As you delve deeper into audio production, you will realize that selecting the right equipment may be a tad complicated, especially when it seems like you have multiple tools that perform the same functions. Audio compressors and limiters are prime examples of such devices; they are both gain reduction tools, but they have specific individual functions, and you must know the differences between the two to get a proper handle on the dynamics of mixing and loudness. One isn’t a substitute for the other; they are both essential in different aspects of audio production.
In this article, you will learn all about the role of compressors and limiters in audio engineering, when compressing and limiting is needed, and when a compressor or limiter should be used. After comparing the audio compressor vs limiter, you will fully understand the world of audio dynamics and can begin your journey to becoming a better engineer. Lets begin.
Audio compressors control, shape, and reduce the gain on an audio signal’s dynamic range; the loudest and quietest portions of a mix. Reducing the range of your audio signal makes the loudest parts softer and the softest parts louder, making the signal more even and level. To truly understand the basics of audio compression, let’s grasp how the threshold and ratio works on a compressor.
Before an audio compressor can reduce the dynamics of your instrument, you must tell it when it should begin compressing and how much it should compress. The threshold measured in decibels (dB) is a control that determines when the compressor starts working. When the threshold is set and the signal passes this point, audio compression kicks in, and the track’s volume is reduced by an amount in dB defined by the ratio setting.
Let’s assume you have a lead guitar part in a track that is all over the place. Some of the notes are too loud and some are too quiet. You could use automation manually turn down the loud parts and turn up the faint notes, but that will take quite a while. Let’s say the volume sits around -16dB and occasionally spikes up to -11dB. So, you set your threshold at -10dB. This way, compression is initiated when the volume is louder than you want.
The ratio is how much you want the compressor to turn the volume down when it gets to the threshold. Typically, the higher the ratio, the greater the compression. Using the above-mentioned example, our threshold is -10dB. So, let’s say your ratio is set at 2:1. This means that for every 2dB above the threshold, only 1dB will be let through. Similarly, a 4:1 ratio decides that a signal that is 4dB over the threshold will be reduced to 1dB.
Audio compressors also have other important controls like attack and release. They determine how quickly compression should occur and how quickly it reverts to an uncompressed state, respectively. The attack and release settings are important in determining whether the compressed sound is smooth or punchy.
Mastering engineers use compression in various ways. For instance, during the first recording process, compression can be applied to a signal to squash any transients, i.e., the sharp volume peaks from things like the sound of picked guitar strings, snare hits, and vocal consonants. Audio compression can also prevent distortion (clipping) during the mixing and mastering process. When compression is applied to a track, it can offer a punchy sound, and it can also be used to control where instruments sit in the mix.
This type of compression is a bit different from regular compression. In side-chain compression, the effect level on one instrument is controlled by the volume level of another instrument in the mix. An example would be making the compression level on a hi-hat controlled by the output volume of the cymbal. So, when the cymbal sounds, the hi-hat gets more compressed. In this way, it keeps cutting through the mix.
You may have previously struggled with getting your kick and bass to play smoothly together due to their shared frequencies. Side-chain compression can be just the answer you are looking for. You can set the kick drum to trigger compression on the bass, meaning that every time the kick drum hits, it will slightly turn down the bass. This allows the kick's transients to be more potent and in turn more pronounced.
In this audio compressor vs limiter comparison, lets next talk about the limiter.
The limiter works using the same principle as a compressor. It has a threshold setting and reduces the gain of an audio signal, preventing it from going above a set point. However, limiters tend to be more “restrictive” than compressors. For this reason, they are less of a creative tool and do not offer as much control over sounds as compressors. In practice, the ratio used to reduce the gain distinguishes them from compressors. Limiters won’t allow the sound to get louder than the threshold, and their ratio is much higher than that of a regular compressor.
Typically, the ratio is 10:1 or higher, but it can also be set as close to infinity as possible. This is done so that regardless of how much the input signal changes, its output level remains the same. In other words, compressors have a low ratio that turns down some volume when it goes higher than the threshold. Limiters, on the other hand, have a large ratio that turns down all the volume that exceeds the threshold.
In this audio compressor vs limiter comparison, you can't talk about limiting without mentioning true peak.
True Peak Limiting must be enabled to ensure that the output signal doesn’t exceed a particular maximum true peak level. True Peak Limiting detects true peaks in the input signal and reduces them appropriately. It also smoothly attenuates any true peak overshoot introduced by the ultra-fast limiting process, ensuring that the final true peak output doesn’t exceed the set maximum true peak output level. This is a must in mastering to meet today's streaming guidelines.
In short, audio compressors gradually reduce the volume of an instrument once it exceeds the threshold, but limiters will not allow audio to go beyond the said threshold. In addition, audio compressors are smoother and more artistic due to how they work, whereas limiters are more aggressive and limiting (no pun intended).
Now that you know the difference between the audio compressor vs limiter and how each works, it is time to understand when each should be used during mixing.
As a rule of thumb, audio compressors are used on individual instruments and busses.
Your decision to use compression also largely depends on the style of music under consideration. For example, you might choose to use compression on all the tracks or just the main focus tracks. Considerably dynamic music will use little or no compression. However, compression will be needed for hard and abrasive music like a rock tune. Pop music that is dynamically consistent but not aggressive falls between the previous two.
You will hard-pressed to not hear some sort of compression on a lead vocal. Depending on the genre it can be light to extreme. Compression can be use to smooth out a vocal but also to squeeze life and attitude into it. On vocals compression is used as much as a creative tool as a corrective tool.
When we talk about an audio compressor vs limiter, it is important to note they both have a place on the mix buss. If your track has a wide dynamic range you will want to put some buss compression on it. In all honesty, most if not all professional mixes have some buss compression on them. The purpose of compressing an overall mix is to shrink it's dynamic range to help prepare it for mastering and also to help make it more smooth or punchy. NOTE: It is very important to not over-compress a mix because it will take the life out of it.
We could easily call this section, “Why do you need a limiter?” Some of the basic reasons you use a limiter are as follows:
Generally, your mix bus is the only place to use a limiter regularly. The idea here is to increase the overall volume of your mix without distorting your song.
Perhaps, you decide to send your mixes off to be mastered. Then, you won’t need to put a limiter on your mix. Limiting happens during the mastering stage. But if you decide to master the song yourself, you will need a limiter to do this successfully.
Your takes may be perfect when recording, but some parts may be peaked and sound distorted. You may decide to delete that take and repeat the process, but you may never get the best performance from your musicians or vocalist a second time. If you had used a limiter, the peaking and distortion could have been stopped from occurring.
Engineers use limiting to turn up the average volume of a track. For example, if you can raise the loud parts like the snare drums against a limiter’s threshold without making noticeable distortion, the entire song can be turned up another 5dB with make-up gain. This way, the limiter works hard to keep your track from clipping, just taming occasional peaks and not squashing the song. It is important to note in this audio compressor vs limiter comparison that a compressor can't do this task.
After reading all about the audio compressor vs limiter, you should now know what the primary difference between the two are. Regardless of which one you are working with, you should know exactly what you are applying the effect to, why, and how you should do it. If you don’t learn what you are doing and how it should be done, you’ll never get the results you desire in your mixes.
Over time, your experience will tell you what sounds right.
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