[LAU] Sync and digital audio transport - was Sample rate vs. SNR

Len Ovens len at ovenwerks.net
Sat Jan 26 17:08:40 UTC 2013

On Sat, January 26, 2013 4:52 am, Fons Adriaensen wrote:

> Word clock only at 48 kHz seems to be a limitation of some particular
> equipment. It's not clear to me why things should be that way, I can't
> see a good technical reason for it.

Maybe, it has to do with the boxes I was looking at being ADAT boxes.

> I don't think there is a 'standard practice' for audio clock distribution,
> it will very much depend on the nature of the installation. If there's
> anything video in house as well the primary source is likely to be video,
> with audio derived from it. I a large facility with many studios the
> system will be layered - a GPS driven master with an atomic standard as
> backup driving a second level master generator in each studio. In such
> a case the signal between the primary and secondaries could be video or
> just 1, 5, or 10 MHz if no video sync is needed.

So with video master the audio clock would be derived from the colour
sub-carrier then? (horizontal seems kinda low) It seems odd that for a
non-video source an even ten based frequency would be used rather than
something like 1.536M for example, that divides evenly.

> A few years ago that could have made sense as there were few MADI routers.
> But e.g. <http://www.directout.eu/en/products/m.1k2.html> will allow per
> channel routing between 16 MADI ins and outs. Of course a wall of AES3
> connectors looks cool... In practice the choice may be driven by any
> existing wiring and in-house standards if e.g. a studio is upgraded.

1024 channels of routing seems like more than anyone could need, but I
remember terminating a wall full of audio lines at one of my first jobs in
a small town radio station, so I am sure there are places with more than
one of these boxes.

> Probably yes, AES3 (known as AES/EBU here) surely is free. AES 3 allows
> unbalanced connections using coax and BNC, this may be a good option for
> installations that have existing video wiring. But if the connector is
> XLR the signal MUST be transformer balanced.

So AES10 (MADI) should be just as free? Or am I missing something? I know
there is a charge for the documentation for both AES 3 and AES 10, but is
there a use fee as well?

Len Ovens

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