WHAT TO LOOK FOR IN AN AUDIO INTERFACE
Depending on your requirement, the things to look for in an audio interface are as follows:
Inputs and Outputs
Let’s say you are a vocalist or someone who plays an instrument, you would need one or a maximum of two inputs. And unless you want to preview a surround sound output or monitor more than one pair of speakers you would not need anything more than two outputs
Now if you are recording any percussion instruments or are recording instruments with multiple microphones you will need more than two inputs. Normally drums are recorded with 8 and more microphones. Even world percussions like Darbukas, Dholl, Tabla etc are recorded with a minimum of 2 microphones but can go up to 4.
Types of Audio Connections
Generally, the connectors on interfaces are combo jacks, i.e they can take XLR as well as 1/4″ jacks as inputs. Having combo jacks is better as you can connect any type of cable to your audio interface. Some interfaces have dedicated jacks for guitar inputs, even these are fine.
Your outputs for your monitor speakers may offer 1/4″ TRS jacks or RCA. If you are to use professional monitor speakers then make sure the outputs are 1/4″ TRS and not RCA, as RCA is an unbalanced consumer output
Connectivity and Power
Most entry level audio interfaces come with USB connectivity and are Bus powered. Bus powered means that the interface gets its power from the computer and does not need an additional power source.
Generally interfaces that have a DSP or have more than 2 inputs need a external power source as the bus is unable to provide the required power. Examples would be the Universal Audio Apollo Series or Motu
Some external powered interfaced give a better results especially on the Preamps and the headphone outs when then are connected to with external power
If your need is a mobile on the go setup then you should look for Bus powered interfaces
The quality of an audio interface is dependent on a couple of things. First is the quality of the preamp, and second the A/D converter. Lastly its the recording bit rate. Just looking at the bit rate should not be the primary benchmark for a good interface, sometimes interfaces that boast 24bit/96kHz fare lower in terms of quality to an interface that is just 24bit/48kHz.