All About Recording Interfaces

Universal Audio Home Recording Studio Interface

So you’re ready to start recording, but you need a way to get your audio into the computer. Your internal sound card isn’t going to the trick. You need an audio interface that accommodates your unique recording needs. Rest assured, we’ve compiled all the practical info you’ll need to make the right purchase!

Connections and Compatibility

This may seem obvious, but you need an interface that is compatible with your computer. Interfaces come in a range of connectivity options like USB, Thunderbolt, Firewire and Ethernet. You’ll have to take a look at your computer’s ports to see what you have to work with. If you’re in need of more connectivity, maybe it’s time to shop for a new recording computer.

The top-end professional devices are currently using Thunderbolt connections, like the Universal Audio Apollo line or the Focusrite Clarett 8pre. Thunderbolt is the fastest connection available and shares many benefits of expensive PCI systems.

However, the type of connection to your computer does not determine your audio quality. USB, Firewire and others carry your ones and zeroes just like Thunderbolt can, but with less speed and bandwidth. So don’t feel left out if you can’t afford a Thunderbolt interface!

Check to make sure your computer has the minimum required specifications for your interface. Sometimes significantly old computer processors are incompatible with newer recording technology.

AD/DA Converters

The primary function of an audio interface is to convert analog signals (like an electrical signal generated by a microphone) into digital samples, and then back to analog again so we can play it through speakers or headphones. There are specially designed circuits in an audio interface called AD converters and DA converters (analog-to-digital and digital-to-analog) that accomplish this.

Many big studios and high-end professionals like to use expensive standalone converter units and digital clocking devices for the AD and DA to capture and play back the most accurate samples they can, but it isn’t really necessary, since most recording interfaces have pretty good AD/DA built-in. You can worry about standalone converters after you win your first Grammy.

Analog I/O

Probably the most important feature when deciding on an interface is the number of analog inputs and outputs (I/O) you’ll need. If you’re using a microphone or several microphones, you’ll need a mic preamp for each channel you’re recording. The preamp will bring the microphone signal to a level useable by the built-in A/D converter. Many interfaces come with useful features like a high-pass filter on their preamps, as well.

Most entry-level models have at least one or two microphone preamps and a ¼” instrument input (for plugging in your guitar, keyboard, etc.). If you’re only recording one channel at a time, you can stop there! One of many small, portable options will serve all your needs. Just double check and make sure they have a headphone output and two balanced outputs for your studio monitors.

Some small affordable interfaces:
Focusrite Scarlett Solo
PreSonus Audiobox USB 96
Focusrite Scarlett 6i6

But let’s say you need to record a drum kit. You’re going to need somewhere in the realm of 8 channels to accommodate all the different pieces of the kit (kick, snare, hi-hat, overhead, toms, room microphones). There is a multitude of great 8-channel interfaces that will do exactly that with studio-grade precision. Most come with two headphone jacks and 8 analog outputs you can route wherever your heart desires.

Some affordable interfaces with 8 preamps:

Focusrite Scarlett 18i20
PreSonus Audiobox 1818VSL
Behringer U-PHORIA UMC1820

Digital I/O

Many interfaces will come with lots of digital inputs and outputs you might need. Let’s say we’re recording that same drum kit, but we want to record the rest of the band at the same time. If your interface has an ADAT input, you can expand your inputs with an 8-channel preamp that has an ADAT output. This adds up to 8 channels of 48kHz, 24-bit audio over a short optical cable for a total of 16 mic inputs. This is a truly great solution for home and professional studios that need more connectivity than a typical interface can offer alone.

SPDIF is another common two-channel digital protocol among interfaces that can add a stereo device (like an external 2-channel mic preamp or a keyboard with digital SPDIF outputs). This comes in over traditional RCA cables to bring the input count up to 18 when combined with an ADAT connection and an 8-channel interface!


Universal Audio Apollo Twin Interface

Universal Audio Apollo Twin Interface


Sample Rate and Bit Depth

Let’s get into the nitty-gritty for a minute. Few things in recording are misunderstood the way sample rates are misunderstood. Your interface’s sample rate will determine how often your converters will “take a picture” of your audio signal. For example, at 48kHz, your interface will be sampling a snapshot 48,000 times per second. Wow!

Many interfaces offer two or more selectable sample rates:


While it may seem like the higher your sample rate goes, the more accurate your recording will be, it just isn’t the case in practical situations. The truth is different converters sound slightly different at varying sample rates. Like top-end converter hardware, we recommend putting off the 96 and 192kHz settings until later, as these require some serious hard drive space and have theoretical limitations due to the Nyquist Theorem (Google it!).

The bit depth of your interface determines dynamic range and digital headroom. Dynamic range is the difference between the loudest and quietest sounds your interface can sample. Headroom is how loud your signal can be before introducing ugly digital clipping*.

Aging digital technologies, including CDs, store 16-bit audio. While these mediums have great sound, 24-bit is a huge improvement in dynamic range over 16-bit. For this reason, we recommend interfaces that can record at 24-bit, 48kHz.

*Don’t confuse the digital headroom of your interface with analog headroom. Analog distortion is often sought-after in recording.

DSP/Zero-Latency Monitoring

If you’ve done any recording, you may have experienced a strange, disorienting delay effect while monitoring yourself sing or play an instrument. This is called latency and it happens because your computer is processing your audio signal before coming back to your headphones or speakers. You’re hearing the gap of time it takes in between your actual performance and the computer’s ability to play the recorded sample. Latency is very bad for the performer, and all digital devices have latency.

There are two ways an interface can combat this problem: through zero-latency DSP monitoring software or just a simple direct mix knob. The mix knob is the most straight-forward, as it merely splits your audio signal—one going to the computer for recording, and one straight to your monitoring path (headphones or speakers). Turn the knob or switch all the way to direct, and you’ll eliminate the latent signal. The PreSonus Audiobox USB 96 and the M-Audio M-Track 2×2 are good examples of small interfaces with a mix knob.

Many devices come with their own monitoring software that is run by a dedicated DSP (digital signal processing) chip inside the interface instead of using the computer’s processor. This takes the computer out of the monitoring path and brings latency below 1 millisecond in many cases, which is imperceptible to our ears. If your interface comes with dedicated software for input monitoring, we highly recommend using it.

That’s all we have today, folks. We hope you’re one step closer to meeting your recording goals! Be sure to check out our other articles for all the info you need on computers, studio monitors, microphones, acoustic treatment and more!

The Best Interfaces For Home Recording

1. Focusrite Scarlett Solo (USB) – one mic pre, comes with Pro Tools First
2. Focusrite Scarlett 18i20 (USB) – 8 mic preamps, Pro Tools First
3. M-Audio M-Track 2X2 C-Series (USB) – one mic pre
4. PreSonus AudioBox1818 (USB) – 8 mic preamps, comes with Studio One 3 Artist
5. Universal Audio Apollo Twin (USB) – 2 mic pres, professional, ADAT, DSP

An interface is only one piece needed for a home recording studio. Here are some other things you may need: