One of the most common questions in the music industry is what exactly is the difference between a mic vs line level signal.
A good starting point for this discussion is the audio interface, which acts a bridge between your microphones and studio monitors and your computer. You would notice that the audio interface comes with mic level or instrument level inputs at the front and line-level outputs at the back of the interface.
The key difference between a mic and line level signal is that microphone signals are the weakest kind of signals which is roughly a few thousandths of a volt. A microphone signal requires a preamp to boost the microphone signal to line level, so that it can be heard on your studio monitors.
By contrast, a line level signal is approximately one volt and is one thousand times stronger than a mic level signal. A line-level signal travels from your preamp to your studio monitors where it can be heard.
What is a mic level signal?
As mentioned above, a microphone level signal is about one thousandths of a volt (i.e., 1/1000 of a volt) and is the weakest signal in your recording studio circuitry. They need to be brough up to line-level so that they can be heard over your studio monitors or studio monitors.
To bring up a mic-level signal to line-level, you will need to pass the mic-level signal through a preamp. Preamps are usually found on audio interfaces, that can supply both phantom power to your mic and boost the mic level signal to line level. Apart from audio interfaces, studio mixers also have multiple channels to convert mic-level signals to line levels and are ideal if you are recording multiple vocalists or instruments in a single setting.
A microphone preamp on an audio interface will usually add around +40dB to +60dB of gain to the microphone signal, allowing it to be heard on your speaker preamps. Most audio interfaces will give you the option of adjusting your microphone gain.
A mic level input is usually an XLR microphone female connector, which connects to the XLR inputs of your audio interface.
The PreSonus AudioBox USB 96, one of the more popular audio interfaces for home recording, features two XLR mic and instrumental level inputs and comes with a built-in preamp to bring these signals to line level. It also allows you to adjust the gain on your microphone.
What is a line level signal?
A line level signal is approximately one volt and is 1,000 times stronger than a mic-level signal. All audio signals from your microphone or instruments must be amplified to line-level before they can be processed through to your studio monitors or headphones.
In short, line-level signals are carried from your preamp to the speaker amplifier.
A line level signal usually uses a 3.5mm input or RCA jack to connect to your speaker amp.
The line-level outputs on the PreSonus AudioBox USB96 runs from the interface to your speaker preamps where your microphone can be heard. The built-in preamps amplify the signal before it is sent through the line-out.
What is an instrument level signal?
An instrument level signal is somewhere in between a mic level and a line-level signal. With that said, you will still need to plug your instrument into the instrument level inputs in your audio interface as the instrument level signal needs to be amplified to line-level before they can be heard.
Most audio interfaces will come with instrument-level inputs or allow you to switch between mic level or instrument level inputs, depending on whether you are connecting your microphone or an instrument (e.g., your acoustic guitar).
Can you connect your microphone to a line-level input?
You should not connect your microphone to a line-level input as the signal produced from the microphone is too weak to be heard on line-level. Even with the channel switched on, you will probably not hear anything on your speaker because the signal is too weak to be heard.
We always recommend connecting a microphone to a microphone input on your audio interface or mixer. If your recording studio setup uses neither of these, you should use a microphone preamp to connect your microphone to your speaker amps.
The same principle also applies to instrument level inputs – they need to be connected to the appropriate inputs to be amplified to line-level.
What happens if you connect a line-level source to a mic level input?
Connecting a line-level source to a mic level input will cause the sound to distort and get very loud. A mic level input is never designed to handle the load from a line-level signal, and this may even cause damage to your recording equipment or speaker preamps. If you are not familiar with which inputs to plug your devices or instruments into, you should first turn off the power for all equipment and reconnect the cables correctly.
To read more on what audio interfaces you should get or how to set up your home recording studio, check out these posts: