Music is stored on a compact disc using a code. Using a laser beam, the CD player reads the information on the disc and converts it into music transmitted to us by speakers. However, the player can make real errors in reading: there can be scratches or little pieces of dirt on the disc, the laser beam just misses the right place on the disc, and so on. Nevertheless we want the music to be replayed as well as possible. We want the CD player to correct its reading errors. The music has to be stored on disc in such a way that the player can correct its errors.

Satellites hang above the earth. Information, for example, a tv program, is sent from one place on earth to the satellite, which sends it back to other places on earth. In this way we can follow important events live on tv. However, the signals going to and coming from the satellite suffer from noise. The tv watcher wants to notice as little as possible of this.

Faxes and e-mail messages are transmitted via telephone lines throughout the world. Telephone lines also suffer from noise. This can cause a fax to be damaged. The fax has to be protected against this.