What is Line Level Signal?

When you look at the back panel of a piece of audio gear, you’re greeted with a bunch of different connectors and mentions of different signal types. So, what do they all mean? Does it make a difference how and where you plug something in and what cables you use?

This little article is ready to answer those questions and clarify some terminology. Let’s talk about line level signal, which is associated with electronic instruments and audio devices that range from new modern tools back to popular vintage machines of decades past.

Line level is a strength of signal generated from mixing consoles, signal processing equipment, and different pieces of consumer and professional audio gear. It’s essentially the strongest level of signal in your chain, and it goes directly to your speakers.

Consumer equipment commonly refers to items like:

• Cassette Tape players (going waaaay back…)
• CD players (more common, I hear that these are still in a lot of cars too…)
• DVD/Blu-Ray players (physical media for the win, not everyone is streaming-only!)
• Home Stereo Systems
• Other fun audio products used by to the public in a standalone way doesn’t require specialized pro audio gear.

The main factor that determines a consumer line-level device is that the signal level is regularly measured at -10 dBV (decibel Volt). RCA inputs and outputs (with their trademark red and white plugs) are often used with these products.

Professional equipment, such as mixers, rackmount signal processers, and performance instrument keyboards and boxes (stage pianos, synths, samplers) have signal levels regularly measured at +4 dBu (decibel unloaded). 1/4” inputs and outputs are often used here.

So, what do these terms and numbers mean?

First, dBV and dBu are not the same. Without getting too technical, the term “decibel volt” measures voltage in relation to one Volt. 0 dBV = 1 V. A positive number for dBV means a stronger signal (more than one volt), and a negative number means a weaker signal (less than one volt).

The term dBu (decibel unloaded) has 0 dBu = 0.775 volts. Why such a seemingly random sounding number? Well, 0.775 volts is the amount of volts that delivers 1 mW (milliwatt) in a 600-ohm resistor, the standard reference impedance in the audio circuit of an ancient technology called a telephone.

Whew, that’s a mouthful.

While there are conversion formulas and deeper definitions aplenty to explain everything this technical in greater detail, that’s another article for another day.

Ultimately, what you need to know is that professional line level signal is going to be much stronger than consumer line level. So, if you’re connecting an external CD player to a mixer, you’re going to need to boost the gain level from the mixer’s end to balance it with other voices in the main front-of-house mix.

Also, a specialized direct box for consumer audio, computers, and keyboard instruments, such as the Radial Trim Two Stereo DI, is a great way to take devices with various types of line-level signal (RCA at -10dBV, 1/4” stereo outputs, 3.5mm outputs, etc.) and convert it to a balanced mic-level signal (we’ll talk more about that a bit below) that can take advantage of long cable runs and make it more straightforward for whoever is working the mixing desk.

Line level signal is just one of the varieties used in live sound and recording applications. Here are some other signal types and how they differ from line level, so you can identify what you need, connect your equipment with confidence, and ensure that your devices are sounding their best.

In terms of signal strength, remember the following:

(weaker) Mic Level < Instrument Level < Line Level (stronger)

Unlike line-level devices which produce internally generated signal and send it directly to a different device, microphones pick up audio from an external source in the surrounding environment - such as a voice speaking into it or obtaining sound from a nearby instrument amp. The level of general stage noise, ambient sound, and audio being picked up from different directions comes down to the type of microphone and where it is positioned. XLR cables are primarily used to connect mics to mic-level inputs.

In order for microphones to capture sound signal accurately and cleanly, their engineering requires a smaller signal footprint than their line-level counterparts. When a mic is connected to a mic input on a mixer or interface, that signal meets a built-in mic preamplifier that boosts the signal in a controlled manner. Think of the preamp as the first checkpoint on the audio signal highway – from there, the gain can be adjusted from the mixer or interface to an optimal level with plenty of presence without unnecessary distortion or clipping.

Note: If you connect a line-level signal source to a mic-level input, you’ll overload and distort the channel with too much signal.

At first glance, an electric guitar or bass looks like it puts out line-level signal, since they also use 1/4” cables like professional line-level instruments. But remember, the cable doesn’t automatically determine the signal type.

Guitars and basses generate instrument-level signal, which is weaker than line level. This instrument-level signal is meant to be paired with a matching amp and speaker cabinet, ensuring an optimal level of sound that isn’t too weak or strongly overblown.

Guitar and bass effects pedals are engineered to work with instrument-level signal. When you plug your instrument into the first pedal’s input then chain from its output to new pedal’s input and so on until you go from the final pedal to your amp, that whole signal path is at instrument level.

Popular multi-effects pedals from Line 6, Boss, and Headrush have both 1/4” outputs at instrument level (to run to your amp) *and* XLR outputs at mic level (to run to a mixing console for front-of-house speakers or audio interface or direct recording).

Note: You can plug your guitar or bass guitar directly into a mixer or audio interface line input, but you’ll need to select the specific “Instrument” or “Hi-Z” preamp switch to boost the signal up to line level…

The science of soundwaves and signal can get academic in a hurry, so don’t feel discouraged if you’re still a bit confused. It always pays to check the device itself and its manual to see what type of signal it generates, so you know how to plan accordingly. It’s not only important to know the features of your devices but their technical specs as well, so you can fit them into the greater scheme of your audio setup.

Ready to add a new creative tool to your setup? American Musical Supply is stocked with popular keyboards, samplers, signal processing hardware, and other line-level instruments and gear pieces to expand the possibilities. We’re also your stop for cables, adapters, power supplies, and accessories specifically designed to help bring out the full potential of your line-level (and other) devices — so bundle away, take advantage of our 0% interest payment plans, and take the next step with your projects!