Specifications

what you're doing, making this adjustment on your own without instrumentation could get you in deep
trouble. If you insist on trying, please write down the numerical settings for every adjustment you plan
to change before you begin. You must have a way of returning to the original settings if you can't get
acceptable results! And be aware that some rear projector manufacturers may void your warranty if
factory authorized service personnel detect that you accessed the service menu.
I spent the next hour or so reworking my projector's six color temperature settings and its brightness
and contrast. I replaced the AVIA DVD with AOTC, jumped to a chapter at random and sat back,
wincing in anticipation. And smiled. The video was highly detailed, the colors well balance, vivid, and
noise free. Fine details and revealing textures make it through the transcoder's circuitry thanks to Key
Digital's video frequency response, -3 dB at 110 MHz, very impressive for a $350 list price product. So
when I later examined bandwidth on my ‘scope with an AVIA test pattern, I was not surprised when I
found no variation in frequency response when I compared Key Digital's input to its output. Nor did the
long coaxial cable runs to my projector cause any drive problems for the transcoder's output buffers;
no visible ringing was imposed by the KD-CTCA2.
Since the transcoder's working configuration is an auto-format mode, it was time to confirm the Key
Digital's ability to handle HDTV's broadcast standards. With the exception of WCBS, which had a
backup antenna and transmitter on the Empire State Building, I haven't been able to receive HD
transmissions from New York since the barbaric attack of 9/11. (Fox and UPN share the CBS antenna,
but since they aren't transmitting in 720p or 1080i, they're certainly not high definition.) Fortunately,
by rotating my antenna toward much farther away Philadelphia, I can receive PBS in HD from Trenton
and HD transmissions from Philly's CBS, ABC, NBC, and WB affiliates.
I'm pleased to report that, with one unique exception, the Key Digital performed flawlessly. Each
format locked in transparently and remained stable. The glorious 1080i resolution from CBS and PBS
looked as great as they did with the Extron. ABC's 720p looked lovely as well and the subtle resolution
differences when compared with 1080i were still apparent; this indicates that the Key Digital's
extended bandwidth was more than adequate for the job of transcoding HD content. There was one
small glitch that will be an issue only for some CRT-based front projectors (CRT-based rear projectors
that are capable of high definition display modes are equipped with component video inputs, so a
transcoder is not required).
The NTSC video system, on which DVD is based, has bi-level sync; each pulse extends below the
image's full black level. HD video signals have tri-level sync pulses; they resemble two linked pulses
of opposite polarity similar to one cycle of a square wave. HD's leading horizontal sync pulse is
negative going, just like NTSC's, but HD's trailing pulse is positive going, and its amplitude pushes well
up into the visible video's amplitude range. When I tested the Key Digital transcoder with HDTV
signals, the positive going portion of HD's tri-level sync was reproduced just like image data. The pulse
was located at the extreme edge of my projector's CRTs, beyond the linear areas projected onto the
screen by the projector's lenses, so I didn't see the pulses as bright artifacts on my screen. But, the
pulses illuminated the phosphors at the CRTs' edges so brightly that a lens flare was projected onto my
screen's right edge. During dark scenes or black transitions, a gray streak was quite visible.
Attempts to manipulate my projector's picture width and blanking did not help. Apparently, those
adjustments only work within my projector's visible video data area, within the linear portions of the
tubes that are projected through the lenses. While this problem will not occur in fixed resolution
projectors (DLP, LCD, D-ILA), it may affect CRT front projectors besides my own. Since this is a
problem I cannot work around, I decided to dedicate the Key Digital transcoder to my DVD player and
to dedicate the Extron Transcoder to my HDTV set top box. I could then switch between the Extron's
RGB-HV and the Key Digital's RGsB signals with my existing high-bandwidth Extron SW2ARHVxi
switcher. Wrong again.
When I connected through the switcher, the HDTV was great, just as it had been for the last few years,
but DVD content was distorted. The right edge of any bright to dark transition was contaminated by a
thin red outline, similar in appearance to misconvergence. At first, I thought there was some kind of
delay in the red channel that displaced red to the right, but red was not absent at the opposite edge on
the left. I then recalled that the Extron switcher, an electronic device as opposed to an
electromechanical device, had restricted input specifications. Perhaps the high amplitude I found on the
red channel was overloading the Extron's electronics and I was seeing a delay in recovering from
saturation. Once again, I investigated waveforms and made a few quick amplitude measurements.
At a video amplitude of 100 IRE, the Extron transcoder produces about 670 mV at the red channel, 690
mV at the green, and 680 mV at the blue. For the same input (excluding offsets), the Key Digital
produces approximately 770 mV at the red channel, 710 mV at the green, and 720 mV at the blue.
Also, unlike the Extron, which was within a couple of mV of zero for 0 IRE, the Key Digital had offsets
of about 960, 165, and 840 mV for R, G, & B respectively. And the Key digital passed the sync pulses,
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DVDFILE.COM: Mr. Blandings Builds his Dream Theater
4/7/2003
http://www.dvdfile.com/news/special_report/tech/mrblandings/upgrades.html