From Wikipedia, the free encyclopedia
A DI unit, DI box, direct box, or simply DI (variously claimed to stand for direct input, direct injection, direct induction or direct interface), is a device typically used in
to connect a high-, , unbalanced output signal to a low-impedance microphone level
input, usually via . DIs are frequently used to connect an
to a 's microphone input. The DI performs level matching, balancing, and either active
or passive / to minimize noise, distortion, and .
DI boxes are extensively used with professional and semi-professional
Passive direct boxes first appeared in the United States in the middle 1960s, most notably in Detroit at radio stations and recording studios like "", "", "", Tera Shirma Studios and the Metro-Audio Capstan Roller remote recording truck. These DIs were custom made by engineers like Ed Wolfrum with his "" and by concert sound companies to solve certain problems associated with amplifying electronic musical instruments, especially . These boxes typically contained an
(like the Triad A11J through 1974) with a turns ratio from approximately 8:1 to 12:1, and thus an impedance ratio of around 144:1. With this kind of transformer, the output voltage of the instrument is stepped down to a range compatible with the typical 's . The typical console preamp input impedance of 1,500 ohms would appear to the electronic instrument as a high input impedance of 216,000 ohms.
The passive direct box was suitable for most electronic musical instruments but it negatively colored the sound of ones with weaker output signals, such as Fender
with single-coil pickups. To accommodate these instruments, active direct boxes were designed containing powered electronic circuitry which increased the input impedance from about 200,000 to above 1,000,000 ohms. In 1975, a 48-volt
active direct box was designed for 's recording studio, its circuitry published in dB, the sound engineering magazine. The sound company , known for supporting large rock festivals such as , offered an active direct box for sale in 1977, a model capable of +9 dBm line level output, with a built-in attenuator to compensate for various input levels.
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 with significantly less signal loss (especially in high frequencies) due to the lowering of the impedance, and greater rejection of interference due to the benefit of common mode rejection in a balanced signal. Furthermore, the lower impedance (around 600 ohms is normal) allows an insignificant load to the input of a mixing console or preamp which is also designed to accept input from low impedance microphones.
A vintage Wolfbox
A very simple passive DI
A high-end passive DI box
A passive DI with "throughput" in addition to XLR output
DI unit typically consists of an audio
used as a . The turns ratio is typically chosen to convert a
50 kΩ signal source (such as the magnetic pickup of an electric guitar) to the 100–200 Ω expected by the input of an . Typical turns ratios are in the range of 10:1 to 20:1.
Less commonly, a passive DI unit may consist of a
load, with or without
coupling. Such units are best suited to outputs designed for
The cheaper passive DI units are more susceptible to hum, and passive units tend to be less versatile than active. However, they require no batteries, are simpler to use, and the better units are extremely reliable when used as designed.
Some models have no settings, while others can have a
switch (to avoid
problems), a
switch (to accommodate different source levels) and a filter switch for coloring the sound.
An active stereo DI with pass-through in mono mode only
DI unit contains a . Active DI units can therefore provide gain, and are inherently more complex and versatile than passive units.
Active DI units require a power source, which is normally provided by batteries or a standard AC outlet connection, and may contain the option for
Most active DI units provide switches to enhance their versatility. These may include gain or level adjustment, ground lift, power source selection, and mono or stereo mode. Ground lift switches often disconnect phantom power.
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. 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
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.
Direct boxes are typically used in instances of instruments or other devices that only contain an unbalanced
which needs to be connected to an
Multiple direct box circuits can be mounted inside one housing. These are used for multiple unbalanced outputs, such as for a bank of electronic keyboards.
DI's can be used on instruments with electronic circuitry and pick ups that do not contain an XLR balanced output. An example of this application would be an electric keyboard that needs to be connected to a mixer board, either directly or through an . Another example would be an acoustic guitar with pickups, an electric guitar or bass guitar that would be mixed through a mixing console into a main or monitor mix.
contain built-in DI units, and can be connected to a mixing console directly without needing an external direct box. This would be a typical setup for a person who wanted to run their instrument through a Public Address (PA) system while keeping the unique sound of the amplifier. Some instrument amplifiers have the ability to turn off the amplifier EQ through a pre eq/post eq switch. This can be used if a "clean" direct output from amplifier is desired.
It is common to use both a DI and a microphone on the same source. One method is to connect a guitar amplifier speaker level output to a DI and then run it to one channel of the mixing console, and run a miked guitar speaker 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 characteristics and some room ambience.
Direct-injection tracking is used on almost every electric bass part on , most prominently on "", "", "", and "", as well as "", "", and the lead-guitar introducing "". Other clear examples include 's "" and 's "".
Whitlock, Bill (2001). "Audio Transformers". In Glen Ballou. Handbook for Sound Engineers (3 ed.). Section 2.2.3: Line to Microphone Input or 'Direct Box'.
"A Remote Powered Direct Box". dB 9.
"Advertisement". DB: The Sound Engineering Magazine 111. 1977.
"Equipment Reports". High Fidelity 27: 117. 1977.
Hodgson, Jay (2010). Understanding Records, p.47. .
- Jensen Transformer's suggested schematic for a split-signal DI Box
- 1998 article by JdB Sound Acoustics giving some technical info on what direct boxes can accomplish英语翻译"LED" redirects here.For other uses,see LED (disambiguation).From Wikipedia,the free encyclopediaA light-emitting diode,usually called an LED (pronounced /ˌɛliːˈdiː/)[1],is a semiconductor diode that emits incoher_百度作业帮
英语翻译"LED" redirects here.For other uses,see LED (disambiguation).From Wikipedia,the free encyclopediaA light-emitting diode,usually called an LED (pronounced /ˌɛliːˈdiː/)[1],is a semiconductor diode that emits incoher
英语翻译"LED" redirects here.For other uses,see LED (disambiguation).From Wikipedia,the free encyclopediaA light-emitting diode,usually called an LED (pronounced /ˌɛliːˈdiː/)[1],is a semiconductor diode that emits incoherent narrow-spectrum light when electrically biased in the forward direction of the p-n junction,as in the common LED circuit.This effect is a form of electroluminescence.
“LED”改方向得这里.为其他使用,看见LED (消歧).From Wikipedia,自由百科全书 A发光二极管,通常称LED (显著的/ˌɛliːˈdiː/) [1],是在p-n连接点向前方向散发不连贯的狭窄光谱光,当电子偏心,在共同的LED电路的半导体二极管.这个作用是电镀发光物品的形式.}