An audio interface is the input and output device that connects microphones, instruments, speakers, and headphones to your computer. It converts incoming analog audio into digital data your DAW can handle, and converts digital data back into analog signals for playback.
A/D and D/A conversion
When recording, the A/D converter digitizes the input signal at the sample rate and bit depth you set. When playing back, the D/A converter turns the data from the DAW into a signal your speakers or headphones can reproduce. Conversion quality affects the sound, the noise, and the levels the device can handle.
Mic preamps and inputs
Most units include a preamp that boosts a microphone signal to a level strong enough to record. Microphones, line sources, and instruments each need a different input mode. Phantom power for condenser microphones is also provided, but use it only when the connected device requires it.
Outputs and monitoring
The speaker and headphone outputs let you check the DAW’s playback and the input while recording. If your unit supports direct monitoring, which lets you hear the input before it passes through the computer, you can record without the latency of the software path.
What to check when choosing one
Check how many microphones and instruments you record at once, the types of input connectors, whether there is an independent headphone output, the supported sample rates, the connection type, and driver support. More inputs is not automatically better; choose based on the inputs and outputs your way of recording actually needs.
Set the recording level separately
Even with a high-quality unit, too much input gain clips before A/D conversion, and too little makes noise stand out when you raise the level later. Set the level with headroom left at the loudest part of the performance. An actual microphone and equipment setup is shown in A simple way to record drums and the gear used (Japanese).
