[time-nuts] 74HCT9046A Max. Operating Frequency

Magnus Danielson magnus at rubidium.dyndns.org
Mon Apr 28 20:30:05 UTC 2014


On 04/28/2014 04:16 PM, Chris Albertson wrote:
> On Sun, Apr 27, 2014 at 11:41 PM, sg sg <micpreamp at yahoo.de> wrote:
>> Thanks very much for your responses!
>> ..
>> The source is an AK4114 AES/EBU audio receiver, which has both master
>> clock (24.576 MHz) and "word select" rate (48-192 kHz) outputs. Perhaps it
>> is better to run the PLL at the latter? Any disadvantages from this?
> So this is for clock distribution in a studio?   While our eras don't care
> about nano seconds or even micro seconds we do care that long of the same
> length have exactly the same number of samples.  In other words at a given
> times into a track, all tracks have the same number of samples.    I think
> what matters in this application is long term stability over days, weeks
> and even years.   So the first step is always to figure out your
> requirements and USE NUMBERS.
> Next.  It is not "either/or"  you can put the PPL at 24..5MHz or 48K or you
> can divide by 10 and put the PPL at 2.45Mhz.  or any place in between.
> One question:  Why use the receiver as a clock source?  Most use something
> independent like an OX or even Rb then use that to drive a DDS chip.

Rb is way overkill. Beyond keeping things in sync to ensure same sample 
rate, what is important is jitter but not ppm level wander.
Jitter can kill your listening experience by to ways, one is bit error 
rate, causing bits to be incorrect. The second is that it creates 
side-bands, which causes issues when you try to achieve 24 bit 
resolution, or for that matter 130 dB dynamics. Do read what Julian Dunn 
had to discuss on that matter, since he look at what sidebands would do, 
considering masking effects of psycho-acoustics etc.

Then again, we being time-nuts, overkill is easy to achieve.
We need to be careful about jitter as we re-synthesize and lock things 
up. Jitter-peaking as a cause of jitter accumulation, and that leads 
to... bit errors and side-bands.


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