On 12/30/2010 03:31 PM, Marcus D. Leech wrote:
I'd noticed a problem with running the M-Audio Revolution 7.1 sound
card at 192KHz as a source in Gnu Radio -- the spectrum was
all "funny", with the spectrum getting "reflected" about 48KHz,
almost as if the actual sample rate on the card wasn't correct, and
perhaps set to 96KHz instead of the expected 192KHz.
To eliminate Gnu Radio as a cause, I used "arecord" with the correct
parameters to record a 20-second chunk of audio from the card,
then used Gnu Radio to plot the spectrum. Sure enough, the spectrum
is still not correct, so I suspect this is a driver issue.
I *know* that I used to be able to use this card at 192KHz several
years ago, and the card advertises 192KHz sampling as a feature.
Yet another follow-up.
It turns out that despite what the hardware reports, the ADC on the
Revolution 7.1 only runs at 96KHz, and the controller apparently does
some kind of half-assed upsampling. Gack!
--
Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org
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