DI unit

The DI - Box (short for Direct Injection) is used in the sound device that converts an unbalanced signal to a balanced signal.

Operation and Use

DI boxes are needed when a signal source with a single-ended output (usually coming from a TRS or RCA connectors) to be (usually via XLR connector) connected to a device with a balanced input. Typical examples of unbalanced signal sources are electric guitars, keyboards and other electric instruments or CD player; usual balanced inputs are about to mixers or audio interfaces. Especially for long distance wiring balanced wiring, allows an effective reduction of noise. Nor can the mass Interrupt connection (English ground lift ), for example, to break ground loops. In addition, DI boxes to adjust the impedances of signal sources to the subsequent inputs.

Building types

DI boxes are available as single units in small, box-shaped enclosures (see picture), and in the form of slots for 19 "racks which will include multiple channels.

A distinction is made between passive and active DI boxes. The former achieve the balanced only by a broadband low-frequency transformer, the latter contain an active amplifier electronics. The power supply then required Operates on battery or phantom power.

Advantages and disadvantages of the two variants

With active DI boxes can in principle be arbitrarily high input impedance and low output impedances realize arbitrary, while the input impedances of passive DI boxes at most of the order of 500k lie. Another advantage of active DI boxes is that you can bypass the disadvantages of transformers through an active balun. Exchangers are high in quality quite expensive, depending on the model sensitive to magnetic interference and can ( especially at low frequencies and higher levels ) have a non-negligible distortion. They also offer a limited bandwidth in comparison with active balancing. However, allow a real transformer galvanic isolation, which is why there are high-quality active DI boxes with Übertragersymmetrierung.

The advantages of passive DI boxes are that they require no power supply and requires galvanic isolation of the signal by the transmitter. You also can also be fundamentally reversed, so use for converting a balanced to an unbalanced signal. An application in which a DI box is used vice versa, is called re-amping. Here a recorded guitar or bass track is subsequently reproduced through a guitar or bass amp and re-recorded.

In practice, therefore we used in signal sources with high output impedance and a small level ( for example piezo pickup ) because of their high input impedance active DI boxes. Behind an instrument with a line output level, however, a high-quality passive DI box is sufficient.

Special variants

Normally a DI box should not cause any sound coloration, but the signal is transmitted as purely as possible. However, a special role is special DI boxes with a sound filter for E- guitars. These include a sound filter to mimic the characteristic frequency response of guitar speakers. The background is that guitar speakers contribute significantly to the sound of a guitar, but this contribution is absent when the signal is not picked up with a microphone in front of the speakers. Typically, these DI boxes can be looped either between the amplifier and speaker, or in the effects loop.

This solution has its advantages and disadvantages and is therefore controversial. This allows the sound of the electric guitar by choice and placement of microphones influence. The replica of the speaker sound is not always satisfactory, especially at very high listening levels. If you renounce the other hand on microphones, so can the problems with crosstalk and reduce feedback on stage.

When E -Bass, however, an active DI box is commonly used, because the coloration plays a rather minor role through the speaker.