What is Line In?

Basically, Line-In is an audio jack that is present in an audio device, which is used to connect the other audio output and input devices like speakers, microphones, etc. A digital or analog line-in can be used. The main purpose of the Line In jack is to help with audio recording or to distinguish incoming audio. Line In can also be said as Audio In or Mic In.

Before the study of line in we have to learn about the audio signal through which we can learn the line-in in brief.

What is an Audio Signal?

An audio signal is a representation of sound that is typically made up of a series of binary digits or, in the case of analog signals, a changing level of electrical voltage.

We use voltage to measure audio signals, which then feed into mixers, interfaces, and amplifiers before sending them to our speakers. One of the most important components of studio setup is understanding the various levels and properly connecting our equipment.

We will go over some technical jargon related to the signals, such as the estimated voltage and how it's quantified in dBV/dBu. These are just numbers that are simple to comprehend, even if you don't understand the underlying complexities.

For our purposes, the goal is to understand the underlying differences between line level, mic level, instrument level, and speaker level.

Types of Audio Signal

1. Mic Level: The microphone is much quieter now. It normally lives in the range of 1 to 10 millivolts, or -60 to -40 decibels. Mic level, as the name says, is what we get from a microphone connected to our system through XLR. To bring it up to line level, it must be amplified.
   The output level of the mic may be hotter or colder, depending on the model. You could also claim that some microphones are more "sensitive" than others, requiring less preamp gain to achieve a safe level. Pads are built into many higher-output microphones to prevent them from clipping when used with stronger sound sources.
2. Line Level: The loudest signal we deal with in audio is line level. It is about 1 volt, or 0 dB volt, in terms of voltage. Line level generally passes through the system after the preamp stage and before the output to our speakers. The mic level is proportional to the line level. For recording and playback, we need to raise the mic level to line level. Another thing to keep in mind:
   • -10dBV is the level for customer products like CD players
   • +4dBu is the level for professional equipment like preamps, mixers, and outboard gear. On a VU meter, +4 dBu equals 0 (fun fact).
3. Speaker Level: We have finally arrived at speaker level. Speaker level is the point at which all of our signals have been amplified to line level and are ready to be output to our speakers. Because the voltage is so high, you will need to utilize special speaker cables to ensure that the signal gets securely from your interface to your speakers.
4. Instrument Level: The mic and line levels are balanced for the instrument. These signals are generated by an instrument such as an electric guitar or a bass. Some interfaces have dedicated "Hi-Z," or high impedance, 1/4'' inputs for attaching instruments. Others use hybrid XLR/1/4'' inputs that let you choose whether to plug in a microphone or an instrument.
   To achieve line level, instrument levels require a little preamp amplification.

Line Level

Line level refers to the normal strength (amplitude) of audio signals from mixers, signal-processing devices, and other consumer and professional audio equipment. Consumer and professional line levels are the two sorts of line levels. A signal with a level of -10 dBV is commonly referred to as consumer line level (0.316). Consumer-level equipment includes CD players and DVD players, for example. Signal-processing equipment and professional mixing consoles, for example, are examples of professional line-level equipment.

Is Line Level Signal Balanced or Unbalanced?

The line-out and Line ports handle line-level audio signals. Line level signals are signals transferred between audio components such as audio amplifiers, mixers, televisions, and DVD players.

Technically, line-level signals can be balanced or unbalanced. This is affected by the type of cable used to transmit or carry the line-level signal. Line level signals are usually unbalanced and transmitted by most 1/4'' and RCA cables. Line-level signals transmitted by 14 TRS connections, on the other hand, are balanced signals.

Noise and interference are less likely to affect balanced signals. The audio connection and cable determine whether an audio signal is balanced or unbalanced. It makes no difference which port the connector is placed into.

Inside the plastic outer shell of balanced audio cables are three conductors. The signal wires are two of these lines, while the ground wire is the third. These two signal lines send out two identical copies of the same signal but with different polarities.

Unbalanced cables, on the other hand, have only two conductors inside the outer covering of the plastic. The signal and ground wires are connected by these two wires. Noise is more vulnerable to unbalanced wires than to balanced cables.

Explanation of Line In

Most audio devices and systems have at least one line-in. Line-In jack uses in the opposite fashion in all the audio devices. When you are on a computer then, the line-in is directly connected to the sound processor or to the sound card of the system. In the computer, there is functionality to reduce the volume and configure another setting at the line-in level.

In most audio devices, the line-in jacks are present on the top, back, or sides. But in the case of the system, basically, it is present in the backside. And in the case of a laptop, it is present on the front side of the laptop. The look of the line-in port is similar to the headphone port, but there is one difference is that the latter is depicted by a headphone logo, but the former is represented by a circle with two inward-facing triangles, and it is in blue color.

The electronic signal is present at the line level. The line-in jack can be used to connect any audio device, such as headphones, a portable music player, a microphone, or anything else. When the motherboard only has four or six channels, and the other jacks are absent, the line-in jack can be used to connect rear speakers.

Audio Input

When you are using line-in jacks, then it allows the systems to accept the audio input. This input is frequently your voice, which can be captured using a microphone. But in many cases, the jack also can record the musical instrument. If you want to record the audio, any device can be connected to the line-in port that can be used as a sound recorder, such as Microsoft Sound Recorder, Audacity, or any other sound recorders.

Line Out

A line out is an audio connector port that lets us send line-level audio signals to other devices for processing. Line-Levels signals are generally signal, which is very strong to transmit without any signal drops.

You can find the line-out on keyboards, digital photos, guitar, bass amps or synthesizers, mixers, audio interface, or some others. It helps in audio signal transmission from one device to another.

The line-out from your guitar amp can be utilized to transport the audio from your amp to the mixer at a specific moment. You can use this method to send an audio signal from a mixer's Aux output, which is usually a line-out, to a keyboard amp's input. You can use this method to send an audio signal from a mixer's Aux output, which is usually a line-out, to a keyboard amp's input.

You can also say the line-out as audio out or Sound out.

Difference between Line-out and Line-in

In every audio system, line-in and line-out ports are designed to work in the opposite direction. Causing that the line-out of the one system is connected to the line-in ports of another system.  There is also some technical difference between line-in and line-out that are following:

Point of View	Line-In	Line-Out
Signal Direction	Basically, the lie-in port is used to input the audio signal or receive a line-level audio signal from another device. So, a Line-in port is used to bring the signals into a device.	Output ports for sending line-level audio signals to external devices are known as line-out ports. So a Line-out port is used to transmit the audio signals out of the device.
Impedance	The term "impedance" refers to the resistance of an electrical component to current flow. Line-in has a higher impedance than line-out connection. Line-out impedance is referred to as the impedance of line inputs is around 10,000 ohms or more.	The impedance of line-out is very lower than line-in. Basically, a line-out connection has an output impedance of range 100 ohms to 600ohms.