Lux, James P skrev:
-----Original Message-----
From: [email protected]
[mailto:[email protected]] 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.
Do they really lock up to the S/P-DIF input? I doubt it for the cheap
boards. Rather, they decode the S/P-DIF signal and ship the samples into
the DSP. The DSP tends to make very rought sample-rate conversions like
dropping samples etc.
A lockable board isn't that expensive. You can get them off ebay for
instance.
Cheers,
Magnus
_______________________________________________
time-nuts mailing list -- [email protected]
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
