00:00Hendrix, Cobain, and Page, they can all shred.
00:12But how exactly do the iconic contraptions in their hands
00:16produce notes, rhythm, melody, and music?
00:21When you pluck a guitar string,
00:23you create a vibration called a standing wave.
00:26Some points on the string, called nodes, don't move at all,
00:30while other points, anti-nodes, oscillate back and forth.
00:34The vibration translates through the neck and bridge to the guitar's body,
00:39where the thin and flexible wood vibrates,
00:42jostling the surrounding air molecules together and apart.
00:46These sequential compressions create sound waves,
00:49and the ones inside the guitar mostly escape through the hole.
00:53They eventually propagate to your ear,
00:56which translates them into electrical impulses that your brain interprets as sound.
01:01The pitch of that sound depends on the frequency of the compressions.
01:06A quickly vibrating string will cause a lot of compressions close together,
01:10making a high-pitched sound,
01:12and a slow vibration produces a low-pitched sound.
01:16Four things affect the frequency of a vibrating string—
01:19the length, the tension, the density, and the thickness.
01:24Typical guitar strings are all the same length and have similar tension,
01:28but vary in thickness and density.
01:31Thicker strings vibrate more slowly, producing lower notes.
01:35Each time you pluck a string, you actually create several standing waves.
01:40There's the first fundamental wave, which determines the pitch of the note,
01:44but there are also waves called overtones,
01:47whose frequencies are multiples of the first one.
01:50All these standing waves combine to form a complex wave with a rich sound.
01:56Changing the way you pluck the string affects which overtones you get.
02:01If you pluck it near the middle, you get mainly the fundamental and the odd multiple overtones,
02:06which have anti-nodes in the middle of the string.
02:09If you pluck it near the bridge, you get mainly even multiple overtones and a twangier sound.
02:15The familiar Western scale is based on the overtone series of a vibrating string.
02:21When we hear one note played with another that has exactly twice its frequency,
02:26its first overtone, they sound so harmonious that we assign them the same letter
02:32and define the difference between them as an octave.
02:37The rest of the scale is squeezed into that octave,
02:40divided into 12 half steps whose frequency is each 2 to the 1 12th power
02:46higher than the one before it.
02:48That factor determines the fret spacing.
02:51Each fret divides the string's remaining length by 2 to the 1 12th power,
02:57making the frequencies increase by half steps.
03:00Fretless instruments like violins make it easier to produce the infinite frequencies between each note,
03:06but add to the challenge of playing in tune.
03:10The number of strings and their tuning are custom tailored to the chords we like to play,
03:15and the physiology of our hands.
03:17Guitar shapes and materials can also vary,
03:20and both change the nature and sound of the vibrations.
03:24Playing two or more strings at the same time allows you to create new wave patterns,
03:29like chords and other sound effects.
03:32For example, when you play two notes whose frequencies are close together,
03:36they add together to create a sound wave whose amplitude rises and falls,
03:41producing a throbbing effect, which guitarists call the beats.
03:45And electric guitars give you even more to play with.
03:49The vibrations still start in the strings,
03:51but then they're translated into electrical signals by pickups,
03:55and transmitted to speakers that create the sound waves.
03:58Between pickups and speakers, it's possible to process the wave in various ways,
04:04to create effects like distortion, overdrive, wah-wah, delay, and flanger.
04:11And lest you think that the physics of music is only useful for entertainment,
04:16consider this.
04:17Some physicists think that everything in the universe
04:20is created by the harmonic series of very tiny, very tense strings.
04:27So might our entire reality be the extended solo of some cosmic Jimi Hendrix?
04:33Clearly, there's a lot more to strings than meets the, uh, ear.
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