Someone is probably now thinking that the word «Correct» in audio is a delicate adjective. I agree, what is correct for one may be incorrect for another and in the art world there is no correction, there are works that excite and works that do not. And what we want is to excite, to impact the listener. That is in my opinion, the goal of all artistic expression.

Now, in our case as producers we have an artistic and a technical side, in which we work with tools such as microphones, mic preamps, audio interfaces, computers, compressors, equalizers, reverbs, etc … And if we want to achieve a great result we need to know those tools and know how to use them.
One of those tools is the compressor and we need to know its use because it is one of the basic tools in audio production.


Types of compressors

Fairchild "Tube Monster"
Fairchild «Tube Monster»


   It is perhaps the oldest type of compressor, they tend to have slow Attack and Relax times and impart a strong coloration to the sound that we normally associate with a vintage sound and «warm» or warm that the Anglo-Saxons say. One of the most famous is undoubtedly the Fairchild, the legendary compressor used by The Beatles among others. These monsters made up of 20 or more valves have their analogues in the plugin world thanks to modeling techniques that try to recreate (with quite success in some cases) their characteristics and qualities in the digital world. Some examples are Sonimus Tuco, Klanghelm MJUC or Ik Multimedia VC670, all excellent tools.
Warm Audio Opto 2a

Warm Audio Opto 2a



    They work thanks to a light emitter and a light sensitive cell. At a higher signal amplitude, the emitter emits more light and the photosensitive cell reduces the output level. One of the most valued qualities of optical compressors is their musicality. It is not an aggressive type of compressor but on the contrary, we could define its character as sweet and pleasant. They are normally used to compress vocals and bass. One of the most famous is the Urei la-2a which of course also has its namesakes in the plugin world such as Waves CLA 2A, Bx_opto the latter in my opinion is excellent and you can get it at a good bargain price taking advantage of the discounts that Plugin Alliance often offers.


Klark Teknik 1176 KT



FET or Field Effect Transistor compressors emulate the behavior of tube compressors but with transistors. They are compressors that are characterized above all by their speed in both attack and relaxation. They are widely used to obtain punch in the sound, so that the sound pumps aggressively, in fact many times they are used to achieve that pumping effect on the drums or to achieve more aggressive voices as in genres like Rap. Its reference in hardware is the Urei 1176 and there are many plugin clones like the Waves CLA76 or Ik Multimedia Black76 (excellent in my opinion) among others.


SSL XLogic G Series Compressor



They can be fast and add a touch of punch to the sound. Its greatest exponent is the SSL bus compressor. A type of compressor widely used in instrument buses and in the master bus to compact the mix (glue as the Anglo-Saxons say) and punch. Their plugin homonyms could be among others Cytomic the Glue, Waves SSL G Master Buss or one of my favorites the Plugin Alliance Vertigo VSC2.


Ok, but how do I adjust my compressor?


Here comes the important thing. In recent years I have heard sound technicians say that compressors «kill» music, that they destroy dynamics. That’s not true at all. It is true that misapplied compression can destroy the performance of the musician or destroy a mix, but it can also make sounds much more interesting or exciting, give punch to a drum bus, make it pump with the rhythm of the song, give aggressiveness to the instrument or support the interpretation of the artist.

When you have a well-recorded and well-executed track, for example, an acoustic guitar making rhythm by strumming the strings, in which you have a fairly constant dynamics and what you want is to give uniformity and consistency to the track, I recommend a ratio of 2: 1 , 3: 1 or 4: 1 depending on whether you want to give it a more aggressive character or not. A medium-fast attack time, between 10 and 20 ms, fast enough to give the compressor some punch and slow enough for transients to pass. If you want to give the track some aggressiveness, try a fast relaxation time, such as 20-30 ms and if you want the compression not to be noticeable, try a relaxation time of 100-130 ms, this way the compression will be more transparent. . Keep in mind that the faster the relaxation time, the more evident the compression becomes and the more distortion you introduce into the resulting sound. Adjusts the compressor threshold to compress about 3-4 db.


If, on the other hand, you have a track in which there is a lot of difference between the soft and the strong parts and you want to give consistency to the track, equalize more the dynamics between the soft and strong parts, you can do something similar to the previous paragraph but with a ratio of higher compression type 10: 1, 20: 1 or infinity: 1, which is a limiter. Adjust the attack and release times according to the criteria in the previous paragraph and in this case adjust the threshold so that the compressor only acts on the strongest signal peaks, in this way you will have a more balanced and uniform track.

Always remember to compensate the output level depending on the compression db you apply, if you compress 3 db recover them so that when you put the compressor on bypass the volume remains the same. It is important to maintain a good gain structure on all tracks in the mix. If you missed my previous article on Gain Staging read it here, it will help you get better mixes.

When you want to punch or pump a track, be it a clean electric guitar or a drum bus, I recommend that you use fast attack times of 5-10 ms and fast relaxation times also 20-40 ms, this way the compression is will make it more obvious and aggressive.

To see if the character that I am giving to the track with the compressor is adequate or not, what I do is adjust all the parameters and then lower the threshold by compressing a lot. So I listen if I like how the compressor pumps and what character it drives the track, I adjust to get the result I want by adjusting ratio, attack and relaxation and then I adjust the threshold to compress the db that the track needs.

Remember that most of the time it is much more effective to compress the signal at different points a little each time than to apply a very aggressive compressor to just one point of the signal.



If you want to give your drums an aggressive and punchy sound, apply a FET compressor to your drum bus with a fast attack and release compressing about 4-7 db.

With the voice you will get good results if you apply a not very fast attack time, from 50 ms and a fast relaxation time 30-40 ms. An optical compressor is more «invisible» and musical but if you want to give the voice aggressiveness you can use a FET type and play with faster attack times to make the voice cut in the mix.

This is a good starting point to understand a little more that powerful tool with which to sculpt sounds and achieve results that I am sure will surprise you.
If you have any questions, put them in the comments of the article and I will answer you as soon as possible.
Remember that I can also help you with your music either mixing and/or mastering.

Feel free to share this article if you think others might also be interested in this knowledge.

A greeting.

Alvaro Delgado.

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