The bass guitar, electric bass or simply bass is the lowest-pitched member of the guitar family. It is a plucked string instrument similar in appearance and construction to an electric or acoustic guitar, but with a longer neck and scale length. The bass guitar most commonly has four strings, though five- and six-stringed models are also relatively popular, and bass guitars with even more strings or courses have been built. Since the mid-1950s, the bass guitar has largely come to replace the double bass in popular music due to its lighter weight, the inclusion of frets in most models, and, most importantly, its design for electric amplification. This is also due to the fact that the double bass is acoustically compromised for its range in that it's scaled down from the optimal size that would be appropriate for those low notes.

A DI unit 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. DIs are frequently used to connect an electric guitar or electric bass to a mixing console's microphone input jack. The DI performs level matching, balancing, and either active buffering or passive impedance matching/impedance bridging. DI units are typically metal boxes with input and output jacks and, for more expensive units, “ground lift” and attenuator switches.