Mac Mini behaves poorly through DVI at 1920x1080 on HDTV displays

Question

I recently purchased a Samsung LN-S4695D - a 46" LCD TV capable of 1080p with HDMI and VGA inputs. I've had been using my 23" Cinema Display + a Mac Mini G4 + Rotel Amp as the centerpieces of my Home Theater, and decided to change out the display to accommodate a gaming system and perhaps some other digital or component inputs (and, of course, nab a larger viewing surface). It seems like a fairly standard use of the Mini, but unfortunately many of us are running into disappointing results using our Minis as connected to an HDTV display. I'm writing here to see if we can clear up the issue with the mini and to attempt to identify reasonable workarounds or solutions until Apple gets the Mini right for HD home theater.
The current problem with the Mini and the Samsung TV/Display is that when the Mini is connected via DVI-HDMI (with a Monster 400 2m cable) to the display and asked to run at 1920x1080 (60hz NTSC) it does a reasonable job until it is required to refresh a lot of pixels (scrolling through album art in iTunes, playing DVD or other video, etc.). At that point, the screen fills with bands of static, and (if the rate of change is sustained) eventually looses the signal all together. With heavy scrolling operations, the signal returns as soon as scrolling stops, but with full-screen video it usually stays out until the mac resets its video resolution. Another article shows examples of this "DVI static" here:
http://www.freewebs.com/themagius/minidvipics.htm
So it is clear that the Mini and HDTVs don't play well at 1080 resolutions, as many of you have attested to. The samsung seems to do a better job than most with the Mini in that it it actually renders the 1080 as well as other resolutions, but flakes out on fast updates. While some other resolutions are also problematic, it is important to note that 1280x720 runs flawlessly on the Samsung, and is currently how I have mine set up (VGA input was too disappointing compared to DVI, though it scanned great and fit the image w/o over/underscanning.). Also, my Powerbook G4 1.25ghz (older than the mini) powers the Samsung perfectly at 1920x1080 as a secondary display, running DVD video or anything else that I throw at it, which leads me to believe that the mini is the problem. Here is another story very similar to mine that reports almost the same results with a Sharp LCD panel:
http://www.avsforum.com/avs-vb/showthread.php?p=5940932
So I've three sets of questions for Apple and the rest of you on this forum:
1) Why does the Mac Mini underpeform with the LCD display? The Powerbook works great, and the mini works great with my Cinema display (also 1920x1080) - where is the disconnect between the Mini and the Samsung? I understand very little about the actual details of DVI signals being carried across the wire, and don't understand what would cause the Powerbook to succeed, but the Mini to falter.
2) Assuming the Mini video hardware is at fault, has Apple improved this with the new Core 2 Duo line? Has anyone had success where previous Minis or other Apple hardware failed at 1080? If not, is there any announced intention to make the hardware that is positioned as being most ideal for the living room (ie, Mac Mini) actually DVI/HDMI-compatible with the finest HD living room devices?
3) An unfortunate sideffect of the DVI connection to the TV is that it requires the image from the Apple device to be oversanned (about a menu-bar's worth of pixels disappear on each edge) or underscanned (2" of black space around the image). Is there a common industry standard to correct this? Who is managing the overscan - the TV or the Mini? Also, can any utility, such as ScreenResX correct this until Apple manages to build in correction options into the OS for their living-room devices?
Thanks for all the help! Hopefully we can outline clear answers here in this thread for everyone else having similar problems.
Mac Mini G4 Mac OS X (10.4.8) Samsung LN-S4695D, Monster 400 DVI-HDMI 2m cable

Answer 1

David,
Great post. There's a lot to digest here. Let's get started!
The first question relating to noise, or static, over a TMDS (DVI) connection has to do with with the interoperability of various TMDS transmitters and receivers and how they are implemented. At this point in the market place there are thousands of combinations of transmitter/reciever pairings and obviously some are working better than others.
If you were to observe a TMDS signal with a scope there is something called the "eye" which is framed by the swing voltage and the bit time. When the eye collapses and is encroached upon, digital noise is the result. The noise margin is degraded by higher bit rates. That is why the mini and your TV are working at 720p but failing at 1080p...because the dot clock is that much higher for 1080p. The solution for cases such as this is to build a custom 1920x1080 timing that has reduced blanking, which allows for the lowering of the dot clock. Generally you can lower the dot clock sufficiently to get the noise to stop. LCD displays are relatively immune to reductions in blanking time so you can squeeze a lot out of a timing that was designed more with a CRT in mind.
To answer your second question, you can't fairly say the problem is with the mini. When you consider TMDS compatibility between two devices you have to take a whole system view. This includes not only the transmitter (mini) but the transmission line (PCB traces from the TMDS transmitter inside the mini to the mini's DVI connector -> the cable -> PCB traces from the DVI connector on the TV to the TMDS receiver in the TV), and the receiver. All three have to work together to make things come out right. You could probably just as easily find a display that works well with the mini that doesn't work with your PowerBook. It can be really had to pin the blame down to one device except in the most obvious cases where a certain device seems to be incompatible with just about everything. But I don't think the mini can be labeled that way. Compatibility is definitely an issue the industry still struggles with, especially at the higher clock rates approaching the 165MHz TMDS speed limit.
As for question 3, overscan is being forced by the TV, not by the mini. And, no, utilities like SwitchRes X and DisplayConfigX cannot be counted on to reliably deal with this except in the case of pure analog displays with magnetic deflection systems (e.g. old TVs and monitors). Once you have a digital processor involved and a matrix addressed display, tweaks to porch timings and blanking and such do not have predictable results. It seems to work in some cases but it is basically voodoo when it does. Purely luck.
If you want, I can help you to build a reduced blanking, 1080p timing that will most likely eliminate the DVI static. But you'll still be stuck with overscan. I should point out that a lot of manufacturers are starting to "get it" with respect to the public's desire to attach computers to their hi-def LCD televisions. I see a real shift in 2006 models. I believe the current crop of FHD (Full HD; native 1080) LCDs from the three "S" companies (Samsung, Sharp and Sony) all can display 1080p bit-for-bit now, meaning no overscan. So at least that is changing for the better. Write back if you want help with the timing.
Cheers. And thanks for starting this great thread.