[TrebleKing]

I'm on Virgin with a Tivo box and have a 55" LED LG telly. Some of the subsidiary channels look absolutely terrible. ITV4 for example. Grainy picture all over the place. ITV HD has sound drop outs out occasionally, has anybody had those? I had the Virgin engineer out to check the signal and box, so I know it's likely to be from source. Why are some channels lousy looking? Is it a bandwidth or signal thing?

[pakokelso93]

I've said it before etc HD Channels are fine, but People who see SD pictures of any channel on a big TV compared to a smaller one are obviously going to see a picture quality reduction. Bigger the TV the poorer the SD picture. You go to a say under 30" tv SD picture is crystal clear.

[Alan Thew]

A 2 Mbit/s MPEG-2 stream blown up to 55 inches is never going to look pretty. The main SD channels have a higher bitrate and should look OK. But nothing less than HD is going to look very appealing on a screen that size.

ITV3 and ITV4 live TV are indeed awful on Virgin (don't know about other platforms). The content looks much better on demand, plus you'll avoid the adverts that way. I don't know if they use a higher bitrate for that, or if it's encoded better. Lewis looks OK via on-demand, but in the past I've switched it off when trying to watch on the live TV channel because the MPEG smearing was so distracting. Also they've had problems in the past with the picture visibly juddering every time an MPEG keyframe is inserted about once a second.

[TrebleKing]

Thanks for the replies, guys. Yeah, the juddering is pretty appalling on some of the channels. I had to watch a football game the other day on a standard definition channel and the picture was horrible until I tweaked some of the settings to get it looking bearable. I can't wait until all channels go HD, it can't come soon enough!

[derek500]

Originally Posted by TrebleKing

I can't wait until all channels go HD, it can't come soon enough!

You need to change your provider, if you want more HD.

[TrebleKing]

Originally Posted by derek500

You need to change your provider, if you want more HD.

Aye, but surely all channels will eventually broadcast in HD format?

[Bspks]

Originally Posted by TrebleKing

Aye, but surely all channels will eventually broadcast in HD format?

Given the cost of re-equipping studios and playout suites, coupled with the fact that many channels broadcast primarily material not made in HD (quite a lot is still 4:3) this is highly unlikely.
Couple that with the millions of SD only receivers still in service and it gets even more unlikely.

The Moral? don't buy a screen size that's too large for your viewing position.
If you sit far enough away from a large screen, SD won't appear so bad.
The other main point is to make sure you audition any prospective purchase with both HD and SD (especially including low resolution channels broadcast at 544 x 576i) to make sure you can live with it.
Some models are much better at upscaling than others.

[TrebleKing]

Well it may be the case that, in truth, I jumped in when I bought my new tv. I'd been left money by my late stepfather, and I was moving into a new house with my girlfriend. I just wanted as big as I could get. I think the living room's a touch too small for a 55" screen, I can see that now. I didn't realise how horrible SD would look when blown up that much. That's not to say all SD channels are like that, but I thought these high cost TVs were supposed to 'upscale' SD to something approaching a HD picture? Expensive lesson learned by me, it seems.

[derek500]

Originally Posted by TrebleKing

Aye, but surely all channels will eventually broadcast in HD format?

You mentioned ITV4. it's already HD, but not on Virgin.

[Nilrem]

One of the things to remember is that not all SD channels are the same,.
IIRC the bitrate for the channels varies a lot depending on who is running it and how much bandwitch they're willing to pay for, so BBC1 will generally look much better than obscurechannel23, as the BBC use a reasonably high bit rate (and are willing to pay for it), whilst obscure23 might be using the bare minimum they can get away with (things like choice of encoder and whether the encoding is left to default values or actually looked at by a human to maximise the quality also has an effect)..

The same is true for DVD's, as some try to stuff as much on a disc as possible (and are willing to lower the PQ to do it), whilst others might be willing to just have the main feature on the disc and maximise the PQ (Criterion from memory did that).

The bigger the display, the more obvious the low bit rate or generally poor encoding stands out, but it's also worth remembering that some displays handle the upscaling of SD to the res of the screen better than others (when I chose my LCD TV I paid close attention to how the model handled SD inputs and ended up going with one that was a couple of hundred more than the cheapest at the time, as it handled SD much better);

[jzee]

Does your Virgin box do the upscaling for you, or your TV, you might find one is better than the other.

[TrebleKing]

Originally Posted by jzee

Does your Virgin box do the upscaling for you, or your TV, you might find one is better than the other.

I wouldn't know how to determine that in all honesty...

[Muzer]

Never used a Virgin box, but it might have an option burried somewhere (usually in the TV settings menu or something similar) to "force" output at a certain resolution... you can change that to 1080 (p preferrably, i if p isn't listed) to make the box do the upscaling, or turn it off (or change it to "Original" or something) to let the TV do it.

[Mal80]

Back in the days when I had Virgin Media cable, i.e. several years ago, the Discovery channels all looked a mess with compression artefacting. All I could assume was Discovery didn't care about the quality of their UK channels because even if it was VM's fault, they should have had minimum standards for their carriers to comply with.

[jzee]

Originally Posted by jzee

Does your Virgin box do the upscaling for you, or your TV, you might find one is better than the other.

It might be in the settings somewhere to output SD as 576/original or 1080, try setting 1080 if it isn't already.

[TrebleKing]

Come to think of it the Tivo box is set to 1080i. Guess I'm stuck with crap SD channels, then. The telly cost £1300 odd, with bells and whistles including a 200 Hz refresh rate which is useless because Virgin only broadcasts at 50 Hz in the first place.

[Mal80]

Originally Posted by TrebleKing

Come to think of it the Tivo box is set to 1080i. Guess I'm stuck with crap SD channels, then. The telly cost £1300 odd, with bells and whistles including a 200 Hz refresh rate which is useless because Virgin only broadcasts at 50 Hz in the first place.

When I was younger, I used to spend most of my money on high end tech like that... one day it dawned on me that it's better to just go for the middle to lower range products. The high end stuff boasts loads of fancy features that might eventually be commonly used, but by then, you could get products for next to nothing with those features.

[martine93]

My TiVo is set to 1080i only and i think the SD picture quality is excellent.

[Ernie_C]

Can someone PLEASE explain to me why the compression algorithm (MPEG2 or MPEG4) has ANYTHING to do with the quality of a picture. Surely it is ONLY the bitrate that is important?

[Alan Thew]

Originally Posted by Ernie_C

Can someone PLEASE explain to me why the compression algorithm (MPEG2 or MPEG4) has ANYTHING to do with the quality of a picture. Surely it is ONLY the bitrate that is important?

Not at all. As the years have gone by, mathematicians have worked out better formulas for representing more useful information (i.e. which will improve the perceived visual or audio quality) using the same number of transmitted data bits. MPEG-4 is a newer standard than MPEG-2, and is much more efficient. Thus it requires less bandwidth to produce output at the same quality.

You're right that MPEG-2 and MPEG-4 can produce pictures of equal quality, but MPEG-2 will require a higher bitrate to do it. Give them both the same bitrate, and the MPEG-2 stream will look worse.

[Alan Thew]

Originally Posted by jzee

Does your Virgin box do the upscaling for you, or your TV, you might find one is better than the other.

If it's connected with an HDMI lead and set to 1080i then the TiVo is doing the upscaling. To force the TV to do the upscaling you would need to either connect the TiVo using a SCART lead or set the TiVo to output 576i. Both of these are a very bad idea as you'd lose all high definition. I doubt your TV's upscaling will be sufficiently better than the TiVo's (if at all) to make your low-bitrate SD channels look better.

I don't have a TiVo, but the upscaler in the V HD box is excellent and produces a far better SD picture than the built-in Freeview in my four-year-old Sony Bravia.

[martine93]

Originally Posted by Ernie_C

Can someone PLEASE explain to me why the compression algorithm (MPEG2 or MPEG4) has ANYTHING to do with the quality of a picture. Surely it is ONLY the bitrate that is important?

SD channels on Sky are also MPEG2 - the same as Virgin Media.

[Ernie_C]

Originally Posted by Alan Thew

Give them both the same bitrate, and the MPEG-2 stream will look worse.

Sorry, but I simply don't accept that!

MPEG2 and MPEG4 are compression algorithms. Their job is to reduce the transmitted amount of data to use less bandwidth. They put the datastream back EXACTLY the same as it was before they compressed it.

The resultant datastream is EXACTLY the same after as it was before compression.

[brangdon]

Originally Posted by Ernie_C

MPEG2 and MPEG4 are compression algorithms. Their job is to reduce the transmitted amount of data to use less bandwidth. They put the datastream back EXACTLY the same as it was before they compressed it.

MPEG2 is a lossy format. See, for example, http://en.wikipedia.org/wiki/MPEG-2. (The same is true for MPEG-4 but I don't have a link.) It achieves its compression partly by throwing away parts of the signal that humans tend not to notice anyway. It gets higher compression, and therefore lower bit-rate, by throwing away more. That's a major reason for video quality varying between channels. The broadcasters vary the bit-rate, and hence the quality, according to how important they think their channel is and how much bandwidth they have available.

[Alan Thew]

Originally Posted by Ernie_C

Sorry, but I simply don't accept that!

MPEG2 and MPEG4 are compression algorithms. Their job is to reduce the transmitted amount of data to use less bandwidth. They put the datastream back EXACTLY the same as it was before they compressed it.

The resultant datastream is EXACTLY the same after as it was before compression.

Not sure how to respond to this... Ernie, I really don't want to be offensive, as that's not why I come on forums, but... are you for real? I promise you, you are wrong. Whether you accept it or not, you are still wrong. They do not put the datastream back exactly the same as it was before they compressed it; and the resultant datastream is not exactly the same after as it was before compression.