User`s guide

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.