How do preamps work and how to use them efficiently ?

How do preamps work and how to use them efficiently ?

If you’re a beginner in the audio engineering field or even even at a certain level of your activity, you might be wondering “What is a preamp ?”, which is an extremely important question. If it’s the case, don’t worry, because a lot of people are in the same situation by starting to work in the audio world.

Focusrite ISA One

I myself discovered relatively late what a preamp exactly was. The reason is simple, it can exist through different forms and can be used by many different ways…

What is a preamp ?

A preamp is an electronic device that can be built under 2 main different forms:

  • As a “small” device built into different sort of audio gear, like our DJ mixers, our consoles, our audio interfaces or sometimes in our USB microphones. Generally found in the amateur field.
  • As a standalone piece of equipment. Generally found in the professional field.

Yep, you probably already used one without even knowing it, simply by connecting your microphone to your audio interface before turning up the gain knob or by plugging your guitar into your amplifier.
Under the first form, preamps can be actually found almost everywhere in a signal flow.

How do preamps work ?

Before trying to understand how a preamp works, we have to compare the two main types of levels we can find in the audio world: MIC level and LINE level.

  • A MIC level is a pretty weak signal (that sits between 25 mV and 100 mV). As we can read in its name, it’s the typical level that comes out of our microphones
  • A LINE level is “electrically” more powerful. The ideal line level is internationally known to be 0,775 V
  • A third type of level is also used, generally in the amateur field, it is called the INST level. That type of signal is even weaker that a mic level, but we won’t dive into that field in this article.

All our pieces of equipment need to communicate at a line level to provide the best audio quality. We say then that the signal / noise ratio is good.
But then…
” How can I go from a MIC level to a LINE level ? “
This is exactly where a preamp becomes useful! The goal of a preamp is to drastically “boost” our weak microphone level to a more powerful signal that should be as close as possible to 0,775 V.

How to use a preamp ?

After all, this is the most important question to answer. You could be a technical genius but never be hired because you can’t use your equipment the right way.
The first thing to know is where the preamp(s) will take place in your studio. Well, the answer is pretty simple, but has to be understood before going further:
Right after your microphone and before the audio interface.
I used the word “right” for the microphone because the first thing to do with a microphone signal is to boost it while, in the other hand, you don’t necessarily have to directly go into your audio interface after boosting the signal to a line level.
In fact, you can use any piece of audio gear you have between the preamp and the interface (as the line level is set). Be careful though if you do that, because any treatment you apply to the signal will be recorded!
By the way… Do you know the correct way to record with Pro Tools ?

Note: Don’t forget to put the input(s) of your interface in line to avoid any sort of distortion. The level is already boosted and don’t need to be boosted again by your interface.

Now that you set up your preamp correctly, how to know if you reached out the line level or not ?
Let’s keep it simple: Trust the lights you see.
Nowadays, in 2021, the technology’s made to help us and to become more and more intuitive.
If you see a red light anywhere in your audio chain, turn down the gain knob. But if everything is green and, more importantly, sounds good to your ears, then you’re safe and you’re probably close to the 0,775V.

Avalon VT-737 Tube Channel Strip | Plugins Audio UAD | Universal Audio

The very last question about preamps would be this one ” Do I need a preamp ? “
Well, it’s actually up to you to judge if the preamp(s) of your audio interfaces are enough or not.
If you want to use more EQ’s and compressors in your recording sessions, buy one.
If you want to shape your sound more, buy one.
Otherwise, to be honest, a preamp is not that useful if you only start in the audio field. Keep in mind that every piece of gear you buy has to be used at least 80% of the time in your process.



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About IDeez

IDeez is the head sound engineer of IDeez Studio. He studied BA and MA in sound engineering at IAD (Belgium) and has been a specialist in vocal mixing for several years, especially in pop and hip-hop music. His goal is to help artists, rappers and singers in their mixing process through online mixing services, tutorials, blog articles and e-books. Contact him for any information!

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