[time-nuts] Plot phase noise spectrum from DMTD measurement?
ehydra at arcor.de
Sat Mar 12 13:28:13 UTC 2011
John Miles schrieb:
> Sound cards will usually end up running within 1 Hz of the desired sampling
> rate, but it's important to pick a sampling rate that's native to the
> hardware, or the driver will resample the data. On Windows, many drivers
> for popular sound cards rely on some imprecise resampling code that
> apparently was distributed by Microsoft in the DDK. Stick with 44100 or
> 48000 Hz, or you'll be lucky to land within a few dozen Hz in some cases.
One can this circumvent by using ASIO driver or a wrapper like asio4all.
This removed the frequency resampling distortion and at the same time
the low-pass filtering above 20KHz for my sound-card.
> Warren's been getting some really nice ADEV plots from a tight PLL sampled
> with a USB sound card, running a quick and dirty command-line utility I put
> together to acquire the data and downsample it. I'll post the next build on
> my web page if anyone else is interested in playing with it.
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