Audio Interface

What Is an Audio Interface?

An audio interface is a physical device that acts as the bridge between sound sources and your computer.

The primary function of an audio interface is to convert signal from microphones to digital signal that a computer can record. This is called analog-to-digital conversion or AD conversion.

As a basic example, the audio interface can be connected to a vocal microphone through an XLR cable. That microphone produces an analog audio signal that passes through the cable into the audio interface. At that point, the signal is converted to digital signal. That digital signal is routed through an output cable that is typically connected to a computer. The digital audio signal can be used by a DAW software to record the audio.

Audio Interface Components

These are the common components you will find in most or all audio interfaces.

Inputs
These are the holes on the front or back where you plug in your sound sources like microphones and instruments. Usually these are either XLR inputs, quarter inch inputs, or combo jacks, which accept both XLR and quarter inch inputs.

Monitor Outputs
Monitor outputs are used for real time playback of the inputs plugged into the interface. Monitor outputs may be stereo or mono and usually each have their own volume knob. Monitor outputs are most commonly for headphones or for studio monitors.

Gain Knobs
Gain knobs are usually located right next to the inputs. There is usually one gain knob per input. These control how much pre-amp amplification will be applied to the corresponding input. The result is a louder sound. But it is not a volume knob. This is actually affecting the amplitude of the signal that will be sent to the outputs.

Preamp
The preamp is a common internal part in most interfaces. It takes the very weak electrical signal from a microphone and boosts it up to a healthy, strong level that is easier to work with.

AD and DA Converters
AD and DA converters are analog-to-digital and digital-to-analog converters. You may see these also abbreviated as ADC and DAC. Inside the box, tiny computer chips do all the heavy lifting. They turn the analog signal from microphones into digital signal for your computer. They also turn the digital code back into real sound waves when you play the song back.

Audio Interface Features

If you are shopping for a new audio interface, you need to know what features to look for. Here are the most important things to consider.

Number of Inputs
Think about how many things you want to record at the exact same time. You will need at least one input for each. Also consider the type of inputs you need. The most common types are XLR inputs for microphones and quarter inch inputs for guitars and keyboards. Many interfaces use combo jacks, which accept both XLR and quarter inch inputs.

Phantom Power
Some inputs, including condenser microphones, require phantom power. That means that the microphone requires a power supply delivered through the same cable that it is connecting it to the interface. Look for a button that says “48V” on the front of the interface. This button sends extra electricity up the cable to the microphone so it can turn on.

Direct Monitoring
This is a very helpful feature when recording. It lets you hear yourself sing with zero delay. It sends the sound from the microphone straight to your headphones before it even enters the computer. When you listen to playback from your DAW instead, the processing happening on the computer can often cause a significant delay. This delay can be calculated and compensated for, but it is often much easier to listen to a direct monitor while recording.

Connection Type
Make sure the interface plugs into your computer easily. Most modern audio interfaces use a standard USB connection. Some expensive interfaces use Thunderbolt cables because they are even faster. Always check your computer ports before buying.

Visual Meters
It is very helpful to have lights or a small screen on the front of the interface. These jumping lights show you how loud your sound is. If the lights stay in the green, you are safe. If they hit the red, your sound will clip and distort. Meters help you set the perfect volume before you record.

Power Options
Some small interfaces get all their power straight from the USB cable connected to your computer. This is called being bus powered. It is great if you want to travel and record in a park or a coffee shop. Larger interfaces require a separate power cord plugged into a wall outlet because they need more electricity to run all the inputs.

MIDI Ports
If you have older electronic keyboards or drum machines, they might not connect with a USB cable. They might use older circular cables called MIDI cables. Some audio interfaces have special MIDI In and MIDI Out holes on the back so you can easily connect this older gear to your computer.

Loopback Audio
This is a special feature that is very popular for people who stream video games or host podcasts. Normally, an interface only records what comes into the microphone. A loopback feature lets the interface also record the sounds happening inside your computer, like a YouTube video playing or a friend talking on a video call. It loops the computer sound back into the recording software.

Expandability
If you buy a small interface with only two inputs, what happens if you want to record a full drum set next year? You might have to buy a whole new interface. However, some interfaces have special optical ports on the back, often labeled ADAT. These ports let you plug in a separate box of extra preamps later, expanding your small interface to handle many more microphones without buying a new main unit.

Included Software
Many audio interfaces come with free software. They often include a basic version of a DAW program so you can start recording music right away. Some also include special mixing software that runs on your computer. This software lets you control the interface settings and route audio paths without touching the physical knobs on the box.

Why Do You Need One?

Computers already have a small sound card inside. But the built-in sound card is not good for recording music. It is usually too slow. This causes a delay when you try to record. It also typically has a low sound quality.

An audio interface solves these problems. It is fast. It sounds clean and clear. It also gives you all the inputs you need to build a real recording studio.