To create mp3, Brandenburg analyzed how the human ear and brain perceive sound. The coding technique effectively fools the ear by eliminating the less essential parts of a music file. For example, if two notes are very similar, or if a high and low tone occur at exactly the same time, the brain perceives only one of them; so the mp3 algorithm selects the more important signal and discards the other.
The resulting audio file is reduced to less than a tenth of its original size. For example, a three-minute track will normally take up about 30MB of hard-disk space. The equivalent mp3 file will use only about 3MB of space with little audible loss in quality.
As he was perfecting his code, one of Brandenburg's benchmarks was Suzanne Vega's song "Tom's Diner". The subtleties of Vega's a capella rendition proved to be the hardest of challenges for his algorithm. Brandenburg had to listen to the song hundreds of times while fine-tuning a code which has become the universal standard today!