What Does the Ratio On Your Compressor Really Do?

audio-compressor-ratio

Compression is a complex subject. Everyone has an opinion on compression and everyone uses it differently. But what do some of the parameters on a standard audio compressor do? In this post, we’ll be looking at the ratio.

The ratio is where you determine how much compression you are going to apply to a signal that goes over your threshold. For every signal that goes over the threshold, it gets compressed according to a certain ratio.

For example: A compressor with a threshold at -10dB and a 3:1 ratio is a nice starting point for vocals. If you have a semi-constant level of the vocal at -1dB it will become compressed so that it only reaches -7dB.

Why?

Because after going over the threshold the vocal reaches its peak 9dB after -10dB, or at -1dB. We take those 9dB and divide them by three, since the ratio is at 3:1. Out of that we get 3dB which we add to the threshold at -10dB. A compression of 6dBs reaching its peak at -7dB. Let’s illustrate this with a simple formula:

In this formula you can see the basics of calculating the output of a compressor.

Audio Compression Formula

Just a simple formula

If we take the example above and apply it to this formula, we get this:

Audio Compressor Example

So you see, that if we have a higher ratio, we compress the signal more resulting in less signal at the output. Say we have an example of a loud kick drum that’s peaking at +4dB but we have a threshold at -20dB and a ratio of 8:1. That’s a lot of compression but serves to illustrate a point.

We have a dynamic range of 24 dBs, from -20dB to +4dB. We are compressing everything that goes over -20dB by a ratio of 8:1.

Let’s plug those numbers into the equation:

Kick Drum Compression

The highest peaks of the kick drum that are reaching +4dB before are now only reaching -17dB! That 24dB dynamic range we had from -20dB to +4dB has been reduced to 3dB. Talk about over-compression!

Even though these formulas don’t have much to do with how you compress – since it’s an artistic process that relies more on ears than mathematics – it does serve a purpose in explaining the underlying principle of the how a compressor works.

Compression doesn’t have to be hard. You just need to understand what you’re doing and how to use it. Learn how to use compression with my video: 10 Ways to Use Compression Effectively that comes included with EQ Strategies – The Ultimate Guide to EQ.

  • Such a concise article that explains the point so well!

    How the ratio works during compression is something I’ve been dying to know. All the numbers that get thrown around during production really get confusing, but this was so well explained, I’m excited to get back home and play around with the settings.

    Thanks so much.

    • Björgvin Benediktsson

      Thank you Mark. Compression is thrown around a lot and used differently by many, so I decided that instead of taking a typical compression tip I’d rather go into what the parameters really do.

      Thanks for the comment, glad I helped.

  • Can I just say what a relief to find someone who definitively knows what they’re talking about on the internet. You does know how to bring an issue to light and make it amazing. More people need to read this and understand this side of the story. I cant believe youre not more popular because you definitely have the gift.

  • I guess your RSS feed does no working because it just gives me a web page of strange characters, would the problem be on my end?

    • Björgvin Benediktsson

      I’m pretty sure it would be on your end. Have you tried it again using Google Reader?

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  • Great article. Waiting for more.

  • Interesting article, thanks!

  • Nice article, but I am unclear on one point. In your vocal example you say, ” If you have a semi-constant level of the vocal at -1dB… ”

    Since dB is a relative measurement, it must be -1dB relative to some absolute thing like 1mV or another signal level somewhere. Can you clarify what you meant in your example?

    • Björgvin Benediktsson

      Good point, in this case I’m meaning -1dB at the faders in your DAW. I’m basically saying if you have a vocal track that has a pretty consistent level, in dBV, dBm, dBSPL, dBFS or magic unicorns.

  • Ah, I see. The signal *is*, of course, relative to some absolute level, but it doesn’t actually matter in *this* particular equation because the answer is still a relative resultant amount of compression, i.e. a ratio relative to the original signal peak.

    • Björgvin Benediktsson

      Exactly, in this particular instance I’m just talking about level, not actual dBwhatever, I could have been clearer on that. Thanks for picking up on that.

  • Nice technical explanation which is a useful concept to have in mind. Though this sould always be considered in relief to what you are hearing.

  • Okechukwu mark o.

    For me, the formula makes it clearer cos i have a fair background in mathematics.tnx. Keep up the great job.

  • Santhosh

    Interesting article…..Plz tell how to use Attack and release?

  • Maxi
  • Djxplode

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                                                     – dj xplode

  • Ha! Thanks for this post! I’ve always had a very basic idea of what the ratio was actual doing but this spole clearly to me. Much appreciated. Cheers!

    Sean
    theglobalguitarist.com

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  • Sir,
    Please tell me the way or settings for indian Rhythm ( Instruments ( Tabls, Dhol, Dholak, etc) / Loops ( mixed)) to make my tracks sound’s good.

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  • How higher the ratio is, how harder you compress your stuff.
    So hard isn’t it is it?
    The only difficult thing is making your mix sound good. 🙂

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  • Andreia

    I wish I could understand this more, I hate math and formulas 🙁
    I don’t know how the 9 db came up. i’m a dummy. lol.

  • Jon

    Great article!

  • Dina Fie Lorentzen

    im not sure how the equation works. I have tried to calculates it myself, but I dont get the same numbers. How do write 8:1 into your calculator?