How to shop for an audio interface

Focusrite Scarlett 2i4 interface

If you’re just starting out your home studio, or looking to upgrade your audio interface, there are many factors to consider in order to make an informed decision that gets you the best bang for your buck. An audio interface is the traffic cop of your home studio, controlling all the physical inputs and outputs.

Using an audio interface is always better for a home recording studio than the built-in soundcard on your computer. An audio interface:

  • will allow you to connect guitars, synthesizers, and professional microphones
  • can achieve lower latency, so you don’t hear a delay while recording or playing a software synthesizer
  • is designed to record and playback at the same time; a soundcard, not so much

With the right feature set for your home studio, you can improve your workflow and focus on the creative rather than the technical. Don’t get me wrong, though – you still have to understand the technical, so here we go.

Number of inputs

The first and potentially most important thing to consider is the number of inputs you have. You need as many inputs as things you’ll be recording at the same time. Interfaces generally come with 2, 4 or 8 analogue inputs.  Manufacturers usually state the number of inputs in the model name, and almost all of the time, it’s the first number.  For example, a Focusrite 2i4 has 2 inputs (and 4 outputs, but we’ll get to that in a bit). A Presonus AudioBox 44VSL has 4 inputs and 4 outputs.

What’s crucial to understand here is that you only need enough inputs for one recording pass. For example, if you record guitar first, then vocals, then bass, you really only need one input. If you’re recording all three at the same time, you’ll need three inputs. Simultaneous recording not only captures the magic of musicians playing off one another, but recording them on discrete channels also gives you isolated tracks in your software for better mixing. (Note, mic bleed is a topic unto itself.)

Types of inputs

Inputs for microphones are XLR inputs – an XLR mic cable has three large pins in a circle on one end. Often, audio interfaces feature “combo jacks” which can take an XLR (mic) cable, or a standard ¼” cable, like a guitar patch cord. Other inputs may only take a ¼” cable.

Inputs are usually designed for one or more impedance levels. The definition of impedance doesn’t matter – just note that microphones, guitars (or any stringed instrument with a ¼” output), and synthesizers all have different types of output, and require three different setting for inputs. Mic level is the weakest of the three, instrument level (for guitars) is higher, and line level (synthesizers, CD players, your mobile music device) is the strongest signal. While most combo jacks automatically detect a mic or line level signal, only some feature a switch or option for instrument level. Activating the instrument level switch (sometimes called Hi-Z), if it’s available on your interface, ensures you get a good signal level from the instrument. This is about the same as patching your guitar through a DI box.

Input channels may also features a 20dB pad. This switch cuts the signal by 20dB, which is a significant drop. This is useful if you’re recording anything particularly loud, like a guitar amp or a drum, and ensures you won’t distort the signal. This feature is usually not found on the least expensive interfaces.

Some interfaces also include 5-pin MIDI input and output. While not strictly part of the audio system of your home studio, this can save you from investing in an additional USB MIDI interface if you have some older synthesizers you want to use. Most modern synthesizes and MIDI controllers connect directly to your computer via USB.

5-pin MIDI IN and OUT ports
5-pin MIDI IN and OUT ports


When you plug in a microphone, the gain knob controls the volume of the input and engages the preamp. Ideally, these knobs are laid out beside each input, so it’s easy to know which knob controls which input. For most home studio setups, the preamps in modern audio interfaces are low-noise and transparent sounding. While some interfaces feature premium quality preamps (for a premium price), you need to keep in mind you should also have a premium microphone and an acoustically treated recording environment to really take advantage.

Phantom Power, or 48V

Every audio interface will have a switch or button for 48V power, also known as Phantom Power. This is required for using condenser microphones. Just remember to always switch on Phantom Power after plugging in your microphone, and switching it off before unplugging your mic. Phantom Power will not affect your dynamic microphones.

Some interfaces put the switch for 48V on the back of the interface. Ideally, the switch is on the front and has a light to indicate that it’s on. Some may even have the switch as part of the software interface, which in my opinion, is the least desirable place for it.


Most audio interfaces will have balanced TRS (tip, ring, and sleeve) connections for outputs. The TRS cable looks similar to a ¼” patch cord (unbalanced TS cable), but it has an additional ring on the connector pin, indicating that it can be used for a balanced TRS connection, or carries a stereo signal, like your headphone cable. Generally, balanced TRS connections are less susceptible to introducing hum or noise in your signal path over longer distances.

TRS vs TS cable
TRS vs TS cable

Outputs are normally reserved to connect your studio monitors. This takes two outputs – one for the left speaker, one for the right. Interfaces with more than one output pair can be used to connect additional speakers, or connect to a desktop mixer. Connecting to a second set of speakers can be useful in testing your mixes.

Don’t discount the value of a big honking volume knob. Some interfaces feature this, and personally, I think it’s a great value add. Volume of your playback is one of the most frequently used controls in your home studio, and sometimes you need to adjust it quickly; you don’t want to be mousing around to find the control. Some interfaces also feature a mute button, which is ideal (i.e. you don’t want your monitors sounding while you’re recording from a microphone).

Digital inputs and outputs

Some interfaces also include digital inputs and outputs. These are used if you have a device with a corresponding output (S/PDIF or optical). The optical (sometimes called ADAT) signal can carry 8 discrete channels. For example, you could expand your two-input setup with an 8-channel preamp with an optical output, for a total of 10 microphone or instrument inputs. The S/PDIF connection only carries a 2-channel stereo signal, and is usually found on synthesizers or CD players.

Sometimes audio interfaces are marketed as having 10 inputs, while only two mic inputs are visible. That’s because the manufacturer is also counting the 8 digital inputs via an optical connection.

Monitoring options

All interfaces have an option for zero-latency monitoring. Generally, if you want to include a reverb in software for your vocalist while recording, you’ll introduce latency while the computer processes the signal, applies the reverb, and sends it back out to be heard. A zero-latency switch (often called direct monitor, or input) allows you to hear the input in real time, without latency, along with the computer playback. Some interfaces allow you to adjust the relative levels of input and playback material.

On-board DSP

Some interfaces include on-board digital effects processing. This allows you to record with very low latency and still apply a reverb or other effect to the monitored input. In my opinion, this is only an issue with older or very budget-level computers. With most modern systems and non-DSP audio interfaces, you can get latency down to a few milliseconds and use a software reverb. It’s best to use a low-CPU taxing plug-in for this. It’s important to note that the reverb in this case won’t be recorded; it’s only used for monitoring. You can still use a better reverb plug-in after the recording is complete. Many singers prefer a bit of reverb in their headphones while recording.

Power supply

Many of the two-channel interfaces are powered by their USB connection to your computer, making them ideal for a mobile recording studio. The larger interfaces, with four or more inputs, usually require a separate power supply in addition to the USB connection, and a power switch. This is something to consider if you’re planning to go mobile with your studio.

Bundled software

The fact is, there are a lot of interface options out there, especially in the two-channel range. One way to decide which one to buy is to look at their bundled software. Many manufacturers include a light version of recording software, like Cubase or Abelton Live. If you prefer one software choice over another, but you haven’t invested in it yet, sometimes getting the light version with your interface gives you a discount when upgrading to the full version. You can check with the software companies to find out more, or download trial versions if you haven’t settled on one yet.


Ultimately, I can’t tell you what interface to buy. If you want to know which one I have, and which ones I’ve had in the past, check out my blog post about the history of my home studio. You have to assess your needs and come to your own conclusion. Hopefully, this article has armed you with the knowledge to make a good choice.

Do you see anything on an interface that I haven’t covered here, or have any questions? Comment below and let me know, and I’ll get back to you. I also accept heaps of praise and accolades.

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