DVD  & Video Signal Formats 

By Russell Storey 

Stones Sound Studio (Australia)

This article answers some basic questions about the video signal formats used in Home Theatre products.

What Video Signal Formats are used for Interconnecting Home Theatre Products?

The Composite video and S-video signal formats have dominated Home Theatre interconnect applications. S-video is often incorrectly referred to as S-VHS since it first came into home use with the introduction of that video tape format. Professionals prefer the name Y/C video rather than S-video since it is more clearly descriptive of the signal format. With the introduction DVD, Analogue component video (or colour-difference video) will become a third common home theatre interconnect signal format. Analog component video should not be confused with RGB video which is also a component video format, but is used almost exclusively for connecting line doublers and quadruplers to video projectors in U.S home theatres.

All of these video signal formats for interconnecting home theatre components are analog today. But each of these video signal formats can be stored, processed, or transported in the digital domain, which is common in professional applications  recording and Television studios . Home theatre digital satellite systems receive MPEG compressed digital component video signals from their satellites, but only some  of the receivers provide analog or digital component video outputs yet. The DVD format is also based on MPEG compressed digital component video, and the top-end players do provide analog component video outputs to achieve the highest possible picture quality providing you have the monitor or TV with  compatible inputs .Some high end Home theatre receivers have Y/C and RGB component input and output facilities this will become common in the near future on all products

How are Video Signal Formats related to Interconnect Cables?

Composite video signals are connected between products with a single 75 ohm coax cable, usually with RCA connectors on each end. Composite video inputs or outputs are present on almost all contemporary video equipment. Composite video signals can also be modulated onto an RF carrier, along with an audio signal, and transmitted over-the-air or on coax cable, by broadcast stations and cable TV systems. RF video signal cables are usually 75 ohm coax terminated with screw-on F-connectors.

Most midrange and premium video equipment provide the additional option of using Y/C video connections. The Y/C (or S-video) cable is terminated at each end with a four-pin DIN connector. Although it may appear to be a single cable, internally it has two 75 ohm coax or twisted pair cables to carry the separate Y and C signals.

Analog component video connections require three 75 ohm coax cables, which carry the Y, R-Y, and B-Y signals separately. Each of the three coax cables is terminated at both ends with RCA connectors. They may be colour coded and bundled together in a single sheath, or three equal length composite cables may be used.

In professional and industrial video equipment all of these signal formats are usually carried by coax cables that are terminated with the more rugged, impedance matched  high bandwidth 75 ohm BNC connectors.

What Video Signal Format Should be Used to Interconnect Products?

This can be a difficult question to answer since you will often have two or even three choices. In general, it depends on the type of product at both ends of the cable. In some cases, it even depends on the sophistication level of the technology used in the products.

There are several no-brainer cases. If you have a DVD player, component video will always provide the best picture if your player and associated equipment have compatible inputs and outputs. Line doublers and quadruplers, and new premium consumer TV monitors have component video inputs. Component video is always preferable with DVD because it reduces artifacts and colour errors by minimizing the number of video signal format conversions between the film source and the display device. If your DVD player and display device doesn't have component video, then you should always use Y/C video as the next best choice. The practical differences in quality between component video and Y/C video are noticeable on a good display device . You should never use composite video with a DVD player if it can be avoided. Composite video will generate several unnecessary format conversions that will unavoidably create Y/C separation artifacts that are dramatic. (Y/C separation artifacts will be explained later.)

As more TVs start to have analog component video inputs for DVD,  satellite receivers will also have analog component video outputs. Their native transmission signal format is compressed digital component video, so you should use these outputs when they become available on equipment . Until then, the Y/C video outputs should be used with digital satellite systems for the same reasons as DVD. Currently, I am not aware of any products that include more than a single set of component video inputs. When component video outputs start showing up on digital satellite receivers there will be a need for a separate, high quality, component video switching device. (Hint to the manufacturers): 

Another no-brainer occurs when interconnecting any two consumer video tape devices together or to a display device. You should always use the Y/C inputs and outputs that are provided with Hi-8 and S-VHS camcorders and VCRs. All consumer analog VCRs and camcorders store the Y and C video signals separately on the tape using what is called a colour-under system. So if you connect any two of these devices together you can avoid Y/C separation artifacts by using Y/C interconnects. The same holds true for connecting any of these tape devices to your monitor. Use the Y/C outputs and you will avoid the Y/C separation process, and the resulting artifacts, in the monitor.

The DVD's digital component video format 

The DVD's digital component video format uses the Y signal and the intermediate colour difference signals, R'-Y and B'-Y. The luminance signal has a bandwidth greater than 6 MHz and the colour difference signals have bandwidths greater than 3 MHz. These three signals are converted to digital and stored on a professional D-1 tape. Then they are compressed with an MPEG-2 encoder for mastering the DVD. In the DVD player, the signals are decompressed by an MPEG-2 decoder. The recovered digital component video signals have a higher bandwidth than the other present  formats. The best DVD players convert these signals to analog and output them with the higher resolution in the analog component video format. A  PAL  encoder IC, with digital to analog converters, band-limits the colour difference signals and then combines them with the Y signal to create the analog Y/C and composite signal outputs.