[time-nuts] Sound Cards for locking to GPSDO 10 MHz references

Lux, James P james.p.lux at jpl.nasa.gov
Tue Jun 2 13:47:33 EDT 2009

> -----Original Message-----
> From: time-nuts-bounces at febo.com 
> [mailto:time-nuts-bounces at febo.com] On Behalf Of Magnus Danielson
> Sent: Tuesday, June 02, 2009 10:08 AM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] Sound Cards for locking to GPSDO 10 
> MHz references
> > 
> > 
> > Some of the "pro" sound interfaces have a "word clock" input.  
> > 
> > There are a variety of things that take a external input 
> and generate a S/PDIF that's properly timed, as well. Lots of 
> boxes will take a S/PDIF sync input (e.g. the Edirol FA-66 
> which was used by lots of Flex-Radio folk), so maybe that's 
> something you could easily generate from your 10MHz. 
> > 
> > A chart at Cakewalk shows that MOTU has a USB interface (828MkII) 
> > which has a word clock sync. It's going to be a pricey 
> beast though, 
> > with 8in/8out ($800?)
> > 
> > Even if you have a word clock input, you're going to have to 
> > synthesize that from the 10 MHz.  Maybe it's easier to just make a 
> > S/PDIF which is a MUCH more common sync signal. ( I think S/PDIF is 
> > something like 3 MHz)
> S/P-DIF [iec60958-3] has a baudrate which is 128 x sample 
> rate and a bit rate which is 64 x sample rate, which is 
> inherited properties from AES/EBU [aes3] [tech3250] [iec60958-4].
> Locking up a S/P-DIF (128 x sample rate) is about the same 
> job as locking up a superclock (256 x sample rate) or 
> wordclock (1 x sample rate).

However, if you're buying an off the shelf audio interface, you're stuck with whatever the mfr is providing for a sync input, and a (very) casual inspection of what's available these days (particularly at low cost) shows that S/PDIF seems to be the most common.

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