analog waveform. Not following Nyquist's Theorem during the analog to digital (A/D) video conversion process, often Coding and Compression leads to aliasing. Aliases show up as moiré (wavy patterns that look like plaid watered silk) and color shifts (where rainbow hues appear in an object of supposedly uniform color). In the analog world, the bandwidth of a signal is the difference between its highest and its lowest frequencies. It is the highest frequency with which sampling is concerned. The metric for the frequency of sound waves is hertz (Hz); an expression of the number of complete cycles that occur in one second. Although those with the most acute hearing can perceive frequencies as high as 20 kHz (20,000 hertz), the public telephone network does not convey them because they do not occur in speech. The human voice typically produces frequencies between 50 Hz and 4 kHz. Since this range is where most of the information in human speech is concentrated, telephone networks were specifically designed to carry those frequencies. Thus, the analog local loop-the connection between an end-user and the telephone company-has a bandwidth of 4 kHz. Nyquist's Theorem instructs that this signal must be sampled at a rate of 8,000 samples per second. The device that does the sampling is a codec (coder-decoder) and it forms the basis for much of today's digital telephone network. The basis of the North American public switched telephone network is an extremely precise 8 kHz (Stratum) clock. This clock produces reference pulses that disseminate across all networks in North America. This clock orchestrates analog signal sampling, in accordance with a digital modulation technique known as Pulse Code Modulation (PCM). In 1938, Alec Reeves, an English employee of ITT, developed the concept of PCM. Unfortunately, in the 1930s, PCM was not deployable in the public network. The pulse generation equipment of the day relied on vacuum tubes that were too large and power-hungry to make wide-scale implementation feasible. In 1947, a grou