WEBVTT 00:00:07.014 --> 00:00:10.777 Hendrix, Cobain and Page. 00:00:10.777 --> 00:00:12.354 They can all shred, 00:00:12.354 --> 00:00:16.235 but how exactly do the iconic contraptions in their hands 00:00:16.235 --> 00:00:21.694 produce notes, rhythm, melody and music. 00:00:21.694 --> 00:00:26.603 When you pluck a guitar string, you create a vibration called a standing wave. 00:00:26.603 --> 00:00:30.530 Some points on the string, called nodes, don't move at all, 00:00:30.530 --> 00:00:35.180 while other points, anti-nodes, oscillate back and forth. 00:00:35.180 --> 00:00:39.584 The vibration translates through the neck and bridge to the guitar's body, 00:00:39.584 --> 00:00:42.432 where the thin and flexible wood vibrates, 00:00:42.432 --> 00:00:46.625 jostling the surrounding air molecules together and apart. 00:00:46.625 --> 00:00:49.730 These sequential compressions create sound waves, 00:00:49.730 --> 00:00:53.932 and the ones inside the guitar mostly escape through the hole. 00:00:53.932 --> 00:00:56.221 They eventually propagate to your ear, 00:00:56.221 --> 00:00:58.790 which translates them into electrical impulses 00:00:58.790 --> 00:01:01.925 that your brain interprets as sound. 00:01:01.925 --> 00:01:06.482 The pitch of that sound depends on the frequency of the compressions. 00:01:06.482 --> 00:01:10.980 A quickly vibrating string will cause a lot of compressions close together, 00:01:10.980 --> 00:01:12.553 making a high-pitched sound, 00:01:12.553 --> 00:01:16.418 and a slow vibration produces a low-pitched sound. 00:01:16.418 --> 00:01:19.682 Four things affect the frequency of a vibrating string: 00:01:19.682 --> 00:01:24.210 the length, the tension, the density and the thickness. 00:01:24.210 --> 00:01:27.030 Typical guitar strings are all the same length, 00:01:27.030 --> 00:01:31.524 and have similar tension, but vary in thickness and density. 00:01:31.524 --> 00:01:35.991 Thicker strings vibrate more slowly, producing lower notes. 00:01:35.991 --> 00:01:37.992 Each time you pluck a string, 00:01:37.992 --> 00:01:40.747 you actually create several standing waves. 00:01:40.747 --> 00:01:44.981 There's the first fundamental wave, which determines the pitch of the note, 00:01:44.981 --> 00:01:47.528 but there are also waves called overtones, 00:01:47.528 --> 00:01:51.339 whose frequencies are multiples of the first one. 00:01:51.339 --> 00:01:57.055 All these standing waves combine to form a complex wave with a rich sound. 00:01:57.055 --> 00:02:01.448 Changing the way you pluck the string affects which overtones you get. 00:02:01.448 --> 00:02:03.185 If you pluck it near the middle, 00:02:03.185 --> 00:02:07.103 you get mainly the fundamental and the odd multiple overtones, 00:02:07.103 --> 00:02:10.076 which have anti-nodes in the middle of the string. 00:02:10.076 --> 00:02:14.358 If you pluck it near the bridge, you get mainly even multiple overtones 00:02:14.358 --> 00:02:16.410 and a twangier sound. 00:02:16.410 --> 00:02:22.257 The familiar Western scale is based on the overtone series of a vibrating string. 00:02:22.257 --> 00:02:27.261 When we hear one note played with another that has exactly twice its frequency, 00:02:27.261 --> 00:02:29.195 its first overtone, 00:02:29.195 --> 00:02:33.203 they sound so harmonious that we assign them the same letter, 00:02:33.203 --> 00:02:36.930 and define the difference between them as an octave. 00:02:36.930 --> 00:02:40.115 The rest of the scale is squeezed into that octave 00:02:40.115 --> 00:02:42.102 divided into twelve half steps 00:02:42.102 --> 00:02:48.039 whose frequency is each 2^(1/12) higher than the one before. 00:02:48.039 --> 00:02:51.290 That factor determines the fret spacing. 00:02:51.290 --> 00:02:57.115 Each fret divides the string's remaining length by 2^(1/12), 00:02:57.115 --> 00:03:00.581 making the frequencies increase by half steps. 00:03:00.581 --> 00:03:02.601 Fretless instruments, like violins, 00:03:02.601 --> 00:03:06.926 make it easier to produce the infinite frequencies between each note, 00:03:06.926 --> 00:03:10.519 but add to the challenge of playing intune. 00:03:10.519 --> 00:03:12.581 The number of strings and their tuning 00:03:12.581 --> 00:03:15.793 are custom tailored to the chords we like to play 00:03:15.793 --> 00:03:17.980 and the physiology of our hands. 00:03:17.980 --> 00:03:20.863 Guitar shapes and materials can also vary, 00:03:20.863 --> 00:03:24.527 and both change the nature and sound of the vibrations. 00:03:24.527 --> 00:03:27.206 Playing two or more strings at the same time 00:03:27.206 --> 00:03:32.205 allows you to create new wave patterns like chords and other sound effects. 00:03:32.205 --> 00:03:36.279 For example, when you play two notes whose frequencies are close together, 00:03:36.279 --> 00:03:41.605 they add together to create a sound wave whose amplitude rises and falls, 00:03:41.605 --> 00:03:46.500 producing a throbbing effect, which guitarists call the beats. 00:03:46.500 --> 00:03:49.506 And electric guitars give you even more to play with. 00:03:49.506 --> 00:03:51.692 The vibrations still start in the strings, 00:03:51.692 --> 00:03:55.931 but then they're translated into electrical signals by pickups 00:03:55.931 --> 00:03:59.084 and transmitted to speakers that create the sound waves. 00:03:59.084 --> 00:04:00.909 Between the pickups and speakers, 00:04:00.909 --> 00:04:04.675 it's possible to process the wave in various ways, 00:04:04.675 --> 00:04:11.758 to create effects like distortion, overdrive, wah-wah, delay and flanger. 00:04:11.758 --> 00:04:16.139 And lest you think that the physics of music is only useful for entertainment, 00:04:16.139 --> 00:04:18.059 consider this. 00:04:18.059 --> 00:04:20.822 Some physicists think that everything in the universe 00:04:20.822 --> 00:04:26.892 is created by the harmonic series of very tiny, very tense strings. 00:04:26.892 --> 00:04:29.468 So might our entire reality 00:04:29.468 --> 00:04:33.770 be the extended solo of some cosmic Jimi Hendrix? 00:04:33.770 --> 00:04:39.125 Clearly, there's a lot more to strings than meets the ear.