[wdmaudiodev] Vista: Input Volume x4 gain on microphone
- From: Keith Larson <klarsondsp@xxxxxxxxxxx>
- To: wdmaudiodev@xxxxxxxxxxxxx
- Date: Thu, 21 Aug 2008 12:36:16 -0400
Hi All
This is the first time visiting this wdmaudiodev, and I have three
questions. Being a newbie, let me begin with a kind 'Hello'.
I am here because I am working with a measurement device and the new
Vista audio interface is, well, variable. After a lot of mucking
around, I am closing on a solution that will lock the input and output
levels. This is a kludge, but at least it works. There are however
remaining snags.
USB Audio Codec -> Classified as microphone -> gain of x4 (+12db) applied
--------------------------------------------------------------------------
The device I am using is a fairly simple 2 channel in, 2 channel out
ADC/DAC. I can deal with the OS classifying the input as a
'microphone', but more importantly it seems that the default action is
to multiply the raw input stream by 4 (+12db gain). I can clearly see
this when I set the application and master volume to 100%. The input is
exactly 4x the expected value. Low signal level values are wrong, and
if the signal is large, the data is clipped.
If I set the master volume to 25% and application to 100%, things are ok
(but maybe not if reversed), but this also means I need to lock the gain
values. The issue now whether or not the x4 microphone gain ever
changes in the future. It would be *far* better if I did not have to
deal with the variable gain.
DSP processing routines
-----------------------
This time it is the output side. The DSP routines modify the outputs.
Again, this is NOT desirable for a measurement system.
Enumerating End Point and Wave Devices
--------------------------------------
My code uses the 'Wavexxx' interface and as such I can get a handle, or
an enumerated value. I can also get an enumerated listing of the 'end
point' audio devices. As expected, these enumerations do not match (an
endpoint can have multiple WAVE connections), so a direct matching is
out. Luckily(?) the identifying strings, eg "USB Audio Codec' *SEEM* to
match. That is, I am looking for something a bit more definitive.
Suggestion
----------
Would there be a way to effectively achieve this for (both input and
output) in some future release of Vista?
[X] Lock master volume at 100% *and* bypass DSP processing
(This endpoint is for a measurement device)
Best regards,
Keith
PS: My code is and needs to be compatible with all Windows platforms.
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