[wdmaudiodev] Re: Understanding USB Feature Unit Descriptors
- From: Tim Roberts <timr@xxxxxxxxx>
- To: "wdmaudiodev@xxxxxxxxxxxxx" <wdmaudiodev@xxxxxxxxxxxxx>
- Date: Fri, 14 Jan 2011 12:50:52 -0800
Tim Roberts wrote:
> RYAN ALLAN wrote:
>> 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?
>
> Can your device really apply 120dB of gain to the signal? That's a
> big amplifier -- a billion to 1 increase. Most volume controls are
> strictly attenuators, so the maximum gain value is 0.
Allow me to provide an executive summary of what both DJ and I have said.
The spec for volume controls has always been in dB of gain or
attenuation, both for USB devices and for Windows audio devices. In the
past, many developers ignored this and simply made it a unitless number,
from some meaningless low number to some meaningless high number. That
resulted in confusion. Starting in Vista, the sound team made the
conscious decision to have dB really mean dB, in a real world sense.
That means most of the range is nonsense.
The right answer is to change your min and max to reflect the actual
attenuation range of your device.
--
Tim Roberts, timr@xxxxxxxxx
Providenza & Boekelheide, Inc.
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