Before we dive into looking at what you might want to consider when buying an audio interface, it’s worth having a quick look at the type of connectors you might come across and what the differences are.
The type of connectors you’d find on audio cables intended to be attached to computers, MP3 players etc. are 3.5mm jack plugs. These are usually stereo cables, such as you’d see on a set of headphones. A mono cable will have a single insulating break around the jack, separating the tip from the sleeve, but a stereo cable will have a second insulating break, creating what is referred to as a tip-ring-sleeve, (TRS), jack. The sleeve provides a common earth, (or ground), whilst the tip and ring carry the left and right channels. The tip is dimpled to allow an internal sprung connection to take the signal and hold the plug in place at the same time. Professional audio equipment, (anything that isn’t meant to be consumer hi-fi), very rarely features these connectors.
Talking of hi-fi, you may find phono, (or RCA), connectors on some equipment. Originally invented by the Radio Corporation of America, these are mono connectors that tend to be found on hi-fi equipment, but are also widespread in the audio-video field. These feature an inner pin and a slightly sprung outer ring held in a plastic casing and the whole thing pushes on to a protruding socket. They rely on their tight fit to make the connection and stay in place, hence they are sometimes called cinch connectors.
Professional audio tends to use two different types of connectors, one which is primarily for microphones and one which is for instruments such as keyboards and guitars. The one we’re all most familiar with is the ¼” jack plug, which comes in both mono and TRS forms. You’ll find a mono ¼” jack on each end of a guitar lead, for example, and sometimes on microphone leads intended for live use. A ¼” TRS jack can be used as a stereo cable, but it’s more common to use them as a balanced cable, where the mono signal is sent down both the “left” and “right” channels. Before it is, one channel is put out of phase with the other at the output, (and I’ll come back to phase in another post). When the signal reaches the input, the phase is reversed. The net effect of this is, over longer cable runs, to cancel out any hum or interference that the signal might have picked up as it ran along the cable.
The final connector that we’re going to consider is the XLR. This comes in male and female versions and, for audio, normally uses three pins. Typically, the signal goes from the male output to the female input and XLR leads normally have a male connector at one end and a female connector at the other. XLR cables are balanced cables, (hence the three pins), but have the unique ability to act as power cables. Why would you want this? The answer is that the type of microphone used in live situations is a dynamic microphone, which requires no power – you just plug it in and it works. In a recording situation, you get a better signal from a condenser or ribbon microphone, but the catch is that they need power to operate. An XLR cable will convey that power from the equipment that the microphone is plugged in to without the end for a separate power cable, hence the term “phantom power”. If the equipment can’t generate phantom power, you can buy a box that goes between the microphone and the equipment, which provides the missing power.
Minimum specification for an audio interface
So now we know what we’re talking about, we can read the specifications for the various interfaces with a little more confidence. If you type “audio interface” into the world’s favourite search engine, it will suggest a number of audio interfaces in the advert that it puts above the first entry and that’s as good a place as any to start. At the time of writing, you can have your choice of several good quality interfaces from name brands for less than £120, (about $200). Which one is right for you comes back to how many inputs you want to use at once, as the most inexpensive ones come with just one XLR and one ¼” jack input. My audio interface has just one of each, but as I only record myself doing one thing at once, that’s all I need.
Some points to consider:
- Does it have the right interface for your computer – USB, Firewire, Thunderbolt?
- Does it need external power?
- Does it have the right drivers for your operating system?
- Does it have enough XLR, (microphone), sockets? One is enough for a solo singer, but if you want to record drums, you’re going to need a lot more
- And does it have phantom power?
- Does it have enough ¼” jack inputs?
- Does it have stereo inputs if you’re going to be recording a live keyboard player or from other audio sources?
- How many headphone outputs does it have? Again, if there’s only you involved, one is fine.
- What audio outputs does it have? You will want to plug some speakers in at some point, if not all the time.
- What software does it come with? We’re not talking drivers etc. here, we’re talking DAW or virtual instruments and effects. It may seem a bit cheeky, but you want to make the most of the hard-earned cash you’re about to spend.
- And finally, (as if that’s not got your head spinning enough), how does it handle latency? And does it have an ASIO driver for Windows, (if you’re a Windows user)?
Latency? ASIO? What’s that? Latency is a whole other issue and I’ll cover that in the next post.