lity, cost, increased bandwidth, and efficiency. Once a Telco converts a signal to a stream of bits, it can easily shuffle that bit stream with other bit streams, regardless of source or content, for better use of telephone lines (often figuratively referred to as pipes). Video and audio signals benefit greatly from analog-to-digital conversion. The universe contains innumerable electromagnetic waves-not all of them relate to any particular signal. That SO many frequencies exist in free space does not matter to human eyes and ears that can only detect a limited range of sights or sounds. However, it does become a problem when these sights and sounds are modulated electronically onto a carrier wave. A carrier wave is an electrically constant energy path that one uses to transport a signal from one place to another. Modulation is the process of altering this stable carrier wave in response to fluctuations in the signal being carried. Analog modulation techniques perform well in controlled environments or over short distances. The signal, when it first is superimposed onto the carrier, is strong and unadulterated. However, because travel steadily weakens a signal, a signal that travels Video Communications: The Whole Picture any distance requires amplification. If amplification were to restore the signal to its original pristine state, it would affect no harm. Unfortunately, frequencies abound and, unless a transmission system is shielded, interference contaminates the signal. The envelope, that originally contained only the signal, collects random waveforms that are not associated with the original signal, but which occupy the same frequency band. Amplification boosts both the signal and these random waveforms, which we refer to as noise. Noise affects video signals. They may arrive on a screen full of artifacts (undesirable elements or defects in a video picture). Image aliasing (subjectively intolerable distortions in the picture) is another noise-related problem. Unlike analog signals, digital ones are resistant