[Portaudio] Inconsistent (buggy) sample rates- Windows 7 Realtek HD Audio

Reid Bishop rbish at attglobal.net
Tue Jul 6 23:55:48 EDT 2010


All,

I have been fighting a very odd problem with my Windows 7 64bit equipped
Dell & a Realtek HD Audio soundcard.  This onboard 7.1 channel soundcard is
actually a very good performer, aside from one of the oddest idiosyncrasies
I have ever seen.

Basically, whenever I try to open a full duplex stream at 96khz or above,
it's hit or miss whether it actually opens properly.  I often will have to
close the stream and re-open several times to try to get it to "catch", and
start streaming the data correctly.  It doesn't matter if I am using WASAPI,
MME, ASIO, exclusive or non-exclusive- you name it.

The best way to describe the problem is with a picture.  Please look at the
attachments, or use the following URLs (which are just small JPG files)

The following is the "Bad" stream.  Basically, this is 96khz of bandwidth,
displayed in the frequency domain.  Notice the five distinct humps, and the
extremely high values (off the chart) in between each hump.

http://www.pervinco.com/images/CNNSDR/Bad96khz.jpg

The following is the "Good" stream.  Same thing- 96khz of bandwidth
displayed in the frequency domain.  This is how it is _supposed_ to look,
and it works fine with my software.

http://www.pervinco.com/images/CNNSDR/Good96khz.jpg

If I close the stream and re-open it after getting the "good" picture above,
it may or may not revert back to the "bad" stream.  Sometimes, once it locks
in, it doesn't matter how many times I close/reopen the stream, it is
perfect every time (within a given session).  I can even change to a
different API, and all looks good.  But more often than not, it reverts to
the "Bad" stream, and again I have to Close/Open the stream many times to
finally get it to start working correctly.

Does anybody have any experience with this particular problem, or the
Realtek HD Audio?  A call to the driver with IsFormatSupported indicates
this device is good to 192khz in full duplex, paFloat32 format.  A call to
GetStreamInfo after the 'bad' stream has been opened reveals what I would
expect- 96khz.

I have updated my RealTek HD Audio drivers, but the problem was not solved.
In fact, it may have gotten a bit worse.

Thanks!

-Reid-
W0CNN
CNNSDR Development



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