[time-nuts] Using cheap sound cards for measurements

[Bruce Griffiths]

Tom Van Baak wrote:
> 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
>
A higher sync frequency than 1Hz, say around 100Hz or so is probably
desirable for better cancellation of sampling clock phase noise.

Bruce