[wdmaudiodev] Re: Vista: Input Volume x4 gain on microphone
- From: "Sam Tertzakian" <sam@xxxxxxxxxxx>
- To: <wdmaudiodev@xxxxxxxxxxxxx>
- Date: Fri, 22 Aug 2008 09:21:16 -0700
Hi, Keith,
Can you explain in detail what your "reprocessing" problem is? Where is the
data being reprocessed?
-----Original Message-----
From: wdmaudiodev-bounce@xxxxxxxxxxxxx
[mailto:wdmaudiodev-bounce@xxxxxxxxxxxxx] On Behalf Of Keith Larson
Sent: Friday, August 22, 2008 9:19 AM
To: wdmaudiodev@xxxxxxxxxxxxx
Subject: [wdmaudiodev] Re: Vista: Input Volume x4 gain on microphone
Hi Sam
Thanks for the tip, but I already have the 'master volume mixer'
functions built into a DLL. I will then call the DLL only if Vista is
detected keeping functionality back through Win98se. My problem (and
only in Vista) is making sure the device I detect while searching Wave
devices is the same as by searching endpoints.
I am also hoping to find ways around the 'reprocessing' of raw data.
This is very problematic with regards to any measurement device.
Best regards,
Keith
Sam Tertzakian wrote:
> Hi,
> One possible avenue you might investigate is to write a WDM Filter Driver
> that would sit over (upper filter) the instance of USB Audio device driver
> that is installed to support your device. In this way you can modify the
> requests that go to the USB driver and the information that is returned
from
> the USB driver. I think you could lock or effectively disable the gain
this
> way...as for the DSP processing, I am not sure. There might be a way for a
> filter driver to send a command to the USB audio driver to disable such
> processing...but I am not sure.
> This solution would be compatible across 2000/xp/vista.
> There are possibly other solutions that depend on some sort of USB Audio
> driver vendor specific support but I am not sure. You would have to look
at
> the USB Audio class driver specification for such information.
> I am sure others will have ideas, but perhaps this is an avenue you might
> investigate.
>
> -----Original Message-----
> From: wdmaudiodev-bounce@xxxxxxxxxxxxx
> [mailto:wdmaudiodev-bounce@xxxxxxxxxxxxx] On Behalf Of Keith Larson
> Sent: Thursday, August 21, 2008 9:36 AM
> To: wdmaudiodev@xxxxxxxxxxxxx
> Subject: [wdmaudiodev] Vista: Input Volume x4 gain on microphone
>
> 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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