Product Code Database
A DI unit (direct input or direct inject) is an electronic device typically used in and in sound reinforcement systems to connect a high output impedance unbalanced output signal to a low-impedance, microphone level, Balanced audio input, usually via an XLR connector and XLR cable.
DI units are also referred to as a DI box, direct box, or simply DI, with each letter pronounced, as in "Dee Eye." The term is variously claimed to stand for direct input, direct injection (a British term), direct induction or direct interface.
"Traditional guitar amps and speakers are fairly lo-fi devices that squash dynamic range, introduce distortion and narrow the frequency range. In contrast, a properly interfaced direct guitar signal will sound super clean, dynamic, punchy and far brighter." - Guitar.com Magazine
DIs are frequently used to connect an electric guitar, electric bass or electronic musical keyboard to a mixing console's microphone input jack. Its signal comes "direct" from the source instrument without passing through the air as , and thus is isolated from other sounds and avoids effects of microphone or room acoustics. The DI performs level matching, balancing, and either active buffer amplifier or passive impedance matching or impedance bridging. DI units are typically metal boxes with input and output jacks and, for more expensive units, “ground lift” and attenuator switches.
DI boxes are extensively used with professional and semi-professional , professional sound reinforcement systems and in sound recording studios. Manufacturers produce a wide range of units, from inexpensive, basic, passive units to expensive, sophisticated, active units. DI boxes may provide numerous features and user-controllable options (e.g., a user-selectable 0dB, 20dB or 40dB pad and/or a "ground lift" switch). They may come in different types of enclosures, usually a metal chassis that helps to protect against electrical interference. Some have built-in DI units, so that the bass amp's output signal can be connected directly to a mixing board in a sound reinforcement/live show or recording context.
These boxes typically contained an audio transformer with a turns ratio from approximately 8:1 to 12:1 to help with impedance bridging from the high output impedance of an instrument's pickup to the relatively lower input impedance of a typical mixing console's microphone preamp. For example, the Triad A-11J used in the Wolfbox has a turns ratio of 10:1 and thus an impedance ratio of 100:1. The typical console preamp input impedance of 1,500 ohms would appear to the electronic instrument as a high input impedance of 150,000 ohms. Section 2.2.3: Line to Microphone Input or 'Direct Box'.
The passive direct box was suitable for most electronic musical instruments but it negatively colored the sound of instruments with weaker output signals, such as Fender and Fender Precision Basses with single-coil pickups. To accommodate these instruments, active direct boxes were designed containing powered electronic circuitry which increased the input impedance to above 1,000,000 ohms. In 1975, a 48-volt active direct box was designed for Leon Russell's recording studio, its circuitry published in the April 1975 edition of dB, the sound engineering magazine. The sound company Tycobrahe, known for supporting large rock festivals such as California Jam, offered an active direct box for sale in 1977 capable of +9 dBm line level output with a built-in attenuator to compensate for various input levels.
The electrical purpose of a direct box is to bridge the impedance of the input and output. Most electronic instruments and microphones cannot be plugged directly into the pre-amplifier inputs of mixing boards or recording devices because of impedance mismatch. Instruments are typically high impedance, whereas microphone inputs are low impedance.
The direct box takes a high impedance, unbalanced signal and converts it to a low impedance, balanced signal. This allows the signal to be sent over long cable runs without signal loss, and greater rejection of interference due to the benefit of common mode rejection in a balanced signal. Furthermore, it allows the low impedance signal to be sent to the input preamp of a mixing console which is designed to accept input from low impedance microphones.
Because all cables are capacitive, long cables used in live sound and recording can become a low‑pass filter which reduces the high end frequencies when used with high-impedance source. Another advantage of DI units is that the DI contains a transformer to provide galvanic isolation that can eliminate a ground‑loop hum.
It is common to use both a DI signal and a microphone in front of the speaker cabinet or combo amp, in both live sound and recording settings. One method is to connect a bass guitar amplifier's speaker level output (via a pad, to attenuate the signal) to a DI and then run it to one channel of the mixing console, and run a miked guitar speaker cabinet signal into another channel of the mixing console. Another method is to connect a DI between the guitar and the amplifier. The DI signal and mic'd guitar speaker can then be selectively blended, with the DI providing a more immediate, present, bright, un-equalized sound, and the microphone providing a more 'live' sound, with instrument amplifier and speaker enclosure characteristics and some room ambience (natural reverb).
The less expensive passive DI units are more susceptible to hum, and passive units tend to be less versatile than active; however, they require no power source, are simpler to use, and the better units are extremely reliable when used as designed. The lack of batteries in passive DIs means that users do not have to worry about batteries losing their power in the middle of a live show or recording session.
Some models have no settings or switches, while others can have a ground lift switch (to avoid ground loop problems or hums), a pad switch (to accommodate different source levels and attenuate too-strong signals) and a passive filter/equalization switch for coloring the sound or tone.
A pass-through connector is a second jack, sometimes simply paralleled to the input connector, that delivers the input signal unchanged, to allow the DI unit to be inserted into a signal path without interrupting it. This allows a user, such as an electric bass player, to plug their bass into a DI unit, which routes the bass signal to the mixing board, and at the same time plug the bass into an onstage bass amp for monitoring purposes. Pass-through is also commonly referred to as a bypass. True-bypass occurs when the signal goes straight from the input jack to the output jack with no circuitry involved and no loading of the source impedance. False bypass (or simply 'bypass') occurs when the signal is routed through the device circuitry with buffer amplifier and no other intentional change to the signal. However, due to the nature of electrical designs there is almost always some slight change in the signal. The extent of change and how noticeable it may be can vary from unit to unit.
Preamplifiers for electric bass typically contain gain knobs, sometimes including an fuzz bass effect unit, equalizer knobs and, for some higher-end units, multiple channels (e.g., a "clean" channel and a "dirty" channel, with the latter containing an overdrive effect).
Preamp-DI units for double bass and other acoustic instruments often omit the overdrive features, but add additional features that help to produce a good sound and tone for acoustic instruments, such as an audio compression effect, a polarity inverter switch and a notch filter (the latter two features designed to help reduce unwanted audio feedback "howls"). Preamp-DIs for acoustic instruments often include two channels and a simple mixer, to enable the player to use both a pickup and a condensor microphone. Some preamp-DIs provide phantom power, in case this is required to power a condenser microphone. Preamp-DI units may be battery powered, have an AC mains plug, or both.
|
|
