[time-nuts] Question about SoundCard stability?
randall.prentice at pscconsulting.com
Wed Oct 13 01:25:54 UTC 2010
1 Hz in 10Mhz is about the same ratio as 5mHz in 64Khz.
This would make sense if the Clock for the A/D is divided off the same
Or am I missing something.
The reason I jumped in, in a recent frequency measuring contest the
winner was using that interpolation for his results.
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of David McClain
Sent: Wednesday, 13 October 2010 2:18 p.m.
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Question about SoundCard stability?
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
On Oct 12, 2010, at 17:57, Bob Camp wrote:
> 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.
> 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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