A Discussion On Poor SD On HDTVs

rbinck

Introduction
Probably the most asked about issue when a person gets a new HDTV is why is the SD picture quality so bad on my HDTV? This discussion will address this issue, the causes and what can be done to get the best picture possible. Any replies to amplify this subject are welcomed and may be incorporated into the body of this post.

The Causes
Probably the number one cause of a poor SD picture is digital transmission. What’s that you say? I thought digital was supposed to provide crystal clear picture quality. Well the truth is, sometimes it does and sometimes it does not. In order to cram as many channels as possible on a satellite or cable the providers will compress the signal using a method called mpeg2 compression. Like zip files on a computer the original data is put through an algorithm to make the data smaller and allow more data through in given space. Unlike the zip file operation the compression is enough more that some of the original information is lost. When the data received is uncompressed, there are small artifacts that are created due to the algorithm trying to fill in the blanks, so to speak.

Artifacts
Artifacts are errors in the picture after decompression that is a result of the decompression process, the source camera or errors in transmission along the way to your TV. The two main decompression artifacts are the posteraztion and the artifact that results in a “ghost” like outline. It is particularly noticeable around text. Other distortions of the picture include pixelization and digital blurring on fast motion. A good introduction to artifacts in digital images is here: http://www.dpcorner.com/topics/. While this mainly covers digital photography, the principles are the same, only remember HDTV scaling and decompression has to happen 30 times per second. In fact you will see stills in that link that describe visually what many of us are complaining about.

The cause of the artifacts is twofold. On video that started out analog the video signal is digitized at the source to a digital compressed frame with the resolution of roughly 640x480i. Just like your scanner when compressed to jpeg file there are errors, albeit slight at the native resolution. When you zoom into a photo scanned in at 640x480, you will begin to see some of the errors and pixelization. Somewhere the signal has to be converted (scaled) from the 640x480 original to the 1280x720 or 1920x1080I your HDTV requires. You are sitting at a computer, if you have a photo editor do that to a photo and see how it comes out.

TV Size
TV size is a big factor as to whether you notice bad picture quality. The really bad SD pictures seem to be reported primarily in screen sizes larger than 40”. Also the viewing distance will affect how noticeable the artifacts are, so it becomes a combination of screen size and viewing distance. 40” and smaller screen sizes seem to be less objectionable with 34” and smaller barely noticeable at normal living room viewing distances.

If you have a large HDTV already, or are looking to buy a large HDTV try this test. At your seating distance use the PIP function to place two pictures side by side. Most HDTVs today have this feature and it does not matter whether you get a picture in both windows for this test. If the smaller picture becomes acceptable in terms of clairity, then the TV is too big for your seating distance and the only solution for a good SD picture is to get a smaller TV or sit further away from the TV. Obviously this test will be better made before you buy your TV. The bigger the better does not necessarily apply to TVs.

Signal Strength
While conventional wisdom says with digital video you either get it or not, there is the possibility of a drop in signal strength for sufficiently short periods of time to not cause a total loss of picture. Loss of signal for very short periods can be error corrected for by your receiver where it will “guess” what the data should be and what you end up with is bad video. If the signal loss duration is long enough that the receiver can not “guess” what the data should be, you get a mpeg2 block or blocks with extreme pixelization. Generally this condition will also show up on the HD picture, but it might not be as noticeable.

TV Settings
There are some TV settings that can aggravate the poor SD picture. These are noise filters and other settings that are intended for the clean up of analog video. When digital video is processed by these filters, it can enhance digital artifacts rather than eliminate them. An example would be the sharpness setting. The sharpness is intended to enhance the edges of objects in an analog video picture. You sure do not want to be enhancing the edges of digital artifacts. I use a setting of no more than halfway, but depending on each particular set, this setting may need to vary. Interestingly enough when I watch SD material on my local DTV stations, the video is so free of compression artifacts I usually set the sharpness to 80 or 90. Play with this and see if it does not make a difference.

Optional Hookups
The one suggestion that is repeatedly said to have some success is the connection of a composite video (yellow) or s-video connection between the receiver and the TV, as well as a second audio L/R connection. Then you can select the SD video input while you’re watching SD programming and the HD input for HD programming. Another possibility if you have analog cable service along with your digital cable service, is to connect the antenna input to your NTSC tuner to the cable. Many TV will scale analog signals to the HDTV screen without the decompression artifacts (because there is no compression with analog) and the picture will look better going through your TV tuner.

Source Scaling
The best SD video will be where the source (DVD Player or TV station) does the scaling. This explains why video from DVD players is better than the video from a SD cable box or satellite receiver. My DTV stations scale the SD picture to the HDTV resolution the station broadcasts before they broadcast it and the picture is about the same as my DVD player. Switch over to my Directv satellite receiver on the same local channel and the picture quality plummets to below that of my VCR.

Voom
Right now the picture quality I get on Voom SD is somewhere between DVD quality and VCR quality, but definitely better than my SD Tivo receiver. Word is they intend to change the decompression method in the future that will improve the picture quality even more. Voom’s receivers are fully downloadable, so a complete software change is possible. Voom only offers HD receivers, so their SD is constant as far as receivers are concerned.

Directv
Directv has both SD only and HD receivers. My experience is the picture quality of their SD receivers is pretty bad when viewed on big screen HDTVs. Most people report picture quality on SD Directv receivers to be below that of a good VCR. On HD receivers the picture quality is generally much better, with some channels comparing to the picture quality of a DVD. It seems to be somewhat brand dependant though.

Dish Network
Most complaints seem to be that the Dish Network SD picture quality is far worse than Directv. Many people with HD service have threatened to switch back to Directv. The issue seems to be the fault of the 811 receiver. One person was able to get a Dish tech to hook up a 311 receiver that produced as good a picture as the Directv receiver. He was able to talk Dish into letting him keep the 311 in addition to the 811 for a year. This leads to the conclusion that the processor in the 811 may be slower in decompressing the mpeg2 data stream than the 311.

Note On Local Channels Over Satellite
I have read repeatedly that local channels in SD over satellite is far more compressed than the regular satellite channels. I don’t know about this as being fact, but I do know that the picture quality is better on my OTA antenna through my TV NTSC tuner than it is coming through the satellite.

Cable
From what I have read, digital cable has the same problems with SD reception that are found with satellite receivers. There have been many people that have suggested splitting the cable signal and connecting it to the TV NTSC tuner connection. Many people have said the TV tuner has improved their SD reception.

Signal Processors
While they may improve the picture somewhat, most of the artifacts due to decompression will not be dealt with. The best results for the use of a signal processor like the DVDO unit is had when the unit is used to scale the DVDO output to match the native resolution of a display, particularly a projector. One DVDO expert has this to say on another forum:

Conclusion
In conclusion I would say if you are looking for a HDTV to purchase and you know you will be watching a lot of SD programming, then I would recommend you shop for the TV by watching SD material. Chances are the TV that looks the best to you in SD will be stunning in HD. Also try to match the source you will be using. If you are going to use satellite, then try to view the set with a satellite feed. The same satellite provider if possible. If you are going to use cable, then view the TV with cable.

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Slvrbulit1@aol

Thanks for the EXCELLENT post. It probably saved me from returning my new HD television. HD is great and is all I looked at in the store. Good advice would be to look at SD (if possible) in the store. I tried the splitter and the results are better, especially on the analog channels of my cable. I realize your many posts must be time consuming, but they are greatly appreciated.

Lurf

Thanks so much, rbinck. We all appreciate your research and time invested on this question. So it seems to be that the compression for transmission of what may have originally been a good sharp picture is the biggest cuprit in producing a soft fuzzy SD picture. And then most of us who believe that bigger is better exascerbate the problem by having big screen monitors way over 40 inches. Hmph! Seems like we're between a rock and a hard place. And you mentioned the the source camera, which, if not high quality, can lend truth to the adage "garbage in, garbage out". (Just notice the difference in picture quality between big budget production commercials and low budget ones.) I had an interesting viewing experience today when watching a locally produced college basketball game. There were three viewing options on my 50" DLP: satellite SD, ota SD and ota analog. The analog picture was excellent and the digitals were just ok. Go figure. Thanks again.

maximus

Thank you rbinck, top-notch post!

miamivice55

Thanks Rbnick For The Informative Post !

jfjimmar

Thank you rbinck. You saved me hours of searching and reading threads. Your post answered so many questions many of us have. We appreciate you sharing your knowledge with those of us whom are new to the HDTV era.

hdtv4me2

I believe someone once wrote that VOOM uses the WM9 video compression and D* and E* use the MPEG2. I have read that VOOMs new birds will not use WM9 but will use the MPEG2 compression. Any idea why VOOM would abandon a better compression scheme for a poorer one?

Very informative post by the way, thanks for spending the time and effort!

rbinck

I read somewhere (maybe on another forum, so grain of salt) that the mpeg2 compression would be used for SD locals (if added) and mpeg4 will be used for cable SD and HD channels. The box is downloadable as far as the software goes, but it will require the change out of the dishes to multi sat.

Forge

What does NTSC tuner stand for?

maximus

National Television System Committee
http://www.ntsc-tv.com/

Forge

Now that I know what NTSC stands for.
What/where is the NTSC tuner connection on a TV, and specifically a Mitsubishi HD DLP?

rbinck

The NTSC tuner is the standard analog tuner that have been in TV sets since the beginning. The ATSC tuner is the new digital tuner. If your TV has an analog tuner (NTSC) there will be an F connector on the rear of the set to which you connect the coax from your OTA antenna.

ewl88

Thanks for this informative and comprehensive post. It is too hard to chase down individual posts. Do you have a preference of connecting a composite video between the receiver and tv with audio l/r connection versus the cable splitter with a coaxial video cable to the tv. I don't want to spend more cash on something that doesn't work. And as other threads have mentioned, cables are not cheap especially if you go with the ubiquitous and pricey monster cables. (I think i will consider other suppliers but I still need to choose one plan vs the other)
I have a panasonic dlp pt50dl54, cablevision with scientific atlanta 4200HD, onkyo speaker/reciver htr500 system
And like many others, I'm not thrilled with the SD quality image on my new system. Thanks.

soonerfan54

With analog cable, length of cable and/or use of splitters can affect SD quality too. In my case, builder ran cable through splitter to new room, and picture was horrible. Used another cable origination and picture was much improved. This may be common knowledge to you pros so please forgive if so.

By the way, I posted a question about how to connect a new TV with a surround sound system in this forum. Was this the correct place to post?

legend1969

thanks very much for the info, iv just started using my HDMI feature of my plasma and as far as DVD movies and my cable HD programing iv noticed a huge difference. It makes perfect sence thanks again for the great info.