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User's Guide HDSP System Multiface II © RME
12.3 Notes on WDM
The driver offers a WDM streaming device per stereo pair, like HDSP Multiface (1+2). WDM
streaming is Microsoft's current driver and audio system, directly embedded into the operating
system. WDM streaming is nearly unusable for professional music purposes, as all data is proc-
essed by the so called Kernel Mixer, causing a latency of at least 30 ms. Additionally, WDM can
perform sample rate conversions unnoticed, cause offsets between record and playback data,
block channels unintentionally and much more. Therefore, for general operation, RME recom-
mend not to use WDM devices.
WDM streaming also replaces the former DirectSound. Synthesizers and Samplers, which
achieved latencies below 10 ms using DirectSound, are forced to use WDM in Windows XP,
now operating at high latency. Meanwhile most of these programs support ASIO as low latency
driver interface.
Several programs do not offer any direct device selection. Instead they use the playback device
selected in Windows under <Control Panel/ Sounds and Multimedia/ Audio>. Such software
often requires the special functions provided by WDM, and therefore will operate better when
using a WDM device. Please note that selecting the HDSP to be used as system playback de-
vice is against our recommendations, as professional interfaces should not be disturbed by
system events.
The program Sonar from Cakewalk is unique in many ways. Sonar uses the so called WDM
Kernel Streaming, bypassing the WDM mixer, thus achieves a similar performance to ASIO.
Because of the driver's multichannel streaming ability (option Interleaved, see chapter 12.4),
Sonar not only finds the stereo device mentioned above, but also the 8-channel interleaved
devices, and adds the channel number at the end:
HDSP Multiface (1+2) is the first stereo device
HDSP Multiface (3+4) is the next stereo device
HDSP Multiface (1+2) 3/4 are the channels 3/4 of the first 8-channel interleaved device.
We recommend to not use these special interleaved devices. Also note that it is not possible to
use one stereo channel twice (the basic and the interleaved device), even with different applica-
tions.