What and How To Use a Limiter (for Music Production)
A limiter is a popular effect used in music production. But many new music producers don’t quite understand how it works – so I’ll be attempting to explain it today.
This post is not a mere repetition of what you see on the internet. Instead, it will cover in full detail, everything you need to know about limiters, and how to use them for your music.
What is a Limiter? (for Music Production)
Imagine being at a crime scene. There would probably be tapes placed around the scene, right?
These barricade tapes act as limiters – they “limit” the movement of people to specific areas to protect them from harm or tampering with the evidence.
In the same manner, an audio limiter is a hardware device or software plugin that “limits” or prevents the level of an audio signal from crossing a threshold. This is done in order to protect the signal from getting damaged.
For example, listen to an audio sample of a kick below.
How the kick waveforms looks like.
Now, observe what happens when I boost the volume by a large amount.
Listen to the now distorted kick sample. (Careful, it’s loud.)
The boosted signal. Notice how the waveforms have been chopped off or ‘clipped’. (Squared instead of rounded)
As you can hear, the kick sounds terribly bad. The distorted sound that you hear is due to clipping. This occurs when the audio signal exceeds 0 dBFS (decibels relative to full scale).
Clipping happens when the audio signal exceeds the 0dBFS mark.
To prevent clipping, a limiter is used.
Limiters used to be hardware effect boxes that sat at the back of recording studios.
These days, with computer-based music production, it is more convenient to use limiter plugins. Most limiter plugins are modeled over their hardware counterparts, just like the one below.
You can get the D16 Frontier Limiter as a free VST/AU limiter, for registered users at D16.
But before you insert a limiter into your DAW, let’s take a closer look at “clipping”.
What is Audio Clipping?
Here’s a quick analogy: If a hefty man were to sit on the plastic chair belonging to a little child, the chair would break. This happens because the weight of the man is greater than the maximum capacity the chair can handle.
In a similar manner, sound systems and your DAW has a maximum limit below which it can operate effectively.
When an audio signal is amplified beyond this limit, the top and bottom of its waveforms are “cut off”, and the resulting sound is distorted.
Digital Clipping and Analog Clipping
Generally, there are two basic types of clipping – digital and analog clipping.
In the digital domain, signals are represented in bits (1s and 0s). When an audio signal’s peak exceeds 0 dBFS, the digital system runs out of bits to process it. This leads to a brutal form of clipping which sounds bad.
If you look at the picture below, you can see that the top and bottom of the original waveform have been completely “chopped off” at 0 dBFS. Instead of being rounded, the ends of the waveform resemble a square wave. This is what digital clipping looks like and should be avoided.
Now, most modern DAWs today have support for 32-bit float audio. This means the dynamic range for sound and the available number of bits is very large such that the signal will never clip, even if the 0dbFS mark is crossed.
Does this mean we should ignore clipping?
Even if a signal does not clip in the digital domain, we have to be wary of analog clipping.
Once a signal passes the 0dBFS mark and is converted from digital to analog, it is going to get distorted. This is because the analog system struggles to produce the required voltage for the sound to be heard.
But the way analog clipping differs from digital clipping is in the nature of the distortion.
For example, if you look at the picture below, you would see that the analog system smoothly clips the signal at 0 dBFS instead of harshly chopping it off.
This is not what a digital system does.
As we saw earlier, a digital system completely chops off the end of a signal’s waveform, producing a badly distorted sound. This is why mixing engineers sometimes put in a little analog clipping to their tracks, as an effect, to add color to a song. You’ll also be able to find digital plugins that emulate this effect.
The Role of Limiting in Clipping
Now that you have a better idea of what clipping is, the role of a limiter should be clearer to you.
A limiter’s main function is to prevent an audio signal from clipping. In theory, no audio signal should exceed the 0 dBFS mark when a limiter is placed on it. This ensures the signal is contained in a safe place, and the resulting sound is without distortion or noise.
To further illustrate, listen to the audio sample of the kick and snare pattern below.
Now listen to what happens when I boost its volume beyond 0 dBFS.
You can hear that the drums sound horribly distorted. Take a look at the audio signal’s waveform below. You can see that the ends of the waveform have been chopped off.
Clipped waveform of a kick-snare pattern
To avoid distortion, we can use a limiter effect on the track. This is how it sounds with a limiter:
Obviously, the distortion we initially heard is no longer there. This is because I used a limiter to prevent the audio signal from clipping.
How a Limiter Effect Works
The thing you should know about a limiter is that it is a type of compressor. An audio compressor reduces the level of an audio signal when it crosses a threshold.
If you are unsure how compressors work, I suggest you read my previous post on audio compressors.
For example, if I place a threshold of -10 dB on a 2:1 compressor and the audio signal peaks at -8 dB, the compressor would reduce the level of the signal by 1 dB.
Theoretically speaking then, a limiter is a compressor with an infinite compression ratio. This means NO SIGNAL can pass through it. In other words, any signal that tries to cross its threshold is instantaneously reduced in volume.
If you look at the picture below, you are going to see various line plots with different compression ratios.
The one with a ratio of ∞:1 is that of a limiter. You can see that for that ratio, the audio signal never exceeds the threshold.
Basic Settings on a Limiter Effect
The settings you’ll find on a typical limiter are essentially the same but may vary a little among different brands. Let’s take a look at some of them.
The threshold knob or slider is a component that determines the level at which a limiter begins to act. For example, if you don’t want the signal to exceed the -5 dB mark, you can set your threshold to that value.
Threshold knob of a limiter effect
This setting is used to boost the level of the audio signal going into the limiter.
Not every limiter has this setting. But for those that have it, it allows you to set the speed at which the limiter acts when a signal crosses the threshold.
- A fast attack means the limiter will act aggressively and try to prevent any transient from going through.
- A slow attack, on the other hand, means the limiter will allow more of the signal’s transients past the threshold.
The release setting determines the speed of gain reduction when the audio signal falls below the threshold.
A slow release value is usually better as it backs out of the gain reduction smoothly. On the flip side, a fast release value can be too abrupt but can come in handy when used creatively as an effect.
Release knob on a limiter
Some limiters have a look-ahead feature that predicts when the audio signal would cross the threshold.
The result of this is that the limiter often acts on the signal ahead of time. This can be good or bad depending on how you use it. In this case, listening carefully as you adjust to get the sweet spot you want.
The knee setting determines how gradually the signal’s gain reduction occurs. A soft knee is more transparent and preferable, while a harder knee can be too sudden.
The ceiling determines the final output level of the audio signal that leaves the limiter. Some audio engineers recommend setting this value to a level of -1 dB because of the problem of inter-sample peaks (more on this later).
Output knob on a limiter
When Should You Use a Limiter Effect?
At this point, you might wonder – when do you use an audio limiter? Should you use it on individual tracks, in a mastering session, or on a mix bus?
There are specific mixing and mastering situations that call for its use. I’ll briefly mention some of them:
1 – Use a limiter to protect your audio equipment.
Audio equipment like your speakers can get damaged as a result of playing too loud.
When consistent clipping occurs, a speaker will struggle to produce voltage beyond its capability. This leads to an increase in temperature which can damage its coils. On the other hand, it’s quite common to get your speakers cone blown out if it’s played too loudly.
Although a lot of speakers today have an inner limiting circuit, it is better to take necessary precautions by using a limiter whenever possible.
2 – Use a limiter to add color to your sound.
VST plugins modeled after vintage analog limiters can help color your sound by adding harmonic frequencies to it. If you are a fan of the analog sound, this might be a situation where a limiter can come in handy.
3 – Use a limiter to ensure your recording isn’t clipped
There is nothing more frustrating than completing a recording only to find a part of the performance damaged, due to clipping – especially when recording high dynamic instruments, such as drums. Sure, you could attempt using restoration plugins like iZotope RX8’s De-clip effect to ‘declip’ the recording, but it’ll never be the best take.
To avoid this, some engineers use a limiter during the recording process to prevent potential recording.
4 – Use a limiter to make your song louder
Need to raise the volume of a track? Just insert a limiter effect and boost the gain.
However, be warned – that pushing a signal against a limiter, will affect how the track sounds. If you overdo the limiter, you’ll only end up with a squashed-up sounding track.
5 – Use a limiter in mastering
Mastering is an important part of the music production process, where a track is enhanced for broadcast playback. Limiters play a big role in mastering.
Basically, in the mastering process, the mastering engineer must make sure the final music track has the right dynamics without distortion. A limiter will almost always be used in the audio signal in the mastering process.
How To Use a Limiter Effect
Using a limiter is fairly simple. I’ll briefly explain the steps.
- First, determine the reason for using a limiter. Do you want to control the dynamics of a vocal or instrument, or are you working on mastering a song (better left to dedicated mastering pros)? Knowing this will help you identify where to place the limiter effect – be it on a track or master bus.
- Set the output level. The first thing to do after inserting a limiter is to set the ceiling/output level. It is important to do this because of “inter-sample peaks” (more on this later). A general rule of thumb is to set the limiter’s output to -1 dB.
- Set the threshold. The threshold determines when your limiter acts on the audio signal. For mastering purposes, you can set the threshold to 0 dBFS or take it slightly lower.
- Boost your input gain. After setting your threshold, boost the input gain of your signal until you begin to see some level of gain reduction. It is important you don’t overdo this or your signal will end up getting squashed.
- Setting the limiter’s attack and release. If your limiter has attack and release settings, you can tweak them to your taste. As you do this, ensure the final result sounds good. Your ears will assist you in making the right decisions.
The Problem of Inter-sample Peaks
Earlier in the post, I mentioned that you should not set your limiter to 0dBFs and push your audio hard into it. Because doing this will cause your audio to distort on most analog playback systems, simply due to digital to analog conversion.
In your computer, sound exists as numbers (1s and 0s) called ‘samples’. For you to hear these numbers as sound, a DAC (digital to analog converter) has to convert them into voltage signals and play them through your speakers. The meter in your DAW measures the peak of an audio signal. This measurement shows you the “sample peak” but not the “true peak”.
Put simply, the true peak is what we hear in the real world.
If we leave digital samples peaking at 0dBFS (see image below), and convert it into a voltage signal, the final analog audio will peak beyond 0dBFS. This new peak called a true peak or inter-sample peak will cause clipping.
Image illustrating the concept of inter-sample peaks
This is why it’s recommended that you set your limiter to at most, -1dBFS. Doing this reduces the possibility of your audio signal to clip when converted into analog audio.
Want to learn more about inter-sample peaking with audio limiting? Check out Ian Shephard’s podcast on the topic to learn more.
True Peak Meters
True peak meters show you the “exact” peak of an audio signal. Unlike other meters, they do not fall prey to the effects of digital to analog conversion – they show all the peaks of a signal including the inter-sample peaks.
A free meter that can measure the true peak is ‘The Youlean Loudness Meter‘. It is one of the best loudness meters in the market and is compatible with many DAWs.
Otherwise, you could also consider true peak limiters like FabFilter’s Pro L2 for your audio mastering needs. It comes in handy for monitoring inter-sample peaks in order to prevent clipping.
Using a limiter is not difficult as long as you understand how it works. One thing to remember is to always trust your ears. Sure, most limiters have pretty GUI and visual meters you can see, however, your should always just mix with its sound, and use the readings as a guide.
Looking for some good audio limiters? Here are some of the best audio limiters plugins:
And if you’re looking for free limiters, here are some I recommend:
Otherwise, most standard DAWs also come with stock limiter plugins that you can use, out of the box.
I hope you’ll find this post helpful. If you have questions, feel free to post them in the comment section down below.