Audio Interfaces take all the various audio inputs and convert them into digital audio data. Though that sounds straight-forward, this was easily the most confusing part for me as I began the quest to design my own home studio. This piece of hardware will end up being the front end for nearly all the inputs that will be used in your home recording studio. Digital audio, electrical analog audio, and MIDI data will all come together in this great sonic melting pot. It acts as the central hub for all the various Audio Signals in your setup... taking them from your finger tips and vocal cords and into the digital realm. By handling all the audio input and output signals of your system it performs the same function as the Sound Card in a typical computer.   The main differences are that Audio Interfaces typically have mic preamps onboard, provide Phantom Power for condenser mics, and have easy-access external inputs and outputs. So technically the terms Sound Card and Audio Interface could be used interchangeably. But for our discussion let's define Sound Cards as hardware internally mounted to your computer, while a studio Audio Interface is an external hardware unit connected via USB or FireWire. Though there are many options, there are 6 main features to consider when choosing Audio Interfaces: Analog / Digital Converters Number of Microphone Preamps Number of Inputs/Outputs Interface Type MIDI Capability Mixing Capability Read on for a more detailed explanation of each criteria on our list. For everyone else I strongly recommend having a firm grasp of the main issues that are outlined below before shopping for specific units. This may be the single most important decision when creating your home studio, so it's critical to have a firm grasp of how these work and what they are used for.

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.

Some instruments like keyboard synthesizers and drum machines can be added via a line level input. These are different than the mic inputs listed above because these instruments' output levels are much stronger than the tiny output signals that come from microphones. Line level inputs can come in 2 different flavors: One accepts the input for a 1/4" instrument cable only, and the other is known as a combination (or just combo) jack that can take either a 1/4" instrument or XLR cable input. The combination jack is becoming very popular because of its versatility, but it's also slightly more expensive for manufactures to produce so don't look for them on the entry level budget units. Just like the mic preamps above these get eaten up fast, especially if you have a left / right output such as that from a digital piano or drum machine. On the output side, all units will have at minimum a stereo main out. Some units may have multiple additional outputs that can expand the possibilities of your home recording studio setup. Additional outputs usually come in stereo pairs and are useful for sending specific tracks to outboard (hardware based) effects or to a custom headphone mix via a Headphone Amp. Even in the higher priced units, the number of outputs can vary drastically, so make sure you consider this carefully when choosing one.

Connection Type and Latency Latency - the delay caused by the time it takes audio to pass from the input to your audio interface through the ADC (analog to digital converter) through your DAW and then out via the DAC (digital to analog converter) - is one of the major factors engineers consider when choosing a new audio interface. Largely dictated by the connection type between the interface and the computer, this is a particularly important consideration if you plan to record with plug-in effects and processors or if you're dealing with high track counts. In general, the faster the connection, the better performance you can expect from your audio interface.USB Audio Interfaces While you might encounter an old USB 1.1 audio interface, USB 2.0 is the most common connection type on the market, providing moderate speed and near universal compatibility on Mac and Windows PCs. To overcome latency issues, many USB audio interfaces include "latency-free" monitoring options, which range from analog routing options that let you simply monitor the live input to more advanced onboard digital mixers that may even include DSP effects/processing. USB 3.0 is over 10 times faster than USB 2.0 and supports higher track counts with far less latency. Class-compliant USB audio interfaces, such as the Antelope Audio Orion 32, can provide up to 24 channels of iPad recording via the Apple Camera Connection Kit.FireWire Audio Interfaces There are two types of FireWire found on audio interfaces: the older FireWire 400, which is the same speed as USB 2.0, and FireWire 800, which is almost twice as fast. For years, FireWire was the standard for high-speed audio interfaces and was found almost exclusively on Mac computers. Most modern computers connect to FireWire audio interfaces via FireWire to Thunderbolt adapters. FireWire delivers ample performance for most project studio needs, and FireWire audio interfaces have the benefit of being extremely affordable while providing high channel counts.Thunderbolt and PCIe Audio Interfaces Audio interfaces connecting via Thunderbolt offer connectivity speeds twice as fast as USB 3.0 and over 12 times as fast as FireWire 800. While Thunderbolt ports are universally found on modern Macs, they're uncommon on Windows PCs, and many popular Thunderbolt audio interfaces don't support the Windows OS. PCIe audio interfaces boast specifications in line with Thunderbolt audio interfaces but require PCIe slots for installation. PCIe systems - such as Avid Pro Tools | HDX and Apogee Symphony - are typically intended for high-volume professional audio-production applications.Analog and Digital Connections Analog connections on audio interfaces come in a variety of formats, such as XLR, 1/4", and RCA connectors, or they sometimes opt for the smaller DB-25 connectors, which pack a lot of I/O in a small amount of space. Onboard microphone preamplifiers can greatly eliminate the need for additional recording hardware, and models such as the Focusrite Clarett line include enough onboard preamps to track entire bands. Audio interfaces may include more analog connections than channels of digital conversion, so you'll want to make sure you have enough channels available to accommodate your recording and monitoring needs. Likewise, digital I/O such as 8-channel ADAT lightpipe may allow you to easily expand your audio interface without outboard preamps, and some interfaces even include MIDI I/O for connecting keyboards and controllers.Choosing the Right Format Audio interfaces come in a variety of shapes and sizes, but they're generally intended for either desktop or rackmount use. Desktop interfaces tend to be smaller with fewer connections, but they put all of the hardware controls you need within easy reach. Some desktop audio interfaces are bus powered, which makes them ideal for mobile use. Rackmount audio interfaces are often permanently installed in 19" equipment racks, providing more I/O but sometimes at the expense of hands-on control.Onboard DSP Many audio interfaces come with onboard digital signal processing and DSP-based mixers, providing built-in effects, dynamics, equalization, and monitor mixing. This allows you to put reverb or delay on vocals for monitoring, or sometimes to record with EQ and compression, all without adding latency to your system. Onboard DSP can be either fixed or expandable, depending on the system. Fixed systems such as MOTU's CueMix FX include a number of effects and other processors, which you can access via dedicated software; whereas systems such as Universal Audio's Apollo line include DSP that can power special plug-ins.Finding the Right Audio Interface Between connection types, I/O configurations, format, and more, there's a lot to keep in mind when looking for the right audio interface to suit your needs.

If you're considering adding MIDI capability to your home recording studio then this is a great place to address it. Unless you have several MIDI devices that need multiple inputs, you can include MIDI in your setup here without having to get a specialized piece of gear. Some of you may have several MIDI instruments that you want to hook up simultaneously (Synth-aholics Anonymous may be in your near future). If this sounds like you, you'll want to explore a dedicated MIDI Interface with multiple inputs / outputs. In other words, the included MIDI inputs on nearly every audio interface will likely be inadequate if you need more than 1 MIDI input and 1 MIDI output for your studio. The good news is that it's often included so even if you're undecided on the whole MIDI thing it won't cost you any extra to have the option to play around with it. Most newer MIDI controllers can also be connected to your setup via USB as well, so this can be another option for adding MIDI capability without the standard MIDI I/O. That brings us to the final piece of the puzzle, mixing capability.