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Sound Compression Guide – A Totally Different Way of Understanding Compression

A Totally Different Way of Understanding Compression

Written by ‘Dacalion’ from illmuzik

A new approach to learning sound compression. The target audience of this article was hiphop producers, but the information in it can apply to all genres.

Part 1:

In the past we’ve seen a lot of different articles and videos explaining what compression is and how it works. This will be different. My goal is to show you how to understand what basic compression does. The basic principles of compression is not that complicated and it’s one of the single most important tools in making a good track, but learning the principles is key in understanding what it is and how it works.
Let’s start with the definition of Dynamic Range Compression or DRC. DRC is a process that reduces the dynamic range of an audio signal, it simply narrows the difference between high and low audio levels or volumes. Most instruments can be very dynamic in volume and range from extremely loud to very soft. Imagine turning on your radio and it’s extremely loud, the first thing that you do is turn it down. Then some days you may turn it on and can barely hear it, the first thing you do is turn it up. In a sense, you’re acting as a compressor!
The principle idea is to find a comfortable volume at which to listen. Now some days you’ll want it louder than others but thats a different story. With compression, we’re looking at any given time, turning on your radio to a pleasant listening volume. In other words, you won’t have to change the volume. Now let’s look at the waveform of a song with high volumes and low volumes…

Audio Compression guide image 1 - uncompressed sound waves

As you can see, this song starts off very loud, then it gets very quiet, then loud again, and finally quiet again. Now imagine this song being played on your radio. When it first comes on, you’ll want to turn it down. Then roughly a quarter of the way into the song, you notice that you can barely hear it so you turn it back up. At the halfway point it gets loud again so you turn it back down. Then at 3/4ths, you can’t hear it. This would get very frustrating after a few songs. So the answer is compression.

      Let’s look at the same song after you have compressed it…

Sound Compression guide image 2 - compressed sound waves

The volumes of each section are closer to being the same and this means that once you’ve found your comfortable listening volume, you won’t have to re-adjust your radio volume anymore. This song will play at a level that won’t distract you and, you can actually enjoy listening to it.
So how did we get from the first picture to the second? This is the key to understanding compression; we squashed or lowered the loud volumes to match the lower volumes, then we increased the volume of the whole song back up. So for now, think of compression in two parts:

  • Lowering the loud parts to match better with the low parts.
  • Raising the overall volume back up

Keep in mind, this is only the beginning of what compression can do. The process can get much more complicated but going in with a basic understanding of compression will allow you to understand the other ways of using it better. In this example we looked at what it does for one song. Producers use compression to shape single hits. Mastering Engineers use compression to shape entire CD’s. I hope this helps you understand compression, now get out there and test it!

Part 2:

Audio compression guide image 3 - focusrite midnight compressor

This is part 2 of A Totally Different Way Of Understanding Compression. The goal here is to show you the fundamentals of what each knob on a standard compressor does and how it relates to applying it to your music. Compression is mainly for controlling uncompressed recordings. Most of the music that we use in our genre requires little to no compression at all. In hip hop, we do a lot of sampling and most, if not all, of our samples are already compressed. Even most of the drums in the form of kits are already compressed and pre-shaped. With this in mind, very little compression is needed.

Input Gain:

The Input Gain is like a volume knob before you start compressing. This is where you set your pre-compression volume level, if you have a weak signal you can turn it up, if you have a signal that’s a bit too loud you can turn it down.

Threshold:

The threshold increases compression as you turn the knob down, think of threshold as the level above which the compressor considers the signal too loud. In part 1 we discussed how compression squashes the loud signal in an attempt to make the volume more even with the lower signals. The threshold knob does that task. High setting means little to no compression, low setting means more compression.

Dynamic range compression guide image 4 - uncompressed track with indicators where the sound should be reduced
Ratio:
Your Ratio controls how much effort is used to correct overshoots. An Overshoot is the signal above your threshold. With a low ratio setting of 4:1, the overshoots will be gently pushed back towards the threshold whereas higher settings like a 11:1 ratio will be more like brutally forcing the overshoots back where they belong. Even higher ratios can be used to not allow them to cross at all. The thing to remember is that compression can re-shape a signal or sound, you do not want to over-transform that original sound, you just want to control it. You have to experiment and use your ears to obtain the outcome that you are looking for.

Attack and Release:

Attack:

This is where most people get confused or frustrated, but it’s not hard to understand their purposes. Attack specifies how fast the compressor reacts in reducing gain. In other words, if you got in your car and turned your stereo on while it was on blast from the night before you would move at the speed of light to turn it down, where as if it were at a regular ‘loud’ setting you wouldn’t have to react so fast. Same principle using your attack settings, it will control how fast the compressor reacts.

Release:

Your Release controls how fast the gain reduction resets. Both of these controls are usually in milliseconds. Don’t get hung up on the numbers. The absolute best way to tackle these settings is to experiment with a one shot hit like a snare that has a loud initial impact and a short sustain, also experiment with something that has a soft impact but a long sustain like a guitar strum. You’ll easily see how changing the values will effect the sound of both and then you’ll understand how it applies to your music.

Makeup Gain or Output:
Very simple, this is where you make up for any gain reduction during compression. Remember we squashed our loud parts which dropped the overall volume of the track, now we want to increase the ‘more balanced’ waveform back up to its original volume.

compression guide image 5 - compressed sound with indicators showing what make up gain does
In Conclusion:
I can’t express how important it is to test using compression. It will definitely take your game up a notch or two. Just remember, compression should be used mildly for what we do unless you’re doing live recordings. It’s extremely important on vocals when the emcee varies in their volume. Also remember that we’re talking about Dynamic Range Compression in general. There are many other types of compression that do different tasks. Continue testing and good luck!

Infamouz Input:

I found this on illmuzik and it was too good of an article to not ask for permission to use it on the site. Big shoutout to Dacalion for writing it. If you haven’t checked out illmuzik yet make sure you do!

For More Information on Sound Compression Visit The Follow Sites:

Audio Compression on Record and Produce Forum | Dynamic Range Compression

January 18, 2013 Mixing and Effects No Comments

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