[wdmaudiodev] MIDI and USBAudio Filter Drivers
- From: Tim Roberts <timr@xxxxxxxxx>
- To: wdmaudiodev@xxxxxxxxxxxxx
- Date: Mon, 08 Oct 2007 15:20:14 -0700
I'm hoping somebody (maybe DJ?) can explain this phenomenon.
It turns out that the presence of a filter driver anywhere between
usbaudio.sys and the USB host controller will prevent usbaudio.sys from
creating MIDI devices. Without the filter, midiInGetNumDevs returns 1.
With the filter, it returns 0.
I've seen this both with a lower filter on usbaudio, and with an upper
filter on the hub driver. There are several Google hits for people
complaining that their USBAudio MIDI devices do not work when they use a
USB sniffer, and this is the reason why.
My question is, why should this be? It can't be intentional. I've
written probably a dozen lower filters to usbaudio.sys for standard
audio streaming devices, and I know what I'm doing. Why should it be
different for MIDI? How does usbaudio.sys even know? Why does it care?
--
Tim Roberts, timr@xxxxxxxxx
Providenza & Boekelheide, Inc.
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