If you have a satellite box and/or DVD player with DVI
ouput jacks, and your DVI input display is across the room, you may have run into a
problem as I did, namely, the image has sparkles. Like this:
The sparkles are due to the DVI cable being too long
for the small DVI output voltage in your sources. Each sparkle is a pixel
that is white instead of whatever color it is supposed to be, and is a
missing bit of information in the stream.
It is sort of like the "snow" that we saw in our old
terrestrial TV broadcast images when our antenna was too far away from the
Whenever I run into problems with DVI or HDMI
distribution, I first check out Gefen's website, as they seem to market a
solution for everything in this area. Switchers, Extenders, Repeaters . . .
you name it, they have it.
The problem comes from the voltage at the DVI output
jacks on sources being too low to work over cables longer than about 12 - 15
feet. The voltage from video scalers seems to be OK, but from satellite
boxes and DVD players, you get the sparkles.
For this particular situation, I obtained a Gefen HDTV Repeater,
which sells for $249. It is also sold as a DVI Repeater, but the DVI
Repeater is not HDCP compliant. So, be sure to get the HDTV Repeater rather
than the DVI Repeater.
Whether it is called a repeater or extender, the
process is basically the same. The incoming DVI signal voltage is amplified
so it will work over a longer cable.
On the Gefen unit, you plug one end of the supplied DVI
cable into your source, and the other end into the DVI In jack on the Gefen.
The other side has a DVI Out jack that you connect your long DVI cable to,
with the other end going to your display. Since the amplifier will amplify
faulty signals, it is important to keep the cable length between the source
and the Gefen unit as short as possible. If you use a long cable before the
repeater, you will still get sparkles because they are in the signal being
The supplied cable is 6'. In fact, I would go to a 3'
or even a 1' DVI cable between the source and the Gefen unit. You could also
Gefen switcher before the repeater if you have two DVI sources.
I tried the Gefen HDTV Repeater between the DVI jacks
of an LG satellite
box and an Hitachi projector, as well as between a Denon DVD player and the
projector. In both cases, if the DVI cable was 18 feet long, with no repeater, I
got sparkles (a 12 foot DVI cable by itself had no sparkles). Addition of the
repeater eliminated the sparkles, even if the total length of the DVI cables was
30 feet. So, the product works beautifully.
In setting up your own
system, keep all the cables as short as possible. Just because you have the
repeater, don't get a longer cable than you need. With 6 feet of DVI cable
between the DVD player and the repeater, and 24 feet of DVI cable between
the repeater and projector, I could still see an occasional sparkle, due, no doubt in part, to
the fact that I had two 12 foot DVI cables connected together between the
repeater and projector (signal loss will occur at the junction between the
two 12' cables). For a
permanent install, I would put a 1 foot DVI cable between the player and
repeater, and a single 18 foot DVI cable between the repeater and projector.
If I were to use a DVI switcher for the two sources, I would have a 1 foot
DVI cable from the DVD player to the switcher, a 1 foot DVI cable between
the switcher and repeater, and a 6 foot DVI cable between the satellite box
and switcher (the satellite box is on a different equipment rack).
We are in the middle of a transition, now, with HDMI
replacing DVI. The life of DVI in home theater was very short, much shorter
than anyone expected, and many of us have DVI products. So, what do you do
if you have a DVI DVD player or a DVI projector, and you are about to get a
product with HDMI that connects to them?
Although HDMI and DVI are pin-for-pin compatible, and
our tests indicate that sources with one or the other connector will work
with displays that have the other connector, there are issues you should
know about if you plan to integrate the two types of connectors in your
DVI is an 8 bit RGB signal, while HDMI can be 8
bit RGB, or 8 bit, 10 bit, or 12 bit YCbCr. If you have a DVI source and
DVI display, there will be no problem. If you have a DVI source and an
HDMI display, again, no problem. If however, you have an HDMI source and
a DVI display, the below-black video information may be lost in the
translation. There is a bug in the Silicon Image HDMI transmitter that
pops up when converting YCbCr to RGB. The HD TiVo and Pioneer 59AVi do not
have this problem.
Even though source information (DVDs, HD) is all 8 bit
color, if DSP is applied in 8 bit, such as in a video processor, rounding
errors will toss out some of the data. On the other hand, if the data are 10
bit, such as with YCbCr, then the rounding errors don't occur. In fact, 14 -
16 bit is optimum for processing. Also, DVD data are YCbCr, and are
converted to RGB in the player for the DVI output. RGB cannot represent all
the data in YCbCr, and this is why the below-black information gets
So, if you have a DVI display, and are buying a DVD
player, you should probably get one that has a DVI output on it along with
an HDMI output, as the DVI-DVI connection will give you the optimum picture.
If you have a DVI source and an HDMI source, along with an HDMI display,
then use an HDMI switcher and repeater (Gefen has these products), rather than the DVI switcher and
repeater. Use a DVI-HDMI converter cable between the DVI source and the HDMI
switcher. Lastly, although DVI has better resolution and lower noise than
component video, DVI can introduce posterization. Since all modern DVD
players have component video outputs, don't forget to compare your component
video image with the DVI image. You may like component video better.
For those of you with DVI sources and a DVI display that
are so far apart, you get the sparkles, the problem is solved with the Gefen
HDTV Repeater. It is inexpensive and it works.
- John E. Johnson, Jr. -