t to the Terms of Use as given at the website. First Things First Chapter 1 behind our narrator. Since airplanes didn't exist in the old west, we had a big problem. Not to be bested, our audio engineer asked us to pipe the sound into the audio booth. Listening to the recording, he went to his wall of audio CDs and selected a collection of airplane sounds. He lis- tened to several of them until he found one that was correct. Setting the levels SO that they matched those of the video soundtrack, he inverted the CD signal (180 degrees out of phase with the soundtrack signal) and electronically added it to the soundtrack. The airplane noise disappeared from the narration. Digital Signaling Data can be transmitted in a digital fashion as well. Instead of a smoothly undulating wave crashing on the computer beach, we can use an approximation of the wave to represent the data. This technique is called digital signaling. In digital signaling, an interesting mathematical phenomenon called the Fourier Series is called into play to create what most people call a square wave, shown in Figure 1-18. In the case of dig- ital signaling, the Fourier Series is used to approximate the square nature of the waveform. The details of how the series actually works are beyond the scope of this book, but suffice it to say that, by mathemati- cally combining the infinite series of odd harmonics of a fundamental wave, the ultimate result is a squared-off shape that approximates the square wave that commonly depicts digital data transmission. This tech- nique is called digital signaling, as opposed to the amplitude-, frequency-, and phase-dependent signaling techniques used in analog systems. In digital signaling, zeroes and ones are represented as either the absence or presence of voltage on the line and, in some cases, by either positive or negative voltage-or both. Figure 1-19, for example, shows a Figure 1-18 Square wave Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGr