: 720 P or 1080i which is better for my LCD?

2008-01-24, 07:25 PM
I have a 40" Samsung LCD (LN- S4051D) that has a native resolution of 1366 x 768 and specifies that it has 720p output.

I have a Rogers Explorer 8300 HD STB and a Harmn Kardon AVR 247 that upconverts to 720P. My STB is connected through the AVR with component cables and digital coax for audio and an HDMI output to my TV.

My questions are:

1. Is 720p resolution better than 1080i which I can get through my STB?
My receiver only passes through 720p unless I go direct from STB to TV.

2. What is the best setting on rogers box Upconvet 1, 2 or pass-through?

I currrently have it on upconvert 2 which sends signals at 420p and 720p.


the hawk
2008-01-24, 10:16 PM
Your TV is native 720p, therefore you are better off feeding it a 720p signal. Feeding a 720p TV anything higher is pointless as the TV's scaler will downconvert it back to 720.

2008-01-24, 11:32 PM
Actually it depends on if the STB puts out actual 720P at 1280x720... 720P is supposed to be 720 lines of vertical resolution, your TV outputs a higher resolution 1366x768, meaning your TV will have to scale 720p up slightly. It may be better to feed 1080i and have the TV scale down.

You'll probably not see any difference either way, but flip back and forth a few times to compare. (I have all my inputs on 1080i for my 768 TV).

2008-01-24, 11:48 PM
The TV is not native 720P, it's 768P, therefore either incoming signal gets converted. It's usually best to send the native signal to the TV and let it convert from a STB standpoint. So, enable 480i STANDARD, 720P and 1080i in the STB and set picture format to passthrough. I'm sure the AVR will also passthrough the signal if set that way. The TV will then do the final conversion, which is usually the best option, however, feel free to experiment.

Setting the STB or AVR to 720P only, is the incorrect choice as then 1080i signals would be converted to 720P, which the TV would then convert to 768P, an extra step. Same for 480i.

See the following relevant threads/posts:

http://www.digitalhome.ca/forum/showthread.php?t=73528 Native formats

http://www.digitalhome.ca/forum/showthread.php?t=17719 SA STBs

http://www.digitalhome.ca/forum/showthread.php?t=57741 Newbie info

2008-01-25, 12:12 AM
I'm another example of personal experience that agrees with what has been said about letting the TV do the final conversion.

Make sure you do try the different settings to see what looks better on your equipment, but when I compared 720p vs 1080i using my up-converting DVD player on my 768p set, 1080i looked significantly better.

2008-01-25, 12:23 AM
Stargazer, your two paragraphs are a bit contradictory. The first paragraph states that you should let the TV do the final conversion, however, SD DVDs are 480i, so based on that comment, you should set the DVD player to 480i and let the TV do the conversion.

Since most upconverting players do a better job of the upconversion from 480i to HD formats, it's usually best to set the player to output 1080i and in some rare cases of TV to 720P. This is because the upconversion is done in the digital domain and closer to the original material.

Therefore the recommendations for STBs are different from those for upconverting DVD players, however, you are correct that 1080i is usually better than 720P and that you should try this for yourself to corroborate.

Also, upconverting players are typically set to output say 1080i, while the SA STBs can be set to "passthrough" the incoming signal, which is usually the better option than setting the STB to output only 1080i.

This is discussed in the first link of post 4.

2008-01-25, 12:39 AM
Thanks for correcting me. What I was trying to do was agree with DJDiggler and say that it worked better for me to set the device to output as high as possible (i.e. 1080i) and then let the TV do the final down conversion to it's native format.

2008-01-25, 12:43 AM
What I was trying to say was to set the device to output as high as possible (i.e. 1080i) and then let the TV do the final down conversion to it's native format.This is the incorrect advice for an SA STB (and for the Motorola as well). As I stated in my previous 2 posts), you should enable the appropriate formats in the STB and enable passthrough.

This is not possible with the Motorola STBs and that may be why you are confused by my statements (although, the Motorola STBs should typically be set to 480i for the 4:3 override, but you only have one option for HD (1080i or 720P). The SA can passthrough all 3 formats.

So, when the SA STB has an incoming signal of 480i, it can be set to passthrough 480i, also if an incoming signal is 720P it can passthrough 720P and if the incoming signal is 1080i, then it can passthrough the 1080i signal. This almost always provides the best PQ because the TV does a better job at converting than the STB does. (unless the TV has very poor conversion). This also eliminates "double conversions"

AVR convert?

Now back to the OP's original questions, it is possible, that after settting up the STB as I have indicated, that the AVR can do a good job of converting the signals to say 1080i and feeding them to the TV, but it's unlikely that that is a better option than letting the signals pass unaffected to the TV, but again, feel free to experiment.

So, should the STB, or the AVR, or the TV do the conversion? My recommendation is that it's likely that it's best to have the TV do it for the STB.

As discussed above, the answer is different for an upconverting DVD player.

2008-01-25, 11:12 AM
Although PQ is often better with pass-through, there is another point to note. Depending on your TV, switching from a 720p signal to a 1080i signal can introduce extra delay in channel changes. I definitely see this with my set. If you are an inveterate channel surfer and your TV behaves this way, you may want to consider having the STB output one signal type (1080i or 720p). FWIW, to achieve the best PQ, I have my STB pass through the signal to my set and live with the extra delay when switching between 720p and 1080i.

2008-01-25, 12:09 PM
Agreed if you have a STB, however, the OP has a PVR, so channel surfing should not be as much of an issue. Also, I find surfing using the guide to be much better/faster than actually changing channels, even with the same format this can take a couple of seconds. This was also discussed in the SA STB FAQ.

2008-01-25, 06:58 PM
Assuming film sources...

Why would it be good to upconvert to 1080i in this case? Even better, if it really does look better, why would that be? The progressive scan/reverse telecine/3:2 pulldown component of the DVD player is wasted, and then the TV has to be relied on to both deinterlace 1080i properly and perform 3:2 pulldown.

If 3:2 pulldown doesn't matter much, then what did the 480p converting units of yore offer? Any benefit of the "p" part is lost by spitting out 1080i...

Just wondering... I may learn something here.

2008-01-25, 07:24 PM
No general rules regarding DVD (not really the topic of this thread) but some TVs fail 2:3 pulldown:

http://www.digitalhome.ca/forum/showthread.php?t=17869 2:3 pulldown

http://www.digitalhome.ca/forum/showthread.php?t=44096 tests on bobbing and 2:3 pulldown.

So, the answer is definitely "it depends".

Interestingly, I've set up a few of the TVs that supposedly failed the bobbing test and tried 720P vs 1080i and neither I nor my client could see a significant difference, but we set the STB to 720P on those TVs, just in case.... ;)