Web PVR in v2.96 - Recording modes

[Jim web]

In article <9BCBF20534D84359B637D3DE316579C1 at RJCDESK>, RS
<richard22j at zoho.com> wrote:
> Has anyone tried to do this?  As Jim says, the propagation/processing
> delays will differ.  The issue is whether the relative delay is
> constant, which would mean a fairly easy adjustment, or whether it
> drifts so that adding in a constant delay will not work.  Many years
> ago (probably pre-NICAM) the BBC occasionally had radio/television
> simulcasts, so it may be that the problem of keeping radio and
> television in sync has been considered.  Do they use the same clock?

Alas, the problems aren't simply a fixed offset.

I did some relative time comparisons some years ago. You can see the
results at http://www.audiomisc.co.uk/BBC/XHQ/TimeTravel.html

The details will have changed since then, but...

The basic conclusion is that, no, the various TV and Radio streams do *not*
use a common sample clock. Indeed, that approach would mean that the BBC
would have to try to synch their entire system of studios, OBs, etc. Not
trivial given how spread apart they may be.

They tend to have asynchronous resamplers in various places to get the
results though the system. This means 'drift' will occur. How much that may
matter will depend on the case.

You can, of course, in principle, re-synch using an asynch cross
correlation process. i.e. One the does a sliding comparison of the
waveforms as it runs though the data. But I personally haven't dared to try
it because it may be a real challenge.

Jim

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