What Is An Audio Interface? [How To Choose The Best Interface]

Any producer, sound engineer, or musician with a home studio will undoubtedly need an audio interface at some point in their journey. It is an extremely important piece of equipment and an entire home studio usually centers around it. What is an audio interface though? How does it work? Why is it so important?

Well, that’s what we’ll be talking about today.

The main purpose of an audio interface is to vastly enhance your recording and playback capabilities in your studio. You’d have a hard time simply recording yourself as a solo musician or podcaster without one in most cases.

That brings me to my first point in this article. You may be asking yourself why you need an audio interface. The answer is actually quite simple.

Why Do You Need An Audio Interface?

Most computers, phones, and tablets have built-in sound cards. In this case, we’re mostly talking about your source computer. Now, that computer you have most likely has a sound card that’s pretty basic, made to handle YouTube videos or casual listening and not much else.

You wouldn’t be here if you weren’t looking to record audio of any sort. Your computer’s sound card was simply not made to handle multiple channels of audio signals. That’s where an audio interface comes in.

An audio interface is essentially a supremely upgraded sound card, so to speak.

A good interface will help you gain more inputs and outputs (I/O’s) and increase the amount of audio channels you can record/playback audio on. Not only that, but an audio interface will significantly decrease your overall latency when recording multiple channels.

One of the main reasons why anyone invests in an audio interface is to record vocals though. The reason being is because they allow you to record seamlessly through XLR inputs directly to your computer.

These are just a few of the many reasons why you need an audio interface if you plan on recording anything for any kind of home studio. To help you better understand the importance of audio interfaces, we need to learn how they work.

Related: Studio Equipment List: The Top 50 Essentials

Related: [9 Easy Steps] How To Set Up An Awesome Home Recording Studio

How Do Audio Interfaces Work?

Audio interfaces provide a number of functions, but their main job is conversion. They convert device signals — like those that come from guitars, microphones, MIDI keyboards, etc. — into a format that your source computer can recognize.

Most interfaces can convert these signals two-way, meaning in both analog to digital (ADC) and digital to analog (DAC). These types of conversions are carried out by the interface itself, and most audio interfaces feature multiple channels of each.

Outside of vocal recordings, an audio interface also has the capability to bring external devices (such as studio monitors, MIDI controllers, guitars, etc.) to line-level, but we’ll get into that later. 

Overall, in every input and output on an audio interface, a conversion of signals is happening. Also, a “gain boosting” of certain signals is happening as well. All of this signal conversion goodness helps to create high-fidelity audio recording/playback in your studio.

Related: The Ultimate Guide To MIDI Keyboards

Related: Small Studio Monitors Buyer’s Guide

Connectivity

When talking about audio interfaces, the first hurdle is figuring out how it’ll connect to your source computer. A lot of this comes down to your budget and how you plan on recording audio in your studio.

Let me start this out by laying out the most popular connection options found in most audio interfaces on the market today:

USB (3.0, 2.0, and 1.1) 

Probably the most common connection type. Audio interfaces that connect via USB generally run on bus power rather than external power. That, among other things, helps to make USB interfaces very convenient and easy to use. The downside is that USB interfaces tend to introduce some latency. More on latency later.

Thunderbolt & USB-C

It’s ultra-fast and low latency nature has made Thunderbolt the new standard connection type in audio interfaces. For instance, Thunderbolt 3 is ten times faster than USB 3.0. You can also opt for an interface with USB-C connectivity, which is universally compatible with Thunderbolt. Nowadays, there pretty much one in the same.

FireWire

This connection type was once the standard in audio interfaces. It was able to transfer data more consistently than USB, and was generally more reliable as well. You’d be hard pressed to find an audio interface that supports FireWire nowadays though. That’s probably because fewer computers come equipped with FireWire ports. In any regard, I don’t recommend buying a FireWire audio interface on used markets.

PCIe 

This is an internal card-based interface that you install directly into your computer’s motherboard. The advantage of PCI Express is that you can eliminate a lot of latency and have virtually limitless track counts. The speed of PCI Express is unmatched as well. That being said, you have to be pretty technical to install these guys and most PCIe interfaces are quite expensive.

Related: Thunderbolt Audio Interfaces Guide

Choosing A Connection Type

Now that we know the most common connection types, it’s time for you to think about what your plans are for recording. 

If it’s worth it to you to save up some money and go for a Thunderbolt audio interface, then that’s my top recommendation. Even more so if you already have a computer that has Thunderbolt ports. It’s simply the best all-around option. You get speed, low latency, and a ton of functionality in Thunderbolt audio interfaces.

With that, a USB audio interface is still a great option, and they definitely perform well. There’s a reason why they’re the most popular options out there. They are also perfect for those of you who only plan on recording yourself in podcast format or as a solo vocalist/musician and can be found in some great startup equipment bundles. 

Related: Studio Equipment Bundles Guide

Inputs & Outputs

Now onto the big stuff. The I/O count, and variations of said I/O count, is by far the biggest factor to consider when looking at audio interfaces. Again, all of this depends on how you plan on recording audio in your studio.

If you just plan on starting a podcast studio, you should only need an interface with an XLR mic cable, a couple line outs, and USB bus power. Alternatively, if you’re planning on recording a whole band with drum mics, multiple vocal mics, and guitars, you’re probably going to need a high I/O count.

To make all of this easier to digest, let’s break this down and talk about all of the input and output types individually:


MIDI I/O’s

Musical Instrument Digital Interface (MIDI) is one of the most prominent I/O’s in today’s music. A lot of modern MIDI devices are connected to an audio interface via USB, but it’s important to have traditional 5-pin DIN inputs as well for vintage synths and better reliability. You can also get a MIDI to USB adapter if need be.

XLR Inputs

XLR inputs allow you to record audio signals captured through a microphone. Every XLR input on an audio interface usually has a mic preamp behind it, but we’ll get into preamps in more detail later.

Hi-Z & DI Inputs

Otherwise known as “high-impedance” inputs. These are typically used for connecting guitars directly into an audio interface. There are other methods for recording guitars (like a DI box), but this is probably the best route to go. Don’t forget that you’ll need standard guitar/instrument cables with 1/4” TS connectors for these inputs.

1/4″ Line-Level Analog I/O’s

Instrument level (or line-level) devices require line-level inputs to produce audio through the audio interface. Line level inputs accept line-level signals, whereas line-level outputs produce line-level signals. Preamps do their job to bring microphones up to a microphone-level, and Hi-Z brings guitars up to line-level. Line-level devices that require an output include studio monitors, hardware effects processors, and others.

DB-25 I/O’s

DB-25 is a 25-port electrical connector used to connect patchbays. This is typically accomplished through TRS snake cables or XLR snake cables in an audio interface. In a nutshell, DB-25, in conjunction with patchbays, allows you to expand your I/O count for recording vocals, drums, and guitars.

S/PDIF I/O’s

Sony/Philips Digital Interface is most commonly used to connect consumer devices via RCA, coaxial, or fiber optic cable with Toslink. It’s great for connecting to amplifying receivers like home theater systems. Can also be used for expanding your I/O count due to the fact that it can carry two channels of compressed audio.

ADAT S/MUX I/O’s

Similar to S/PDIF in terms of how it connects (RCA, coaxial, fiber optic) but ADAT is used to transfer up to 8 channels of uncompressed 48 kHz, 24 bit audio. We’ll get into bit depth and sample rate later. ADAT can also be used to expand your I/O count on your audio interface.

Word Clock I/O’s

Every audio interface has a built-in word clock. It’s job is to determine how often to process one sample of audio. Dedicated word clock inputs and outputs are used to keep other devices with differing internal clocks in-sync. In this type of signal flow, the audio interface will become the master clock, and other devices will be the slave clocks.

Headphone Outputs

Most audio interfaces should have at least one headphone output to be used with your studio headphones. This is a no-brainier, you absolutely need headphone outputs. The only thing here is to consider an audio interface that has two headphone outs for some additional flexibility, especially if you use both open-back and closed-back headphones.


Okay, that was a lot. Determining what your I/O count should be is super important though. What’s even more important is deciphering what types of I/O’s you need.

Related: Open-Back vs Closed-Back Headphones Guide

Resource: Studio Subwoofer Buyer’s Guide

Latency And “The Snowball Effect”

Have you ever played an online video game like COD and your internet starts acting up? You aim at an enemy and he moves 50 feet away in a split second? Well that’s called “lag” and the overall measurement of that lag is called latency.

The same thing happens in audio, but can have even more severe consequences than just messing up your K/D ratio. 

Latency, in regards to audio, refers to the lag between your audio signal and source reproduction. When latency is high in a device (like an audio interface), there is a significant delay in the signal flow. Imagine trying to record vocals and you hear the playback of the audio a half a second later. That can certainly spell disaster in the studio.

It goes without saying that the more delay there is, and the more latency a device has, the worse things will be. It can easily become a snowball effect and get out of control quickly.

In most cases, these delays will be hard to notice to the untrained ear. You’ll only notice it when you’re far into a project. All of this is to say that it’s important to invest in an audio interface (or any device for that matter) with low latency.

It’s important to remember that there are many factors that can contribute to latency, not just an audio interface. Every device in your studio will have a certain amount of latency. It’s virtually impossible to completely eradicate the lag in any given signal flow.

With that, there are a number of ways to limit lag. For instance, line-level analog connections don’t introduce any lag, but the interface can still introduce a little bit. 

Another great way to treat latency is to get an audio interface that connects via Thunderbolt. Thunderbolt is the king of latency, I’m telling you! USB interfaces do struggle with latency, but it’s really not significant enough to create a cascade, just make sure that the devices connected to it are as “low-latency” as possible.

Latency is a wildly important factor in all of this though, and it’s definitely something to keep in mind when looking at any studio device, not just audio interfaces.

Phantom Power

Phantom power in an audio interface is pretty straightforward seeing as it only involves condenser microphones. Phantom power (+48V) is needed to properly power condenser microphones, which are the best option for recording high-fidelity vocals.

It only works through XLR cable connections and isn’t required for dynamic mics or most instrument mics. This is not to be confused with mic preamps, which are needed to bring microphones to microphone-level gain.

In an audio interface, Phantom power, XLR cables, and mic preamps all work together to create high-quality microphone recordings and playback. Speaking of preamps…

Related: Studio Microphones Guide

Preamps

Most interfaces should come equipped with at least one preamp. They are yet another component that’s used to amplify low-level audio signals to line-level or mic-level.

Preamps boost levels specifically in gain. Gain boosting has the potential to introduce a lot of “noise” whether it be white-noise or high-frequency feedback. That being said, the higher-quality preamp you have, the better because they will introduce the least amount of unwanted noise.

Preamps will undoubtedly add some color to whatever you’re recording, it’s just the nature of things. This isn’t necessarily a bad thing though. Every preamp included on an audio interface will sound different, and that’s where things can get complicated.

Some preamps focus on clarity, while others focus on warmth. It’s similar to amp heads for electric guitars. High-end audio interfaces such as Universal Audio’s Apollo series have the ability to emulate different preamps through their included software.

All I’m saying here is to do your research and make sure you’re getting high-quality preamps in your audio interface that you think will sound good. You can also look for external hardware preamps if you want to really control the situation.

In summary, don’t cut corners with your preamps. They are an awesome, and important component worth mulling over with a fine-tooth comb.

Sample Rate & Bit Depth

Any decent audio interface in today’s market will come with adequate specs. The question is: what do those two terms mean anyway? Well, let’s start out with bit depth.

Bit Depth

In a nutshell, the higher the bit rate, the more headroom you’ll have to avoid clipping. Higher bit rates also give you a quieter noise floor, meaning recording at lower level won’t introduce unwanted noise. Basically, you have more sonic room on both ends of the spectrum with a higher bit rate.

By today’s standards, there are two main options in terms of bit rate in an audio interface: 16-bit or 24-bit. While it’s true that 16-bit is the bare minimum that I’d recommend, it’ll still give you enough headroom. 24-bit is ultimately the better choice though.

Sample Rate

Same thing here with sample rates. The higher, the better. Higher sample rates ensure a smoother sound without any distortion or misrepresentation of the audio signal. 

Think of frame-rate (or FPS) in video games. Nowadays, 60fps is the bare minimum required for games to look right on a screen, anything lower than that and you’ll notice some jitter.

Same thing with audio. The absolute minimum sample rate in an audio interface that I’d recommend is 44,100Hz (or 44.1kHz), but that’s even pushing it. Modern musical equipment pushes the sample rate/bit rate boundaries more and more every year. With that, I’d even say to avoid any interface less than 24-bit/48kHz, just so you can keep up with everything as it continues to progress.

You can definitely go higher than that if you want to. 32-bit/192kHz audio interfaces are out there, and they’re quite impressive, but you don’t absolutely need to go that route right now. Rates like that are also typically only found in rack mount interfaces as well so they’re pretty pricey.

What About USB Microphones?

I’ve mentioned USB interfaces a number of times in this article, but what about USB microphones? You might be wondering if you even need an audio interface if you already have a USB mic. Well, in short, my answer is yes you do.

You should look into expanding your recording capabilities beyond a USB microphone. USB microphones do typically come with a rudimentary built-in audio interface, but they’re usually extremely limited. 

USB microphones are great for simple jobs. Solo entry-level podcasters/content creators should only need a USB mic, but they’re not great for higher-level recording because they struggle with latency, even more so than a USB audio interface.

All I’m saying is that, in most cases, even a low-end audio interface with a condenser microphone will be far superior to a USB microphone. That’s especially true if you want higher-quality audio recordings for music or content creation.

Planning For The Future

  • Expansion – through S/PDIF, ADAT, and even MADI, you can chain your I/O count in the future if you plan on taking on bigger recording jobs. If you’re in a band or plan on recording one, plan for the future and choose an interface with expandable I/O’s.
  • Portability – a lot of modern audio interfaces have a small footprint without sacrificing their I/O count and technical capabilities. Perfect for recording on the go or live performances as your sounds grow and mature.

Additional Features To Look For

  • Zero-latency monitoring – great for real-time monitoring while recording. Though there might still be some input lag, this feature will cut out most of the delay for excellent monitoring.
  • Digital Signal Processing (DSP) – great for offloading some of the work from your computer and onto your audio interface for larger projects.
  • Alternative speaker outputs – some interfaces offer a couple of different ways to connect studio monitors, double check this before you make a decision on either an audio interface or studio monitors.

What Audio Interface Is Right For You?

Now is the time to assess what your studio needs are and how you plan on doing things. Here are a number of questions you should ask yourself:

  1. How many microphones are you planning on recording at once?
  2. How many instruments do you need to record?
  3. How many line-level outputs do you need?
  4. Do you need an interface that can expand for the future?
  5. What is your budget for higher-end interfaces with lower latency and better connectivity?

Once you have an answer to all of those questions, you should be able to narrow down what you need from an audio interface in your studio. After that, you’re off to the races!

Conclusion – What Is An Audio Interface?

So there you have it guys! We went over a lot in this article. Audio interfaces are the main hub of any home studio though, so it’s worth it to dive deeper into them. Just know that there is an audio interface out there for every budget and every need.

All that’s left is for you to find the perfect one for your studio based on everything that’s been laid out in this article. My only hope is that this piece has given you some useful information on your search.

One last thing, don’t let me deter you entirely from investing in a USB audio interface. For most home studios, they will work just fine. Just double check the I/O count and sample rate/bit rate and that should be plenty for you.

As always, feel free to reach out with any questions you may have!

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Jeremy Bongiorno
I have been a musician and producer for over 15 years. My goal is to provide reliable, honest information and hopefully help to improve the quality of life in your studio.

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