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

[Fons Adriaensen]

On Sat, Jan 26, 2013 at 09:08:40AM -0800, Len Ovens wrote:
 
> 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.

Video and audio would be derived from a common source, so that any
video pull-up/down is also applied to the audio sample rate.

Frequency standards (GPS, atomic) are not application specific and
usually provide 10 MHz (1 and 5 MHz are also used but less popular).
All serious laboratory measurement equipment (oscillators, frequency
counters, spectrum analysers, digital scopes, ...) accepts 10 MHz as
an external reference, as does most RF equipment. Satellite ground
stations usually derive the hundreds of frequencies they need from
a single 10 MHz reference, etc. It's an industry standard. Deriving
e.g. 48 kHz from 10 MHz is no more difficult or less accurate than
using an exact multiple.

Professional A/V master clocks will accept 10 MHz as one of the possible
references.


> 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?

AFAIK there is no license fee for using MADI. The AES wants your credit
card for *everything*, even for papers published 40 years ago ($25 for
non-members, for a download).

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)