Unable to capture audio from USB Audio Device when the for..

Archived from groups: microsoft.public.windowsxp.device_driver.dev (More info?)

Hi,

We've developed a USB audio device hardware. Currently we are making the
device to work under Windows XP. The hardware is implemented as a WDM audio
device with USB interface. We can connect the device to Windows and it
shows up in device manager properly.

This device has a chip that can capture/playback audio in compressed Mu-Law
format, instead of uncompressed PCM format. However, when we test the
device with DirectShow SDK (part of DirectX SDK) using GraphEdit, we are
unable to see the Mu-Law format supported in the list. If we switch the
device back with PCM format, then we can see it in the list and work with
it. Therefore, the problem is that we are unable to capture audio from USB
Audio Device when the format is set to MuLaw.

Scenario - We developed USB Audio Device that produces Audio in MuLaw
Format. The USB descriptors are correctly set to indicate that the Audio
format. Please see the attached file showing the descriptors.

Description - We want to capture Audio in MuLaw format. Windows DDK
documentation states that it supports all "All Type I formats" (MuLaw being
one of them). Refer to
http://www.microsoft.com/whdc/device/audio/usbaud.mspx (document name -
USB_Audio_and_Windows.doc). Also refer to the same information in Windows
DDK documentation at
mk:@MSITStore:C:\WINDDK\2600\help\stream.chm:hh/ddkslm/stream/aud-design_8gmr.htm.

When we connect the Audio device Windows recognizes it properly as an Audio
device and shows it in the Control Panel. When we check the Audio formats
using both GraphEdit (DirectX 9.0) and Adobe Audition, it shows as "None".
As a result we are unable to capture Audio from the device.

Additional Info - When we change the USB Audio Device properties (by
changing the descriptors) to PCM8 the device works without any problem.

Development environtment: Microsoft Visual C++ with Visual Studio .NET 2003,
Windows XP with SP2, Windows DDK with SP1.

This looks like a typical question since Mu-Law audio format is quite
popular in Microsoft audio devices. If anybody has encountered this problem
or did not see this problem when implementing your own audio device, please
let me know your solution as soon as possible. Thank you.

- Fei -