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Re: [Discuss-gnuradio] Followup: M-Audio Revolution 7.1 as audio source

From: Marcus D. Leech
Subject: Re: [Discuss-gnuradio] Followup: M-Audio Revolution 7.1 as audio source at 192KHz: Fedora 14/Alsa/ICE1724 driver
Date: Thu, 30 Dec 2010 18:36:13 -0500
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20101209 Fedora/3.1.7-0.35.b3pre.fc14 Thunderbird/3.1.7

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

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