DI Boxes

Direct Injection Boxes

di boxes

The Direct Injection box or DI Box traditionally was a separate box that allowed the output of an electric / bass guitar, or synthesizer to be connected to an audio mixer for recording and/or the PA system as well as the musician's amplifier. Now it is often an additional part of a Channel Strip or Microphone Pre-amp.

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Its function is to convert the un-balanced, high impedance signal into a balanced low impedance signal that can then be sent to an XLR connector on the mixer or mic pre-amp/channel strip. It is also known as a Direct Box, Direct Inject Box, Direct Interface and Injection Box or even simply DI. Well known makers of DI boxes are EMO, Demeter, BSS, Radial, Countryman and Samson.

Active or Passive DI Box?

The first readily available DI boxes were passive i.e. they don't need any form of power supply, essentially they comprise a transformer, resistors and a capacitor and there is no amplification (active) circuitry incorporated. So any loss of gain has to be made up by the next device in the chain. They tend to be cheaper than active DI boxes, however the high cost of the very best transformers can make them more expensive.

Active DI boxes do contain amplification circuitry which will allow long cable runs from the box without signal loss (especially the high frequencies). Also they are usually balanced electronically so that a transformer isn't required (though some still have a transformer as well), active circuitry helps to preserve audio quality too.

They do need a power source, either from an integral battery or power supply which is external to the box or integral if it's in a channel strip or mic pre-amp. Some active DI boxes can get their power from the phantom power supplied by the audio mixer.

di box controls
DI Box Controls

Earth Lift switch

This switch is used when you have an 'earth hum' to remove, this is a constant humming sound. It happens when the audio signal can get to earth via the earth wire in the XLR lead and the mains cable's earth wire in one of the devices in your audio chain. Lifting the earth connection in the Direct Box will then only allow the signal to get to earth at one point, thus the 'earth hum' is removed.

Thru socket

This socket allows the signal to be fed to the guitar/keyboard amplifier. The instrument's jack lead would normally go into the amplifier but when you need to send that signal to a mixer or recording system you need to plug the instrument into the DI box first and then use another jack lead from the thru socket to go to the amplifier. The output lead for the mixer or recording equipment is from the XLR connector.

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Mogami Monster Leads

Other considerations for DI Boxes

The signal from an electric guitar or synthesizer is greater than that of a microphone, however it can still be degraded by using very long or poor quality guitar cables (mono jack leads) from the instrument to the DI box, good quality guitar cables have low resistance and low capacitance and often have gold coated jack plugs for the best electrical connection. The quality of the shield wire will have a great effect on reducing interference from electromagnetic and radio frequency sources.

Well known guitar cable manufacturers are Lifelines, Mogami, Whirlwind and Planet Waves.

If you can't afford two of these cables then buy one to use from the instrument to the Inject Box and a cheaper short one to go to the amplifier.

Remember that the sound of a DI signal is just that, it's not the sound of the amplifier that the musician hears, so some form of guitar amplifier emulation software will be required in the Digital Audio Workstation (DAW).

You can record the amplifier sound separately and mix the clean DI sound to taste or you can put the DI signal through an amplifier later on at the mixing stage and record it with the amount of distortion you require.

The 'sound' created by the transformer (in passive and some active DI's) is preferable to some guitarists, even though it is effectively a form of distortion, so try out all versions to see which you prefer.

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