[time-nuts] Using cheap sound cards for measurements

Bruce Griffiths bruce.griffiths at xtra.co.nz
Sat Aug 22 03:03:27 UTC 2009


Add balanced inputs to the list of desirable features.

Bruce
Don Latham wrote:
> On this track, what's the group opinion as to the best USB sound "card"?
> I'm looking for one for time as well as sd radio use. Should have the best
> separation, best s/n, highest digitization rate, 24 bit, etc. Any
> recommendations?
> Thanks
> Don
>
> 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
>>
>>
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>>     
>
>
>   






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