Published July 16th, 2021
Setting up your audio interface to maximize the input signal and to minimize the inherent noise is arguably the most important step in optimizing its sound quality. PreSonus® has put together this brief tutorial to help you to understand how to properly set input levels throughout your signal path, as well as how to avoid some of the most common misunderstandings and pitfalls.
Step 1: Setting the Gain
- First plug in your microphone or instrument into your desired channel input. If your microphone requires Phantom Power (+48v) the please activate the 48V button. Put on your headphones and listen.
- Turn the trim knob clockwise while speaking or playing. Watch for the signal/clip indicator to turn red in your DAW or on your interface (if it has input meters), then back it down until the level indicator is green only. Please see below images of an AudioBox USB 96, which has no onboard metering, and the Studio 24c, which does. Studio One meters can be seen to the right of the interface. It is important that the input meters are not clipping red.
How high you have to turn the trim knob depends on several factors: the volume of the source, the sensitivity of the microphone (if the source is miked), the maximum input and gain range of the preamp, and the gain curve of the potentiometer. Again, it is important to note that you do not clip your input signal as outlined in the images and steps above.
Let’s take a look at each of the different factors that inform your input gain settings in more detail:
- Source volume. This is a bit of a trick, because sometimes you have very little control over how loud the source is set. For guitar amplifiers and keyboards, you may need to tell the musician to turn up or down to get a good signal. For sources that rely on a microphone, this factor depends on the type of microphone you’re using. If you are miking a very loud source (e.g., a kick drum) with a very sensitive microphone (such as a large-diaphragm condenser microphone), you’re going to have to set the input trim much lower than you would when miking the same source with a less sensitive microphone (such as a low-output dynamic microphone). So, why mention it? You should always take the volume of your source into consideration when selecting a microphone and troubleshooting gain staging issues.
- Microphone sensitivity. In general, you must apply more gain to a less sensitive microphone, regardless of the type of source, but consider this: If you are using a microphone that is not very sensitive to pick up a source that is not very loud, and you can’t get enough gain, perhaps you have chosen the wrong tool for the job. Let’s take the common example of a shy vocalist. Not all singers can project very loudly. This is not necessarily a bad thing, but you can’t use the same commonly used dynamic microphone to pick up a shy singer-songwriter who barely sings louder than their acoustic guitar that you would use to pick up the lead singer of a Swedish Death Metal band and expect the same result. While not always possible, changing to a more or less sensitive microphone can solve a plethora of gain staging issues before they've presented themselves.
- Preamp Maximum Input Level and Gain Range. As its name indicates, the maximum input level is the loudest a source can be with the preamp gain set to a specified level (usually unity) without overloading the circuit. But just like source level, this is not an independent variable. How much gain range a preamp provides also factors into how much it can amplify a source. A mic preamp like the PreSonus XMAX, which provides +60 dB of gain, will be able to amplify a signal much more than preamp with a gain range of +40 dB.
- Potentiometer Curve. Depending on the design, a potentiometer can provide most of its gain up front, with very little control, or most of its gain at the end of its throw, giving you slightly more control. In general, the “sweet spot” for most potentiometers is between one and four o’clock. This can be quite a bit further around the clockface than some people expect. And while it should go without saying, the only time you should be mixing with your eyes instead of your ears is when that red clip light comes on—but we’re going to go ahead and say it: Mix with your ears not your eyes.
If you have to turn the trim knob on your mixer or audio interface to five o’clock to get a good signal level, but you’re not hearing noise or distortion, that’s okay. If you only turn the trim knob on your mixer or audio interface to seven o’clock, and you get a good signal level, that’s okay, too. What matters is what you hear, not how perfectly aligned to the midpoint your trim knobs are set. End of lecture.
Step 2: Setting the EQ and Dynamics
After you have set the input gain, you can use your channel EQ to sculpt your source. The more bands your EQ offers, the more control you will have, but you’ll also add more potential for improper gain staging, so use with caution.
- To set the EQ, you will need to adjust both the channel and the main faders to unity. This is just for the purposes of dialing in the sound you want. You’ll dial in the mix next. Often, when people are new to using an equalizer, they listen for what is missing from their source signal and try to boost it in.
- Let’s take a common problem: the kick drum.You want the kick drum to be big and bassy, so you cut all the highs and mids and boost up the low bands as much as possible, right? Maybe not. Sometimes, it’s what you remove that filters out the frequencies that are overwhelming the sound that you want to hear.
- Let’s take a look at our kick drum again. If you cut all the high frequencies, your kick drum won’t punch through the mix, because the frequency at which its attack resonates will be gone. So, try boosting your high EQ in the 2-5 kHz range, until you find the attack frequency of your kick drum.
- Cutting your kick drum EQ around 400 Hz will reduce muddiness. Cutting below 80 Hz will reduce boominess. And a slight boost at around 100 Hz will give you that big bottom end you were looking for to begin with.
More information on instrument and EQ frequency ranges can be found in the PreSonus EQ Frequency Guides.
Dynamics processors can be difficult to work with at first because they both reduce gain and amplify it.
- Let’s take a look at a compressor for a moment. A compressor works by lowering the dynamic range — and by extension, the gain — of a signal, but it also gives you a make-up gain control that allows you to get some of that back.
- If you apply a lot of gain reduction to a signal, then boost it too far with the make-up gain, you are essentially amplifying a laser, and it can get very unwieldy very fast, especially if you have done the same thing across multiple channels. As with an EQ, only compress a signal as much as you need to, unless you’re using it for an effect, and only gain it back up as far as you have to for it cut through the mix.
More information on compressors can be found in the PreSonus Brief Tutorial on Dynamics Processing.
Step 3: Mains
Adjusting the level between your Main output and your speakers can take a little work to find the right balance. As a rule of thumb, set your Main output level so that the Main Output meters on your interface or in your DAW are consistently below the red 0 dB light. If this light is coming on, especially on an audio interface, you are overloading the circuit and/or the converters and are going to hear distortion. See images below.
Once you’ve set your Main output level, adjust the level of your speakers’ amplifiers (onboard or outboard). In the case of some powered loudspeakers you will need to set an input and an output level. As with your audio interface, set the input level first, so that you have a good level without distortion, and then set your output level until your speakers are loud enough but are not overdriven.
If you can’t set the input level of your speakers low or high enough, you will need to adjust the output level of your interface.
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Please contact PreSonus Technical Support by creating a Support Ticket at My.PreSonus.com for further assistance.
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