How to choose the perfect Audio Interface for your recording computer (Part 1)

Choosing an audio interface can be a daunting task.  There are literally hundreds of options on the market and choosing one can be confusing and even frustrating.  As you can imagine we get to touch, experiment with and test many of the popular interfaces out there and would like to share with you some of the features, qualities, and benchmarks (Part 2) that will hopefully help make this decision a bit easier.  To me there are several major factors that come into play when selecting an audio interface.

Number of inputs and outputs – connectivity:

The first thing we need to determine is how many inputs we will be recording simultaneously and how many different monitor mixes we need to provide at the same time.  Songwriters are often fine with 1 or 2 inputs, while recording studios will often find a need for 24 or even 64 channels of input.  Many interfaces will have both analog and digital inputs.

Analog Inputs and Outputs

-Line level inputs and outputs usually use a ¼” jack for TRS connectors.  You can use line level inputs for things such as keyboards, signals coming from microphone preamp outputs, harware synths etc…  Many interfaces will have more line-level inputs than XLR pre-amped inputs to keep the cost of the interface down.  This does not mean that you cannot use these inputs for microphones; you will simply have to use and ‘outboard’ microphone preamplifier.  Many standalone ‘outboard’ microphone preamps can be used to add color or character to your sound where as built-in preamps are specifically designed to have a more transparent, general use, sound quality.  This connection type is also the optimal choice for keyboards or any device that have line level outputs.

-HI-Z guitar/instrument inputs also use a ¼” jack and provide connectivity that matches the high impedance signals from guitars and basses. If the interface has a HI-Z (High Impedance) Guitar/Instrument input it essentially means you have a built-in a direct input (DI). This type of input is perfect if you want to use your guitar with FX software such as GuitarRig, Amplitube, Revalver, Line6 POD Farm etc..

-XLR inputs are the most common type of microphone connection type.  Most interfaces that have XLR inputs will have a microphone preamps on those inputs with gain control (either via knob on the interface or a digital control in your mixer software).  ( Many interfaces with microphone preamps will also provide toggle-able phantom power required by many condenser and high end microphones.

-TRS/XLR Combo inputs provide, as the name implies, a combo type connector allowing you to insert either a line level input using a ¼” connector or an XLR microphone connector.

-RCA inputs and outputs provide connectivity with everything from mixers, record players, samplers, and sound modules.

Digital inputs

-TOSLINK or ADAT inputs and outputs provide lots of flexibility to audio interfaces that use it.  An ADAT connection is a digital connection that supports up to 8 channels of audio at 44.1-48kHz or 4 channels at 88.2-96kHz.  Many interfaces will have both ADAT inputs and outputs.  The most common use for ADAT is to use external microphone preamps and A/D converters.  Many ADAT capable preamps will offer a total of 8 microphone inputs making it easy to expand an audio interface that has an ADAT input – here are some examples:

Focusrite OctoPre MkII, RME OctaMic II, ART Tube Opto 8, Presonus DigiMAX

Some examples of A/D converters with ADAT outputs:

Lynx Aurora 16 w/ LT ADAT card, Apogee Rosetta 200, RME ADI-8 QS

-S/PDIF inputs and outputs provide a 2-channel (stereo) signal using a single cable with an RCA coaxial type connector.  Many keyboards will have S/PDIF connectivity allowing you to record their output without any D/A – A/D conversion.

-AES/EBU inputs and outputs provides 2-channel (stereo) signal using a single cable with an XLR type connector or up to 8 channels of audio using a 25 or 50 pin D-Sub connector.  An example of an interface that uses the AES format as its main source of connectivity is in the Lynx AES16e which allows you record the digital outputs of the Lynx Aurora 16 directly.

-MADI inputs and ouputs provide up 64 channels of audio using a single MADI cable.  Interfaces that use MADI are more common in bigger studios that have a need a large number of channels and are often used in multi-room studio configurations. A good example of an interface that uses MADI is the RME HDSP MADI.

MIDI inputs and outputs

With virtual instruments becoming more and more popular both in the production of electronic music as well as emulation of real instruments. The old standard of MIDI is still the best way to send note information to your computer to be interpreted by your virtual instrument software.  Many interfaces will have MIDI I/O but some don’t – make sure to check this specification if you plan to use virtual instruments.

Connection type and form factor

There are many different ways you can connect your audio interface to your computer.  Furthermore the inputs and outputs on an interface are made available using different form factors.  First I will go over connection type.

Connection Type:

-Firewire/IEEE interfaces are very common and are perfect for many small to medium size configurations.  It must be noted that many computers offer Firewire connectivity but this hardly means the audio interface will play nicely.  In fact it is a fairly well known fact that only a number of IEEE chipsets will play nice with the low latency requirements of Firewire audio interfaces.  Generally if your computer has a Texas Instruments firewire chipset you will have success.  There are some VIA firewire chipsets that also play well with these interfaces but results tend to be a bit more hit or miss.  Avoid NEC firewire chipsets at all cost. Firewire Interfaces

-USB interfaces are seemingly becoming more and more popular, presumably due to the troubles many people have had pairing Firewire interfaces with the proper IEEE chipsets on their computer.  There are no real (dis)advantages between the two connection types other than that USB 2.0 interfaces get along better with a variety of motherboards and USB chipsets. USB Interfaces

-Firewire & USB Interfaces can use both Firewire & USB to connect to the computer.  This is probably the most flexible of all external interfaces as they work with both connector types.  Firewire & USB Interfaces

-PCI and PCI-Express interfaces are mounted directly to your motherboard inside your computer.  These interfaces will often offer more digital connectivity as they are often used with outboard equipment.  Because these interfaces have a direct connection with your motherboard they often provide lower latencies than Firewire and USB interfaces.  Because these interfaces are internal connecting your inputs and outputs require access to the back of the computer, this is why these interfaces are most popular in permanent – non-moving studio type configurations. PCI-Express Interfaces & PCI Interfaces

Form Factor:

-Portable audio interfaces are perfect for the musician that needs the flexibility of being able to take their rig on the road or simply wants easy access to the inputs and ouputs.  Most portable audio interfaces will use a Firewire or USB. Portable Audio Interfaces

-Internal audio interfaces are common in studios where most of the I/O comes from external preamps, sound modules, or converters.  The interfaces use the PCI and PCI-Express slots on your computer.  These interfaces are very popular in rack mounted computers where the computer and I/O gear is all centrally located in a rack. Internal Audio Interfaces

-Some PCI and PCI Express interfaces will use a breakout box that will provide the I/O connections. PCI w/Breakout Box Interfaces

-Rackmount interfaces are popular both in studio and mobile applications and provide easy access to I/O connections.  Instead of having a probable unit that sits on your desk, meaning you’ll have cables everywhere, a rackmount interface allows you to hide your cable, this is especially useful in high input count configurations. 1U Half Rack Interfaces & 1U Rackmount Interfaces, 2U Rackmount Interfaces

That concludes my quick guide to some of the feature sets to look out for on your audio interface.  In the next installment I will go over the following topics: Round Trip Latency, Bit Depth and Sample Rate.  Stay tuned!


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