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Delving Deeper into the Audio Interface

Let’s delve even deeper into I/O territory and also touch on some other features and extras that will help you narrow down your interface choices.

The versatile and compact RME Fireface UCX interface includes onboard DSP effects.

Are you ready to continue our quest for the best home studio gear? In last month’s column [“Choosing an Audio Interface,” May 2012], we looked at one of the primary pieces of gear in most modern studios—the audio interface. By talking about inputs and outputs, monitor outputs, and headphone outputs, we’d gotten as far as considering an interface’s basic connectivity. This time around, let’s delve even deeper into I/O territory and also touch on some other features and extras that will help you narrow down your interface choices.

MIDI I/O. MIDI signals are used to control various pieces of equipment, as well as store performance data from keyboards, drum controllers, guitar synths, and more. While many synths and drum machines are virtual instruments or software, and USB connections are available on a lot of new gear, you will still likely run into the need to connect a device by MIDI sooner or later. You might have an older keyboard with MIDI connections. Or it may be a digital processor that needs to connect to your computer so you can edit patches, update the software, or back up presets. In these scenarios and others, it’s necessary to have a MIDI input and output available. While you can buy separate MIDI interfaces, having the connections built into your audio interface means one less piece of gear to purchase and hook up.

Word Clock. Digital signals can be very picky about who’s in charge. When routing signals in S/PDIF, AES/EBU, or ADAT Optical format, one device has to be the master and the other has to be the slave. The master establishes the sample rate and locks everything together, while the synchronized slave follows merrily along. This is easy in a basic system where you’re only sending around one digital signal. In fact, it may all be handled in the background by your software, without you having to worry about it.

But in a more complex system—be it mic preamps with digital outs, effects with digital ins and outs, or a digital mixer— managing digital synchronization can take a bit more planning and effort. Word clock I/O (often carried on BNC/barrel connectors) makes this easier since the digital clock part of the equation can be separated out from the digital audio signal and managed independently.

Perhaps we’ll dig deeper into this in a future column, but that’s as far as we need to go into word clock I/O for now. Having word clock I/O may or may not be a dealbreaker for you, but it’s definitely a handy bonus to have on your interface.

Mic Preamps. Microphones put out very low-level signals that must be preamplified before other electrical devices can deal with them. Having built-in mic preamps means that you don’t need to purchase additional gear for routing microphones into your interface. And the number of mic preamps in your interface will determine how many mics you can plug in at once. Though it may seem like a good idea to go for the most mic preamps possible, be realistic about what you really need. Unless you are recording multiple musicians at once, one or two may be plenty. But you’ll need at least eight mic preamps, if not more, to record a full band. If an interface doesn’t have enough built-in preamps for your projects, you can always add more and route them into the analog inputs of your interface (assuming the interface has enough free analog inputs). Other features to look for include phantom power, which will allow you to use condenser mics with the interface. Also, a low-cut/high-pass filter is useful for cleaning up low-frequency rumble when recording with a mic.

Control Room Features. Some interfaces with monitor outputs provide additional “control room” features, such as the ability to switch between two sets of speakers. Interfaces with a dim switch allow you to reduce the speaker level so you can converse with your collaborators without stopping playback, while a mute switch will temporarily silence the speaker output completely. Other interfaces include a mono switch for summing the stereo output to a single channel, which is handy for checking for problems with phase cancellation in the stereo outputs.

Direct Monitoring/Latency Management. Sending an audio signal into an audio interface, converting it to digital, sending it down the line to your DAW software, turning around and sending it back out, converting it back to analog, and then routing it to your speakers or headphones takes some time. And the time it takes will cause a delay that can often be audible. This delay is called latency and it can be especially problematic when overdubbing tracks. Many interfaces have special features for reducing or eliminating latency, and I consider it essential to have this technology onboard.

Onboard DSP. Some interfaces feature built-in chips that can be used for a variety of tasks. While some use onboard DSP for handling latency, others use these built-in chips for generating reverb, delay, or other effects that can be used when tracking. Having effects available that don’t add latency or load down your computer can be a godsend in certain situations—many a take has been saved by providing “comfort reverb” for a singer who isn’t used to singing in headphones. Though onboard DSP isn’t a must-have, it is a useful tool.

Metering. Level meters on your interface’s front panel can be a real help in recording healthy levels without worry of clipping or distorting a track.

With that, we’ve completed our discussion of both the computer and the interface— the core of our system. Next time, we’ll start looking at capturing and monitoring our signals!

Mitch Gallagher is the former editor in chief of EQ magazine. He’s written more than 1000 articles and six books on recording and music technology, and has released an instructional DVD on mastering. His upcoming book is entitled Guitar Tone: Pursuing the Ultimate Electric Guitar Sound. To learn more, visit