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

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To: Len Ovens <len@...>
Cc: <linux-audio-user@...>
Date: Saturday, January 26, 2013 - 12:52 pm

On Fri, Jan 25, 2013 at 05:44:32PM -0800, Len Ovens wrote:

> The AES seems to recommend AES3 (like s/pdif... almost) as the sync signal

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.

AES3 inputs (at least the balanced ones) are rare or semi-pro equipment
anyway. Those that have them will be capable of syncing to them, the
inputs would be useless otherwise. Syncing to AES may have some advantages
as you sync to the data clock which has a much higher frequency than the
sample rate. The inverse, regenerating a higher frequency from a lower one,
is usually a bad idea, phase noise is mutiplied by the square of the ratio.

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.

A lot of master clocks only provide word clock, these tend to be the
'audiophile' ones used to 'make the sound more transparent' or some such
nonsense. Pro equipment will always have AES3 outputs in addition to word
clock.

> Question two: I read a comment that a studio ( I am not sure if this was a

A few years ago that could have made sense as there were few MADI routers.
But e.g. 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.

> I thought it odd that MADI cards were so expensive when AES3 equipment is

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.

S/PDIF pro is a variation of the consumer S/PDIF format, some of the
extra bits take another meaning. This is also the AES3 format.

Ciao,

--
FA

A world of exhaustive, reliable metadata would be an utopia.
It's also a pipe-dream, founded on self-delusion, nerd hubris
and hysterically inflated market opportunities. (Cory Doctorow)

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Messages in current thread:
[LAU] Sample rate vs. SNR, Len Ovens, (Wed Jan 23, 2:52 pm)
Re: [LAU] Sample rate vs. SNR, Ralf Mardorf, (Wed Jan 23, 4:43 pm)
Re: [LAU] Sample rate vs. SNR, Joe Hartley, (Wed Jan 23, 8:20 pm)
Re: [LAU] Sample rate vs. SNR, Len Ovens, (Wed Jan 23, 10:10 pm)
Re: [LAU] Sample rate vs. SNR, Florian Faber, (Thu Jan 24, 7:53 am)
Re: [LAU] Sample rate vs. SNR, Len Ovens, (Thu Jan 24, 9:52 pm)
Re: [LAU] Sample rate vs. SNR, Fons Adriaensen, (Fri Jan 25, 1:43 am)
Re: [LAU] Sample rate vs. SNR, Len Ovens, (Fri Jan 25, 2:45 pm)
Re: [LAU] Sample rate vs. SNR, Fons Adriaensen, (Fri Jan 25, 3:21 pm)
Re: [LAU] Sync and digital audio transport - was Sample rate..., Fons Adriaensen, (Sat Jan 26, 12:52 pm)
Re: [LAU] Sync and digital audio transport, Len Ovens, (Fri Feb 1, 2:38 pm)
Re: [LAU] Sample rate vs. SNR, Ralf Mardorf, (Fri Jan 25, 7:15 pm)
Re: [LAU] Sample rate vs. SNR, Len Ovens, (Sat Jan 26, 2:04 am)
Re: [LAU] Sample rate vs. SNR, Ralf Mardorf, (Sat Jan 26, 9:42 am)
Re: [LAU] Sample rate vs. SNR, Len Ovens, (Sat Jan 26, 3:18 pm)
Re: [LAU] Sample rate vs. SNR, Ralf Mardorf, (Sat Jan 26, 3:26 pm)
Re: [LAU] Sample rate vs. SNR, Len Ovens, (Sat Jan 26, 5:21 pm)
Re: [LAU] Sample rate vs. SNR, Ralf Mardorf, (Fri Jan 25, 2:53 pm)
Re: [LAU] Sample rate vs. SNR, Paul Davis, (Wed Jan 23, 11:13 pm)
Re: [LAU] Sample rate vs. SNR, Charles Z Henry, (Thu Jan 24, 1:14 am)
Re: [LAU] Sample rate vs. SNR, Paul Davis, (Thu Jan 24, 2:31 am)
Re: [LAU] Sample rate vs. SNR, Len Ovens, (Thu Jan 24, 3:48 am)
Re: [LAU] Sample rate vs. SNR, Ralf Mardorf, (Thu Jan 24, 1:32 am)
Re: [LAU] Sample rate vs. SNR, Charles Z Henry, (Wed Jan 23, 10:50 pm)
Re: [LAU] Sample rate vs. SNR, Fons Adriaensen, (Wed Jan 23, 4:17 pm)
Re: [LAU] Sample rate vs. SNR, Len Ovens, (Thu Jan 24, 4:26 am)