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What is a Sound Limiter?

What is a Sound Limiter?

A guide covering the basic use of sound limiters for beginners.

Sound 101:

Before I get right into what a sound limiter is and how to use it, I’d like to start with a very simple understanding of sound in general. As you probably know sound is actually waves of energy that oscillate up and down hence the term “sound waves”. There are many properties of a sound wave such as frequency, wavelength, wavenumber, amplitude, sound pressure, sound intensity, speed, and direction. We don’t care about any of that right now. Regardless of the complex system of nuerons firing in your brain to allow you to hear sound, the part we’re focusing on in this guide can be explained very simply. All we need to know right now is this:

Sound is actually waves
A visual representation of sound being waves.

A visual representation of sound being waves.

You can hear sound
We Hear Sound

We Hear Sound…And I’m an amazing graphic designer lmao.

and sound waves can change in amplitude or volume (louder/quieter).
Dynamic Range

Sound Waves can vary in amplitude.

Mind boggling stuff…

Okay, so what’s a sound limiter?

So we have these sound waves travelling up and down (somehow that’s as far as I’ve gotten with the first paragraph). The 2 things about sound waves that we’re interested in when regarding a sound limiter is whats known as dynamic range and clipping. In simple terms the dynamic range is the distance between the highest and lowest points of amplitude in the wave, also understood as the loudest and quietest parts in the waveform. Clipping is what occurs when a waveform is distorted and essentially cut off or “clipped” at a certain point, and can occur in both analogue amplifiers and digital processing units.

The reason we’re focusing on the dynamic range is because a limiter’s sole purpose is to destroy it (muahahaha!). As cheesy as that sounds it’s somewhat true. This isn’t the sole purpose of a limiter, but limiter’s are used to reduce the amplitude of peaks in a waveform when they get too high, essentially “limiting” the sound from going over a certain ceiling that’s been set by the audio engineer (thats you), which results in a smaller dynamic range. If that’s confusing you can simply think of it as stopping the loud parts of a sound from becoming too loud. So not only can a limiter sculpt the dynamic characteristics of sound, but at the same time it can prevent clipping by not letting the sound go beyond a point that clipping occurs.

What is a sound limiter? A dynamic range destroying, clipping preventing, audio shaping device. Or…Something that limits sound.

Common Parameters of a Sound Limiter:

Threshold:
The threshold is a set value measured in dB (decibel). This value is the set level you want the signal to reach before the limiter reacts. Once the threshold is met or exceeded the limiter forces the signal against the output ceiling.

Ceiling:
The ceiling is the maximum level a signal going through the limiter can reach. Ideally the signal output from a limiter will never be higher than the ceiling, and this is especially true for modern limiters that are more precise. One great aspect of modern software limiters is they have the advantage of being able to look ahead and see what’s coming up next, reacting before the ceiling is surpassed.

Input Gain:
The level of the signal entering the limiter. The more input gain the more the dynamic range of the signal is reduced, due to the distance between the low and high parts of the sound being shortened more and more. Applying too much gain can completely remove the dynamic characteristic of your sound.

Attack and Release:
The attack phase is the duration during which the signal is reduced after reaching or exceeding the threshold or hitting the ceiling. The release phase is the duration of the signals rebound after being reduced from the limiter. Both attack and release parameters will change the time it takes for these changes to occur. This is a nice feature because it gives you more control over the way the sound is altered. Sometimes gradual gain reduction sounds better in certain scenarios where other times its nescessary to make it happen quickly. Both attack and release are depicted in the image below:

Attack and Release

Notice how the signal doesn’t drop instantly after going over the threshold, but has a short duration (the attack phase) of gain reduction. The release phase is basically the same thing in reverse.

 Isn’t this compression?

If you have an understanding of sound compression you might be thinking a lot of this sounds familiar. That’s because to an extent it’s the same thing. The difference between compression and limiting is the intensity or degree of compression. Many times limiting can be achieved with a compressor or vice versa (compression with a limiter), so sometimes compressors and limiters are referred to by the same name. It’s generally accepted that extreme dynamic range compression is “limiting” regardless of the tool causing it.

Summing up Sound Limiting:

So the typical application of a limiter is to apply gain reduction when a signal reaches a certain point. This can occur in a couple different ways, and it’s important to remember that not every limiter is the same. Some sound limiters have very few functions while others can have numerous parameters and applications. If you have any other questions about sound limiting, feel free to leave a comment on this page.

 

Definitions of Key Terms Throughout the Sound Limiter Beginners Guide:

Sounds Wave – Oscillation of pressure in a medium such as air or water. Sound waves can also be understood as compression and decompression (rarefaction) of a medium’s density. The emulation of sound waves has also been achieved inside of computers represented by bits of information.

Dynamic Range – In simple terms dynamic range is the difference between the loud and quiet parts of a waveform.

Clipping – Clipping is the distortion of a waveform, occurring when an amplifier is driven beyond it’s limits and attempts to output energy that surpasses its maximum capability. In digital sound processing, clipping occurs when a audio signal is cut off due to the limited range of the chosen representation being exceeded.

Ceiling – A set level on a sound limiter that the signal cannot surpass.

Attack – A parameter controlling the duration that it takes a signal that’s exceeded the threshold or reached the ceiling to be reduced.

Release – A parameter controlling the duration that it takes a signal that’s been reduced after exceeding the threshold or reaching the ceiling to rebound back to it’s original amplitude.

 

February 2, 2013 Mixing and Effects No Comments

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