Line Out vs Line In: What’s the Difference? (Explained!)

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Line-out and line-in are terms that are commonly used among musicians and instrumentalists alike. These inputs and outputs are found in professional audio devices such as mixers, amplifiers, audio interfaces, etc. Line-in and line-out ports can be found on desktop computers as well. However, a lot of these people struggle to tell the difference between the two.

Confusion between line outputs and line inputs usually leads to an improper stage or sound setup. Therefore, understanding what a line out and a line in is will help you avoid common mistakes often made when connecting audio devices together. 

But first, what’s the difference between line out and line in?

Line Out (or Audio Out) is an output port that is designed to send line-level audio signals to another device. On the other hand, Line In is an input port made to receive line-level audio signals from another source.

What Is Line Out?

A line-out is an audio connection port that allows you to send a line-level audio signal to another device for further processing. Line-level signals are usually signal that is strong enough to be transmitted without any signal drops.

Line out is found on keyboards, synthesizers, digital pianos, keyboards, guitar, or bass amps, mixers, audio interfaces, and more. It allows you to send audio signals from any of these devices to another.

For instance, line out from your guitar amp can be used to send your amp’s audio to a mixer. Similarly, you can send an audio signal from a mixer’s Aux Output which is basically a Line Out into the Input of a keyboard amp. You get the idea.

Line out is also known as Audio Out or a Sound Out. 

Before we proceed, one thing you need to know about Line Out is that they do not have an amplifier built into them. Keep this in mind. I’ll explain why later in the article.

What is Line In?

Line in is the exact opposite of Line Out. Line in (or Line Input) is an audio input port that allows audio devices to receive line-level audio signals from another device.

Line in is found on audio devices such as amps, mixers, audio interfaces, integrated amps, effect units, and even on some keyboard workstations. And primarily, Line Ins is connected to Line Outs. 

Line out sends the line-level audio signal from one device, and another device receives the signal through the line in port. For instance, you can send a keyboard amp line Out signal into a power amplifier’s Line In. Once the Line In receives the audio signal, it can be processed further.

In most audio devices, line in ports can be located at the device’s side, top, or back. And they are usually labeled as Line In, Audio In, Sound In, or simply Input.

Difference Between Line Out And Line In

Line-out and line-in ports are designed to work in the opposite fashion in every audio device. That is why the line out of one device can be connected to the line in of another device. Let’s look at some of the technical differences between these two audio ports.

Signal Direction

One of the differences between line-outs and line-in is the signal direction. This signal direction refers to the signal path in which the signal travels or where it is going. A line out is responsible for transmitting audio signals out of an audio device. On the other hand, a line-in is designed to bring a signal into an audio device. They are the exact opposite of each other.

In plain terms, line output is designed to serve as the source of the signal, while line input serves as the load or recipient component of the audio signal.

Impedance

Impedance may seem technical for many people. And you probably shouldn’t bother understanding. It’s not really useful for how you use these ports. However, since we’re talking about the difference between line out and line in, I might as well include it.

Impedance refers to the opposition to the current flow of an electrical component. Generally, line out connections has an output impedance that ranges from 100 ohms to 600 ohms. 

On the other hand, line-in connections have higher impedances than line-out connections. The impedance of line outputs is known as input impedance. Line inputs have impedances of about 10,000 ohms or more.

This level of impedance of line inputs makes them able to accept voltage levels in the range provided by line outputs.

What is Line In Line Out?

There is no audio port that is labeled or referred to as “line in Line out.” This is because, in theory, no audio port can function as both a line-in and a line-out. Line outputs are designed to send out audio signals from your audio device to an external amplifier. 

The work of line inputs is the inverse of line outputs. Line inputs receive the signals transmitted from the line outputs of audio devices like keyboards, guitars, etc.

In short, there is no audio port that is designed to serve as both a line-in and a line-out. This is because the role of line inputs is unique and varies from line outputs. Line out transmits an audio signal output. Line in port is responsible for receiving audio signal input.

Is Line Level Signal Balanced Or Unbalanced?

Line out and line in ports deal with line-level audio signals. Line level signals are signals that are transmitted between audio components like audio amplifiers, mixers, televisions, and DVD players. It is the standard signal level for the transfer of analog audio between devices.

Technically, line-level signals can be either balanced or unbalanced. This is dependent on the type of cable used for transmitting or carrying the line-level signal. Line level signals that are carried by most 1/4″ and RCA cables are usually unbalanced. However, line-level signals carried by ¼ TRS connectors are balanced signals.

Balanced signals are less susceptible to noise and interference. Whether an audio signal will be balanced or unbalanced depends on the audio connector and cable. It does not depend on the port in which the connector will be inserted.

Balanced audio cables come with three wires inside the plastic outer casing. Two of these wires serve as signal wires, with the third one serving as a ground wire. These two signal wires transmit two identical copies of the same signal but of opposite polarities.

 On the other hand, unbalanced cables have only two wires inside the plastic outer casing. These two wires serve as the signal and ground wire, respectively. Unbalanced cables are more susceptible to noise than balanced.

Do Speakers Go In Line Out Or Line In?

If your speakers are active or powered speakers, you can connect them to Line Out. Active speakers have a built-in power amplifier that will amplify the line-level audio from the line out so that it can be played through the speakers. However, if your speakers are passive, you should not connect them to Line Out or Line In.

Neither line in nor line out should be used for passive speakers. This is because passive speakers require external power amplifiers to drive them. And as I mentioned earlier in the article, Line Outs don’t have a built-in power amplifier. So it will not be able to drive the speakers.

So if you’re using passive speakers, you want to connect the line out of the audio device, sending the audio to the line in of a power amplifier. The amplifier will boost the line-level signal from the line out into a speaker-level signal. And then connect the speaker to the Speaker Out of the power amp.

In pro audio devices, speakers go into speaker ports or speaker outs. Speaker outs are ports designed to send speaker-level signals that are capable of driving speakers. Line level signals are not strong enough to drive speakers.

However, if your speakers are powered or active speakers, you can connect them directly to the line out. The difference between an active and a passive speaker is that active speakers have a power amplifier built into them.

This means when it receives an from the line output of an audio device, the built-in power amp will amplify the signal and then play them through the speakers.

When you plug a speaker into a line out, you may hear little to no sound at all from your speakers.

Do Headphones Go in Line Out or Line In?

Headphones do not go in line outputs or line inputs. This is because, as I mentioned, line-level ports do not have an amplifier built into them. Hence they are not powerful enough to drive headphones. You will get less to no sound in your headphones when you plug them to line outputs.

 I explained this in detail in my article, where I compared Line Outputs and Headphone Outputs. You should definitely check it out.

Headphones ports are different from line outs. They have headphone amplifiers built into them. And that makes it possible to drive headphones and get them to work.

Do Microphones Go in Line Out or Line In?

Just like headphones, you should not connect microphones to line-level outputs. When you connect a microphone to a line-level input, you will generate little to no sound at all. This is because microphones generate microphone-level signals. These microphone-level signals are quite weak as compared to line-level signals.

Because microphone level signals are weak, they cannot be transmitted through line inputs. For this reason, microphones must be connected to a Mic Input (or Mic In). Why?

Mic inputs have a preamp built into them. The preamp essentially receives the weak microphone signal and then boosts it into a line-level signal.

So here is what you need to know. Suppose you need to connect a microphone to a device that has only a line-level input. In that case, you have to connect your microphone to a dedicated preamp or mixer before connecting this to the line-level input. These devices will amplify the low-level output signals produced by microphones to line level.

Conclusion

A line out is an output that enables you to transmit audio signals from audio devices like guitars, keyboards, etc., to mixers and amplifiers. Line inputs receive signals from the line outputs of audio devices. 

This means line out transmits an audio signal output while a line in port serves as the recipient of signal inputs.