Football on Sat TV and AM radio way out of sync? Speed of

January 15, 2008 1:30 AM

Football on Sat TV and AM radio way out of sync. Is it a technical thing or a maths issue? Speed of light, azimuth, etc

I like watching football on sat TV but like listening to the commentary on AM radio. The AM radio is about 1.5 seconds ahead of the Sat TV. My maths goes like this. All is equal leaving the ground, they both then send the signal through a sat uplink to the studio. Then one is transmitted via satellite on the equator near West Africa (80,000km round trip) and one comes over the air from a big tower (say 1000km). The delay should be 1/4 second (79,000k/speed of light 300,000km/sec). What gives? BTW if you are in the UK and want your bearings then look for a grey sky TV disc on a house and mimic the way it is facing, turn to your right about 35 degrees and you are facing due south. The angle varies a bit by location but not by that much.

posted by priorpark17 to technology (12 comments total)

Your maths, they are good.

I suspect the additional second may be the difference between the radio and television broadcasts' profanity/nipple delays.
posted by dhartung at 1:53 AM on January 15, 2008

Also, forget not that you probably experience a titch of delay on the satellite decoding side, or encoding, if you're running through a DVR.

My TiVo will be about 1-1.5 seconds behind live from an upstairs, non-TiVoed TV because it has to MPEG encode first. Frame buffers, etc.
posted by disillusioned at 2:05 AM on January 15, 2008

If you have a Mac, Griffin's RadioShark can be used like a Tivo for your radio, recording and playing the broadcast as it records with a time delay to sync up with the TV. (You'll need to spring for a good quality AM antenna, as the one built into RadioShark sucks.)
posted by Slap*Happy at 4:09 AM on January 15, 2008

A profanity/nipple delay would have to be a lot longer than 1.5 seconds. Five seconds at least, and I think I once heard that seven is the industry standard.
posted by Dec One at 5:27 AM on January 15, 2008

It's mostly video compression, plus a little due to the satellite hops. Video compression eats about 1000 ms, and satellite eats at least 250 ms (it's 250ms per hop, and for a live game there is usually more than one hop). I'm surprised it's not more than that. And actually, if you watch via a direct broadcast satellite like DirecTV or Dish (instead of OTA or cable) then it'll be well over that 1.5 seconds because of the extra encode/decode and satellite hop.

It's fun to listen to the radio though and see the event (e.g. touchdown) well before hearing your neighbors whoop :)
posted by intermod at 5:48 AM on January 15, 2008

Not that this adds much, but the delay is noticeable in satellite vs. cable, not just AM/FM. At a local bar, they've got both cable and satellite and the 2 second difference in responses is often humorous.
posted by unixrat at 6:14 AM on January 15, 2008

This sort of delay occurs in just about any system, I'd wager. Our digital cable (Comcast, near Boston) broadcasts the local channels with approximately 4 seconds of delay. It can get really obnoxious hearing the same Ford truck commercial in delayed stereo when the little kitchen TV with rabbit ears is tuned to the same station as the living room TV on cable.
posted by explosion at 6:22 AM on January 15, 2008

You're also missing a hop at least for Sat TV

Sat TV is going to go from game -> studio -> DirectTV (or satellite) aggregation point -> DirectTV distribution sat.
posted by bitdamaged at 6:57 AM on January 15, 2008

I asked a similiar question here:
http://ask.metafilter.com/23666/How-can-I-add-delay-to-a-radio-broadcast

I know i've found the problems different, when different stations carry games
posted by yeahyeahyeahwhoo at 7:02 AM on January 15, 2008

There's also a delay for HD, which I assume has to do with processing and digitization. We were at a bar this weekend watching the playoff games, and in a room of 8 televisions tuned to the same game, all but one was tuned in HD. The standard def TV was about 3-7 seconds ahead of the other TVs. We called it "Future TV" and wouldn't watch it so we wouldn't ruin the big plays for everybody else by cheering or crying early.

This anecdote is merely aimed to add to the general feeling that there are many factors in the timing of "live" presentations.
posted by General Malaise at 7:11 AM on January 15, 2008

In the UK, at least, radio commentary often goes via ISDN circuits (in this context, it's a good quality phone line.) Even with coding the delay is often a few milliseconds, as opposed to the minimum ~250ms + video coding delay for sat links. Plus it's usually cheaper than a satellite link, and most stadiums provide an ISDN point for each commentary position.
posted by Luddite at 9:12 AM on January 15, 2008

Over here (UK and Ireland) the gap used to be up to about half a second, being the time taken to bounce it off a satellite twice -- once to get it from the stadium to the broadcaster, and once from the broadcaster to your house. The extra second seen these days is muxing and demuxing time introduced by the move to digital broadcasting.
posted by genghis at 3:15 PM on January 15, 2008