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Re: [Shop-talk] radio/tv sync?

To: Matt Wehland <>
Subject: Re: [Shop-talk] radio/tv sync?
From: David Scheidt <>
Date: Mon, 31 Dec 2012 00:07:50 -0600
References: <> <>
On Sun, Dec 30, 2012 at 10:47 PM, Matt Wehland <> wrote:
> Ok a quick search turned this up-
> or
> No Idea if they work.
> -----------------------
> When I worked with this was a real problem.
> Sometimes we would get audio not in sync from the broadcast truck.
> There solutions ranged from ten's of thousands of dollars (could only delay
> audio, not video) to a custom million + dollar A/V router system that had
> audio/video delays built in for just this problem (and many others)
> You basically need a program/hardware that will delay the audio (normally
> ahead of video) or delay the video (not often the issue) and then manually
> sync them up and hope the delay doesn't change for the duration of the
> event.
> Heck just try having 2 TV's on cable, one HD one SD, there is normally a
> significant delay between the 2 boxes on the order of a second or more on
> the local cable system.

When I lived in northern Indiana, most of the sports bars had both
cable and satellite service, because one considered Chicago the local
market, the other detroit, which changed which games were available.
So it was not unusual when they were showing the same thing on all of
them to have half tuned to one source, the other half to the other
source.  One would be two to five seconds ahead of the other.  You
could tell when important plays were made, just by watching the heads
move to the delayed screens.  Somewhat surprisingly, the delays
weren't constant, they'd change over the course of a football game.

 A lot of the delay is inherent in digital television.  Not only are
there encoding and delays (which make it lag behind the non digital
version, were the non-digital version actually broadcast.  it's not,
so it's really the digital signal, decoded, converted, and
retransmitted, so it's often behind on cable), there's an error
recovery buffer (two sorts, one built into the format, the other into
the hardware.) and the speed of the hardware.  There's also often a
satellite hop (or two, rarely three), good for a third of a second or
more each.   Radio is just audio, even if it gets turned into digital
signals, the conversion overhead is a lot lower.  (I know at least
some of the network feeds are now over the internet, essentially
guaranteeing they're not over a satellite link, too.)

> Makes it funny listening to the neighbors scream for a play a second or more
> apart.
> Even worse if the 2 TV's are in the same room/house.
> Useless knowledge Alert-
> In the old analog video days it was standard practice to use long runs of
> cable (100's of feet) to time the delay of video signals through different
> pieces of equipment.

Some of the first computer memory used audio pulses sent through
mercury tubes.  you knew how long it took for sound to travel the
tube, so you knew when you'd have to listen for it.  Required constant
refreshing, and wasn't random access, but it worked, and the
technology already existed.  It's a variation of the technique to
remove the signals from fixed objects from early radar screens.
Compare two successive scans,  anthing with the same delay isn't
moving, and can be ignored.

David Scheidt

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