I’ll go over what an audio interface is, what it does, and what to look for when buying one in this post.

Traditional microphones record the sound you make in the air and send it to your computer as an analog electrical waveform. This output must be transformed into a stream of discrete electrical voltages that correspond to 1s and 0s in order for your computer to understand it—this is a digital signal. Internally, USB microphones manage this operation. The analog electrical signal is produced by standard microphones using a (male) balanced XLR connection. Microphones that can produce both analog and digital forms at the same time are also available.

So, how do you hook up an XLR mic to a computer? That’s where an audio interface (sometimes known as a “soundcard”), a useful accessory, comes in. Today, we’ll go over the basics of USB and Thunderbolt audio interfaces. Until recently, Firewire audio interfaces were very popular, and they are still easily accessible on the secondhand market. We advise against using them since many of them are no longer supported by the manufacturer or modern operating systems.

What are audio interfaces and how do they work?

Audio interfaces do both analog to digital (ADC) and digital to analog conversions (DAC), and typically include several channels of each. One or two inputs for line levels or microphones, microphone preamps, and a stereo output to feed monitor speakers or headphones are included in the most basic versions. Something basic like this will be small enough to put in a laptop bag easily.

Each mic channel should be able to provide +48 volts to condenser mics and have a variable input gain range of at least 60 dB. Extra headphone ports and volume controls are common additions that come with price hikes. High-pass filters to reduce rumbling; attenuator pads for powerful sounds; phase inversion switches (useful when recording multiple microphones); and input impedance selection may all be added to the mic preamps to make them more sophisticated (for better matching and signal transfer). Some mic channels have buttons that activate hidden magical technology using iron, tubes, or “air” in some combination. Because this isn’t something that provides a lot of value, don’t go overboard on it.

Even the most basic interfaces should have one or two high-impedance instrument inputs for DI guitars and basses. Additional line-level inputs and outputs will be carried on balanced TRS connectors (jack sockets).

If you’re recording several sources at once, such as a live drumkit, you may require more than the basic interface’s limited number of analog inputs. Many interfaces will enable extension through a connection carrying additional digital inputs or outputs if this situation is in your future, which it will be if you enjoy the concept of recording bands.

What kind of user interface do you require?

Some microphones offer a USB output, as we’ve previously stated. If you just need to record one voice at a time, a USB mic will suffice, and an interface will be unnecessary. Continue reading if you’re looking for a mic with an analog output.

Consider the following factors before deciding on an interface:

  • How many mics are required to record simultaneously?
  • How many analog line inputs will you be recording at the same time?
  • What number of line outputs will you require?
  • Is it possible to extend it?
  • What is the significance of portability?
  • Thunderbolt’s advantages and latency

I won’t go into great detail on sampling rates and bit depths; instead, I suggest that you avoid anything that doesn’t support at least 24 bits at 48 kHz, since this is a reasonable minimum performance goal for most audio capture applications.

The number of XLR inputs with mic preamps you require on the interface is determined by the number of microphones you need to record at the same time. Count the amount of analog inputs on any equipment that produces line-level signals, such as external mic or guitar preamps, outboard processors, or vintage synthesizers. Because most mic preamps can handle line levels without problem, you’ll need to consider which combinations of mic and line inputs you’ll need to account for. Most home recording situations should be covered by four inputs.

Outputs

The third question is essential and will vary significantly based on your application, even if it isn’t the first thing that comes to mind. If you don’t plan on bringing any signal back into the analog world for processing (or re-amping guitars) and simply need to feed your monitor speakers, a pair of outputs will enough for most individuals working in stereo. If you want to use a surround system for monitoring, you’ll need at least eight output (DAC) channels. A separate stereo headphone monitor is very useful and will increase the number of DAC channels required by two.

Portability and expandability

Do you intend to take on bigger projects in the future? You may need to mic more persons or numerous instruments, thus an interface with extra digital inputs/outputs is a good investment.

Consider S/PDIF (two channels), the popular ADAT port (up to eight channels per port), or the less common MADI (up to 64 channels) BNC connection, which will provide you with future-proof expandability without sacrificing portability. These will let you to “piggyback” an external multichannel AD converter, which may frequently offer extra DAC channels if you need them.

If you want to take your recording equipment on the road, to a jam session, or to a friend’s home, portability is critical. In addition to searching for something small and light, keep in mind that some basic interfaces are bus-powered, which means they receive their power from the host computer and don’t need a separate power source. This simplifies setup and allows you to work where there are no power outlets for as long as your laptop battery can keep things operating.

Thunderbolt’s advantages and latency

The last factor to examine is latency, which refers to how much lag your recording equipment has. It will decide the amount of time you have to wait while live-monitoring the audio being captured. For performers watching themselves throughout the recording process, too much latency may be extremely distracting.

The overwhelming majority of audio interfaces on the market connect to a host computer through USB. The speed at which audio is processed and the round trip delay time are both limited by USB connections. Some businesses address this by including proprietary audio drivers with their interfaces, although these are often the more costly options. For a circular journey, the absolute lowest latency is thought to be about 4.5 milliseconds, although most take more. Some devices on the market offer a simple solution for avoiding the internal processing lag by mixing the direct sound from the mic input with the headphone output.

If latency is a top priority for your application, check at Thunderbolt-enabled interfaces, which utilize Apple’s newest peripheral connection standard. Lower lag periods (less than 1ms) are possible, but there is less options in terms of technology.