Why Y/C?

You don’t have to go far into the realm of the high-quality consumer video formats before you run across the terms Y/C or S-video. Manufacturers love to tout the benefits of this special video connector, and well-meaning salespeople will give you an earful on the topic if they learn you’re in the market for a VCR or camcorder.

Unfortunately, this deluge of helpful information may take you no closer to understanding the real benefits of that little 4-pin jack. In spite of what you may have heard, plugging in a Y/C cable will not miraculously correct errant white balance, make your sixth-generation tape look like a first-generation master or make your Hi8 decks outperform a digital Betacam setup. Truth be known, the advantages of Y/C cabling–which carries brightness and color information on separate conductors–are subtle in certain setups and nonexistent in others.

Which may prompt the question, "Why even bother with Y/C?" The answer lies in what Y/C cabling will do for your image quality, which is to offer cleaner copies with better color accuracy. In many video setups, this benefit lies just a single cable away.


Looking Back
Over the years, engineers have come up with numerous different methods to record and transmit video images. While many of these systems came about to offer the best-possible image quality, an equal number sprang up where image quality took a back seat to more pressing concerns. In these cases, low data capacity (or bandwidth) was usually the main bottleneck, making it an engineering triumph to deliver even adequate picture quality.

Take the North American NTSC color system, for example. The original NTSC (National Television Standards Committee) broadcast standard was a relatively simple black-and-white signal. In the 1940s, when the Committee decided on the standard, no one foresaw the need for color–it wasn’t until the 1960s that the Committee recognized the advantages of adding color to the original standard. Because backward compatibility was of paramount importance, engineers had to find a way to squeeze a low-resolution color signal into the existing monochrome signal. They eventually achieved their goal, but the end result was the somewhat compromised color system we still use today.

It’s no accident that NTSC offers the greatest compromise in the same area that Y/C video offers the greatest improvement: color accuracy. To understand why, let’s explore the ins and outs of color video.


Addition and Subtraction

At the heart of every color camera is a system of electronics and optics that slices the visible spectrum into three smaller sections (usually red, green and blue or "RGB"). When added back together–inside a TV set, for example–these three signals carry the information necessary to re-create the image. This additive color offers the best possible image quality, but requires a large amount of bandwidth. This is why you’ll usually only find RGB color on computers and high-end video gear–it just isn’t practical to transmit an RGB video signal over the airwaves.

RGB video is a type of component video, where the various signals are discrete from one another. Again, component video offers optimum image quality at the expense of bandwidth.

To reduce the color signal down to a more manageable size, engineers came up with subtractive color. In this scheme, video equipment separates the color and brightness signals. Then, components of the color signal are subtracted from each other to create "difference" signals. These difference signals take up considerably less space than the full RGB signal. Combined with the luminance signal, the subtractive color signals can recreate the full visible spectrum.

The NTSC system uses subtractive color for several reasons. First off, TV engineers needed to add color to an existing monochrome signal. This meant the color signal had to be small enough to piggy-back onto the monochrome signal, something subtractive color made possible. Second, color TV required a color-only signal to supplement the existing luminance signal–subtractive color again fit the bill. Finally, subtractive color allowed engineers to further compress the color signal so it would tuck inside the monochrome signal. Color accuracy suffered as a result of the squeeze, but color TV became a reality.

We call the resulting signal (which carries brightness, color and sync information) a composite signal. This blending of the color and brightness signals, though a great convenience for broadcast, creates the potential for unwanted interaction. And minimizing this interaction is where Y/C video comes into the picture.


For the Record

The various video formats we’ve talked about so far–RGB component, NTSC composite–only address how a video signal gets from one point to another in the air or on a cable. The recording of video signals, which is what interests us videographers the most, involves a completely different set of standards.

In the early days, color video decks recorded the composite video signal intact. These one-inch and two-inch machines did minimal processing or filtering of the NTSC composite signal. As formats shrank, however, there wasn’t enough capacity available on the tape to record the NTSC signal as-is. So engineers devised the color-under system, which extracted the color portion from the composite signal and recorded it on tape at a lower frequency. Color accuracy took another hit, but engineers were able to squeeze color video on 1/2-inch tape. Today, all analog consumer VCRs use the color-under system for recording video.

Consider all of the things a video signal has been through by the time it’s recorded on a consumer VCR or camcorder. The original RGB signal from a camera or camcorder is converted into luminance and subtractive color signals, re-combined in NTSC composite format for the trip down a wire, then split apart again at the VCR to be recorded in two separate chunks. At each conversion, filtering introduces artifacts and other distortions into the video signal. "If we could just eliminate a few of these steps," you’re probably thinking, "we might have better-looking video."

You’re right. Any place we can bypass unnecessary filtering, our video signals will be healthier. Take the jump between two Hi8 VCRs, for example. Luminance and color signals roll off tape separately; the VCR then processes and re-combines the signals for output at the composite video jack. At the record VCR, filters break the composite signal back into its luminance and color components before recording. The playback deck combines the luminance and color signals together for one reason–so they can travel a few feet down a single wire before being separated again.

A Y/C cable carries the luminance and color portions of the video signal separately. This means the source VCR doesn’t have to combine the two, and the record VCR doesn’t need to split them apart again. One Y/C cable can cut two filtering and conversion steps from the record process, along with their associated nasties–that’s benefit number one (see figure 1). Benefit number two is the end of unwanted interaction between luminance and color signals as they travel down their separate conductors.


Where Y/C?

As you’ve probably figured out by now, Y/C jacks don’t show up on standard VHS and 8mm equipment. Manufacturers put Y/C jacks only on high-end camcorders and VCRs (Hi8, S-VHS, DV), laserdisc players, DBS receivers and better-quality monitors and desktop video equipment. Y/C jacks are often a step-up feature–a selling point–among various models and formats.

In spite of what many salespeople may tell you, a Y/C jack does not increase the resolution of your original recorded footage. Because Y/C cables are commonly referred to as S-video cables, their benefits are sometimes confused with those of the S-VHS videotape format (even by salespeople, who should know better).

It also comes as a surprise to many that Y/C jacks would offer the same benefit to standard VHS and 8mm formats as they do to their high-band brethren. Y/C jacks make a difference any time video equipment has to combine luminance and chrominance signals just to run them down a single conductor. Playing back a standard 8mm or VHS tape in a high-band VCR, for example, still gives you the benefit of Y/C connectors.

On the flip side, there are times when Y/C jacks offer no significant advantage. If a piece of equipment stores, receives or processes the composite video signal intact, there’s no real advantage to splitting the signal apart before sending it down the wire. There may be slightly less interaction between the two signals as they travel down the Y/C cable, but the real advantage of less filtering doesn’t apply. Most laserdisc players, satellite receivers and tuners keep the composite signal intact, as do some DTV components. This type of gear will glean little or no benefit from Y/C cabling.


Wire It In
If you’re like most videographers, your setup has a mixture of Y/C and composite equipment. In such a system, there’s a right way and a wrong way to interconnect most components. Wire things properly, and you’ll enjoy the best-possible video quality your system can deliver. Wire things wrong, and your images will suffer.

Using Y/C cabling is most important between VCRs. Running a Y/C cable between two high-band VCRs, for example, eliminates unnecessary filtering at both machines. Be careful to not string both Y/C and composite video cables between the two. You won’t get twice the signal with this move, and the record VCR may actually ignore the cleaner Y/C connection in favor of the composite signal.

You may have heard the following misinformation: unless you use Y/C cabling for every connection in your system, you’re completely negating the benefits of Y/C. In reality, having just one key Y/C connection (between source and record decks, for example) can net you all the benefit of Y/C that will ever end up on tape. Even if your video signal is running through several different components, a single Y/C link in the chain will help. Anywhere a Y/C cable can eliminate a filtering stage, your video signal is better off.

When connecting monitors into your system, Y/C cabling is optional. Separate luminance and chrominance may clean up your monitor image slightly, but such cabling will have no effect on your recorded video. Unless the video signal is on its way to a record VCR or computer digitizer, Y/C cabling will offer no lasting benefit.

Titlers, SEGs and computer gear may or may not have Y/C connectors. And because different types of equipment process video in different ways, the benefits of using Y/C cabling with these components may be significant or almost nil. Here’s where the one rule of thumb for Y/C cabling comes into play: if you’re unsure whether to run a Y/C cable, plug it in anyway. Your video signal will never be worse off for a trip through a Y/C cable.


That’s Why
Y/C cabling won’t revolutionize your video productions, but it will offer some definite advantages. It can give you a noticeably better image than composite cabling, and a dramatically better image than RF cabling.

Sometimes it pays to separate your luminance from your chrominance.

Contributing Editor Loren Alldrin is a freelance video and music producer.

Y/C Cabling: What It Will, What It Won’t












Y/C Cabling WillY/C Cabling Won’t

  • eliminate filtering artifacts

  • improve resolution of the original footage

  • offer less harmful interaction between color and brightness signals

  • provide the same benefit as S-VHS or Hi8 recording equipment

  • offer benefit even if used inconsistently

  • offer benefit in pure-composite equipment

  • improve playback of standard 8mm and VHS tapes

  • eliminate generation loss

  • improve monitor image
  • improve editing accuracy
  • Glossary of Terms

    Additive color

    A color system that combines three colors (usually red, green and blue) in various proportion to create all possible hues.

    Bandwidth

    The available "space" for carrying electronic information.

    Chrominance

    The portion of a video signal that carries color information.

    Color-under

    A recording system that records the chrominance signal separately and at a lower frequency than the luminance signal.

    Component video

    A video system that carries three color signals separately.

    Composite video

    A video system that combines all signal components into one.

    Conductors

    The metal part of a cable that carries the actual signal.

    Filtering

    An electronic process to "break apart" or combine signals.

    Luminance

    The portion of a video signal that carries brightness information.

    RF

    (Radio Frequency) A video cabling scheme that bumps the video signal up to broadcast frequencies, where it can then be decoded by a tuner. Offers the poorest video quality.

    S-video Same as Y/C.

    Subtractive color

    A color system that subtracts primary colors from a reference signal to create all possible hues.

    Y/C

    A 4-pin wiring standard that carries the luminance (Y) signal separate from the chrominance (C) signal.

    Videomaker
    The Videomaker Editors are dedicated to bringing you the information you need to produce and share better video.

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