[time-nuts] Allan Deviation question

[Magnus Danielson]

On 07/06/2012 04:58 PM, John Ackermann N8UR wrote:
> I think a number of higher-end sound cards accept a "word clock" or
> "world clock" (I've seen it both ways) that's intended to allow syncing
> to an external source. The challenge I've seen is that the frequency
> (either in the 12 or 24 MHz range) is one that's not simple to
> synthesize precisely (i.e., zero offset from nominal) and with low
> jitter/phase noise from a 5 or 10 MHz reference.
>
> I think it would be a great project to come up with a synthesizer block
> that could do that. It's been on my list for a long time, but hasn't yet
> risen near the top.

A correct word clock should run at sample rate, i.e. 48 kHz or 96 kHz, 
which isn't stellar in synthesis difficulty.

For description of Word Clock, please see Appex B in AES 11.

There are system clocks also being used, typically x128 of the sampling 
rate, so 6.144 MHz, 12.288 MHz and 24.576 MHz hence is popular. Again 
not stellar to lock.

Cheers,
Magnus