Compact disc player
A CD player has a laser and an optical sensor. A CD has tracks and bumps on the tracks. The CD player passes a laser beam along the track of the CD. The areas that are reflected (without the bumps) are 1s to the player and the areas that are reflected (with the bumps) are 0s to the player. The CD player uses these 1s and 0s and turn them into sound waves which are made louder into speakers or ear/headphones so you can listen to your music or sound recordings. In addition to the bumps used for the audio, there are extra bumps for error correction, so that if the CD gets a scratch, it will still sound OK, although a very bad scratch can make the disc skip.
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