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The record groove

The only code on this site that needs no key, no chart and nobody to teach you.

the air moves

The shape is the sound

Nobody agreed what a wiggle means. The groove in a record is the same shape the air made when the sound happened, cut into plastic. A needle dragged along it wiggles the same way, and the air wiggles again.

That is why you can play a record with a sewing needle and a paper cone, with no electricity and nobody to teach you the code. There is no code. There is a copy of the shape.

Build one with a needle and a paper cone

Two ways to keep a sound

By resemblance
The groove, a tape, a sundial's shadow, a footprint. The record is the same shape as the thing. Anyone who works out the relationship can read it, and a scratch gives you a crackle in the middle of the music.
By agreement
A CD measures the wiggle forty-four thousand times a second and writes the heights down as numbers. Nothing resembles anything. Damage one number badly enough and you can lose the whole file rather than one crackle.

Both are on this page. The wiggle above is resemblance. The numbers below are the same wiggle, measured and written down, which is where hexadecimal and every other machine code on this site comes from.

Why it matters here

A code that resembles its subject cannot keep a secret: anyone who notices the resemblance can read it. A code by agreement can, because the agreement can be private. That is the line between this section and the ciphers.

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