|  | 4.3 | Basics of Signals and Noise in Communcations Systems
| 4.3.2 | Using digital signals to build analog signals
Jean Baptiste Fourier is responsible for one of the greatest mathematical discoveries. He proved that a special sum of sine waves, of harmonically related frequencies, which are multiples of some basic frequency, could be added together to create any wave pattern. This is how voice recognition devices and heart pacemakers work. Complex waves can be built out of simple waves. A square wave, or a square pulse, can be built by using the right combination of sine waves. The main graphic shows how the square wave (digital signal) can be built with sine waves (analog signals). This is important to remember as you examine what happens to a digital pulse as it travels along networking media.