[wdmaudiodev] Re: GFX/LFX fullduplex support.

  • From: Tim Roberts <timr@xxxxxxxxx>
  • To: wdmaudiodev@xxxxxxxxxxxxx
  • Date: Thu, 04 Sep 2008 11:10:30 -0700

pete c wrote:
> id like to capture both a capture and render stream to perform some
> echo cancellation on an audio stream in Vista, However the LFX/GFX
> archiecture does not lend itself well to full duplex support.

Microsoft's philosophy is that echo cancellation is an application
problem, and as such belongs as a filter in the application's graph.  In
fact, Microsoft includes an acoustic echo cancellation DMO with Vista
that does exactly this.

> My question is could one use a GFX to collect render data and an LFX
> to collect capture data and use shared memory for the LFX to process
> the GFX rendered data that was collected?

Yes, this can be done, but it isn't easy.  Remember that it is always
dangerous to attempt anything that goes against the prevailing Microsoft
philosophy, and that's what you're talking about.  Also remember that,
in the Microsoft philosophy, GFX and LFX APOs are considered part of the
hardware driver.  Your LFX would be considered part of the microphone
driver, and your GFX would be considered part of the speaker driver.  If
your company doesn't produce both, then you have a very serious
installation issue.

> Also is there anyway to synchronize an LFX and GFX in this case?

Of course, you are going to NEED such synchronization if you hope to do
echo cancellation.  That's another thing that makes this tricky.  You
will need some pretty brainy algorithm scientists to make this work.

Tim Roberts, timr@xxxxxxxxx
Providenza & Boekelheide, Inc.


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