[time-nuts] disciplining sound card

John Ackermann N8UR jra at febo.com
Sat Jul 7 13:10:02 UTC 2012


Hi Don --

The problem with the Clock-Block is that it can't generate exactly the 
correct frequency in this case -- the closest it can get is several PPM 
off.  And, I'm not sure the phase noise/jitter from the Clock-Block is 
good enough.

I don't know whether you could program a PIC to generate a precise 
wordclock; the maximum output frequency you can get from either TADD-2 
device is about 800 kHz, so it couldn't generate a 12 or 24 MHz 
oscillator replacement frequency.

John
----

Don Latham said the following on 07/07/2012 01:26 AM:
> 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.
> 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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>>
>>
>
>




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