[wdmaudiodev] Re: Understanding USB Feature Unit Descriptors
- From: "Daniel Sisolak" <dsisolak@xxxxxxxxxxxx>
- To: "wdmaudiodev@xxxxxxxxxxxxx" <wdmaudiodev@xxxxxxxxxxxxx>
- Date: Fri, 14 Jan 2011 12:06:05 -0800
Hi Ryan,
So are you saying that you really have a device that has a 255 dB range that
steps 16dB at a time? This is a most unusual device then.
XP would generally take any range and map it to the slider, but Win7 is a
little more particular/realistic about these things. Most devices will report a
range of Max: 0db to Min: -64db or so (though there definitely are exceptions).
If your device is still in development I would suggest that you map your volume
range similarly if possible. This should give you the XP/Win7 parity you seek.
Cheers,
DJ
From: wdmaudiodev-bounce@xxxxxxxxxxxxx
[mailto:wdmaudiodev-bounce@xxxxxxxxxxxxx] On Behalf Of RYAN ALLAN
Sent: Friday, January 14, 2011 2:32 PM
To: wdmaudiodev@xxxxxxxxxxxxx
Subject: [wdmaudiodev] Understanding USB Feature Unit Descriptors
I am developing a USB-to-analog audio device, and am seeing strange volume
scaling behavior from Windows 7/Vista machines. The problem is not apparent
with XP machines.
I am using the following Feature Unit Descriptors.
Get_Min: 0x01, 0x80
Get_Max: 0xFF, 0x7F
Get_Res: 0x00, 0x10
This tells me that the volume will be in the range from Min:0x8001 to
Max:0x7FFFF, and each step (each time the volume is incremented via volume+
button on a multimedia keyboard) will be of size Res:0x1000. Is this correct?
When I move the volume slider in a Windows 7/Vista machine, the volume (I am
looking at Set_Cur packets) moves in a range from 0x7FFFF to 0x3900 with step
sizes of 0x0100. The same experiment on a XP machine sees the volume move in a
range from 0x7FFF to 0x8001 with step sizes of 0x1000. Why do the two OS's have
different behavior?
I would like volume to be in the range from -127db - +127db (as per USB spec),
and I would like step sizes of 0x1000. Basically, I would like the Windows 7
machine to behave like the XP machine.
Thanks!
--
Ryan
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