Color Subcarrier

• The PAL and NTSC analog color video systems use a secondary signal, called a subcarrier, to carry the color information. Secam uses two subcarriers. In NTSC the subcarrier frequency is set at 3.57 MHz; in almost all versions of PAL it is 4.43 Mhz. See the references for the exact frequency for each country. Furthermore, some video recorders can convert the subcarrier frequency to 3.57 MHz to make it easier to play back on an NTSC TV without having to make a full standards conversion.
  
  

Flipping Phase on Each Line.

• NTSC takes the original red, green and blue signals from the camera or other source and extracts two signals called I and Q, which it codes onto the subcarrier. The receiver extracts the I and Q signals and combines them with the black and white signal to recreate the original red, green and blue. The main disadvantage of NTSC is that the color can change if the TV signal is weak or distorted. PAL codes the red and blue signals onto the subcarrier, but flips the code on each line. Consequently, any distortions in the signal get averaged out and there is no need for a "hue" control on the TV set.
  
  

Different Bandwidths and Audio Carriers

• The color system has to be adapted to fit in with the different broadcasting standards (number of lines, frames per second, channel spacing etc) in each country. That is why there are so many different versions, such as PAL-I in the U.K PAL-B/G in most of mainland Europe, and even PAL-M in Brazil. TV sets and video recorders for one country will not work in another with a different version.
  
  

Video Cassettes

• The different "flavors" of PAL only concern the tuners; the recordings on a cassette are all made identically. For example, you cannot use a German VCR in the UK, but there is no problem in taking a cassette recorded in Germany (which uses PAL-B/G) and playing it back in Britain (which uses PAL-I) or vice versa. Brazil is the one exception to this rule, because it uses 525 lines and 60 frames/second with PAL. You cannot play back a PAL cassette on an NTSC VCR, or vice versa. On the other hand, a multi-standard VCR can play back both PAL and NTSC, but it plays them back in their original formats, so you need a TV receiver in the corresponding standard to watch the cassette.
  
  

DVD and Blu-ray

• DVDs and Blu-ray discs are digital media and so are not affected by the PAL or NTSC system. The players sold in each country produce a signal that is coded in the corresponding system line and frame rate, and is connected to the TV by audio-video cables, by-passing the tuner. However, the film studios and producers include "regional coding" to prevent people watching them in countries where they do not want to sell them.