What does a DI box do? | The Basics


A Direct Injection or Direct Input (DI) unit converts an unbalanced, high-impedance signal (like a guitar or keyboard’s output) into a balanced, low-impedance signal like that of a microphone. A DI allows the user to insert an instrument signal directly into a preamp, mixer, or recorder at the proper impedance for a cleaner sound and lower noise.

At the most basic level, a DI box consists of an unbalanced ¼” input, an internal transformer, and a balanced XLR output. Inside the transformer, two coils of wire are wrapped around a magnetic metal core. The high-impedance input signal is passed from one coil of wire to the other via electromagnetic induction, and the different winding of the two coils is what changes the electrical impedance.

Since there is no direct contact between the wires like in a traditional circuit, the input and output are completely isolated from each other, eliminating ground loops, which can create noise. Because of the minimal components involved, the transformer dictates much of the device’s sound (and price).

Typical Features of a DI

DI boxes often include several switches for utility features that can be engaged in different scenarios:

Radial ProAV2 Passive Stereo Multimedia DI Box
  • Ground lift switches can eliminate noise by breaking the ground wire connection between the input and the output.

  • Pads are useful for attenuating signals that are too strong for the DI circuitry or the input of the destination device.

  • Throughput jacks pass a copy of the unaffected input signal for plugging into amplifiers or effect pedals.

  • Phase switches reverse the positive and negative sides of the signal, which is useful when a DI is used in conjunction with a microphone and the two signals are cancelling out due to phase differences.

Types of DI Boxes

DI boxes come in many designs, from extremely simple circuits to advanced, multi-featured units:

R Baggs Align Active DI
  • Passive DIs use only passive components and do not require power to operate. As such, they can only attenuate signals, not amplify them.

  • Active DIs have an integrated preamp, which requires power but allows a higher-level output, eliminating the need to amplify the signal after the DI. Active DIs sometimes incorporate onboard equalizers.

  • Multichannel DIs have multiple inputs, outputs, or both. They can be simple stereo DIs for keyboards or can permit switching between multiple guitars going to a single output.

  • Integrated DIs are built into amplifiers and effect pedals as a convenience, like the line output common on bass amps. They sometimes include a feature that can place the output before or after the preamp and EQ stages, depending on the situation.

  • Reamp boxes are essentially reverse DIs meant to send recorded signals back to amplifiers for re-recording. They often include controls to fine-tune output level and impedance.

Different Uses

The most common use of a DI is to record a clean, unaffected guitar or bass signal, often in tandem with an amplified signal. They’re also ideal for long cable runs that would pick up a lot of noise if a standard guitar cable were used.

Sometimes, a DI is used solely for the tonal properties of its transformer, coloring a clean signal. Direct injection can also be used to intentionally overdrive a preamp, creating a unique type of clipping distortion.

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