ASIO stands for Audio Stream Input/Output. ASIO is a sound card driver protocol typically used by musicians and sound engineers. If you’ve been considering upgrading your home recording studio or are shopping for a new sound card or interface, you’ve probably heard the acronym ASIO bandied about heavily—usually in a good context. But why is ASIO good and how does it work? Read on to find out.
The ASIO protocol was developed by Steinberg, the makers of the popular multi-track recording software Cubase. The primary goal of ASIO sound card drivers was to solve one vexing problem for digital music producers: latency. Latency is a short delay between the time an audio signal enters into a system (i.e. your computer) and the time when it exits the system. You’ve probably noticed latency before while talking on the phone with someone watching the same TV channel as you. There’s a slight delay between the time the audio from their TV enters into their phone and emerges out your handset, so that the two devices are out of sync. This is latency.
On the phone, and for normal audio applications, latency is hardly noticeable and mostly inconsequential. But high latency is absolute anathema to music producers. That’s because even a millisecond’s worth of delay—particularly unpredictable delay—can mean the difference between a note being off beat or spot on. Latency is doubly bothersome to those working with digital audio because there is latency in playback and latency for recording. So, the more tracks you are layering, the worse it becomes.
Latency, for the most part, only exists in digital audio formats. That’s because the audio must be captures as an analog sound and then processed into ones and zeros before being recorded onto the hard disk. Furthermore, there are a number of other processes that the data must pass through that are part and parcel to the Windows operating system. Each layer that the sound must pass through before reaching the speakers or the writeable memory adds a split millisecond of latency.
ASIO sound card drivers seek to reduce this problem by bypassing all unnecessary layers and communicating with the hardware as directly as possible. For example, most Windows applications must pass their audio data through the Microsoft DirectSound intermediary or another Windows-based mixer before reaching the soundcard or an application being used to record audio. ASIO sound card drivers provide an alternate route for digital audio to pass through that skips most of these additional processes.

Aside from lower latency, ASIO drivers have the benefit of providing “bit transparent” outputs. That is, the audio has not been mixed down or resampled, meaning that it will usually be of higher fidelity than if you were to use a non-ASIO driver.
Professional audio hardware and sound cards designed for musicians will usually come with ASIO drivers bundled with them. But you can find ASIO drivers for virtually any consumer-grade sound card. A good place to start is ASIO4ALL, a universal ASIO driver for Windows. Get it here: http://www.asio4all.com/