On Nov 8, 18:07, Richard Erlacher wrote: not 625. One is a consequence of the other. The most obvious difference between PAL and NTSC is the use of different vertical scan rates (50Hz vs 60Hz) but they use the same horizontal scan rate (15.something kHz), so if you do the arithmetic, you'll see why they use different numbers of scan lines (625 vs 525). They both use interleave; so the number of full frames is 25 per second or 30 per second. They also differ in the way they encode colour information. The basic scheme is similar but the subcarrier frequencies differ, and in the case of PAL, there is a "colour burst" of pure subcarrier at the start of every line. This allows the circuitry to synchronise better. Also, the colour signal is 180deg different in phase on every second line (hence the name, Phased Alternate Line) which makes it a little more stable. In the context of broadcast TV, they also use diffent audio subcarriers (in fact, there are several PAL variants, used in different countries. They're called PAL/G, PAL/K, PAL/I, etc). The net result is that you can often use a PAL display instead of an NTSC one or vice-versa, but you would expect to lose the colour and sound. You might possibly have to tweak the vertical hold to get a steady picture. Since the sync pulses are encoded in the same way, any monitor or TV should lock on to the horizontal signal perfectly, but the vertical might be beyond the range of the sync circuit (it's usually OK in practice, though). I bet Tony knows more about this than I do. -- Pete Peter Turnbull Dept. of Computer Science University of York