Direct injection in music production is a method whereby studio instruments, especially bass guitars, can be plugged directly into a mixing console for a better, more present signal and sound. This is as opposed to micing up a bass amplifier.

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Direct injection in the petrol internal combustion engine is the use of a special fuel injector to spray fuel directly into the combustion chamber rather than into the intake charge or throttle body as is the more conventional method.

Direct injection in the diesel internal combustion engine is the injection of fuel as an atomised spray directly into the cylinder, rather than into a swirl chamber (indirect injection) connected to the cylinder by a short passage.