the signal at 1kHz and its harmonics is digital noise coming from the
USB power supply.
it is gone if i connect headphones or my Oscilloscope instead of my pc
soundcard.
julian
Am 10.04.2012 12:02, schrieb Tim Goetze:
[Julian Schmidt]
here are some screenshots...
the beating bell shape on 440Hz sinus with 84 harmonics
http://i.imgur.com/B4s0M.png
I think that beating could well be caused by Nyquist-mirrored
harmonics.
a simple sine table 220Hz
http://i.imgur.com/hPKj1.png
In both plots, there's also a strong signal at 1 kHz (likely being
accompanied by harmonics at kHz intervals but that is hard to make out
in the spectrum plots given their emphasis on the low end.)
Cheers, Tim
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