[time-nuts] disciplining sound card

Chris Albertson albertson.chris at gmail.com
Sat Jul 7 02:10:14 UTC 2012


There is a profesional "standard" for clock distribution for computer audio
interfaces.  They call it a "Word Clock" and it is usually distributed over
75 ohm coax cable.   It is common for a studio to have a master word clock
generator and to use audio interfaces that accept an external clock.  Some
of these master clocks have rubidium or OCXO inside.  Most can also PLL to
any external clock

The trouble is that lower priced audio interfaces lack a "word clock" input
and you'd need to get into something like this as a minimum to have that
feature
828mk3Hy <http://www.sweetwater.com/store/detail/828mk3Hy/>

So if you are going to hack a cheap consumer interface it might be a better
hack to install a word clock input.  At some point inside the interface
there MUST be a sample rate clock running at 44.1, 48, 96, 192 kilohertz.
 Find then cut that trace and bring it out to a 75 ohm BNC connector.  Now
you have a standard pro level feature.

Now when you divide down your 10Mhz lab standard divide it to "word rate"
and you only need to build the divider once and you can use it with any
audio interface that has word clock I/O.

Yes of course you can send 14.4356MHz or whatever but that is a one time
design and it will be different with every audio interface depending on
whatever TTL can oscillator the engineer used.

All that said.  I have a "cheap" Presonus firewire audio interface that has
S/PDIF input and it has the option to accept word clock over the fiber
s/pdif.  Many low priced interfaces can do this.   Then you happen to have
a quality s/pdif device around you are set.



On Fri, Jul 6, 2012 at 12:05 PM, Bill Dailey <docdailey at gmail.com> wrote:

> What if I post a schematic with a Lattice M4-64/32 CPLD? If you can program
> this CPLD I can send the .JED file, the schematic...
>
> ---------------------------------
>
> I could probably get that done... would have to get a board made... never
> done it but could probably manage...some kind of usb blaster to program
> it.  I presume the .jed is the code?  I can solder for sure.  Would I be
> able to look at the code so I can learn something?
>
> --
> Doc
>
> Bill Dailey
> KXØO
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-- 

Chris Albertson
Redondo Beach, California


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