Notes On Wdm; Channel Count Under Wdm - RME Audio Hammerfall HDSP 9652 User Manual

12.3 Notes on WDM

The driver offers a WDM streaming device per stereo pair, like HDSP 9652 ADAT (1+2). WDM
streaming is Microsoft's current driver and audio system, directly embedded into the operating
system. WDM streaming is hardly usable 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.
Several programs do not offer any direct device selection. Instead they use the playback device
selected in Windows under
XP: <Control Panel/ Sounds and Multimedia/ Audio>
Vista/7: <Control Panel/ Sound/ Playback>
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 9652 ADAT (1+2) is the first stereo device
HDSP 9652 ADAT (3+4) is the next stereo device
HDSP 9652 ADAT (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.

12.4 Channel Count under WDM

The HDSP system's ADAT optical interfaces allow to record sample rates of up to 96 kHz using
a standard ADAT recorder. For this to work single-channel data is spread to two ADAT chan-
nels using the Sample Multiplexing technique. This reduces the number of available ADAT
channels from 8 to 4 per ADAT port.
It is nearly impossible to change the number of WDM devices without a reboot of the computer.
Therefore whenever the HDSP 9652 changes into Double Speed (88.2/96 kHz) all devices stay
present, but are partly inactive.
User's Guide HDSP System HDSP 9652 © RME
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