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Audio Interface Guide

How to choose which sound card to use

What is an audio interface?

Regardless of whether you have a Mac or a PC, your computer’s standard built-in soundcard almost certainly isn’t up to the job of high-quality, low-latency audio recording and playback. It might be able to record a simple line input, but anything more than that and you will start to struggle.

For making music you will need a dedicated audio interface, which is a box designed for capturing and streaming sound to and from one or more sources and destinations at once. It transforms your computer from being just a machine into something that can record multiple high-quality audio streams, connect to mixing desks, let you plug in your mics and guitars, and monitor as you record. You can even create separate headphone mixes and connect sound sources over digital connections with some units.

The second reason you need an audio interface is that they greatly help to reduce – or even eliminate – latency, which is the time delay between you playing a note and hearing it back through your speakers or headphones. Your computer’s built-in sound hardware is not powerful enough to do this, but modern audio interfaces are, and it’s a vital part of recording audio to be able to monitor with as little latency as possible.

Different audio interface formats

It used to be the case that a sound card was just that – a card that lived inside your desktop computer and had a breakout box for connecting audio jacks. Nowadays, tower systems are not the only game in town, with many people using laptops or iMac-style all-in-one computers, which don’t have card slots accessible by the user.

As a result, plug-and-play formats such as USB and FireWire have become much more commonplace in the audio interface market. Some laptop users will be able to use PCMCIA cards – though these are quite specialised – and there are also many PCI card-based solutions for desktop setups.

In the future, Intel’s new Thunderbolt protocol looks likely to have a big impact in the pro audio market, though this will take at least a couple of years to come around.

So what are your options at the moment, and why might you pick one over the other?

The USB Audio Interface

USB – or more accurately, USB2 – is found on almost every computer around, so there are unlikely to be compatibility issues with interfaces that use it. A USB audio interface is great for recording several tracks at the same time, though perhaps not so good for very high track counts.

The USB cable can also carry power, so small- and mid-sized interfaces can often be used without a separate power supply. This makes it an ideal choice for laptop sound. USB3 has now appeared and is faster than USB2, but it will be some time before it becomes established in the pro audio world.

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The FireWire Audio Interface

FireWire is not found on all computers, though it’s more likely to be present on higher-end models. You can add FireWire to a desktop computer with an inexpensive expansion card, or to a laptop if it has a PCMCIA slot.

There are two formats – FireWire 400 and FireWire 800 – and adaptors are available that convert between them so they’re fairly interoperable. A FireWire audio interface has traditionally been the choice of the professional because it handles sustained high data transfer rates more reliably than USB. It’s also more expensive, but it does carry power and some FireWire audio devices can be daisy chained without the need for a hub.

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The PCI Audio Interface

PCI card-based interfaces live inside your computer’s case and so are only compatible with tower machines that have free slots. You need to open up the case to fit one, but this is quite straightforward. Because of this they are not really ‘hot-swappable’ – as USB or FireWire interfaces are – and prefer to stay put inside one machine.

The big advantage of PCI sound cards is that since they interface directly with the motherboard of the computer, they offer the fastest possible path to your computer’s processor. Both USB and FireWire data require some processing, and at high data volumes can suffer from bottlenecking. A PCI audio interface generally does not, so they are good where you need to run high track counts in and out of the system. And as they are bolted directly into the computer it’s virtually impossible to accidentally disconnect one.

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How many inputs and outputs?

When deciding on an audio interface, a very frequently asked question is: "how many inputs and outputs do I need?" The answer to this common query is that it depends entirely on what your aims are.

A good rule of thumb is to think of how many sources you are likely to want to record at the same time, and then get an interface with a few more inputs than that. The reasoning is that your music making will inevitably develop and require more inputs, so it’s better to have extra inputs and use them occasionally than to not have enough when you do need them.

Naturally there are limits – if you’re a singer / songwriter then you’re unlikely to need 24 inputs. You might be happy with two or four – for mic and guitar. It’s also worth bearing in mind how you record – unless you particularly like to have lots of kit permanently connected, you can always record one track, then unplug the source and plug in a new one to record the next.

If you want to mix on a desk, you will need more outputs to fire sound out on individual channels to your mixer. If, on the other hand, you want to mix ‘in-the-box’, meaning in your DAW software, you could get away with just using a pair of stereo speakers and maybe even just headphones, so you wouldn’t need direct track outputs.

Someone recording an entire band would need more inputs – for drums, vocals and guitars at the same time – but someone using FL Studio to make a dance music track, for example, would need fewer.

Remember that some devices can be ‘daisy chained’, which means you can add a second or third unit to expand the number of channels available to you. Smaller and more portable units tend to have fewer channels, and larger units more physical I/O, though the addition of digital or optical inputs means you can stream further channels of audio in and out with the right cables.

Other factors to consider

The vast majority of audio interfaces have well written drivers that work both on Macs and PCs, but there’s the odd one that isn’t dual-platform so it’s worth checking. Some units make great play of the quality of their preamps, and better preamps mean better quality recordings, better level and less interference in the signal.

The ability to power a FireWire or USB model direct from the recording bus can be helpful in cutting down cable clutter. Some models also offer dual headphone outputs, which is great for monitoring with more than one person.

S/PDIF and other digital connections let you introduce extra pieces of outboard kit into the recording chain, and most interfaces support sample rates of at least 48kHz, which is higher than CD quality. Some go up to 88kHz, 96kHz or 192kHz, though these rates tend to be used only by very serious engineers and producers.

Some audio interfaces also have MIDI I/O, which is a nice bonus, and others have onboard DSP power. This is used to power zero-latency monitoring or onboard effects such as reverb for recording, and is a great thing to have as it means you hear yourself playing before the signal is passed through the computer.

Software control panels

The vast majority of interfaces come with some sort of software control panel, and these let you set up things like sample rate and audio routing. More advanced control panels allow you to reconfigure the signal path virtually, without touching the hardware. You can create multiple headphone or monitor mixes, for example. These are good for slightly more complex setups where you might need to play with the routing more often

Bundled Goodies

The market for audio interfaces is crowded, especially at the more portable end of things. So some interfaces come bundled with free extras like ‘lite’ versions of a DAW, loops, or even software instruments and effects. These may not be a deal breaker in making your decision, but they don’t hurt and if you’re just starting out, getting a free DAW with your interface can be useful to get you up and running.