What Is An Audio Interface Used For? (Read This Before You Buy)

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  • What is an audio interface?
  • How do they help with recording and monitoring?
  • Find out why interfaces are essential for all producers.

Audio interfaces are crucial for all serious producers. Without this humble device, there is no way to connect your microphones and instruments to your computer – unless they have USB or Bluetooth built in. This may be fine for YouTubers and streamers, but for serious music production, you’re going to want an interface at one point or another.

Your monitor speakers also need an interface to work properly. If you’re planning on using headphones alongside them, then the interface will – at the very least – save you a lot of time.

But our interfaces do much more than just send and receive audio signals. We’ve broken down every feature you’re likely to find on an audio interface, from common things like preamps to more exotic features like ADAT for the gear heads.

If you’re new, we highly recommend you also check out our guide on how to get started with music production.

What Is An Audio Interface?

An audio interface is the bridge between your microphones, instruments, audio gear, and your computer. It’s a crucial device that you need to have in order to record high quality audio into your DAW and send the signal back out to the speakers.

When interfaces record mics and instruments they convert from analog to digital (A/D). When the signal goes back out to your speakers or headphones, the conversion is, of course, digital to analog (D/A). The quality of these converters can make or break an interface.

There are a bunch of different interfaces on the market with various numbers of inputs, outputs, and other features.

You can expect to pay more as the in / out count increases.

Audio interfaces will also often have MIDI functionality for controlling (and being controlled by) hardware, and we’ll talk about that more later.

“Why Do I Need An Audio Interface?”

You’ll need an interface for any serious recording or monitoring. Trying to get by without one is like trying to swim with your arms tied behind your back.

Even if you’re aiming for the bare minimum amount of gear for production – or not even doing any recording – an interface is still crucial.

Sound Card vs Audio Interface: What’s The Difference?

Your computer’s sound card may be good for gaming, but it’s not designed for making music. This means you won’t be able to plug in XLR cables or guitar leads (though if your gaming rig can do this, send us a pic and we’ll post it here).

The D/A converters on any interface will beat the ones used for your sound card, hands down. Headphone sockets on laptops also tend to be flimsy and getting them fixed is no easy task. Interfaces are much more reliable on this front as well!

“Can I Use A USB Mic Instead Of An Audio Interface?”

USB mics can be handy but more often than not they are designed for YouTubers, podcasters, and human speech rather than for musical applications. USB mics have converters and preamps inside just like interfaces, but the quality is not always ideal for music production.

USB mics are perfectly fine for podcasting, but recording musicians will want an audio interface.

You can get away with low-quality A/D conversion for human speech because here we’re not as interested in the tone quality of the audio, just what is being said. ASMR nerds will beg to differ but still, don’t expect miracles with any old USB mic.

A common USB microphone may only have 16-bit depth and 44.1kHz resolution. Some of the best ones can go up to 24-bit/96kHz but will cost a lot more.

Comparatively, a cheap audio interface can easily go up to 24-bit/192kHz. Here you can see that for a similar price, buying an audio interface is clearly a better investment than buying a high-quality USB microphone.

Common Audio Interface Features

Preamps

Preamps are a crucial part of an audio interface. Although we’ve come a long way with recording, you still need to consider gain staging, and the preamps on your interface are vital for this.

Each model and brand will have different preamp configurations, and the quality of the preamp will directly affect the cost of the audio interface.

A preamp is essentially an electronic amplifier that boosts weak signals that come from our mics and instruments. Most times the more gain a preamp can provide, the better.

When a preamp can pump a lot of gain, the audio interface can better separate the signal from background noise. Each microphone will require different amounts of gain and some need much more than others. If you are plugging your guitar or bass straight into your interface, you’ll definitely need to crank the preamps to get any decent level (see Hi-Z later).

Some musicians prefer to have a separate preamp unit that they plug into before their interface. These units often have tubes and other circuitry that color the audio, but your interface’s preamps are designed to be ‘transparent’.

On almost all commercial audio interfaces, you will see a gain or volume knob for each and every input preamp. This means you can set how loud things are before they are recorded in your DAW.

The Focusrite Clarett 8Pre has excellent preamps and a lot of inputs!

If you’re serious about professional recording, good quality preamps are essential.

If this is you, make sure you research the interface well before committing to anything.

But if you’re just looking to get your very first one, you won’t need to worry too much here. The preamps on budget interfaces are still perfectly fine for recording, but you won’t get the same level of clarity in the mixing stage compared to more expensive interfaces.

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Inputs and Outputs

Audio interfaces can record multiple signals at once, and this is one of the best things about them. Thunderbolt and USB-C interfaces can record a ludicrously high number of tracks simultaneously, assuming your computer can handle it!

For example, if you’re a singer-songwriter who wants to record vocals while playing guitar, an audio interface will allow you to record your vocals and guitar at the same time. Drummers with many mics will appreciate interfaces with a larger number of inputs.

Plus, many quality interfaces with multiple inputs can be found brand new for under $200.

Number of Inputs

One of the main ways to determine the cost of an audio interface is by the number of inputs. The cheapest ones around $130 will likely have 1 or 2 inputs.

Expensive audio interfaces could have 16 or more inputs, and it’s simply a matter of what the purpose of the recording is. If you’re a guitarist or a singer and you’re only recording one thing at a time, even two inputs are more than enough!

But for drummers, band recordings, instrumental duets, or a podcast with guests – any of these situations will require more than one input.

Take recording drums for instance – the bare minimum of microphones required for recording decent drum tracks are four microphones: two for overhead, one for kick drum, one for snare drum. So for a full band recording, at least eight inputs are needed. If this is you, I highly recommend having at least a couple of extra inputs available if your budget allows.

Recording situations vary a lot and you don’t want to be just short of having enough inputs available. It’s happened to me at least a couple of times!

Companies like Focusrite cover all bases by offering a variety of different interfaces within the same product range.

XLR Inputs 

These inputs are the most common on all interfaces. XLR inputs are used for connecting microphones. They have a distinctive circular shape – three pins on one end, and three circular holes on the opposite end.

XLR inputs use 3 pins to minimize noise, otherwise long cables would be susceptible to all sorts of electromagnetic interference. So if you find yourself dealing with noise, check it isn’t your cable first.

Hi-Z Inputs

Hi-Z input is an abbreviation for hi-impedance input, and these inputs are used for directly plugging in guitar or bass into an audio interface. Hi-Z inputs are designed for pickups and ensure optimal sound for DI recordings.

Hi-Z inputs are not separate to your other inputs, usually there’s just a switch that enables it. These inputs can also be found in mixers, direct boxes, and tape decks.

If your interface lacks Hi-Z as an option, you will need a special DI box for your guitar and bass tracks.

Line Level Inputs and Outputs

These are not used for plugging in microphones or instruments, but they are useful in connecting outboard processors like reverb, delay, headphone amps, and studio monitors.

Monitor outputs are for the speakers you use to listen back to your session. In most cases there will be a pair of studio monitors – left and right. Each side will require a line output, and most audio interfaces will have at least two of these. 

Headphone Output

It’s hard to imagine an interface without a headphone socket.  There will be a separate control for headphone volume vs monitor output in almost every interface.

Headphones are of course very useful for minimizing bleed when recording, and some interfaces will let you set a separate headphone mix if you need to focus in on certain parts.

Keep in mind that interfaces rarely support 3.5mm audio plugs, despite this being the default size for consumer headphones and earbuds. So you can expect to need one of those ubiquitous plugs that always seem to go missing at the worst times…

MIDI Inputs and Outputs

MIDI stands for Musical Instrument Digital Interface, and it’s simply the language that allows digital music gear and programs to speak to each other.

The MIDI sockets on a Yamaha DX11 synthesizer. Without MIDI in your interface, you won’t be able to control this synth from your DAW.

Having MIDI inputs and outputs will allow you to send information to a MIDI instrument from your computer and vice versa. Modern MIDI keyboards will have a USB connection to a computer, but old MIDI instruments don’t have a USB port available. So in this case, a MIDI input port can save an old gear from being junk.

S/PDIF & ADAT Inputs and Outputs

S/PDIF stands for Sony/Philips Digital Interface, and can be used for transmitting multiple digital audio signals at once. If your interface has a S/PDIF port, then you can plug in digital hardware without pointlessly converting to analog and back. This will also free up inputs for mics and other instruments.

Alesis Digital Audio Tape (ADAT) is another way of transmitting digital audio signals. ADAT, Lightpipe, and TOSLINK are terms that can be used interchangeably.

ADAT can process up to 8 extra channels of 48 kHz, 24 bit audio. ADAT is super useful if you need to increase the number of inputs in a pinch, though it is not as common. 

These days, S/PDIF and ADAT are somewhat antiquated, but can be still be found on interfaces designed for large studios with older gear.

Word Clock Inputs and Outputs

Here is one more confusing term to know about, especially if you are dealing with digital audio hardware. A word clock is an internal clock inside digital gear that times the calculation of audio information.

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This internal clock will tell the interface how often to capture one sample of audio. Ideally, this matches the sample rate perfectly to the nanosecond. Unfortunately, this is not always possible, so each internal clock will have what is known as ‘jitter’ – tiny imprecisions in the sample value as a result of mistiming.

With a single digital unit, this is not a problem. But in a studio with multiple rack processors, these miscalculations really add up. So it makes sense to use only one timing source for everything.

Obviously, you should pick the highest quality clock to control all your gear. So if your interface comes with one, there’s a good chance it will be very precise as it is expected you will use it as the master clock.

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Thunderbolt vs USB vs Firewire Interfaces

Thunderbolt

Thunderbolt interfaces are a relatively new type of audio interface but are becoming increasingly popular. It’s based on the hardware interface called Thunderbolt, which is a connection originally developed for Mac systems by Intel and Apple, but now it’s available for PCs and laptops as well.

Thunderbolt connections have set a high standard for multitrack recording.

The popularity is growing exponentially, and Thunderbolt is becoming the new standard for audio interfaces due to its incredible speed and low latency.

Just to give you an idea, Thunderbolt 3 is 8 times faster than a USB 3. So if you have lots of instruments recording at once and your computer has a Thunderbolt connection available, you’ll have no problems with drop-outs and other glitches.

Check out our list of best thunderbolt soundcards here.

USB

USB interfaces are still the most common. Though Thunderbolt and USB-C are lightning-fast, standard USB is still good enough for modest recording sessions.

However, with different types of USB available, it can be a little confusing. First, we have the rectangular-shaped USB that we are all used to, and this is called USB Type-A

And then there’s a new kind of USB that has emerged in the past couple of years, and it’s called USB Type-C (or just USB-C). It’s smaller and more compact, intended as a replacement for the myriad of past USB types.

Many modern audio interfaces will be available in USB C. It is important that you check both your computer and interface are compatible before making any purchases.

Firewire

Firewire is an older connection that has been largely replaced by Thunderbolt and USB-C. For this reason, it’s uncommon to find Firewire ports on devices anymore. If you have an older computer, Firewire will still be much faster than standard USB, allowing you to record more tracks of audio simultaneously without dropouts.

But because it’s not as commonly used, you should only get a Firewire interface if it’s second hand and you have an older computer that supports it.

What is Phantom Power?

Phantom power is a type of amplification that is required to operate a condenser microphone. Condenser microphones use plate diaphragms to detect sound waves, but the resulting signal is extremely soft, so we need extra power to hear them.

If you accidentally put phantom power into a dynamic microphone, nothing bad will happen. But certain ribbon mics may be damaged by phantom power.

You should always turn phantom power off when plugging cables into your interface – you can damage preamps and mics if you are not careful.

Phantom power is sometimes labelled as ’48V’ which is, of course, the level of voltage it uses. Other levels exist but are less common.

Do You Need Direct Monitor?

Many modern audio interfaces like the Focusrite Scarlett (check out our full review here) series have a feature called “Direct Monitor”. This allows you to listen directly to inputs on the audio interface in real-time, instead of listening to your DAW’s output which has latency.

Direct monitor control is usually found as a switch or knob that fades between preamp input and your DAW’s output. It’s a great feature if you want to hear yourself as you record without being distracted by the delay, or if you just want to plug your phone in to listen to Spotify using your interface as an amp.

Choosing The Right Interface

Finding your first audio interface can be a daunting task. There are thousands of models from different brands to choose from, and many will have very similar features with only slight differences.

When choosing an interface, ask yourself what your specific needs are. Are you a singer-songwriter, EDM producer, aspiring sound engineer, or trying to start your own podcast?

Then determine exactly how many inputs you would need in your ideal interface. Most people who use an audio interface for home recording purposes just need one or two inputs. You can purchase this kind of audio interface easily under $200. 

The PreSonus AudioBox USB 96 is a great interface for those starting out.

Then you can start looking at the kind of audio interface you would like to buy. Like I mentioned before, in terms of processing speed, Thunderbolt audio interfaces are by far the fastest.

But they will also cost a whole lot more, so for your first audio interface, USB is probably best. They are the most convenient and easy to carry around as well.

PreSonus AudioBox USB 96 2x2 USB Audio Interface, Blue, PC/Mac - 2 Mic Pres
  • Bus-powered USB 2.0 audio and MIDI interface
  • Compatible with almost all recording software for Mac and Windows
  • 24-bit resolution; 44.1, 48, 88.2, and 96 kHz sampling rates
  • 2 combo mic/instrument inputs with high-performance, low-noise, high-headroom mic preamplifiers
  • Includes Studio One Artist DAW software and 6+ GB of third-party resources

Final Thoughts

Now that we’ve explored exactly what an audio interface does and why they are important, you should know what to look for when choosing one for yourself. Or maybe you’ve realised your current interface isn’t working out and it’s time for an upgrade.

If you’re starting out, you should definitely go with an established brand. Popular brands for audio interfaces include but are not limited to: Focusrite, PreSonus, Apogee, Behringer, Steinberg, and TASCAM. It’s really hard to go wrong if you just do a little research beforehand!

Last update on 2020-08-13 / Affiliate links / Images from Amazon Product Advertising API