pluck my string like that and I get a fairly clear note. Now you can tell when you hear that that is not a perfectly clear note if you hear a perfect sine wave that it sounds very much like a computer-generated signal to you. And the reason for that is like exactly like a computer signal. And the reason for that is that it's very hard to make such a pure single frequency except with a computer. However what we're getting here is we're getting largely that fundamental frequency. So we've got the wavelength being twice the length between here and here with that fundamental frequency and we also have some of the other harmonics as well. So in fact the one where we have it going up and down with an anti-note in the middle we've got that. We've also got some of the first harmonic and the second harmonic and the third harmonic and so forth all on top of each other because all of those have a node down here and a node up there. So I can affect exactly how much of each I get and so I can hear that. If I put my finger on the 12th fret which is halfway I'm going to make it really hard to make the harmonics that have an anti-note there. So I'm just gently putting my finger there. If I pluck that see it's much higher. So I've got low and high and all I've done is I've taken out some of the harmonics all the ones that had an anti-note in the middle. And similarly you can find other harmonics or other ways of emphasizing particular harmonics by playing carefully. And of course the whole point of these frets is to totally change if I press hard then I'm totally changing the length. Instead of being stopped by the nut up here and stopped by the bridge I'm going from the bridge to my fret and I can get different notes. The other thing is of course I have more than one string and these strings you can see they're made of different things and so they have different tensions as well. I can change the tensions with my pegs up here and so with the tension and the kind of string even though I have exactly the same length between these two things and therefore I'm largely getting the same wavelength I'm getting very different frequencies because the speed of the wave is different in those two strings. And so by controlling the speed of the wave in each of my six strings and by controlling which harmonics I get it. And what my total length is I can sing waves although some of us probably shouldn't.