Notes On Wdm - RME Audio MADIface XT User Manual

30.9 Notes on WDM

Background
In the older manuals one will find this explanation why it makes sense to get rid of some WDM
devices:
WDM Devices
Not before Vista the OS had been capable of handling more than 32 WDM stereo devices.
Therefore under W2k/XP it often makes sense to intentionally limit their number. Otherwise
some channels or MIDI ports might vanish from the system.
Today Microsoft gives us even more reasons to deactivate WDM devices that are unused. One
particular issue is that on any device change, but also on simple device queries (like during the
start of Cubase/Nuendo) the audioendpoint builder is started, visible as svchost.exe in the task
manager, blocking a whole CPU core for some time. On older computers with Dual Core CPU a
simple change from 44 to 48 kHz will cause one core to be fully blocked, equalling 50% CPU
load, for more than a minute. The start of Cubase is blocked at the MIDI screen for more than 5
minutes with a MADIface XT.
In stereo mode the MADIface XT sets a new world record: 99 WDM devices! Of course nobody
ever expected that at Microsoft. Possible consequences: freeze of the computer, hanging proc-
ess svchost,.exe, wait time of more than 10 minutes. So be careful!
The duration of this CPU load increases with the number of WDM devices (no matter if 2 or 8
channel ones). The less the quicker your CPU is back to normal – and with 0 WDM devices you
won't even notice anything.
On a more modern i7 3770 computer with Z77 chipset and Windows 7/64 the CPU load is only
around 12% (8 cores, still Cubendo wait and wait...), and under Windows 8.1 Microsoft reduced
the load duration by 50%. Better, but not good enough!
In real-world operation you will also sometimes find the svchost.exe process hanging forever –
only a reboot will fix this completely.
On a more positive note: server based computers (x chipset) do not seem to suffer from this
effect. But this kind of computer is expensive and not widely used as DAW system.
Therefore a flexible WDM configuration is required that can minimize these effects. All current
RME drivers now support deactivating unused WDM devices. If you just need one for listening
to whatever Media player then simply disable all other devices, reducing the svchost illness
easily. If you don't need WDM, because ASIO is all that you use, then deactivate them all. ASIO
and MIDI will still work.
The Speaker property of a WDM device changes its name to: Speaker. Many years ago, soft-
ware relying on Windows' own sound system used the speaker configuration in the Sound con-
trol panel to decide whether it can playback surround or not. One had to set the device to 5.1
mode or similar before it would work. These days this scheme seems to be no longer neces-
sary, the software just checks whether the device is only stereo or a multi-channel one, no mat-
ter if its called speaker or not. The Speaker property became a renaming feature for home en-
tertainment users.
So while most users can disregard this function, some will use software that needs the property.
We are even aware of custom software that needs more than one 'Speaker' to work correctly.
Driver version 2.x gives the user the freedom to configure whatever is needed to work properly.
User's Guide MADIface XT © RME
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