These provide the ability to take the electrical signal from your microphone or instrument and convert it into the digital signal that computers can understand.
Just as Doc Brown needs the Flux Capacitor to make time travel possible... so do we need A/D converters to make digital recording a reality.
Audio Interfaces are the quickest and easiest way to introduce this essential component into your setup.
A/D converters are described as a set of 2 numbers: a bit depth (i.e. 16-bit, 24-bit) and a Sampling Rate (such as 44.1 kHz, 96 kHz, etc).
This set of values represents the maximum bit depth and sample rate possible with a given interface, you can always set them lower as you choose.
A bit depth of 24-bits and sampling rate of 48 kHz are solid target values to shoot for when shopping around.
A common mistake is to assume that a mixing console will provide this capability, but unless it has a USB or FireWire output it will not.
Furthermore you'll have to pay top dollar (~$1500) for a digital mixer with the ability to record each input to it's own dedicated track, something even moderately priced audio interfaces can provide.
The more affordable digital mixers (~$300) will only output the Left/Right main outputs through the USB or FireWire interface.
These guys take the relatively low mic-level output signal and boost it to a usable level.
When choosing this piece of your rig, a critical consideration is how many individual microphones you plan to use.
You will need a mic preamp for every mic you want to record at the same time!
You will also need one of these for every mic level signal (such as the one coming out of a direct box) that you plan on recording.
For example, if you want to record an electric guitar & bass via direct boxes with 2 mics for vocals - you will need a total of 4 mic preamp inputs.
This will allow you to record each instrument and vocal on a dedicated track on your DAW Recording Software at the same time. This is a big deal.
Why? Because it gives you the ability to alter the level, assign processing FX, and generally edit each input without affecting the others in your mix.
But are these built-in mic preamps any good? Or should I buy individual mic preamps instead??
The onboard Mic Preamps found on the commercially available audio interfaces I discuss on this site are quiet and powerful enough to make beautiful recordings with.
You do not need to spend a king's ransom buying these individually, even though that is an option you may consider at a later time.
I'd recommend against this until you have some more experience because it does get a bit more complicated, and it's more than you need to worry about starting off.
Mic preamps tend to get swallowed up quickly so err on the side of getting an interface with a few more than you think you'll use.
After considering the number of mic preamp inputs you need, the next question is how many other inputs and outputs will you require.
