Line level

Line level is the specified strength of an audio signal used to transmit analog sound between audio components such as CD and DVD players, television sets, audio amplifiers, and mixing consoles.

As opposed to line level, there are weaker audio signals, such as those from microphones and instrument pickups, and stronger signals, such as those used to drive headphones and loudspeakers. The "strength" of these various signals does not necessarily refer to the output voltage of the source device; it also depends on its output impedance and output power capability.

Consumer electronic devices concerned with audio (for example sound cards) often have a connector labeled line in and/or line out. Line out provides an audio signal output and line in receives a signal input. The line in/out connections on consumer-oriented audio equipment are typically unbalanced, with a 3.5 mm (0.14 inch, but commonly called "eighth inch") 3-conductor TRS minijack connector providing ground, left channel, and right channel, or stereo RCA jacks. Professional equipment commonly uses balanced connections on 6.35 mm (1/4 inch) TRS phone jacks or XLR connectors. Professional equipment may also use unbalanced connections with (1/4 inch) TS phone jacks.

A line level describes a line's nominal signal level as a ratio, expressed in decibels, against a standard reference voltage. The nominal level and the reference voltage against which it is expressed depend on the line level being used. While the nominal levels themselves vary, only two reference voltages are common: decibel volts (dBV) for consumer applications, and decibels unloaded (dBu) for professional applications.

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