mportant standard covering digital television sound transmission is A52, ATSC Standard Digital Audio Compression (AC-3; www.atsc.org). Video Content Think compression is a modern technique? Think again. Mono- chrome television pictures, or video, originated around the notion of a scanning mechanism conceived by two inventors working inde- pendently in the early 1900s, neither of whom was aware of the other's idea until many years later. Essentially, the system approved by the FCC and adopted with minor variation by government and regulatory bodies in the rest of the world over time, involves two 1 BASIC FUNDAMENTALS, DEFINITIONS, AND KEY TERMS line rates and two frame rates. Along the way, someone figured out and probably filed an improvement patent on a technique called interlaced scan. Interlaced scan cut the required transmission band- width in half without significantly impairing perceived picture qual- ity. Essentially, half the picture is traced on the screen one line at a time, and then the process repeats from the top of the picture, scan- ning additional lines between the lines of the initial area. Thus, fields and frames were born, a field being one-half of a frame. Occasionally the interlaced scan technique is referred to as 2:1 compression. Compatible color television was standardized in the United States in 1953 when the NTSC recommended and the FCC adopted rules covering transmission of color television signals. Use of the term compatible means that monochrome receivers could receive and display color signals on a monochrome display from signals trans- mitted and received on color receivers as a color signal. The reverse is also true, to the extent that color receivers can receive and display monochrome pictures. Several years later, similar practice of back- ward compatibility followed with adoption of stereo transmission technology in FM radio and television sound. Color television pictures are made from primary color signals de- rived from red, green, and blue signals produced by pickup devices, 