If we talk about the basic function of an audio interface, it comes as a device that connects your computer to analog/digital Instruments. That digital instrument could be anything like your guitar to a MIDI Controller Keyboard. An audio interface acts like a sound-card of your PC or Mac. But the audio processing quality you get is far better than that of the sound card. Along with this, you get various features that are important for music producers or singers, who record their vocals or instruments. The features are as follows: 1. High-Quality Audio The quality of the sound of any instrument or the vocals that you record automatically gets increased using an audio interface. Many people choose a USB microphone but using a USB microphone, you have to compromise with the sound quality. So yes, If you want to get a good quality in your production, using a budget audio interface is a must. 2. Phantom Power There is a condenser microphone that runs or say requires a 48V DC voltage in order to get the power. That stepped-up 48V increases the quality of microphones for recording high-quality voice or instruments. Audio interfaces have the support of phantom power which gives you the accessibility to use those high-powered condenser microphones. 3. Multiple Input and Output channels If you are a singer, two inputs and a single output would be enough for you. Two inputs for a microphone and your instrument, and output for a headphone. But, if you are a music producer and often record various artists at a time, you may require many inputs as well as outputs. Many singers will sing together and at the same time, the same number of headphones will also be required. So you get higher numbers of I/Os on an expensive range of audio interfaces.