[wdmaudiodev] Re: Real Time Processing

  • From: Pieterjan Demarcke <pieterjan.demarcke@xxxxxxxxx>
  • To: wdmaudiodev@xxxxxxxxxxxxx
  • Date: Thu, 3 Mar 2005 00:33:34 +0100


thank you for the extremely fast answers! (btw I'm from Belgium, not
such a hard guess if you look at my name indeed ;-))

This ASIO interface indeed seems to be a better solution than WDM but
there's only 1 problem: for my project i can (have to) use a computer
owned by the university and i don't think buying a new professional
soundcard is an option. So I'll have to stick with a standard one.
Maybe this site (http://www.asio2ks.de/) is a solution?

To clarify what the purpose is of the project: we have to make a
profilometer (measures relief at microscale) with a dvd OPU (optical
pickup unit, the laser head and surrounding electronics of a
dvd-player). The OPU uses the astigmatic method of focus error
detection, so it is possible to measure the amount of out-of-focus by
summing and substracting 4 specific output signals of the OPU. The
resulting signal (DC because the sensed variable is changing
relatively slowly) is transformed to an AC signal so the sound card
can detect the amplitude. The pc then sends a rescaled value of that
amplitude to the line-out to activate the focus actuator of the OPU.
When the OPU is back in focus, we can move the OPU for example 1
micrometer further and after all that  we are ready to sample again.
(in fact this is simplified: the opu is moving at constant velocity,
but the idea is the same) The big problem now with a latency is the
speed: assuming we want to have a resolution of 1 micrometer and there
is a latency of 2 ms, we quickly find a scanning speed of 1 mm/2 sec.
This is still acceptable because we never scan further than 1 cm.

So i'm looking for the fastest solution with a normal sound card. If
it seems to be that the minimum latency is for example 10 ms, so be
it. But the faster the better of course.

thank you very much for your input and goodnight (for those in europe)


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