Sunday, February 26, 2012

HOW TO USE THE LIMITER (free Vst Plugins included)

Hello and welcome to this week's article! Today we're going to talk about Limiters!
Limiters are basically compressors set with a high ratio (often infinite) and a hard knee, and their aim is to create a volume threshold that cannot be exceeded. Usually this function is needed in the Mastering phase, and it allows you to maximize the impact of your mix and to control the headroom of the sound, reducing the peaks in volume and bringing up the quieter parts (headroom is the dynamic range of a sound before it reaches the distortion level).
Another important use of Limiters comes in the Mixing phase: often you will need to limit certain tracks with a high dynamic range (such as snare drum, guitars, bass, and sometimes vocals), in order to make sure that, although the sound may already be compressed, there will be no chance that any peak will cross the chosen threshold. Each instrument must seat on its place, in order to avoid bad surprises in the Mastering phase! The use of Limiters in the mixing phase is not to maximize the sound or squeeze it, as it may happen in the mastering phase, but just to set the ceiling for the single signals, so don't be aggressive with limiters when mixing: the aim is just to mantain the maximum headroom possible!

During the the Mastering phase, looking at the spectrum of your wave (using Meters, if needed) you will probably notice that there are some high volume peaks (around the 0db area), and others which are a little too low, and you cannot just turn up the volume, since the higher peaks will exceed 0db and distort.
So what we need is to reduce those peaks, thus giving us the opportunity to raise the global volume of the song without surpassing the distortion threshold.

There is a limiter in almost every DAW, but Here is a selection of the best free ones, and among those our suggestion goes to the Yohn W1, a clone of the famous Waves L1 Limiter.

Let's take a look to the basic controls featured on this kind of effect:

- Threshold: controls where the limiter will start to kick in (just like a regular Compressor), eliminating everything above the threshold (in this, limiters are different from compressors, since with comp you can control the amount of the reduction via the Ratio Control). The headroom created by removing those peaks is automatically compensated by raising the quieter sounds. Usually a threshold that goes from -2db to -4db is enough to make the sound punchier, preserving the headroom and without compromising the dynamics, but the most important thing is to always check the meters for clipping and distortions, and whenever they occour, try applying less aggressive settings.

- Ceiling: determines the maximum volume reachable by the limiter. E.g. : if we lower the threshold down to -15db and the ceiling to -6db, the threshold will cut all the peaks above -15db and raise the rest, then the global volume will be raised to -6db. In the mastering phase is suggested to bring the Ceiling Control to around -0.1db, but if our music will be listened mostly on mp3 or Youtube, it's better to set it at -1.0db, in order to avoid unwanted distortions.

- Release: it's the less important control here, and most of the times can be left to a default of 100ms. As on the other Compressors, the release control determines the amount of time the sound takes to go from full limiting to no limiting.

It is very important to keep a Dynamic Range (the difference between the quieter and the louder parts) between 14 and 10db, not less, or the sound will result overcompressed and flat, and in order to keep an eye on this we suggest you to use a Metering Tool. To learn More about the Dynamic Range, and how to measure it, check out our article about the Loudness War.
We can also use more than one limiter instance: the first one to raise the perceived volume, then an EQ to compensate if the limiting is taking out some lower frequencies (which may happen sometimes), and then another limiter to trim the volume, just remember that a limiter should Always be the final plugin, and the last limiter should be POST FADER (on the Cubase/Nuendo interface this means that should be placed on the last 2 slots of the effects insert).

- How to use the Limiter: as we've already seen, the base idea is to reduce the highest peaks in order to clear space to raise the overall level of the whole mix, so we must lower the threshold and the ceiling controls of the same amount (many limiters, such as the Waves L2 have an option to link these 2 controls), while keeping an eye to the "Attenuation" meter: we should lower the 2 controls until we have some attenuation, but not too much, just the peaks of the loudest instruments (which is often the snare drum). When we have found the right spot (too much attenuation means distortion and we don't want it! We just want to use the "unused" room to heighten the overall level!), which is when we have just a very occasional attenuation, we have found the right threshold level. Now we can unlink the Treshold and the Ceiling controls, and raise the Ceiling fader up to -0,1 in order to use all the volume we can before the distortion!

Limiters often have other controls like Attack, an in-built Maximizer, a Stereo Expander and others, but here we've just analized the core functions of limiting. Feel free to experiment!

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