How do audio interfaces work? Why are they important?

Image Credit: Sweetwater

An audio interface is the negotiator between your microphone, your computer, and your studio monitors. Your computer only understands binary information, but your microphone and monitors only understand electrical signals.

Digital music has presented us with so many pieces of useful technology. In addition to MIDI controllers, which allow us to interact with our DAW without using our mouse, audio interfaces allow us to record professional audio. Additionally, audio interfaces allow us to integrate studio monitors in our bedroom setups!

Audio interfaces are crucial tools for anyone looking to record audio at home. Which is better – audio interface or a mixer? Well, we use audio interfaces in place of mixing desks that you’d find in a professional recording studio. As with everything digital music-orientated, audio interfaces embody just why music production is now so accessible.

MIxing desks are very costly and take up a lot of space. Unless you have a lot of spare cash and have a big space, an audio interface is far better suited to your needs than mixing desks.

How audio interfaces work… what are audio interfaces used for?

Whether on Mac or Windows, audio interfaces convert analog signals into a digital format for your computer. In addition to studio monitors, audio interfaces route signals through a headphone jack for monitoring too.

Let’s put ourselves in the space. Whether you’re singing into a microphone or you connect your synthesizer/guitar directly to an interface line input, you’re sending an electrical (analog) signal to your audio interface.

A microphone converts an original soundwave into an electrical signal. Likewise, synthesizers output line-level signals that can be balanced or unbalanced. In effect, your audio interface is there to convert these signals into digital information (binary code) that your computer can read.

Then your computer sends your audio back to your audio interface (still as binary code). At this stage, your interface converts it back into an analog electrical signal. Finally, your audio interface sends this electrical signal to your active studio monitors that amplify it and play it back as audio.

An audio interface can feature multiple inputs. Microphone and instrument input signals are converted from electrical/line signals into digital (binary) signals so that your computer can read them.

As the name may suggest, routing audio is the only purpose of an audio interface. It’s their only mission in life. This makes them sound cards, and you don’t actually need a sound card in your computer if you have an audio interface.

Do audio interfaces improve sound quality?

Well, it depends. Will they improve the sound quality of your headphones? It depends on whether your headphones have a high impedance rate – and how good your headphones sound anyway. Will an audio interface enable you to record better quality music? The answer is yes – every time.

To illustrate, let’s briefly talk about microphones. If you’re looking at what microphones will give you the best results for recording high-quality audio, we recommend avoiding USB microphones. Instead, look into getting yourself an audio interface and a large-diaphragm condenser microphone.

Condenser mics are perfectly suited to recording sonic details in high quality due to their build. And in order to connect one to your computer, you’ll need an audio interface. USB microphones are better suited to podcasters and any task that doesn’t require as much detail as possible. We’ll explore this in more detail soon!

Like USB audio interfaces, the analog to digital conversion happens within the USB microphone – hence how you can connect them via a USB cable. Therefore, the quality of your signal through your USB microphone is limited by the A2D conversion of the mic and USB data rate. Furthermore, due to their smaller size, the quality of the analog to digital conversion is limited when compared to audio interfaces.

Anyhow, an audio interface coupled with a condenser microphone together will give professional-grade recording with a mountain of detail.

Do I need an audio interface if I’m not recording?

No, you do not need an audio interface if you’re not recording any audio. But if you want to connect studio monitors to your setup or use headphones with high impedance… then an audio interface allows for seamless connectivity for both. Additionally, if you want to connect a synthesizer or a line-level instrument to your setup then you will need an audio interface too.

Is an audio interface worth it? If you find your needs fit into any of the above mentioned, an audio interface is definitely worth your money.

How does an audio interface connect to a computer?

On the subject of USBs, the majority of audio interfaces connect to your computer via USB connections. Audio interfaces provide a soundcard to process digital audio in high definition.

In addition to computer systems, we can connect USB audio interfaces to tablets and even smartphones – provided you have a USB adapter. if you have a USB adapter. USB audio interfaces are the most common on the market because the vast majority of consumers have home studios rather than access to a professional studio.

For Mac, there are a growing number of audio interfaces with Thunderbolt connectivity as well as standard USB 2.0/3.0.

Thunderbolt connections have the advantage of faster data transfer speeds compared to USB, but they do have the disadvantage of being pricier. On the other hand, USB connectivity continues to get faster and the majority of home studio owners find that a USB recording interface serves each of their needs (including me).

The Focusrite Scarlett 2i2 audio interface back panel features two 1/4" stereo monitor outputs and a MIDI - USB connection. The MIDI-USB connection allows you to connect your audio interface to your computer.
Image Credit: Westland DJ

What are the outputs on an audio interface for?

Audio interfaces give us a stereo pair of 1/4″ line outputs. In a bedroom studio scenario, these are the only two outputs you need to concern yourself with (other than a headphone jack). These 1/4″ stereo outputs provide us with left & right channels that we can use to connect our studio monitors.

Some audio interfaces also provide analog outputs too. In more technical setups, we can use these various outputs to connect external gear.

How does 48V phantom power work?

Phantom power, often listed as +48V or P48 is a way of sending an essential direct electrical current through balanced XLR cables. Condenser microphones need this voltage to power their diaphragm and its internal amplifier.

The front panel of the Focusrite Scarlett 2i2 audio interface features two microphone/instrument inputs, a headphone jack, 48V phantom power on/off toggle switch, and preamp/input gain control knobs.
Image Credit: Amazon

Therefore, when you switch +48V phantom power on it sends a direct current through your XLR cable and delivers voltage that powers your microphone and amplifies the electrical signal. In turn, this allows for more precise recordings that condenser microphones are known for.

Audio interface specifications – what to look for in an audio interface

Now that we’ve covered the uses of audio interfaces, we’re leaving a list of audio interface specifications that you will find when you shop for one.

Total Harmonic Distortion + Noise (THD+N)

THD+N is all output that’s leaving your interface that isn’t your desired signal. In other words, noise. All gear produces a certain level of noise, and audio interfaces are no different.

When you’re shopping for an audio interface, look for as low a number as possible.

Dynamic Range

Dynamic range is the difference between the loudest and quietest signal that your interface can process at any one time. In contrast to THD+N, we want as big a number as possible here!

Frequency Response

Frequency response represents how accurate an interface can process frequencies across the frequency spectrum. As standard, interfaces will say 20Hz – 20KHz with a ± at the end.

For example, when browsing for an interface, the tech specs may say possible between 20Hz and 20kHz. When reading a tech spec for an interface, the frequency response will display like:

20Hz – 20KHz, ± 0.01 (dB).

We want the value that follows the ± symbol to be as low as possible.

The value that follows the ± represents volume cuts and/or boosts at specific frequencies. In this example, the interface will only apply cuts or boosts of 0.01 dB – which will not be unnoticeable to you unless you have the sonic hearing of Superman.

I share music production tips, tricks, and tutorials for RouteNote. When I'm not writing, I'm listening to and making music, occasionally DJ'ing, and reading - but I haven't figured out how to do them all at the same time.

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