[time-nuts] Using cheap sound cards for measurements

Tom Van Baak tvb at LeapSecond.com
Sat Aug 22 00:32:45 UTC 2009


Could you sync the sounds cards in software?

If you feed an external 1 PPS into the unused stereo channel of
each sound card, then you can solve both card-to-card phase
differences as well as card-to-card frequency differences with
simple software fitting after, or even while, samples are being
collected.

I use the R-channel for my 1PPS timing, leaving the L-channel
for analog input. A time-synced PC can resolve the seconds
time-of-day ambiguity.

Note that a sharp 1pps will give you 22 us (1/44100) precision.
If you used a slower ramp'ed 1pps then software interpolation
should give you sub-microsecond precision.

If you want to measure the stability of your sound card, see:
http://www.leapsecond.com/pages/sound-1pps/

Win32 source code to the tool is very simple; see:
http://www.leapsecond.com/tools/1hz.c

/tvb




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