[time-nuts] disciplining sound card

Chris Albertson albertson.chris at gmail.com
Sat Jul 7 14:55:28 UTC 2012


On Fri, Jul 6, 2012 at 10:26 PM, Don Latham <djl at montana.com> wrote:

> Foe word rate generation from 10 MHz, perhaps the TAPR devices:
> http://www.tapr.org/kits_clock-block.html
> or:
> http://www.tapr.org/kits_tadd-2.html
> with a type D f/f to get a square wave?
> generate your clock for cheap.
>

Maybe look to see how this is done in commercial units.   I think they use
crystal oscillators that run at the word clock rate (or small multiple of
it)  This oscillator is phase locked to some reference and on the
commercial units you can select the signal used as a reference.   I don't
think they use DDS or integer division of some unrelated frequency (like
10Mhz)



> Don
>
> Chris Albertson
> > 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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> >
>
>
> --
> "Neither the voice of authority nor the weight of reason and argument
> are as significant as experiment, for thence comes quiet to the mind."
> R. Bacon
> "If you don't know what it is, don't poke it."
> Ghost in the Shell
>
>
> Dr. Don Latham AJ7LL
> Six Mile Systems LLP
> 17850 Six Mile Road
> POB 134
> Huson, MT, 59846
> VOX 406-626-4304
> www.lightningforensics.com
> www.sixmilesystems.com
>
>
>
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-- 

Chris Albertson
Redondo Beach, California


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