Audio Compressor and Limiting Tutorial – What Is Compression In Music Production?

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What Is Compression In Music ProductionWelcome to our new audio compressor tutorial that will show you how you can compress correctly including compression in series, limiting and coloring the sound using analog style compressors.

An Audio Compressor Is Not So Complicated As It Seems

Audio Compression create a sense of “fear” to people that just start their music production journey. The most familiar questions that people ask are “what is compression, why do we need it and when should we use it”.

Truth is that if someone explains it with simple words then everybody will understand its use. And if you understand clearly what compression does then it’s really easy to use it.

What Compression Is… In Simple Words

Think of a singer in front of his mic singing.

It’s impossible for him to sing at a constant level during the whole song, there will be times that he will sing a bit louder and times that will go closer or a bit further from the mic, which is perfectly logical to happen cause no human can sing at the same exact level during the song.

It’s also almost the same thing for everything. For example:

The bass player will hit the bass string a bit stronger and the drummer will hit the kick/snare/cymbal a bit stronger comparing to the other hit. This makes perfect sense cause they are humans.

Think of a Rock song – or Trance or Rap – imagine this song playing and its volume to constantly change or the singer’s voice to be heard sometimes louder and some times quieter in the same song

Wouldn’t this be terrible? For this exact reason people have created the compressors!

To reduce volume if it exceeds a particular level of your choice, even if the singer sings louder at some point of the song, or the bassist hits the string noticeably louder or anything…

You can think of compression as a man standing in front of the volume faders/console and reducing the volume only to the louder parts of a song so that we can have a more “constant” volume throughout the whole song.

That’s the main role of a compressor… We can also say that:

Compression is the procedure that we compress the audio signal in order to reduce the louder song parts and “match” them with the softer parts and achieve a more “constant” volume throughout the whole song.

Knobs, Controls and Settings

Like we said before, when the volume surpasses a particular volume level then the compressor starts compressing/reducing it in order to match it with the volume of the other parts.

But which is this particular volume level we’re talking about and how do you configure it?

Well, you are the one that controls how much decibels the compressor will reduce, how fast it should cut them, when the compressor should start working… Everything can be configured by you and we’ll see how right now:

compressor-fabfilter

  • Threshold – How loud the signal should be in order for the compressor to start working. If the volume doesn’t touch or surpass the Threshold then we will have no compression at all.
  • Ratio – How much compression we use. For example, if the Compression Ratio is set at 6:1, then from the 60db that surpass the Threshold we keep only the 10db. If we set the ratio at 2:1 we’ll only keep 10db out of the 20db that will surpass the threshold and so on…
  • Attack – How fast – in milliseconds – the compressor “catches the signal” that surpasses the Threshold.
    30ms Attack means that it will wait 30 Milliseconds and then it will “catch” the signal and start compressing it.
  • Release – How fast – in milliseconds – the compressor will release the signal after it compresses it and drop it back out of the Threshold. Most of the times the Auto function works properly.
  • Knee – It’s similar to Attack but not so important that’s why you may not see it on every compressor. Hard Knee means that our compressor will catch the signal aggressively and Soft Knee means that the compressor will catch it smoother and get “angrier” the further-er it surpasses the Threshold.
  • Make-Up Gain – When we use compression we reduce the signal so we need to get it back to where it was. If we compress 2db then we need to add 2db back.
  • Gain Reduction (GR) – This is how much db we reduce – Our main aim. Most of the times I find myself using up to -6db. Use more of this and the audio will sound “squashed” and definitely edited and we don’t want the listener to think “something weird is going on here”. If the listener that has no knowledge about recording and music production thinks that something is going on then we definitely didn’t do a good job.
  • Output – You can increase or reduce the final volume. But since the compressor’s job is not to increase the overall volume it’s pretty useless for me. We have Volume Maximizers for that (which we will talk about in a different article).

Knee is not so important so you may not find it on every compressor.

Spend time practicing using the Threshold, Ratio and the Attack and the rest settings will be easier to configure.

How Do We Use A Compressor

1. No matter if you use an analog compressor or a VST compressor the setup is almost the same. Open your favorite compressor as an insert on the track that needs a compressor (mono, stereo, bus, group)

2. Adjust the Threshold so that the Peaks (sudden volume changes or “spikes” that need to be reduced) will surpass the Threshold narrowly. Unless you want to compress instruments that there’s no problem if the compressor compresses continuously, for example the bass guitar that can accept a sh*tload of compression cause it needs to be stable throughout the song.

3. Make the Ratio and the Threshold work together. Ratio is purely configured depending on the sound source but here’s some nice starting points:

Bass – 4:1 to 8:1, Drums Group:  2:1, Vocals: 2:1 έως 4;1, Electric Guitars: 2:1 έως 6:1

Please treat the above information as starting points don’t follow them blindly, take the initiative to experiment cause each sound is different.

4. Adjust the Attack and Release buttons, following the guidelines that I gave you above.

If your compressor has an Auto function on your Release button, then use it cause 80% of the situations it’s gonna work right.

Too fast Attack will reduce the dynamics and kill the “feeling” of the song.

Let me explain…

If in a specific part of a song the drummer must hit the snare harder only at this spot – cause the song demands it (it sounds better and make the listener go “whoa!”) – then cutting this “attack” of the snare with too much fast compressor attack is not the best thing you can do.

But if you mix sounds with crazy peaks (sudden volume changes of the volume level) then you can easily chop off these peaks with really fast attack, even if it’s only 1ms or 3ms.

I usually use fast attack on Mono Tracks with Instruments/Vocals with sudden peaks and slow attack on Group Tracks, where the compressor here plays the part of  “ I glue instruments together” rathen than “I work for a more stable volume between the louder and the quieter parts”.

So as I always say… Keep your ears open and hear the changes that you make!

5. Use the Make-Up Gain to get the volume level back to where it was. The compressor’s role is not to give volume.

But it is to give back the volume that the compressor reduced so that when we bypass the signal we hear the before and after sound with the same volume level.

If you have for example 6db Gain Reduction then you need to add 6db Make-Up Gain.

6. You’re ready! Take a break and listen again. Make sure the volume levels between the sound with and without the compression to be the same. Why?

You may have compressed the signal in an awful way but your ears would think that you did a nice job because of the louder volume. Our ears always think that louder is better.

So for this reason, keep the volume the same NO MATTER IF THE COMPRESSOR IS ENABLED OR DISABLED.

THAT’S VALID FOR EVERY TOOL NOT ONLY FOR COMPRESSION.

Limiters VS Compressors

fabfilter-limiter-mixing-mastering

I’ll create a different tutorial for Limiters but I would like to explain to you their basic difference with the Compressors.

When the Ratio of the Compressor exceeds 10:1 (meaning that it aggressively “chops off” the sound and doesn’t “forgive” the decibels that surpass the Threshold) then we can say that the Compressor plays the role of a Limiter.

A Limiter is nothing more of a Compressor with a really strict Compression Ratio. Whatever audio signal surpassing the Threshold it gets chopped off aggressively so we must keep an eye on our Gain Reduction.

There’s no written rule but you should aim not to exceed 3db Gain Reduction on a Limiter. The Limiter’s role is to cut the sudden peaks and not to apply a smooth compression.

Limiters With A… Maximizer Role

Many Limiters, like Fabfilter L in the above photo, can also play the role of a Maximizer. They are hybrids.

Normal Limiters have a Threshold. You compress the signal to create stable dynamics and then you can dial back the volume using the Make Up Gain.

The hybrids though work the other way around:

The threshold is locked at 0db. You use the gain knob and give volume to the signal. When you reach and exceed the threshold then you apply limiting.

This way… you also make the volume louder plus you apply limiting to the peaks. 2 birds with 1 stone!

These kind of Limiters/Maximizers hybrids are perfect during mastering. You increase the final volume of the whole song and also cut the remaining peaks that would may bother the listener.

That doesn’t mean that we can’t use Limiters on Mono Tracks though.

If you have a Mono Track with a vocal/instrument that was recorded so bad and no compressor can fix the peaks then you can easily choose a limiter to do the job!

A Second and… “Alternative” Use Of Compression

As we said, the main purpose of a compressor is to match the higher volume levels with the lower ones.

But music and sound is art. So if we can create a new sound or modify the existing sound using the compressor… Why not do it?

Music producers like to experiment and use lots of Gain Reduction with ultra high ratio (sometimes up to 30:1) just so that they can “squash” the signal and push the compressors to the maximum.

This “overuse” of the compressor forces it to add a characteristic sound to the audio signal. While the “rules” say do not over-compress, sometimes by experimenting you can achieve some wonderful sounds.

What I like to do when I want to experiment – but also want to make sure that I don’t destroy the sound by over compressing it – is to duplicate a track of mine and use all the crazy effects that I want on the 2nd track.

Then I blend the 2 signals together by adjusting the volume faders.

The Reason There Are Many Compressors

If you’ve ever wondered why there are many compressors out there since they do the same job then this is the answer: Some compressors have their own unique sound.

Also, some analog compressors don’t have every single knob that I showed you above. Companies create them their own way, with only the most important knobs (Ratio, Threshold, Release, Attack).

That’s the reason you come across thousands of topics on the internet “discussing” which compressor is better for vocals or guitars or bass…

From time to time you will end up creating your own favorite compressor list, no matter if it’s analog or a digital VST.

Conclusion

I hope this tutorial to have answered all your questions about the basics of a compressor! If not please don’t hesitate to leave a comment, positive or negative.

I don’t know the exact money a teacher or a music school would ask you to give you this kind of information but I hope that this article will make you start practicing and improving yourself.

If you’d like to thank me consider sharing this post below or/and leave a comment, I am happy to see that this tutorial helps people, it motivates me creating more material for you guys.

Happy mixing and happy practicing! icon wink Compression και Limiting   Τα βασικά, απλά και κατανοητά

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21 Responses

  1. vizionheiry

    February 16, 2015 5:46 am

    Thank you. I’ve been reading that compression is the second step in mixing after balancing the faders but I didn’t know its function. Now i understand its purpose and how to use it.

    Reply
  2. LUIS

    February 18, 2015 12:51 pm

    Thanks for this very helpful information, I really learned allot; but i have some questions.

    I just started making beats recently and i’m still fighting to improve my mixing. I normally set a compressor on master channel to compress whole instruments at once in the end of the mixing.
    Therefore, i want to know if it is advisable or not?
    The other question is , do i have to compress each of the instruments in a beat? cause i actually don’t do it.

    Thanks, and i hope hearing from you soon

    Reply
    • Paschalis

      February 21, 2015 6:26 pm

      Sure. I do the same too. I use an SSL type compressor with gentle settings (2 ratio , slow attack, auto release) and I compress around 2db. I mix drums and bass and then apply a compressor on the master channel just as you do. It’s perfectly fine, but don’t overdo the plugins on the master channel during mixing , a compressor to glue things up is fine though 🙂

      Reply
  3. LUIS

    February 22, 2015 3:44 am

    Thanks for the reply; Paschalis.
    I actually use Fl studio and i use fruity compressor rather then fruity multiband compressor. Its the one that i understand better and I think it does the job pretty well. But i sincerely dont know wherther im using the right one. Can anyone tell me?

    Reply
    • Paschalis

      February 23, 2015 3:03 pm

      A multi-band compressor (as the name implies) works to a specific band of frequencies, while a normal compressor compresses the whole signal (1 band of frequencies). You only need a multi band compressor if you want to “enter” a specific range of frequencies and you won’t need to do this much. A compressor is fine unless you want to do something particular that can’t be completed otherwise. No worries friend!

      Reply
  4. Fran

    August 29, 2015 2:15 am

    This website is really amazing !
    This article was really helpful to me , because everything was so clear .
    The only thing I cant get from compressor is that what is the difference between Ratio and GR , If ratio decreases the sound so what exactly GR do , and how these two elements work together ?!

    Reply
  5. Steve

    March 11, 2016 11:03 am

    What do you do when the incoming signal is a lot hotter than you want (i.e., kick and snare)? I try to gain stage at around -18dB. My signal may come in around -3dB, which is too hot. I usually put EQ as the first insert to my track and then go to compression. If I reduce the output on my EQ (say, by -10dB to lower the signal volume) and then send that to compression, I seem to lose the punch I’m looking for. Are the dynamics still there, but I can’t hear them (everything sounds better louder!)? Will these dynamics (and punch) be there when I’m mastering everything? What do you recommend?

    Reply
  6. Austin

    September 26, 2016 6:37 pm

    I so much thank God that i came across this wounderful site Thanks for this very helpful information, I really learned allot; but i have some questions I just started making beats recently and i’m still fighting to improve my mixing. I normally set a compressor on master channel to compress whole instruments at once in the end of the mixing.
    Therefore, i want to know if it is advisable or not?
    The other question is , do i have to compress each of the instruments in a beat? cause i actually don’t do it.again is it good to add a compressor on a mono track in stayed of Putin it in a group stereo bus pls tell me which one is addviceble to use.

    Thanks, and i hope hearing from you soon

    Reply
    • Paschalis

      October 5, 2016 10:42 pm

      It depends on your genre. If it sounds nice with much compression, then compress it a lot 🙂 As a metal lover I compress each track, then each group and in the end the master channel as well. Some people think it’s an overkill but in metal and modern music it’s not. The trick is to use compression in series and cut small amounts GR instead of slamming a compressor to death. Example: 3 compressors of -4GR rather than 1 of -12GR. You get the idea 🙂

      Reply

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