Setting the Preamp Level Correctly!

One of the most common problems I see at churches and venues is not utilizing the preamp correctly on the mixer. When this one step is missed, it can cause a litany of issues, from musicians not being able to hear themselves, to massive amounts of noise in the PA.

Thankfully, it is a simple solution once you understand what to do!

What is a Preamp?

To talk about the preamp, we first need to understand the differences in levels between Line-Level and Mic-Level.

Line-Level vs. Mic-Level:

Line-level and Mic-level are two different audio signals, however, the main difference between the two is their amplitude and voltage levels.

Line-level is a high-level signal that is typically used to transmit audio signals between different audio devices such as mixers, amplifiers, and audio interfaces. Line-level signals are generally standardized to have an output voltage of around 1 volt and are generally not affected by impedance.

On the other hand, mic-level signals are much lower in amplitude and voltage. Mic-level signals are generated by microphones and have a much weaker signal than line-level signals. Mic-level signals are generally standardized to have an output voltage of around 1 millivolt and are often affected by impedance.

In general, line-level signals are considered to be stronger and more robust than mic-level signals. Line-level signals are less prone to noise and interference and can be transmitted over long distances without significant degradation in quality.

Mic-level signals, on the other hand, require more amplification and are more susceptible to noise and interference.

Preamp Purpose:

An audio preamp, short for "preamplifier," is used to amplify low-level audio signals, like from a microphone or musical instrument, before they are sent to a power amplifier or recording/streaming device. Amplifiers, recorders, and streaming devices typically work on line-level signals.

The primary function of a preamp is to increase the signal level of the audio input, allowing it to be further processed or amplified without introducing noise or distortion. The difference between line-level and mic-level is that the line-level signal is about 1000 times louder than the mic-level. Because of this, the preamp in most mixers or soundboards is very low noise and has circuitry to help protect the audio from interference.

Using the Preamp

The Preamp is important to set correctly to make sure you have sufficient enough signal but are not distorting your channel. The proper way to set the preamp gain is to give a strong signal of around -20 dBFS or +4 dBu on the meters. A properly gained-up signal like that will have a high level of signal-to-noise ratio and sound clear and clean through the speakers.

If you set the gain too low, you will then have to push the fader up higher, and then the master fader up higher, to then amplify through the speakers. This will result in extra noise in the signal as seen in the diagram above.

Setting the Preamp Level

Have your musicians check their instrument one by one. Ask them to play their instrument at the loudest setting they will be playing during the show. Press the 'Solo' button on their channel to listen to the channel in your headphones. Then set your preamp gain to hit nominal/unity gain (-20 dBFS). It is okay if the channel goes above -20 dB from time to time, but the majority of their signal should be around the -20 dB mark when they are playing at their loudest.

It's important to note that the optimal gain level will depend on the specific source material and the desired output level, so it may require some trial and error to find the best setting. Additionally, it's important to avoid setting the preamp gain level too high, as this can introduce noise and distortion into the signal.

One last thing to mention is after you set the preamp gain if you ever need to adjust it, out of courtesy mention to the band that you are going to adjust it. When you adjust the preamp gain, it will affect the levels that are sent to monitors, so the band should know if they need to adjust things.

Is your PA too loud?

Once you set your preamp gain correctly, you might notice that you need to turn your main stereo fader down as it is too loud in your room or venue. If this is the case, you should turn your amplifiers down to a better volume with your stereo fader at +0 dB. Doing this will not only give you a better signal into your speakers, but it can reduce the noise of your system in the quiet moments.

Until next time,

Drew

Whenever you're ready, there are three ways I can help you:

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