ASIO is a professional sound card driver developed by Steinberg. Its full name is Audio Stream Input Output, which literally translates to mean audio stream input and output interface. Typically, this is a feature found in professional sound cards or high-end audio workstations, though currently many multimedia and high-fidelity music sound cards also support ASIO (such as the updated X-Fi series, Lezhibang PS, and US series). Using ASIO technology can reduce system latency for audio streams and enhance the processing capabilities of sound card hardware. For example, if a sound card using MME drivers has a delay time of 750 milliseconds, switching to an ASIO driver could potentially reduce the delay to below 40 milliseconds.
### Table of Contents
- Definition of ASIO
- Functions of ASIO
- Usage of ASIO
- Essence of ASIO
- Comparison between ASIO and DirectSound
- Which sound cards support ASIO
- How to determine and apply ASIO
- ASIO4ALL - ASIO Emulator
- Listening to Music via ASIO Channels
#### Definition of ASIO
The full name of ASIO is Audio Stream Input Output, which directly translates to audio stream input and output interface. Usually, this is a feature found in professional sound cards or high-end audio workstations, but now multimedia sound cards and high-fidelity music sound cards also adopt ASIO (such as the updated X-Fi series, Lezhibang PS, US series). Using ASIO technology can reduce system latency for audio streams and strengthen the processing capabilities of sound card hardware. If a sound card using MME drivers has a delay time of 750 milliseconds, then after switching to an ASIO driver, the delay could be reduced to below 40 milliseconds.
#### Functions of ASIO
Simply put, the purpose of ASIO is to reduce audio latency; simultaneously, ASIO acts as an independent audio channel in the system that avoids interference from DirectSound (or other channels), allowing ASIO applications (like music creation software) to operate without interference from other programs running on the system.
When a program uses the ASIO channel, it avoids situations where other programs operating in "exclusive mode" take over the channel, thus ensuring your work isn't affected. If you use programs that rely on DirectSound or other channels (like KS, WASAPI), when a program using the same channel starts in "exclusive mode" (for instance, Tencent QQ), your program will experience interference, with the most obvious result being that all programs except Tencent QQ become silent. Therefore, during audio editing, using the ASIO channel not only reduces latency but also avoids interference.
Let's talk about latency. Perhaps you still don't fully understand the significance of resolving audio latency. Let's explain with a simple example: Many people have tried voice calls using computers and the internet, including the famous chat tool QQ which offers this function. In fact, internet-based voice communication works on the same principle as IP telephones provided by telecom companies, but due to network bandwidth limitations, the former experiences far more significant sound delays than the latter. When voice delay is within a certain range, people may find it tolerable; however, if the delay becomes too large (for example, having to wait more than 5 seconds after each sentence), everyone would find it intolerable. If you're still unclear, let me give another example: Imagine playing an online game like World of Warcraft, perhaps following a guild raid progression, and your network latency is 1000ms. You would likely feel very uncomfortable and find it difficult to continue the game. By now, you should understand that if audio similarly has significant latency, it would cause considerable trouble for its usage. What kind of usage? Usually, it refers to professional tasks such as music composition, audio editing, and recording.
#### Usage of ASIO
Standard sound cards have some delay when playing audio streams, although most users are unlikely to notice it. After all, for playing DVDs, stereo MP3 music, or gaming, hundreds of milliseconds of sound delay has almost no noticeable impact on usage and can be completely ignored. However, for professional sound engineers and music producers, these hundreds of milliseconds of delay have consequences similar to what we general users would face with extremely slow internet IP phones or playing World of Warcraft with a ping of 1000 - they cannot tolerate it. Imagine pressing a piano key and having to wait over 0.6 seconds to hear the sound; any performer would find it hard to play at their normal level, let alone express musical emotion. During post-production, sound engineers need to apply real-time effects to different audio signals and mix multi-channel audio streams recorded separately to obtain the final stereo or 5.1 surround sound format. When mixing multiple audio tracks, if there is latency and the delay times are unequal, synchronizing signals across multiple channels becomes a major issue, making it impossible for sound engineers to accurately judge the results of the mix. For this reason, they urgently need a technology that allows audio equipment to achieve "zero latency," which is the ASIO technology defined by Steinberg.
#### Essence of ASIO
To realize the ideal of "zero-latency audio equipment," the developers of the famous music production software Cubase VST, Steinberg, proposed the standard known as Audio Stream Input Output. The goal was to allow devices developed by various hardware manufacturers to integrate well with Steinberg's audio processing software Cubase VST, thereby achieving optimal performance levels in digital audio processing and software sound source simulation. ASIO completely frees itself from the centralized control of the Windows operating system, enabling multi-channel transmission between audio processing software and hardware while minimizing system response time for audio streams. According to the details defined in the ASIO standard, sound card manufacturers can develop highly efficient ASIO drivers for their hardware products, reducing the response time of sound card hardware to audio streams to within a few milliseconds. Even for extremely picky professional music producers, such low latency is basically imperceptible.
#### ASIO vs. DirectSound
The goal of ASIO is to minimize system latency when playing audio streams. Some readers might associate this with DirectSound - indeed, ASIO and DirectSound are quite similar, both aiming to bypass the control of the Windows operating system over hardware devices and communicate directly with hardware ports to improve response speed. However, ASIO is more revolutionary than DirectSound: if DirectSound is compared to a program written in a high-level language, then ASIO is akin to a program written in assembly code - not only is its structure more compact, but its efficiency is greatly improved. Moreover, ASIO is not just a revolution in drivers but also requires support from hardware chips. Under the tight integration of drivers and hardware, it is inevitable that ASIO reduces latency to an extremely low level.
However, if your sound card supports only ASIO and not DirectSound, you won't be able to control volume using the small speaker icon on the Windows taskbar. When running common entertainment software like SuperDeca or WinAmp, you also won't be able to control the volume using the volume fader in the player interface.
Some sound cards can support multiple standards like MME, DirectSound, ASIO, GSIF [2] simultaneously and switch between different compatibility methods through software. For those who need to balance professional creation with daily use, such sound cards are undoubtedly very convenient.
#### Which Sound Cards Support ASIO
Not all sound cards support ASIO. As mentioned earlier, ASIO not only defines driver standards but also requires hardware support from the main chip of the sound card to be implemented. In the past, only expensive professional sound cards considered supporting ASIO in their design.
Currently, whether mainstream multimedia entertainment sound cards or music sound cards oriented towards PC-HIFI, most retain the ASIO function, such as Creative Audigy series, Creative X-Fi series, Lezhibang US series, Lezhibang PS series, ASUS Xonar ST, Audiotrak MAYA 44, etc. Of course, common integrated sound cards like Realtek ALC or VIA VT do not natively support ASIO.
[--- The following content is outdated information for reference; the gist is that SB LIVE hardware actually supports ASIO ---]
Interestingly, the main chip EMU10K1 of SB Live! itself supports ASIO, but this feature wasn't reflected in the bundled LiveWare! 3.0 driver. Therefore, when you replace the SB Live! driver with one designed for E_mu APS recording cards, audio processing software will report finding ASIO!
Another interesting example is various multi-channel sound cards using the CMI8738 chip. CMI8738 itself has the potential for ASIO support, but so far no suitable driver has been developed to enable it.
The first consumer sound card publicly claimed to fully support ASIO technology is the newly launched SoundBlaster Audigy by Creative. This successor to SB Live! not only provides up to 24bit / 96 kHz sound quality but also comprehensively supports the latest advanced technologies like ASIO and SB 1394. The release of SB Audigy has further narrowed the gap between consumer and professional sound cards.
#### How to Determine and Use ASIO
How to determine if your sound card supports ASIO?
The simplest method is to check the sound card specifications and technical support, such as Creative sound cards which have the "ASIO" logo printed on their packaging.
Other methods involve checking compatibility through software, as detailed below:
- **Audio Processing Software**: In the menu bar of audio processing software, find "Setup Preferences Audio" or "Setup Audio Hardware." In the Device drop-down list, it will display the currently available audio devices. If your sound card does not support ASIO, the drop-down list will only show "ASIO Multimedia Driver," which is actually a soft simulation of MME drivers. If your sound card uses ASIO drivers, there will be another option in the drop-down list, such as "MAYA ASIO Driver" or "SB Audigy ASIO."
- **Music Playback Software Foobar 2000**: Install the ASIO plugin for Foobar 2000, find the "Output" tab in the settings, locate "ASIO virtual device," and then add devices in the right window. If your sound card adds successfully, it means it supports ASIO.
- **Music Playback Software QianQian Jing Ting**: After installing QianQian Jing Ting, set the output to ASIO in the settings. If the player can play music smoothly, it means your sound card supports ASIO.
- **Music Playback Software CPlay**: After installing CPlay, if it can play music normally, it indicates your sound card supports ASIO.
#### Application of ASIO
After setting the software's audio output to ASIO device, you will get nearly perfect results when playing multi-track audio, using real-time effectors, and using VSTi soft sound sources. However, to truly achieve "zero latency" (referring to a delay time below 10ms), you still need to configure the buffer of the ASIO device.
Click on "Control Panel" in the audio property settings to open the ASIO control dialog box, and click the "Advance" button to enter the advanced settings. The most important parameter here is "Buffer Size," which refers to the size of the audio buffer. Generally speaking, setting a larger buffer can increase system stability and alleviate crackling caused by differences in data transmission or processing speeds; conversely, setting a smaller buffer will improve system response time and reduce audio latency. In summary, the size of the buffer needs to be determined based on the performance of your computer's CPU and memory.
After configuring the audio buffer, the audio software will prompt that the environment settings have changed and require testing to ensure future normal operation. The test mainly checks for data packet loss and typically takes tens of seconds to about a minute. Upon seeing the successful message shown in the image below, you can fully enjoy the fun brought by "zero latency" in audio processing software!
#### ASIO4ALL - ASIO Emulator
ASIO4ALL is a driver that allows unsupported devices to emulate ASIO functionality.
ASIO4ALL is a green and compact ASIO driver developed by Wuschel, claiming to make almost all sound cards, including AC97 onboard sound cards, support ASIO, achieving the low latency usually associated with professional audio cards. It is applicable to almost all sound cards and onboard AC97 sound cards, especially suitable for laptops.
Please note that ASIO4ALL does not force sound cards to hard-support ASIO.
#### Listening to Music via ASIO Channels
The quality of sound is a rather subjective topic. You might see similar articles online, perhaps understanding that the channels commonly used for everyday listening include KS, DS, DSOUND, WASAPI, and of course, ASIO.
There is no definitive conclusion regarding whether these channels affect sound quality, but you can rest assured that there are differences in sound representation among these channels, as experienced by most music enthusiasts. However, whether the differences in sound representation among these channels are significant or whether you can hear the differences depends entirely on you. In other words, whichever channel sounds better to you, use it, since music is ultimately for your own enjoyment.
So why listen to music via ASIO? Here, my answer is to avoid interference from other channels and system coloration. Among these, avoiding system coloration is the most crucial point, especially for audiophiles who are keen on monitoring. They generally dislike excessive coloration and equalizers.
In summary, if you do not belong to the HI-FI audiophile or audio worker groups who are relatively obsessive, you do not need to worry about necessarily using ASIO. Just choose one that you like.
#### Extended Reading:
1. ASIO Development Documentation: http://blog.csdn.net/changpei/archive/2008/06/11/2537080.aspx