DBSTalk Forum banner

football time delay

1952 Views 13 Replies 9 Participants Last post by  scooper
I am curious about NFL television football broadcasts. I have been watching the Monday night football game on TV while muting the television sound and picking up a radio byplay of the game directly from the stadium. I have done this in past seasons before I got satellite TV. Now that I'm using the satellite, I notice about a 4 second delay between the action described on the radio and the video broadcast on the TV. The TV is behind the radio. Is this normal? I'm watching a local into local TV station and my receiver is a Sony TIVO T60 if it matters. It's not a particularly distinguished game so I decided to leave the radio on while attending to some housekeepting on the computer. Thank you for your assistance.
Not open for further replies.
1 - 14 of 14 Posts
It's normal - the satellite signal has to travel a looooong ways up and then a looooong ways back down to your dish before it gets to your television. (something on the order of 22000 miles each way, or something like that.)
Actually in most cases the signal has to travel up to the satellites twice. Once from the actual game location and then the other to DirecTV. Each round trip takes a couple seconds.
Plus your Tivo takes a little bit of time processing the signal.

A stand alone Tivo or ReplayTV takes about 1 1/2 - 2 seconds while a "DirecTivo" unit probably takes a little less, since it doesn't have to encode the data.

So satellite plus stand alone Tivo or Replay can yield a delay of about 3 -4 seconds all together.
The following factors are contributing to the delay:

  • Round trips to satellites, EM waves traveling at the speed of light. About 1/4 second each round trip. (may be two of them, may be one of these in your radio broadcast as well).
  • MPEG encoding, statistical multiplex look-ahead buffer delay (STATMUX processing at uplink center) and MPEG decoding (pipeline). About 2 seconds.
  • TiVo's buffering to the hard drive. About 2 seconds.

So, you see, the majority of the delay is the result of processing, about 1/2 second or so is actually due to speed-of-light issues to the satellite.

Indeed, if you compare a regular receiver to a DirecTiVo, the DirecTiVo is about 2 seconds behind the regular receiver due to its disk buffer.

You have probably noticed that when on a news show, they interview someone live via satellite, sometimes there is negligible delay, and sometimes there is significant delay.

When there is negligible delay, it is because their link is an analog C-Band link. The total delay is about 1/4 second from anchor desk to interviewee, then another 1/4 second from interviewee to anchor desk, for a total of about 1/2 second delay. Barely noticeable.

However, when you see a big delay in such a satellite interview, it is because they are using a multiplexed digital (MPEG) C-Band link (which are cheaper and becoming more and more common because of their more frugal use of increasingly limited satellite bandwidth). In this case, the total delay is about 2 seconds from anchor desk to interviewee, and 2 seconds from interviewee to anchor desk. A total of about 4 seconds, quite noticeable to the viewer!
See less See more
I just want to say I appreciate the well reasoned responses I received to my posting. I learned something and satisfied my curiosity all at the same time. One of the advantages of this board is the number of well informed members who participate in it. I always consider any time I spend browsing it as time well spent. Again, thanks.
I have two Ultimatetv units in rooms next to each other (Family Room / Master Bedroom) and they aren't in sync with each other. They are about a second apart. I could never figure that out as they are identical units (well, one has a larger HD), are fed from the same dish and multi-switch and are about the same distance from the multi-switch. I've just come to accept it as I can't figure out why.
Originally posted by karl_f
I have two Ultimatetv units in rooms next to each other (Family Room / Master Bedroom) and they aren't in sync with each other. They are about a second apart.
DirecTiVo's, Dish PVR's, and DishPlayers also do this.

This is the reason:

When you first change the channel, the UltimateTV (or other brand of PVR) establishes a disk buffer that is some fixed number of kilobytes.

However, from the moment that buffer is established, it must retain a constant amount of time. If it didn't, the playback would slow down and speed up!

Since the bitrate of any given channels is constantly varying with it's content, the disk buffer must grow and shrink to keep the same number of seconds worth of programming in the buffer.

The bitrate of any given channel can vary from slightly lest than 1 megabits per second to about 5 megabits per second.

So, lets' suppose the initial disk buffer size is 500 kilobytes. After the 500 kilobyte buffer is established, it will grow and shrink so that it always buffers a constant amount of time.

So, suppose you tune to HBO on UltimateTV unit number 1. At the moment you tune to HBO on unit 1, HBO is delivering 3 megabits per second.

Three megabits per second is .375 megabytes per second (3/8 = 0.375) or 375 kilobytes per second.

So, the 500 kilobyte buffer established would contain 1.333 seconds. (500 / 375 = 1.333).

Now, suppose you tuned UltimateTV receiver 2 to HBO at a moment when HBO was occupying 2 megabits per second.

The buffer in this case would contain 2 seconds of video. (2 / 8 = .25) (500 / 250 = 2).

So, in this example, UltimateTV unit 1 would be buffering 1.333 seconds worth of video, and unit 2 would be buffering 2 seconds of video. A difference of 0.666 seconds.

If you could manage to tune both units to the same channel at the very same nanosecond, they would be in perfect sync. ;)

(BTW: I don't know that the buffer size is actually 500 kilobytes, this is a guess, but it is probably pretty close.)
See less See more
so now that it has been explained..is there a remedy to this situation????

I don't think it is something that needs a "remedy." That's just the way it is :) At least everything works.
I badly want to listen to the radio broadcasts of Browns games while I watch my Sunday Ticket broadcast of the Browns game. If anyone has any ideas as to whether I can do this & synchro the delay somehow...please let me know...


Any solution to synchronize is going to be expensive, if it can even be done at all. If you are REAL good with programming and have 2 sound cards in your PC, you might be able to take the audio output of your radio, feed into line1 on one sound card, insert a user-adjustable delay, and output it on the other sound card. It may even be possible to do this with just 1 sound card.
I once had the same show on in 3 rooms---a waste I know. One was OTA, one a DISH 3700 and one a DP. The sound which i could pick up in the hallway was different ona ll three.
If I want to do that, I tune ONE satellite receiver, then each TV is tuned to that channel from my modulator. MUCH cleaner...
1 - 14 of 14 Posts
Not open for further replies.