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November 11, 2018 2 min read

An audio interface is a device that transmits audio signals to and from a computer. They essentially replace a computer’s sound card but provide better sound quality with more inputs, outputs, and features. Interfaces come in all shapes and sizes with various feature sets, including everything from portable USB-powered boxes to massive rack-mounted professional systems.

Inputs and Outputs

Focusrite Scarlett 2i2 with two inputs

Also known as I/O, inputs and outputs are all of the ways that audio signals go in and out of an interface. They can include inputs for microphones, guitars, and line-level sources; outputs for headphones, monitors, and auxiliary sends; and even optical, ethernet, or SPDIF connections for digital audio.

Different combinations of I/O are useful in different scenarios. For example, a small bedroom studio may only need headphone and speaker outputs with one or two microphone and guitar inputs, while a commercial studio may need 32 or more line inputs, main and secondary monitor outputs, and multiple headphone jacks.

Digital Audio Converters

PreSonus AudioBox 44VSL has a blend control that gets rid of any delay
from A/D and D/A conversion

Digital audio converters are chips inside of an interface that convert analog audio signals into digital audio (A/D) and vice versa (D/A). Converters can have a huge impact on sound quality, but technology has advanced so much that even entry-level modern interfaces feature high-quality converters. Most interfaces feature controls to adjust the converters’ sample rate (similar to a video’s frame-rate) from the CD standard of 44.1 kHz all the way up to 192 kHz for audiophile quality.

Unlike purely analog equipment, converters take a few milliseconds to process audio into digital information, introducing an audible delay called latency, which can be distracting when overdubbing to pre-recorded tracks. For this reason, interfaces usually include an on-board monitoring system to route signals directly to headphones or monitors, circumventing the latency problem.


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