RME Audio Fireface 400, Руководство пользователя, Страница: 26 / 100

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User's Guide Fireface 400
© RME
12.4 Notes on WDM
The driver offers two devices per stereo pair, like
Fireface Analog (1+2) and Fireface Analog
(1+2) MME .
Fireface Analog (1+2)
The devices having no MME at the end are WDM Streaming Devices . WDM Streaming is Mi-
crosoft'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 processed 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 recommend
not to useWDM 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.
And now operate at high latency. Meanwhile most of these programs support ASIO as low la-
tency 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 Fireface to be used as system playback
device 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 as ASIO
and our MME driver (see below). The superior low latency operation that was originally ex-
pected from WDM Kernel Streaming has not become reality. This is not astonishing when ana-
lysing the driver model. Early reports about a sensational performance around 1 ms latency at
up to 100% CPU load have been quickly revealed to be faulty drivers, operating at much higher
latency than 1 ms.
Meanwhile Sonar supports ASIO too. So simply test and try for yourself which driver interface
will work better for you on your system.
Information on multichannel WDM is found in chapter 12.5.
Fireface Analog (1+2) MME
The devices with the MME suffix bypass the Windows Kernel Mixer. This way, they achieve
nearly the same performance as RME's previous (true) MME drivers. Also their behaviour (off-
sets, start/stop, multi-client) is identical. So when not using GSIF or ASIO, MME should be your
preferred choice.
A small note on
ASIO and GSIF : these drivers are completely independent from WDM Stream-
ing. They work and perform the same as our previous 'just WDM' drivers.