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'[EE]: bluetooth and cordless phone interference. L'
2007\01\01@034546 by Robert Rolf

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Herbert Graf wrote:
> On Sun, 2006-12-31 at 11:10 -0200, Gerhard Fiedler wrote:
>>This probably makes in not suited for TV, right? Sometimes there is a
>>channel with audio and video slightly out of sync, and it seems it's less
>>than 1/4 second that can create this out-of-sync feeling.
> Absolutely, 250ms may not sound like much, but to me that much delay in
> the audio would intolerable. TTYL

And extremely obvious.

The typical lip syncing error you see is due to the 'frame sychronizers' that
stations use to sync their incoming live feeds with station sync. They SHOULD
be sending the audio through the synchronizer so that it can insert a matching delay,
but often the video then goes separately through a couple of digital switchers and ends up
being delayed by a frame or two or three (33ms delay *IS* visible to practiced eye).
This leads to that out-of-sync feeling.
Newer stations have the synchronizers built right into the switcher, so the audio never
gets processed in the first place.

It is also possible that there is a clock rate error in the playback of an MPG recorded
program, where the audio and video clocks on playback are slightly off, so that by the
end of the program, there is a noticeable error between the two streams.
You often see this with Winblows media files.

My wife just received a bluetooth earpiece for Christmas, and when testing it in
the house the 1/4 second delay was MOST annoying, particularly since I was also hearing
my OWN voice back from the earpiece (Motorola H350 with Samsung A920).
This delay is MUCH less when NOT using the bluetooth connection.
CDMA phones have a noticeable delay anyway, but the bluetooth made it much worse).
Given that the BT slot rate is 1600 Hz (1Mbs packet/625us long) I can see no reason
for a 1/4 second delay for the audio. At most I would expect 2/1600 sec (double buffer).

Any bluetooth experts care to comment on why BT audio seems to have inordinate delays?


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