COMB FILTER

It allows the color information, which is interleaved with the black and white signal, to be combed out, preserving much more detail in the black and white. If a Comb Filter is incorporated in a TV set, the horizontal resolution wedge will remain in black and white over its entire visible range. There are exceptions. Sometimes you'll see a little bit of color in the wedge. This is usually an indication that the Comb Filter hasn't done a good job of separating the two. The first generations of Comb Filter decoders were analog. They incorporated a delay line so that adjacent TV lines could be added or subtracted, yielding black and white at one point and color at the other. Once the color carrier and its information is separated from the black and white, it's necessary to pull the two pieces of color information away from their 3.58 MHz carriers. The absence or presence of Dot Crawl in the picture is an indication of how well the 3.58 MHz carrier has been removed. In less expensive implementations of the Comb Filter, the subcarrier is notched out, taking some black and white information with it. Most consumer sets with a Notch on or off option in the menu system are applying the notch to the color signal rather than using it to separate the color from the black and white. This separated black and white and color signal forms what is known as an "S-Video" signal. It's two channels of information, the black and white on one and the color sub-carriers and their information on the other.