NTSC Decoding Basics (Part 1)

by Steve Somers, Vice President of Engineering

Recently, Dave Pincek, our V.P. of Product Management, asked me to write about notch filtering and comb filtering within the NTSC decoding process. When the subject of decoding NTSC comes up in conversation, I think of the task as the single greatest gift of challenge man has given himself. Dave said that he had yet to see a simple, straightforward explanation of those concepts. As I stared at him with some disbelief, I replied, "Well, why not…I'll give it a go" (as they say "down under"). Then, suddenly, this became a multi-part series. Well, that makes sense because it's a complex subject, but it occurred to me that an explanation of decoding concepts is not as meaningful without an understanding of the reasons for construction, or encoding, of the NTSC signal. Therefore, we'll take this topic in three to four separate sessions.

The history predating the FCC's adoption of the NTSC color television system is certainly 'colorful', but beyond the scope of this column. For those interested in more depth here, go to web site: www.mediahistory.com and click on keyword "television". In 1951, the FCC adopted the National Television Systems Committee's proposal for 525 line, 30 hertz per frame monochrome television transmission. This predates me by a few years, but I'm sure there was nearly as many debates about the placement and allocations for television then as there is today regarding digital television. Even though the industry is about to embark into DTV, consider that NTSC is a monumental legacy that will be with us for years to come.