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:
WDM audio driver model
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.
ASIO (Professional audio device drivers)
ASIO is the professional solution to digital recording. ASIO works by bypassing the Windows kernel and directly accessing and communicating with the audio device (such as an audio interface) such as shown below:
ASIO audio recording interface
What is one big advantage about using ASIO is that the bit depth and sample rate are preserved as originally as possible since it cannot be altered by Windows kernel/Mixer. For example if you are recording at 24-bits/48KHz, the recorded audio is exactly 24-bit/48KHz digital audio.
ASIO driver is different from WDM drivers in such a way that the stability of these drivers exactly depends on the quality of the hardware drivers. Unlike WDM where its dependent on Windows kernel, ASIO based drivers are independent on how Windows kernel works.
This leads to lowered CPU processing, lower latency and memory usage. With ASIO, multi-channel recording is possible (more than 2 channels) because of decreased load on Windows kernel and by directly accessing the audio hardware.
This will have a profound effect on reducing audio dropout and multi-track recording latency.
Best practices in using ASIO or WDM
1.) WDM is restricted to non-professional music production environment because of latency and recording quality related issues. If you analyzed carefully how WDM audio drivers work, it will communicate with the Windows kernel first before reaching the audio to its intended destination (like recording software); thus adding latency in the process.
Also WDM will implement sample rate conversion and bit depth in the background which can alter the quality of the recorded audio stream. High latency is not recommended for professional digital home recording because these can introduce lag and timing issues in your multi-track recording project.
2.) If the objective in using audio is gaming or non-recording related applications where high latency is acceptable, you can stay with your WDM device as it will usually offer a cheaper hardware solution.
3.) When recording a high number of channels simultaneously, such as recording a live band; you need a high bandwidth solution in communicating between your audio interface and the computer. For very high bandwidth implementation, you can use Firewire or USB 2.0 and USB 3.0. If you are using Windows operating system, you can read this tutorial on how to optimize Windows XP for firewire & USB audio interface.
4) There are some recordings software that only supports WDM drivers (like Adobe Audition 1.5). In this case, you cannot use them for ASIO multi-channel recording (targeting low latency implementation); you need a DAW software that can support ASIO drivers. A good example is Reaper. Below is a screenshot of REAPER configured to use ASIO drivers from Saffire Pro 40 audio interface:
Reaper ASIO installed
Read this Reaper DAW tutorial to know the details on how to associate ASIO with your digital audio workstation software.
5.) WDM is the most recommended solution for desktop and consumer audio applications for your computer (mp3 streaming, internet audio streaming, gaming, movies, etc.). ASIO is the most recommended solution for professional music productions using your computer.
6.) ASIO can only handle a single audio hardware at a time. So if the computer has multiple audio devices, they cannot be used because ASIO can only be associated with one ASIO device at a time. This is different with WDM which can support multiple soundcards or audio devices.
Content last updated on July 23, 2012