Recording on a computer or a digital system is a standart for a while instead of recording on a tape. As technology advances, making records gets easier. Anyone can record his/her idea in just a few minutes to a computer, using an “Audio Interface”.
So, what does it do? Do you really need one?
Audio interface is the bridge between the analog world and digital world. The sound as we hear it, is a physical phenomena. It needs to be transformed into electrical signal in order to be recorded. This transformation is microphones’ or electric guitar pickups’ job. But this is an analog signal.
Computers process the data digitally. Something has to convert analog signals into digital data so that computers operate. That’s where the audio interface comes in.
An audio interface takes the analog signal, samples it periodically, gives a number to every sample according to their amplitude and sends this number to computer. At the same time, computer sends numbers to the interface. Interface takes these numbers and generates an electrical signal according to the size of the number. This signal becomes the audible sound.
This process called “Analog/Digital – Digital/Analog conversion” or simply A/D D/A.
There are different forms and kinds of interfaces according to the needs. Some has 2 inputs and outputs, some has 28. Some has only analog inputs and some has both analog and digital.
Choosing the interface depends on your purpose. If you’re a studio owner, you might find it useful to have an interface that has multiple ins and outs. Because you are going to record a full drum set and it takes at least 4 microphones.
If you’re a singer-songwriter, that much ins and outs are clearly pointless. What you need is just 2 inputs. A microphone input and an instrument input.
A microphone input is different than an instrument input. Mics use XLR connectors. Whereas instruments use TS connectors, similar to TRS (headphone jack) but TRS has 1 more cable inside. The bigger one is XLR. It is often clearly visible on the front side of the interface.
If you’re a guitar player, you can plug your guitar into the interface directly. Then using a host program like Cubase or ProTools, you can open up some amp/cab simulation plugins and play through your computer as if it is a tube amp.
These mic and instrument inputs have some important specs that set aside them from regular onboard sound cards.
An instrument input consists an instrument pre-amp inside the unit. It has high enough impedance (1M ohm) to load the guitar pickups.
Similarly, a microphone also needs a pre-amp. Some microphones need an extra power supply called phantom power to operate.
So, an audio interface acts like an amp for guitars, a pre-amp for microphones which a regular on-board sound card could never achieve. And also their high sampling rates, bit depths and high quality clocks make the A/D D/A conversion very transparent as if there’s nothing in between your guitar and computer.