[time-nuts] Question about SoundCard stability?

David McClain dbm at refined-audiometrics.com
Tue Oct 12 21:17:51 EDT 2010


Ahh.. so... Now since my TCXO is drifting to and fro by 1-2 Hz over  
the period of 45 minutes, why don't I see similar drift in the 100 Hz  
audio signal, down around 5 mHz amplitude?

This happens to be about the same size at the FFT bins. So I am led  
to conclude that "interpolated" peak frequencies are a bogus  
technique, and you can only truly count on variations on the order of  
the FFT cell size as being measurable...

Dr. David McClain
Chief Technical Officer
Refined Audiometrics Laboratory
4391 N. Camino Ferreo
Tucson, AZ  85750

email: dbm at refined-audiometrics.com
phone: 1.520.390.3995
web: http://refined-audiometrics.com



On Oct 12, 2010, at 17:57, Bob Camp wrote:

> Hi
>
> Yes it is a reasonable expectation as long as you don't have a lot  
> of drafts. A good TCXO can get down to sub 0.1 ppb over that period.
>
> Bob
>
>
> On Oct 12, 2010, at 8:21 PM, David McClain wrote:
>
>> Okay, perhaps I should rephrase the question... Is is reasonable  
>> to expect a TCXO to perform at 4e-9 over the FFT window period of  
>> about 87 sec? I can only imagine that the enormous (87 s)  
>> averaging period is making my measurements look so good.
>>
>> Dr. David McClain
>> Chief Technical Officer
>> Refined Audiometrics Laboratory
>> 4391 N. Camino Ferreo
>> Tucson, AZ  85750
>>
>> email: dbm at refined-audiometrics.com
>> phone: 1.520.390.3995
>> web: http://refined-audiometrics.com
>>
>>
>>
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