How did Thomas Edison’s phonograph record and play back sound?

Thomas Edison’s phonograph, invented in 1877, was the first device capable of both recording and playing back sound.12

To record sound, a horn focused sound waves onto a diaphragm, causing it to vibrate. These vibrations were transmitted to a stylus, which embossed or traced a physical replica of the sound waves as indentations or grooves into a rotating cylinder coated with a yielding material, such as tinfoil or wax.31

To play back the sound, the process was essentially reversed: a stylus tracked the grooves or indentations on the rotating cylinder. As the stylus moved along these undulations, its mechanical motions were reconverted back into sound waves. While later innovations, such as Emil Berliner’s gramophone, shifted the medium from cylinders to flat discs, Edison's fundamental mechanical process of using a vibrating stylus to store and retrieve sound remained the foundation for early sound recording technology.12