Audio Interface

A computer's built-in audio connections are designed for listening, not for recording music. An audio interface does the job properly: it gives you inputs for microphones and instruments, clean preamplifiers, accurate conversion, and outputs for headphones and studio monitors. Most connect to the computer over USB or Thunderbolt.

What it does

1. Amplifies. A microphone produces a very small signal. The interface's preamp raises it to a usable level, and the gain knob sets by how much (gain).
2. Converts. An analog-to-digital converter measures the signal many thousands of times per second and turns it into numbers the computer can record, at the sample rate and bit depth you choose. A digital-to-analog converter does the reverse for playback.
3. Routes. It sends the computer's audio to your headphones and speakers, often with a separate volume control for each.

Inputs and features to know

• Microphone inputs (XLR), often on combination sockets that also take a guitar or line cable.
• Instrument (Hi-Z) inputs for plugging an electric guitar or bass straight in.
• Line inputs for keyboards, synthesizers and other line-level equipment.
• Phantom power (+48 V), which most condenser microphones need. Most dynamic microphones don't.
• Direct monitoring, which lets you hear your input straight from the interface, without the small delay of a round trip through the computer.
• MIDI ports on some models, for connecting older keyboards (MIDI).

Latency and buffer size

Sound takes a little time to travel into the computer and back out. That delay is called latency. Your DAW's buffer size setting affects it, alongside conversion, drivers and processing. A small buffer gives low latency, which feels better while recording, but works the computer harder; a large buffer is safer for mixing big projects. A common habit is a small buffer while recording and a larger one while mixing.

How many inputs?

Count the sources you need to record at the same time. A singer-songwriter recording voice, then guitar, can manage with one or two inputs by overdubbing one part at a time. Recording a full drum kit or a band playing live usually takes eight or more inputs (multitrack recording).