Do I Need a Direct Box, A.K.A a “DI” ?

Congratulations, you’re in a modern band.  In addition to the basic vox, guitar, drums, bass, you’ve got yourself a keyboard player.  Or maybe you’re using a laptop.  Or maybe you’ve got a sampler or an iPod, or anything else that lacks the standard 3-pin XLR output.  You’ve probably heard about a DI or a Direct Box, and how it might make these devices sound better or perform better during a live performance.

So, do you need one?

Part I – Technical Aspects

Keyboards, laptops, samplers, and iPods all deliver what’s called a ‘line level’ signal.  This type of signal works fine with most consumer equipment and in most consumer applications.  But there are a couple unique attributes of a line level signal that can cause problems with your live performance.

Line level signals are not shielded from random electrical noise and interference.  If you’re just plugging in some headphones, that’s not a problem.  The length of the cable is, likely, not long enough to actually pick up any significant interference.  But running across a barroom floor or friend’s garage is a different story.  If you’re far away from your mixer, unwanted electrical interference can leak into the poorly shielded signal coming out of the line level device.

To prevent this, a direct box converts that poorly protected method of connection (an ‘unbalanced’ signal with only two conductors per channel) to a well protected method of connection (an XLR or other ‘balanced’ cable’ with 3 conductors ).  That third conductor is what’s keeping out the unwanted noise.

Even if distance isn’t an issue, if the mixer you are connecting to does not have any available ‘line-ins’ you still may need a direct box. You could, in theory, use an adapter to split your 1/8″ headphone or line out directly to two XLR (or microphone) connections. The problem with this is that you’ll probably be giving the XLR inputs on the mixer a signal that is far to hot to handle. Most XLR inputs on a mixer are routed directly to preamps that amplify the relatively weak signal from a microphone.  When you ram an already amplified signal through it, it will clip and distort. To solve this problem, a direct box (in addition to the protecting the signal from noise) will also convert a loud signal to a quiet one ready for amplification.

So, for rehearsing with your friends – no direct box is likely necessary. You’re probably not far from the mixer, and that mixer probably has a line in ready for the nice hot output from your laptop.

But for a live gig where you’re connecting to someone else’s (a bar’s) sound equipment, none of those things may be true. You might be some distance from the mixing board, or that mixing board may not have enough or any line ins. . . . .

Part II – Practical Application [A Question and Answer Session]

Q: “But Phil, the mixer’s not that far away. Plus, I looked right at that mixer saw that it definitely has an available line in. Several of them, in fact. And it doesn’t make sense, how can a club or bar have a mixer with no line ins? I’ve looked at hundreds of mixers and they all had, at least, a couple. Is it even possible to buy a mixer without that capability?

A: Indeed, the line ins you seek are ubiquitous and robust.

But the sound guy has to know what they are and want to use them.   Perhaps your sound guy predates the widespread use of electronic instruments that might make use of a line input, and, thus, does not really know what they are for. Or the club itself might not have an unbalanced cable of any length whatsoever. Or both. Either way, that without an XLR connection just won’t get connected.

Q: “OK, in that case, GREAT NEWS, I called the venue and they said that they have some Direct Boxes I could use for just such an occasion.

A:  . . . . they LIE!

When they say they have Direct Boxes, they likely mean that they have one mono direct box (whereas you will need two). In the event that they have two, they will not be of the same make and manufacture, and they will have wild discrepancies in the way that they attenuate either channel of the stereo signal.  When the venue tells you they have a guitar amp you can use, you can probably count on the fact that it works because it gets used every time they have a show.  If something goes wrong, or someone manages to steal it, they notice right away and they do something about it.  Direct Boxes, on the other hand, are not something that get used often. So when they go missing they aren’t missed (and then replaced), and when they stop working or break they aren’t fixed.  It’s best to rely on your own.

In short:

Starting out: probably no need for DIs.

Gigging regularly: definitely find a couple inexpensive DIs.  You don’t need to spend $200 to get the benefit of a DI.  $30 per channel should do the trick.

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