What goes in, must come out.
These jacks are fine for basic tasks like making an Internet phone call or listening to a CD while you work. But if you’re serious about using your computer for music production, before long you’ll want to add a dedicated audio interface. An audio interface is an external box that plugs into one of the computer’s digital connectors. These days, it will most likely use either a USB or a FireWire connector. Audio interfaces are available from a variety of manufacturers, and range in price from under $100 to many thousands of dollars.
There are three reasons why an audio interface is desirable: features, performance, and sound quality. Let’s look at each of these factors briefly.
FEATURES
Your computer’s built-in audio I/O (input/output) is most likely stereo. That means you can send in and get out, at most, two audio signals at any given time — the left and right sides of the stereo signal. But many audio interfaces have four or more inputs and four or more outputs. For instance, the unit may have both a stereo headphone jack with its own level knob for comfortable listening and a pair of 1/4" mono jacks for sending the left and right signals to your powered monitor speakers. The inputs may be equipped with microphone preamps, and you may find three-pin XLR connectors suitable for high-quality mics.
Some audio interfaces also provide MIDI in and out jacks. This saves you the cost of buying a separate MIDI interface, and also lets you get both MIDI and audio in and out of the computer on one USB or FireWire connector — very convenient.
Audio interfaces are also built into some mixers and MIDI keyboards. The Alesis Photon X25 (shown) is both a 25-key MIDI keyboard and an audio interface.
PERFORMANCE
If you’re making music with a software-based synth or sampler, you’re probably sending it MIDI from an external keyboard. In this situation, you want to be able to play the keys and hear the notes immediately, not half a second later. The delay between when you send a command (such as a MIDI message) to a computer and when the computer responds is called latency. To be usable for serious music production, an audio interface has to be low-latency. That is, the latency has to be less than 20 milliseconds, and preferably less than 10.
The built-in audio in Macintosh computers is already low-latency. But to get low-latency performance from Windows, you need an audio interface that uses either the WDM or the more popular ASIO protocol. Most audio interfaces support these protocols, and in most cases you don’t need to do anything other than install the interface and select it as the output for your music software.
The control panel for the interface (see Figure 1) may let you set the amount of latency. Lower latency makes more demands on your computer.
SOUND QUALITY
Generally, an audio interface will provide better sound quality than the computer’s built-in audio. Several factors affect sound quality, and they’re a topic for a separate column. Briefly, a good audio interface will add less noise to the signal, and it will be able to record and play back extremely high frequencies with better fidelity.
All audio interfaces, including your computer’s built-in jacks, use analog-to-digital converters (ADCs) to change the analog electrical signal coming from a microphone, keyboard, or guitar into digital form. When sound is played back from the computer, you guessed it, digital-to-analog converters (DACs) are used. The converters built into your computer are not likely to be as good as the ones you’ll find in even an inexpensive audio interface.
INSTALLING AN INTERFACE
Because the Mac OS provides a standardized environment, many audio interfaces can simply be plugged into a Mac: Plug it in and you’re ready to go. Windows users will need to install driver software before the interface can be used. This software will come with the interface, on a CD-ROM, but you should check the manufacturer’s website to see if a more recent driver is available. To install the driver, insert the CD into the computer and follow the on-screen instructions. When installation is complete, restart the computer. You’ll need to shut the computer off to plug in a FireWire interface, but a USB interface can be plugged or unplugged while the computer is running.
