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| Thread ID: 121677 | 2011-11-05 22:59:00 | digital/freeview vs analogue broadcast | GameJunkie (72) | PC World Chat |
| Post ID | Timestamp | Content | User | ||
| 1242142 | 2011-11-05 22:59:00 | senario: the big tv which is digital/freeview, it is on TV1 HD the smaller tv has analogue TV1 on the analogue tv is a couple seconds ahead of the digital tv, so we'd hear the same thing twice. when we had two analogue tv's , the broadcast is at the same time. what's the reasoning/cause behind the delay??? thanks |
GameJunkie (72) | ||
| 1242143 | 2011-11-05 23:12:00 | Doppler Shift? Analogue signal goes direct line of sight where as digital signal is bounced off a satellite. I had noticed this effect when watching the last shuttle flight with the Fox TV coverage on the sky box being faster than the digital coverage on the NASA internet site. Same effect present with international communications with a few seconds delay you might have noticed? |
driver (16592) | ||
| 1242144 | 2011-11-05 23:39:00 | I have a similar delay effect with satellite Freeview. I have Freeview satellite connections to my lounge (closest connection to the satellite dish), my computer and to my bedroom. If I have all three going at the same time the broadcast to the lounge TV is ahead of the broacast to my computer and my bedroom TV. It is not a huge problem but it appears that the longer the wire the longer it takes for the signal to reach the TV. The delay is only a second or two. |
Bobh (5192) | ||
| 1242145 | 2011-11-05 23:45:00 | Doppler Shift?Nope - doppler only applies when the distance between the transmitter and the receiver is changing, which isn't the case here. Analogue signal goes direct line of sight where as digital signal is bounced off a satellite.The OP states they're watching in HD, which means terrestrial transmission from the same towers as the analogue signal. The satellite feeds aren't in HD. Same effect present with international communications with a few seconds delay you might have noticed?Similar effect, but a different cause - the delay in most international communications is caused by the slow speed of light and the long distance between the endpoints. Some of the delay is also caused by routing / switching equipment. The delay will never be more than about half a second unless there's something else in the way, or you're trying to route via geosynch satellites. It is not a huge problem but it appears that the longer the wire the longer it takes for the signal to reach the TV. The delay is only a second or two.It's nothing to do with the wire - unless you're talking about a circuit thousands of kilometers long, or some very slow relays, the wire length won't have a noticeable effect. The delays talked about here are caused almost entirely by buffering on the freeview receiver, error correction, and a little bit for encode / decode latency. None of these issues apply to the analogue transmission, hence why it displays slightly ahead of the digital broadcast. |
Erayd (23) | ||
| 1242146 | 2011-11-05 23:49:00 | Ok not to get to technical :D Communications Satellites in geostationary orbits are far enough away from Earth that communication latency becomes very high — about a quarter of a second for a one-way trip from one ground based transmitter to another via the geostationary satellite; close to half a second for round-trip communication between two earth stations. For example, for ground stations at latitudes of φ=±45° on the same meridian as the satellite, the one-way delay can be computed by using the cosine rule, given the above derived geostationary orbital radius r, the Earth's radius R and the speed of light c, as This presents problems for latency-sensitive applications such as voice communication or online gaming. |
driver (16592) | ||
| 1242147 | 2011-11-05 23:55:00 | Nope - doppler only applies when the distance between the transmitter and the receiver is changing, which isn't the case here. The OP states they're watching in HD, which means terrestrial transmission from the same towers as the analogue signal. The satellite feeds aren't in HD. Similar effect, but a different cause - the delay in most international communications is caused by the slow speed of light and the long distance between the endpoints. Some of the delay is also caused by routing / switching equipment. The delay will never be more than about half a second unless there's something else in the way, or you're trying to route via geosynch satellites. It's nothing to do with the wire - unless you're talking about a circuit thousands of kilometers long, or some very slow relays, the wire length won't have a noticeable effect. The delays talked about here are caused almost entirely by buffering on the freeview receiver, error correction, and a little bit for encode / decode latency. None of these issues apply to the analogue transmission, hence why it displays slightly ahead of the digital broadcast. makes sense Erayd thanks |
GameJunkie (72) | ||
| 1242148 | 2011-11-06 00:05:00 | makes sense Erayd thanks I thought I said the same thing in less words i the second paragrah of my reply earlier? Maybe the red herring of Doppler shift through you off....lol |
driver (16592) | ||
| 1242149 | 2011-11-06 00:07:00 | technically, that's Ok not to get too technical :D |
bevy121 (117) | ||
| 1242150 | 2011-11-06 00:39:00 | Interesting (seriously). I'd never really thought about it until now. ;) Sort of OT, can anyone tell me why the delay happens when TV crosses to a on location link. That's where the anchor says "we cross now to Paul Henry-Holmes live from beautiful downtown Urenui". Henry-Holmes then has 5 - 10 seconds before duplex communication is available, while trying to look like a masterful interviewer in control of the situation instead of playing charades with the appropriately apt name of the town. What is happening? :lol: |
WalOne (4202) | ||
| 1242151 | 2011-11-06 00:47:00 | Interesting (seriously) . I'd never really thought about it until now . ;) Sort of OT, can anyone tell me why the delay happens when TV crosses to a on location link . That's where the anchor says "we cross now to Paul Henry-Holmes live from beautiful downtown Urenui" . Henry-Holmes then has 5 - 10 seconds before duplex communication is available, while trying to look like a masterful interviewer in control of the situation instead of playing charades with the appropriately apt name of the town . What is happening? :lol: Same as that time delay you get when talking to someone on the phone in another country . Not so bad these days but that delay and echo really used to drive me nuts . . . lol |
driver (16592) | ||
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