Audio Interfaces Topics:
» What is an audio interface?
» "Why isn't my computer's built-in sound card sufficient?"
» Inputs and Outputs
» Audio Interfaces for Pro Tools
» Computer Compatibility
» Connectivity
» Software control
» Do bit depth and sample rate matter?
» What to look for...

The world of audio interfaces can be a little overwhelming. With all the different input and output configurations, not to mention format choices - FireWire, USB, PCI, and PCIe - which one is right for you? This Sweetwater Buying Guide will steer you through the countless choices to find the interface that meets your needs. As always, feel free to call 1-800-222-4700 with any questions you may have.

What is an audio interface?

In simplest terms, an audio interface connects your microphones and other sound sources to your computer - it bridges the gap from analog to digital. Audio interfaces are commonly equipped with mic preamps, line inputs, and a variety of other input options.

You might be asking yourself, "If audio interfaces are often equipped with preamps, why wouldn't I just buy a channel strip or preamp?" Well, the answer to that question lies in the analog-to-digital conversion. Traditional preamps and channel strips send out an analog signal, and for audio to be usable by a computer, it needs to be digital. The audio interface converts the analog signal from its inputs to a digital output, making it easily digestible for a computer.

"Why isn't my computer's built-in sound card sufficient?"

If you're serious about recording audio, you'll quickly become dissatisfied with your computer's limited audio capabilities. Most consumer sound cards aren't equipped with high-quality analog/digital converters to adequately make the transition from the analog world to digital. They're fine for gaming or listening to MP3s, but consumer sound cards lack the headroom and the power to preserve the signal integrity. It is important to note that poor A/D conversion is largely what led to early forays into digital recording to be regarded as "harsh."

Another drawback of consumer cards is that most of them only support two channels of simultaneous audio, making it nearly impossible to track drum kits or entire bands without a LOT of submixing and creative bussing. Aside from the poor-quality conversion, consumer cards are prone to excessive latency, jitter (errors in timing that "smear" the audio signal), and overall inferior sound quality.

Inputs and Outputs

With the exception of computer connectivity, no other feature set plays as big a role in choosing an interface as the number of, and type of inputs and outputs. From the 2-channel PreSonus Firebox to the 12-channel Mackie Onyx 1200F, there are audio interfaces to meet almost any I/O need. If miking a full drum kit with close mics everywhere, an interface with eight inputs would be a good choice. Conversely, if your only intentions are to record your voice and an acoustic guitar, two inputs will do nicely.

Manufacturers have recognized the need for specialized interfaces for the different types of performers and introduced application-specific devices for guitarists and keyboard players. Line 6's TonePort series include both mic preamps and hi-Z guitar inputs, and also offer emulations of amps, guitars, effects, and vintage studio gear, perfect for axe-slingers with recording aspirations. On the keyboard side of things, M-Audio's Ozone MIDI controller/audio interface provides a mic pre along with a 25-key MIDI controller.

Many interfaces have the ability to output a digital signal. This digital connection usually comes in the form of S/PDIF or ADAT lightpipe formats. Digital inputs are cool since digital signals obviously don't need conversion. Plus, ADAT lightpipe is capable of carrying eight channels of up to 48kHz audio via a single cable, which can be a very handy tool for upping the number of simultaneous inputs.

Of course, it does no good to record your masterpiece as great-sounding digital audio if you can't hear the playback. A viable audio interface should have monitor outputs for the connection of a set of studio monitors. These can take the form of digital or analog outputs. And while we're talking about outputs, many current interfaces have at least a few outputs for sending audio from the interface to external processing devices, and back again.

Audio Interfaces for Pro Tools

Digidesign's Pro Tools audio editing software has been a major player in project and professional studios for a while now, and entering the Pro Tools world requires a Digidesign interface. These range from the simple Mbox 2 to the 003 with a dedicated control surface. There is also a rackmount version of the 003 - the 003R - that offers the same I/O options minus the control surface. A recent development in the Pro Tools realm is the addition of Pro Tools M-Powered, which supports a variety of M-Audio interfaces (20 of them at the time of this writing) including the Black Box, Audiophile 192 and 2496, and the popular Delta series.

There are some serious advantages to going the Pro Tools route. First, since Pro Tools is only compatible with Digidesign-approved hardware, there will never be incompatibility issues between the software and the interface. Plus, since most professional studios are equipped with Pro Tools, having a Pro Tools system ensures that you can take your files to just about any studio for mixing.

Computer Compatibility

Are you Mac or PC? What software do you intend to use with your interface? Compatibility between your hardware and software is essential for a stable system. Most current audio interfaces are cross-platform (meaning that they will run with either Window or Mac computers) and are supported by most audio software. In fact, many manufacturers bundle light versions of audio software with interfaces as a means to get you started right out of the box. For example, the PreSonus Firebox ships with Cubase LE.

But like all things audio, there are exceptions. Apogee's Ensemble was designed in cooperation with Apple to be optimized for Apple's Logic software, and supports any Core Audio-based software on the Mac platform. On the flipside of that, E-MU interfaces (0404, 1212M v2) are compatible with Windows systems only.

Connectivity

Today's audio computers are available equipped with ports to accommodate a whole host of connection options. In recent years, FireWire has emerged as a powerful format for transferring data between two or more devices such as an interface and a computer. The Digidesign 003 and 003R, as well as the MOTU 8Pre and many others, are FireWire-based interfaces.

An equally fast protocol, USB 2.0 supports multi-channel audio and is found on a variety of interfaces. From the Mbox 2 to the Lexicon Omega, there are a number of boxes with a variety of inputs and outputs. The great thing about USB is that while FireWire isn't available on every computer (without the purchase of a FireWire card, that is) virtually every computer manufactured in the last few years is equipped with USB 2.0. The USB 1.1 format can handle two channels at a time, and is found on devices like the Alesis MultiMix USB series.

Technology doesn't sit still for long, and one thing we can always count on is a manufacturer upping the speed of data transfer. Enter the PCI and PCIe protocols. PCI is described as high-bandwidth and processor-independent data path between the CPU and high-speed peripherals. The PCI spec allows for the capability to transfer up to 132 megabytes per second at a bus clock speed of 33 MHz. PCIe (or PCI Express) uses existing PCI programming concepts, but bases it on a completely different and much faster communications protocol. Since it's based on the existing PCI system, cards and systems can be converted to PCI Express by changing the physical layer only - existing systems could be adapted to PCI Express without any change in software. The higher speeds of PCI Express (ranging from 250Mbps to 4,000Mbps) allow it to replace almost all existing internal buses, including PCI. The M-Audio Delta 1010 is a popular PCI interface, and MOTU has recently issued PCIe versions of their PCI interfaces, such as the 2408 Core mkIII.

Though it's becoming less prevalent due to the increased availability of FireWire-equipped notebook computers, PCMCIA is a data-transfer protocol for laptops. Originally the PCMCIA Card (or PC Card, as it is commonly called) was developed as a memory device that could be hot swapped in and out of any computer with a compatible slot. Later, other applications such as modems, networking, audio and video recording, and playback were applied to the technology. These cards provide laptop owners the power and sound quality often found in desktop systems. Many PCMCIA cards, such as the RME Multiface 2 bundle have breakout boxes that connect to the card as a means of audio input.

Software control

Many of the interfaces we've discussed have software that comes in the box that allows you access to more complex routing of audio to and from the interface and the computer. This software typically allows you to use your interface like a mixing console, bussing audio to external devices and back again. For example, virtually every MOTU interface ships with Cue Mix Console, a software package that lets you set up anything from individual headphone mixes to talkback for communicating with the artists in the studio.

Do bit depth and sample rate matter?

Yes and yes. Next question. Seriously though, bit depth and sample rate are very important considerations when it comes to choosing an audio interface. The number of bits determines the theoretical maximum dynamic range of the audio data regardless of sample rate. Each additional bit adds 6dB to the dynamic range of the audio. More bits help capture quieter signals more accurately. On the sample rate side of things, think of it as snapshots. At 44.1kHz, the computer is taking 44,100 "pictures" of the audio every second as it enters the computer. Obviously, the higher the sample rate, the more "pictures" get taken, resulting in a more accurate representation of the original audio.

If your only expectation is to produce demo-quality CDs to hand out to friends and family, or maybe sell at a local show, 16-bit/44.1 kHz (commonly known as "CD quality") will be fine. Conversely, if your objective is to record string quartets, an audio interface that is capable of doing 24-bit/96kHz or even 192kHz is desirable. With DVD video and audio capable of utilizing 24-bit/96kHz audio, today's market is full of devices capable of reproducing high-resolution audio. Ask any group of engineers and you'll get many different answers concerning bit depth and sample rate, but keep in mind that the bit depth provides more headroom when recording, so greater bit depth is more desirable than high sample rate when it comes to basic music recording. Plus, stepping up to a higher sample-rate sometimes comes as a trade-off, reducing track count.