RME HDSP 9632 [23/87] Notes on wdm

User's Guide HDSP System HDSP 9632 © RME

12.3 Notes on WDM

The driver offers a WDM streaming device per stereo pair, like HDSP 9632 (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 9632 (1+2) is the first stereo device

HDSP 9632 (3+4) is the next stereo device

HDSP 9632 (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.