There are actually two types of audio drivers that you can use in computer audio recording. These are the ASIO (Audio Stream Input/Output) and the WDM (Windows Driver Model) audio drivers. These two operates very differently and their behavior has strong impact on the quality of your recording. In this post, you will exactly learn how these driver model works and their effect on digital recording.
Beginners in home recording often do not know the technical distinction between these two drivers. As a result, they tend to treat these two as interchangeable, the same or compatible which in reality is not and the results are completely different.
WDM (Windows Driver Model)
Windows OS starting from Windows 98 implemented the WDM driver model for audio. In fact, there are lot of home based engineers during that time that were exactly depending on WDM drivers for their projects. In this driver, an audio device (such as a soundcard) will have drivers that become part and binded with the Windows kernel.
When an audio device is communicating in and out of the computer, everything goes to Windows kernel and will be handled by WDM. See below:
Thus you have observed that that the communication between your recording software (DAW) and audio device will pass through Windows. In a recording session, analog audio is converted to digital audio by your soundcard by a process known as pulse code modulation. If the soundcard is using WDM driver, digital audio streams will undergo sample rate conversion or bit depth conversion by WDM .
Conversion will happen if there is a mismatch in bit depth and sample rate somewhere along the signal chain. The sample rate conversion and bit depth version in WDM may not produce expected results by audio engineers in terms of quality. Poor quality design sample rate converters in sound cards or in your audio system can produce aliasing which is a form of audio artifacts or distortion.
On the other hand, programmers of audio device drivers will simply design its drivers based on WDM compatibility with ease and minor edition, because a lot of the work/code are already provided by Microsoft. This feature is the reason why WDM is very popular and supported by most consumer based soundcards before and even until now.
Also WDM drivers are depending on the Kernel mixer (Kmixer or Windows mixer) for controlling volume levels, etc. Although the soundcard may have its own mixer, Kmixer will still influence or even override the soundcard settings since the soundcard is binded with the operating system.
6 Responses
I’m just getting back into DAW recording, I have Sonar 6, an Amd fx 8320e, eight gigs of ram. I used the Asoi drivers, but still I get dropouts. But, with the Wdm drivers, I have no problems at all, and can change bit dept and resolutions. I keep pushing my DAW with many plug-ins, so far so good.
Thanks David, sad to say but I have to agree with this. No drivers can be made perfect no matter what. some old school might still say Analog is still best and you won’t be dealing with these software drivers ever. But this looks like an unavoidable reality. The truth is, one can be get easily started with building a home studio based on a computer today. But they have to deal with all these driver issues. It’s cheaper as well based from what I’ve observed when compared to real analog technology.
The real problem in my years of working with this stuff Software and hardware (audio interfaces) is the drivers being incorrectly created by engineers not completely following and even thoroughly testing the drivers they ship with the products. 99% of the issues quality, latency, and rock solid connectivity issues are directly related to this ongoing problem. The advancement of technology over the last 10-12 years hasn’t drastically improved or totally resolved this fact. Manufacturers and tech support people always want to blame your computer system for this. Not enough RAM or CPU not sufficient. Mostly, this response is hogwash and BS. I currently work in my studio with a Quad Core Intel Zeon 3.1Ghz processor – 8 cores for Hyperthreading and 32GB of RAM and I still have driver issues. Some interfaces are better than others, but I’ve tried Tascam, Focusrite, Steinberg, Behringer, PreSonus, and Roland interfaces and they all have issues from time to time. Most of them just losing contact with the device itself for no apparent reason. This also relates to the Audio Engine in the software suddenly stopping or crashing. Again all driver related. My advice – make sure whatever audio interface device you choose make sure they produce driver revisions and updates often. Many drivers are 1-2-3 years old and never improved much from the entire lifetime the device is on the market.
Hi Tony,
Yeah it’s alright. I also drink two cups of coffee just this morning to energize things up 🙂 Happy New Year!
Woops, sorry, confused WASAPI with WDM… All the points i made were for WASAPI. Didn’t have enough coffee, i guess… :-/
A few corrections.
First, WDM driver wasn’t there until Windows Vista. Windows 98 had different (and MUCH slower) model for accessing audio devices, which involved not only Windows kernel, but also Windows mixer and other stuff.
Second, there’s nothing wrong with sound having to pass through kernel, because that’s what it does in any case. ASIO does that too. ASIO, just as WDM, is a driver, hence it is loaded by the kernel and hence audio gets to the kernel one way or another. The difference between ASIO and WDM is with ASIO driver you get to choose exactly how much latency you can get (buffer length etc.) while WDM just tries its best.
Finally, WDM can achieve comparable (if not equal) latency with ASIO, and bit depth/sample rate conversion can be turned off (just as the same can be turned on in many ASIO drivers). WDM can also be used with “prosumer” equipment (i use WDM driver with my M-Audio gear just fine) with little to none problems and latency issues, plus the added benefit of being able to use audio devices in different programs simultaneously.
I enjoy reading technical articles, but please get your facts straight first.