Audio Interface Buying Guide: What to Know Before You Buy

1. How will the interface connect to my computer? USB or Thunderbolt? PCIe or FireWire?

- Thunderbolt interfaces take advantage of the high-speed Thunderbolt ports found on newer computers. These interfaces are now common in pro recording studios. They're a modern alternative to PCIe (PCI Express) card interfaces, since they can reliably handle high track counts without requiring users to install PCIe cards in their computers. Original Thunderbolt 1 and 2 ports use an Apple Mini DisplayPort connector, while Thunderbolt 3 ports are also USB Type C 3.1 ports, and use the USB Type C small, reversible connector. However, not all USB-C ports actually support the (much, much faster) Thunderbolt 3 standard. Check your computer's specs to see if your ports are actually Thunderbolt 3 -- and look for the tiny lightning-bolt logo near the connector.
- USB interfaces are a popular choice for home studios, since the USB connector is so common. USB-A ports are commonly found on PCs and older Macs, newer PCs may have USB-C ports, and newer Macs have Thunderbolt 3 ports which support USB-C audio interfaces. The iPad Pro even uses a USB-C connector. Some audio interfaces ship with both USB-C and USB-A connector cables included, so you can use your interface with a wider variety of devices right out of the box. Of course, if your Mac only has Thunderbolt 3 ports, you can use a Thunderbolt dock to connect a USB hub and plug in a USB audio interface.
- FireWire interfaces mainly use the FireWire 400 standard, which is comparable to USB 2.0 in speed. FireWire can be slightly more reliable than USB when recording multiple simultaneous tracks. However, the once-popular FireWire port is now usually only found on legacy computers, so FireWire interfaces are becoming a rare breed.
- Apple 30-pin and Lightning connectors are found on iPads and iPhones -- and on audio interfaces that are made for iOS recording.

2. How many mic preamps/analog inputs do I need?

- You'll need XLR mic preamp channels for each microphone you're recording simultaneously. If you're planning to use condenser microphones, make sure the preamps can provide +48V phantom power -- a standard feature on most interfaces.
- You'll need an instrument-level (Hi-Z) input channels to plug a guitar or bass directly into your interface with a regular 1/4" instrument cable. If your interface doesn't have these high-impedance input channels, you'll want to use a separate DI box.
- You'll need analog line inputs to record the outputs from any analog outboard gear you may happen to have.

3. How many analog outputs do I need?

- At minimum, you'll want one headphone output. Some interfaces offer two headphone outputs with their own volume knobs.
- You'll need a pair of monitor outputs to feed your left and right stereo monitor speakers. If you're setting up a 5.1 surround monitoring system, you'll need at least 6 outputs to feed your 6 speakers.
- Got analog gear you want to "insert" on your tracks? You'll need a few analog line outputs to feed your outboard gear.

4. Do I need digital I/O?

An interface with digital inputs and outputs can make your studio much more flexible. If you have outboard gear with digital I/O -- think high-end standalone preamps, hardware mastering processors, or dedicated A/D converter boxes -- you'll want an interface that can accept those digital sources. Check the back of your gear to see what kind of digital connection you'll need: S/PDIF coaxial stereo audio uses RCA-style cables, while S/PDIF optical stereo and ADAT 8-channel optical need TosLink fiber-optic "lightpipe" cables. Shop digital audio cables »

5. What about MIDI I/O?

Built-in MIDI I/O can help streamline your setup. If you use gear with 5-pin DIN MIDI ports -- whether it's a keyboard controller, synth, sound module, or even lighting gear in a live rig -- you may want an audio interface that has MIDI In and Out ports. If your audio interface doesn't have MIDI I/O, you'll need to use a standalone MIDI interface (and use up another USB port on your computer). Either way, you'll need some MIDI cables.

6. Does the interface have on-board DSP?

DSP stands for digital signal processing -- and in an audio interface, it means a specialized hardware chip dedicated to audio tasks. Higher-end interfaces with on-board DSP usually come with control-panel software for your host computer, which you can use to route signals, adjust monitor mixes, keep an eye on levels, and add real-time effects like delay, reverb and compression. For example, RME interfaces have TotalMix software, and Universal Audio Apollo interfaces have UAD's Console software.

7. What software is included with the interface?

These days, almost every interface comes with some kind of recording software to get you up and running out of the box. Sometimes, the bundled software is the main attraction. For example, Universal Audio's Apollo series gives you access to the UAD-2 plug-in library, and PreSonus audio interfaces come with Studio One DAW software and the Studio Magic plug-in suite.

8. What's the interface's maximum sample rate and bit depth?

When it comes to audio resolution, higher is better. Look for an interface capable of recording at a minimum of 48 kilohertz. For detailed classical/jazz/acoustic recording, film sound design, or anything archive-worthy, look for 96 kHz or even 192 kHz. As far as bit depth, don't even think about recording with less than 24 bits -- it's the professional standard. Even better, some newer audio interfaces are capable of 32-bit floating point recording, which gives you an exponentially greater dynamic range -- a game-changer for field recording, live performances, or anytime that setting proper recording levels may pose a challenge.

9. What is jitter? Do I need an external clock?

Digital recording works by sampling an analog audio signal thousands of times per second, at precise, regularly repeating intervals. The digital audio clock within your audio interface measures these intervals, and its accuracy is critical to audio quality. A clock's timing variations can add distortion known as "jitter." So, will an external master clock device improve your audio quality? The jury is still out on this issue. But higher-end audio interfaces generally offer more accurate internal clocking and lower jitter -- just another reason to invest in the best audio interface you can afford for the heart of your home studio.