A direct box, or DI box, is a device used in the audio industry to convert an unbalanced, high-impedance signal (such as that from an electric or acoustic guitar) to a balanced, low-impedance signal suitable for use with professional audio equipment. The term "DI" stands for "direct injection," which refers to the fact that the device injects the signal directly into a mixing console or other audio equipment.
The main purpose of a direct box is to help eliminate noise and signal degradation that can occur when an unbalanced signal is sent over long cable runs or into a mixer or other device with a low-impedance input. By converting the signal to a balanced, low-impedance form, a direct box helps ensure that the signal remains clean and free from interference.
In addition to converting unbalanced signals to balanced ones, many direct boxes also provide other features such as ground-lift switches (to eliminate ground loops and hum), pad switches (to attenuate high-level signals), and phase-reversal switches (to correct phase problems in the signal).
Direct boxes are commonly used in a variety of audio applications, including live sound reinforcement, studio recording, and broadcast production. They are especially useful when working with instruments like electric guitars, basses, keyboards, and drum machines, which typically produce unbalanced, high-impedance signals.
When using a direct box, it is important to ensure that the input impedance of the device matches the output impedance of the instrument being used. For example, if you are using a direct box with an electric guitar, you should select a direct box with a high input impedance (typically 1 megohm or higher) to match the high output impedance of the guitar.
In conclusion, a direct box is an essential tool in the audio industry for converting unbalanced, high-impedance signals to balanced, low-impedance signals. Whether you're working in a live sound, studio recording, or broadcast environment, a high-quality direct box can help ensure that your audio signals remain clean, clear, and free from interference.