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Mic, line & instrument level signals: their differences and how to use them

Mic, line & instrument level signals their differences and how to use themThree different signal levels which you will come across in audio recording are mic level, line level and instrument level. These terms refer to the voltage level of a signal. Instruments, microphones, outboard equipment etc. all put out different signal levels. When you connect such items to something like an audio interface, then it’s important to only connect items which produce a certain signal type to inputs which are designed to receive that signal type.

Firstly, this is because it will ensure proper gain structure in your recording process. Secondly, this is because failure to match the signal levels can cause substantial problems. For instance, if you connect a microphone which produces a mic level signal to a line level input, then the signal will be too low to use. Similarly, if you connect something which produces a line level signal to an instrument level input, then the signal will be too high and will likely cause distortion.

What’s the difference between mic, line & instrument level:

Mic Level: the lowest of the three signals is mic level. Mic level refers to the level of the signal which is produced by a microphone. Microphones produce a relatively weak signal. As such, they require a preamp to boost them to line level.

Instrument Level: sitting between mic level and line level is instrument level. The term instrument level refers to the level of the signal produced by something like an electric guitar or bass guitar. Like mic level, instrument level also requires a preamp to boost the signal up to line level.

Line Level: when it comes to line level, there are actually two different kinds:

  • Consumer line level: this is -10dBV and is the standard for things like Blu-ray players and MP3 players.
  • Professional line level: this is +4dBu and is the standard for things like mixing desks, preamps, outboard processing equipment etc.

Some equipment has a switch which allows you to toggle between -10dBV and +4dBu. This allows you to take a signal from either consumer level or professional level items on a single piece of equipment.

Why bring mic & instrument level signals up to line level?

As previously mentioned, most pro audio recording equipment operates at professional line level. If you’re connecting two pieces of equipment which both operate at line level, a mixing desk and an outboard compressor for instance, then that’s fine. But if you’re connecting something which produces a signal which is weaker than line level, like an acoustic guitar’s pick up (instrument level), or a microphone (mic level), then you need to boost the level of the signal up so that it is also at line level. This ensures good gain structure.

How mic & instrument level are raised to line level:

If your audio equipment has mic level inputs or instrument level inputs, then these inputs will be accompanied by a preamp which is their to boost the signal. So, when you plug a mic into a mic input on a mixing desk or audio interface for example, then it expects to receive a mic level signal. You then use the built in preamp to boost the signal up to line level. You do this by adjusting the gain control of that input’s preamp. When you plug an instrument such as a guitar which is producing an instrument level signal into an instrument level input on your mixing desk or audio interface, the input expects to receive an instrument level signal. Once again, you bring the level of the signal up to line level by adjusting the gain control of the preamp on that input.

Don’t let connectors confuse you:

It’s important to be aware that the type of connector you are using does not signify the signal level. On things like audio interfaces, mic level inputs are commonly female 3 pin XLR sockets. Line level inputs are commonly 1/4″ jacks. But these are not hard and fast rules. For example, you may also come across line level XLR inputs and outputs as well as line level RCA connectors. Whilst 1/4″ jacks are often line level, instrument level also operates on a 1/4″ jack. So you mustn’t assume what a signal level will be based on a connector type. It’s important to make sure you know what kind of signal level an input or output has. Luckily, input and output types on things like audio interfaces are usually labeled.

Using instrument & line level devices when only mic inputs are present:

Not all equipment has instrument and/or line level inputs. If you want to connect something producing either an instrument level or line level signal to your audio interface or mixing desk for instance, but only mic inputs are available, then you need to use a DI box which allows you to plug an instrument or line level signal into it via a 1/4″ jack and then take the signal out of the DI box via an XLR. You can then connect the DI box’s output to your audio interface or mixing desk’s mic input. This way, you are feeding a mic input with an appropriate signal. You can then use the mic input’s preamp to raise the signal up to line level via the gain control.

Speaker level:

For the sake of wholeness, it’s worth noting that there is a fourth signal type. This is called speaker level. Speaker level is the type of signal which is produced by an amplifier which is designed to feed loud speakers. Because speaker level is much higher in voltage than mic, line & instrument level, a speaker level signal should never be connected to a source which is designed to receive anything other than a speaker level signal.

Does this help you to understand the difference between mic, line & instrument level signals. Have you previously made sure to use mic, line & instrument level signals properly? Leave any questions or thoughts you might have in the comment section.

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