What is Line Level?

A Line level is in the region of 0 dBV (1.0 volt), Line level signals have a much higher voltage output than mic or instrument level, usually somewhere around 750 millivolts.It is about 1,000 times as strong as a mic-level signal, so the two do not ordinarily use the same input. This signal travels from your pre-amp to the amplifier that powers your speakers. -10 dBV (0.316 V RMS) for consumer equipment (like MP3 and DVD players), +4 dBu (1.23 V RMS) for professional equipment (mixing desks and signal processing gear). The 4 main connector types we see in line level audio, and in fact all of analog audio, are the 6.35mm jack, 3.5mm mini jack, RCA and XLR connector.

Connecting a line-level source (such as mixer output) to a mic-level input will cause the sound to be loud and distorted because the line signal is much stronger than what the mic input will accept. Inputs and outputs on many mixers are switchable for either mic or line level operation.

Line outputs have signal impedance ranging typically from 100ohm to 600ohm, while a line input has an impedance of 10,000ohm (10k ohm). The difference in impedance between the IN and OUT is what is used to drive the signal. Although keyboards and guitars do not output at the same level they are usally somewhere between mic and line level. To take the signal of an instrument to line level an active DI (Direct Injection or Direct Input) Box is required. To take the signal of an instrument to mic level an active or passive DI Box can be used.

Now, what happens if you want to connect a consumer-grade device to a professional device? You’ll need to amplify the voltage level before passing it on. This is why amplifiers are a big deal in audio. You’re always connecting consumer devices to professional devices when you’re producing music, audio or whatever.

Lastly, a line level signal can either be balanced or unbalanced. Unbalanced line inputs and outputs are generally only the 3.5 mm and RCA plugs connections that you see. RCA plugs can only ever carry a mono, unbalanced signal. While 6.35 mm line jacks on pro audio gear are often TRS (tip, ring, sleeve) enabling them to accept and send a balanced signal. Also note that XLR inputs on a mixing desk are “mic level” inputs, however the XLR outputs (generally 2 of them) are always set to line level, ready for connection to a line input on a powered speaker, amplifier or processing device. XLR outputs are generally always balanced, whether mic or line level.

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