How Music Gets Onto A Record
How do grooves in a vinyl record translate into music? The magical collaboration between math, technology, and biology.
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You’ve probably wondered the same thing: how does music turn into grooves on a record? And how do grooves get translated back into a song with words, voices, instruments and harmonies? It really feels like magic. Yet humans figured it out before we even had computers!
I have been interested in this question forever and have never found a satisfying explanation of it online. So I spent the past Christmas break researching the physics of sound, and making a whole video series about math & music. But how does sound get recorded?
Behold, and listen to the first sound recording in history! (Source)
This sound was recorded on April 9, 1860. It’s meant to be the French song Au Clair De La Lune. The faint voice you hear is that of a French bookseller named Edouard-Leon Scott de Martinville, who invented the phonautograph.
The Phonautograph
The phonautograph was the earliest sound recording machine that we know of. It was made of 4 main parts:
A big box or barrel that the user would shout into
A thin membrane on the other end which vibrates from the noise
A needle attached to the membrane which shakes from the vibrations
A sheet of glass covered in soot that the shaking needle could write on
You know how you can feel vibrations standing next to a loud speaker? Those are the vibrations that the needle (which was actually a pig’s hair bristle) would try to capture.
The problem was that the needle would just shake in the same spot unless you could figure out a way to slowly move the sheet of glass underneath it, thereby recording the vibrations over time. So Scott updated it with a cylinder that you crank by hand while the needle vibrates. The result was a physical signature of the sound: the waveform!
You’ve seen waveforms before if you’ve ever tried making a voice note. You’ll notice the waveform is high when you’re loud, and low when you’re singing more softly. But if you zoom in, you’ll find there are hundreds of oscillations per second! Here’s me singing On The Radio and then zooming in to show you exactly what I mean:
What do those waves actually represent?
Sound comes from vibrations of air pressure: the air oscillates between high air pressure and low air pressure. When it reaches our ears, our eardrum vibrates hundreds of times per second too. When the vibrations are very fast, we perceive higher pitches, like Mariah Carey’s whistle notes. When the vibrations are slower, we perceive that as a lower pitch, like a deep bass voice.
In theory, Scott’s needle would vibrate slower for low-frequency notes, and faster in response to high-frequency notes, thus drawing the physical waveform of a melody. Which is exactly what he got!
Except he had no way of playing it back. The idea of converting sound into a physical, permanent record was already completely new! Seismographs do the same thing with earthquakes, and nobody expects them to play the earthquake back to us.
So what did he intend to do with these waveform drawings if he couldn’t play them back? The guy was actually a printer and bookseller. He was trying to invent a way to photograph words, like an automatic stenographer! He thought the phonautograph might one day be an alternative to handwriting, like the very first speech-to-text machine. Look at his experiments comparing waveforms to written signatures:
Scott may have been the first person to record sound, but he was not the first person to play back a sound recording.
That audio file at the beginning? We only figured out how to listen to it in 2008!
In Scott’s day, the only way to listen to music was to hear it played live. Most people alive during the 1800s had never heard a song by Beethoven or Mozart. Even if you were a rich aristocrat, if you wanted to listen to Beethoven’s Ode To Joy, you only had maybe 3 chances in your entire life. Once in Vienna in 1824, then London in 1825, and New York in 1846. Now you can listen to it as much as you like.
It’s hard to imagine a world without recorded sound! When was the last time any of us listened to music at a live performance without the aid of technology to record it?
So how did we go from sound recorded as squiggles on a piece of paper to recordings that could be played back?
The Paleophone
The logical leap that Scott failed to make was that if you made the needle trace the squiggles and recreate the vibrations, it would reproduce the sound that created them. The first person to make this connection was Charles Cros, a French poet. In 1877, he theorized a machine called a paleophone, which could trace the squiggly soundwaves created by a phonautograph and play the vibrations back, thereby reproducing the original sound. Except he didn’t have the resources to build a prototype. But Thomas Edison did.
The Phonograph
Thomas Edison was the first person to build a machine that could reproduce recorded sounds. And he did it by accident.
What he was actually working on was a machine that could read Morse code.
Morse code translates each letter of the alphabet into a sequence of dots and dashes, which can be transmitted through pulses of electricity in a wire, like flicking a light switch on and off. Those sporadic pulses of electricity are then translated back into letters of the alphabet by an operator listening in real time.
In 1877, Thomas Edison built a machine that recorded Morse code messages embossed into a strip of paper as a permanent record. He then built a separate machine which read the indentations on the paper and played back the same sequence of dots and dashes out loud.
As part of a test, Edison ramped up the speed of his machine until the sequence of dots and dashes were played back so quickly that no one could recognize the Morse code anymore, just a bunch of fast-paced pulses. What he heard was a humming, musical sound.
Eureka!
Now let’s put together the three big ideas we’ve learned:
Edouard-Leon Scott de Martinville discovered that sound can create jittery waves on a piece of paper.
Charles Cros theorized that waves can be traced by a needle to reproduce a sound.
Thomas Edison built a machine that read waves indented on a paper and made a musical hum.
What we have are the basic mechanics of a record player. Here’s what Edison’s chief assistant Charles Batchelor had to say as soon as they realized what they had created:
We fixed the instrument onto a table and I put in a strip of paper and adjusted the needle point until it just pressed lightly on the paper. Mr. Edison sat down and, putting his mouth to the mouthpiece, delivered one of our favorite stereotyped sentences used in experimenting on the telephone “Mary had a little lamb” whilst I pulled the paper through. We looked at the strip and noticed the irregular marks, then we put it in again and I pulled it through as nearly at the same speed as I had pulled it in the first place and we got “ary ad elll am” – something that was not fine talking, but the shape of it was there. We all let out a yell of satisfaction and shook hands all round.
Now let’s listen to a recording created on Edison’s phonograph in 1888, which took over 4000 voices to record. (Source)
The Math Of A Sound Wave
Why does Edison’s machine work (albeit very faintly)? How do indentations on a piece of paper correspond to sound?
It’s the same way that dots and dashes in Morse code correspond to words and sentences!
Waveforms are the Morse code of nature. Sound is a vibration of air pressure, and each unique sound has a distinct sequence of pulses, just like how each letter of the alphabet takes a distinct sequence of dots and dashes in Morse code. Our ears are the operators translating the sequence of pulses into information.
Let me explain with an example.
Here’s what a pure 440 Hz sine wave looks like and sounds like. There are exactly 440 vibrations per second:
If we go to a piano, we can match this note by playing an A4 (the A above middle C). We can also match this note on a flute, or even just by singing with your voice. But they’ll all sound different. And the waveforms look different too:
The waveform of a sound doesn’t just record the frequency (how high or low the pitch is). It also records all the harmonics coming from that sound.
Watch this video I made explaining it:
The reason different instruments sound different is because they produce harmonics at relatively different volumes. Here’s the spectrum of harmonics that occur after playing the exact same note on a piano, a flute, and then my voice:
When you listen to a single note, you’re also hearing its harmonics! And when we record the waveform coming from a flute, piano, or singer, we’re also recording the harmonics that make those instruments sound unique.
When a waveform is stamped into the grooves of a record and gets traced by a needle, the reason we’re able to make out words, voices, and instruments is because our ears are magnificent pattern recognition machines.
As technology advanced past Edison’s phonograph, we learned how to capture more sensitive, complicated waveforms. At some point, we switched from cylinders over to flat vinyl records, and then we switched to digitally recording waveforms using numbers on a computer. That’s a whole other blog post!
The next time you listen to music, think about all the layers of history, mathematics, technology, and biology that have to collaborate so that you can press play and start feeling those sound waves hit your eardrum. Think of all the frequencies stored in a single note, all the notes played by a single instrument, and all the instruments in a single song. Every recording is a masterpiece.
If you’re interested in watching the video series I made about math and music, here are the videos!
The Fourier transform (how we dissect waveforms into individual frequencies)
The perfect fifth (how harmonies work)
The pentatonic scale (why the black keys of a piano sound “Chinese”)
Sources and more info: