Musicians and performers often have to connect to an
existing PA system in a pub or club, hall, auditorium, church, etc.
You might think that’s as simple as plugging a lead from the
output socket of an instrument, effects unit, preamp, etc into an appropriate
input on the PA system. But it’s not usually quite that simple.
Just some of the uses . . .
Connecting unbalanced signals
Public Address Amplifier inputs and mixers.
Ideal for connecting to
(Not suited for high-impedance guitar
unless via a preamp or effects unit, etc.)
For a start, most musical equipment has 6.35mm phono jacks,
while most "pro" mixers and amplifiers use XLR connectors. Even if the
incompatible leads problem can be solved (why is it that your lead always has
male plugs and their equipment has male sockets?), even using a special
interconnecting lead, there is usually a far greater problem.
Hummmmmmmmmmmm . . . . .
There will sometimes, even often, be a large amount of mains
hum and noise introduced into the long leads generally associated with these
So by the time the signal reaches the mixer, which is the heart
of a typical Public Address System, hum and noise will mar the performance.
If you’re lucky, it’s barely tolerable; usually it’s not!
That’s where the DI Box comes in. Just in case you were
wondering, the term DI stands for Direct Injection and refers to the direct
coupling-by-wire of a musical instrument to a sound system rather than using a
microphone to pickup the sounds.