DI unit
A DI unit (direct input or direct inject) is an electronic device typically used in recording studios and in sound reinforcement systems to connect a high output impedance unbalanced output signal to a low-impedance, microphone level, balanced input, usually via an XLR connector and XLR cable.
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).
These DIs were custom made by engineers like Ed Wolfrum with his "Wolfbox" and by concert sound companies to help amplify electric musical instruments.
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 phantom powered 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.
Of course the reverse is true—many times musicians and audio engineers seek this coloring because it fits the style of music or recording.
Most electronic instruments and microphones cannot be plugged directly into the pre-amplifier inputs of mixing boards or recording devices because of impedance mismatch.
These may include gain or level adjustment, ground lift, power source selection, and mono or stereo mode.
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.
Direct boxes are typically used with electric instruments or other electronic musical devices that only contain an unbalanced 1/4" phone output which needs to be connected to an XLR input of a mixing board.
An example of this application would be an electric keyboard that needs to be connected to a mixing board, either directly or through an audio snake.
This can be used if a "clean" direct output from the amplifier is desired, which does not contain the tone shaping created by the bassist's adjustment of the EQ controls.
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.
Pepper's Lonely Hearts Club Band, most prominently on "Lucy In The Sky With Diamonds", "When I'm Sixty-Four", "Lovely Rita", and "A Day in The Life", as well as "Only A Northern Song", "I Me Mine", and the lead-guitar introducing "Revolution".
[12] The main guitar riff on Led Zeppelin's "Black Dog" was recorded directly through a mic-preamp and fed through a pair of 1176 Peak Limiters.
[13] Byrds frontman and guitarist Roger Mcguinn achieved his famous jangly guitar sound in the studio by recording his 12-string Rickenbacker direct-in through a compressor to emphasize the treble.
