Click here<\/a> if you want to know what dynamic range is. There are lots of reasons why someone would want to reduce the dynamic range–I’ll give a few reasons why you’d reach for a compressor in music. <\/p>\n\n\n\nA Lower Dynamic Range Sounds Louder<\/h3>\n\n\n\n Louder music sounds better to us.<\/strong> Part of what sounds “loud” to our ears isn’t necessarily the amplitude, although that certainly is a factor, but rather the average amplitude over time. In other words, if you hear a loud blip that lasts a quarter of a second, or if you hear the same loud blip that lasts 5 seconds–the 5-second blip will sound MUCH louder even if they are the same amplitude. <\/p>\n\n\n\nTherefore, if your piece has really high amplitude mixed with lower amplitude, your brain perceives the song overall as being quieter, and therefore not as interesting.<\/p>\n\n\n\n
If, on the other hand, you have a lower dynamic range and you boost the output gain, your brain hears a more consistent volume. Even if your dB meter is registering lower after compression, your brain can perceive it as being louder.<\/strong><\/p>\n\n\n\nEven after that, producers will often use make-up <\/strong>gain to boost the entire signal, further increasing loudness.<\/p>\n\n\n\nLonger Sustain<\/h3>\n\n\n\n Sustain is what gives instruments their depth. If there is no depth to our voices it sounds like we’re talking into a hat. <\/p>\n\n\n\n
One simple way to increase the sustain of an instrument is simply to compress it and adjust the threshold so that the quieter sustain can be boosted and thus be more perceptible.<\/strong><\/p>\n\n\n\nHere’s an example of a compressed piano where I tried not to change the final peak volume, but you can hear a lot more sustain:<\/p>\n\n\n\n<\/audio>Piano Sustain Before Compression<\/figcaption><\/figure>\n\n\n\n<\/audio>Piano Sustain After Compression<\/figcaption><\/figure>\n\n\n\n
<\/picture>The amplitude of the piano sound signal is about the same, but notice the top is flatter, and notice how the sustain at the bottom of the curve is higher<\/figcaption><\/figure><\/div>\n\n\nPunchier Sound (especially for drums)<\/h3>\n\n\n\n Now, this is where music producers use those terms that don’t seem to make any sense–until you become a producer and you say those drums aren’t “punchy” enough because it’s the only way you know how to describe it. <\/p>\n\n\n\n
Producers often use compression <\/strong>to make drums sound more punchy<\/strong>. More “in-your-face”. It’s because drums that have a high dynamic range sound weaker and less present in the mix. <\/p>\n\n\n\nI’ll give you an exaggerated example with a bass drum. <\/p>\n\n\n\n<\/audio>Bass Drum Before Compression<\/figcaption><\/figure>\n\n\n\n<\/audio>Bass Drum After Compression<\/figcaption><\/figure>\n\n\n\nIf you’re like me, you may be undecided about which one is “better”. However, for the sake of learning, if you listen closely you notice that in the “before compression example,” the bass drum signal is very present at the very beginning (called the transient), and dies off very quickly. The compressed signal has a lower dynamic range and doesn’t have this drastic volume change. <\/p>\n\n\n
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<\/picture>Bass Drum, Before compression and After Compression. The Compressed signal has purple which represents the compression, so relatively the sharp punch at the beginning is less drastic, now<\/figcaption><\/figure><\/div>\n\n\nThis depends on your own tastes–but producers often use compression to make their drums sound more punchy (and that is the term you’ll hear). <\/p>\n\n\n\n
Getting Rid of Transients (Or at least toning down the transients)<\/h3>\n\n\n\n Transients are those “spikes” in your signal that represent brief high-volume parts of your audio. <\/p>\n\n\n\n
Sometimes these transients are desirable<\/strong>. Often instruments, like drums, have a sharp transient at the beginning of the sound and it’s part of the sound. Even instruments like trumpets and guitars have transients at the beginning of their sound.<\/p>\n\n\n\nSometimes transients are not desirable.<\/strong> Or you may want to tone down the transients so they are not so obvious.<\/p>\n\n\n\nCompressing an audio signal will shrink the difference between the transients and the rest of the waveform. You can see an example of this in the Bass Drum Compression example (just before this description)<\/p>\n\n\n\n
Removing Clipping (Limiting)<\/h3>\n\n\n\n Lastly, compression is used during “Limiting<\/strong>“. Limiting is simply using a compressor as a way to prevent clipping.<\/p>\n\n\n\nClipping is when your sound signal goes above 0db. <\/strong>This is beyond the reproduction volume of digital sound, and if you clip, you’re going to hear pops that are really terrible sounding. <\/p>\n\n\n\nLimiting will compress the sound so that it won’t peak above 0db. If you limit at too low a threshold, or if your volume is too high, your sound quality will suffer<\/strong>. <\/p>\n\n\n\nHere’s an example of very obvious limiting. It kind of looks like a flat-top haircut. <\/p>\n\n\n\n <\/picture><\/figure>\n\n\n\nI want you to hear what this sounds like–this limiter is WAY too aggressive, and so the sound and timbre of the instruments are affected. <\/p>\n\n\n\n<\/audio>Example of Sound Before Limiting<\/figcaption><\/figure>\n\n\n\n<\/audio>Example of Sound After Limiting<\/figcaption><\/figure>\n\n\n\nSo that’s not an example of WHAT to do, but rather in why it’s used. Often all of these tools are used in ways that are extremely subtle and difficult to tell you side by side which is better.<\/p>\n\n\n\n
What Else Can A Compressor Be Used For?<\/h2>\n\n\n\n Audio compressors are not just used in music, as you can imagine, I’ll share a couple of examples of how they’re used:<\/p>\n\n\n\n
Recording an Interview\/Podcast\/Audiobook<\/h3>\n\n\n\n Recording audio is difficult. The reason why it’s difficult is that you have to tweak the input volume just right or you get peaking. Peaking can distort and ruin your audio. <\/strong>We’ve all heard it and it’s a quick way for us to want to stop listening.<\/p>\n\n\n\nFurthermore, a speaker’s voice volume can change rapidly. Your interviewee can get particularly passionate about a certain topic and their voice can raise in volume. You as the interviewer have to adjust the volume just so it’s not too quiet and not too loud. <\/p>\n\n\n\n
Compressing your audio is one way that makes this easier. Using compression, you can make the too-loud parts quieter and bump up the volume of too-quiet parts, making a more consistent waveform. <\/p>\n\n\n\n
Compression can be used much more aggressively for an interview rather than music (for voices) because the importance is more on whether you can hear and understand the speaker and not so much whether their voice sounds a bit weird from the compression.<\/p>\n\n\n\n
Making Your Own Videos<\/h3>\n\n\n\n I’ll tell you if you’re not compressing your audio in some way for your videos, then you’re making life harder for everyone. Compressing your audio in your video will help your sound be more level and consistent. <\/strong><\/p>\n\n\n\nMaking a video is hard and it’s very difficult for everything in your video to be the same volume. Sometimes you move away from your mic, or sometimes you have something in your video that makes sound and it can be much louder or quieter than everything else. Applying a limiter to your entire video’s audio can do the trick to make everything much more even in your audio. <\/strong><\/p>\n\n\n\nHow To Use a Compressor In a DAW? <\/h2>\n\n\n\n This is the nitty gritty–these instructions are actually how to use a compressor in a DAW. You’ll see how each of these affects the waveform as obviously as possible. You’ll be able to look at this section and understand how to use a compressor. <\/p>\n\n\n\n
I’ll be using the limiter plugin from FL Studio because its visuals are so brilliant. <\/p>\n\n\n\n
What Is Output (Make-Up) Gain On A Compressor?<\/h3>\n\n\n\n\nGain that is applied to the sound signal after <\/strong>processing<\/p>\n<\/blockquote>\n\n\n\nSo changing the output gain of a signal during compression is completely optional. As far as the compressor technology is concerned, its job is finished! <\/strong>The compressor has compressed the signal. <\/p>\n\n\n\nHowever, a tool that’s often used is called output gain (or sometimes make-up gain). Essentially the producer may want to boost the amplitude of the signal after compressing it so that the entire compressed signal is louder. <\/p>\n\n\n\n
A picture will help you see this:<\/p>\n\n\n\n <\/picture>Output Gain Before and After<\/figcaption><\/figure>\n\n\n\nAs you can see the white output peaks are much bigger. It essentially looks like a taller version of the “Before” waveform. <\/p>\n\n\n\n
But that’s important to understand, output gain doesn’t change the waveform like the other controls,<\/strong> it’s simply boosting the entire signal (irrespective of the threshold). <\/p>\n\n\n\nThe difference between output gain and input gain is that output gain is AFTER the compression while input gain is BEFORE the compression.<\/strong><\/p>\n\n\n\nWhat Is the Knee In A Compressor?<\/h3>\n\n\n\n\nSlope (smoothness) between states like passive, attack, release, etc.<\/p>\n<\/blockquote>\n\n\n\n
Knee is probably the most difficult thing to explain as far as how a compressor works, but it’s basically how quick the compressor transitions between full compression and non-compression and back again.<\/p>\n\n\n\n <\/picture><\/figure>\n\n\n\nA “soft knee”<\/strong> means the transition between no-compression and full-compression will be more gentle and smooth (it will also take slightly longer).<\/p>\n\n\n\nA “hard knee”<\/strong> means the transition between no-compression and full-compression will be more abrupt. <\/p>\n\n\n\nIt’s difficult to hear the difference, I’ll let you listen and see if you can tell:<\/strong><\/p>\n\n\n\n<\/audio>Soft Knee<\/figcaption><\/figure>\n\n\n\n<\/audio>Hard Knee<\/figcaption><\/figure>\n\n\n\nTo tell you the truth I think I can only tell a difference in this particular sample because I know there is a difference, I definitely would not be able to tell you which is which without knowing ahead of time.<\/p>\n\n\n\n
What Is the Threshold In Compression? (Gain Reduction)<\/h3>\n\n\n\n\nThe dB level above which the compressor applies the volume ratio to the signal<\/p>\n<\/blockquote>\n\n\n\n
In normal person speak, this is the dB level in which the compressor kicks in. <\/p>\n\n\n\n
Amplitude is expressed in -dBs in music creation. -60dB is a barely audible amplitude, while 0db is the “max” volume. <\/p>\n\n\n\n
It will help if we can see what we’re talking about here:<\/p>\n\n\n\n <\/picture>How To Understand Threshold in Compression<\/figcaption><\/figure>\n\n\n\nThe blue horizontal line in these visuals is the threshold. The lower the threshold, the more compression occurs. <\/strong>Notice how at -0dB the threshold dial is all the way up. This is as high as this compressor is set to go. Notice how at -24dB that the threshold is almost all the way down, this is a very aggressive compressor setting.<\/p>\n\n\n\nJust for fun, you can listen to the compression at 0db (in this case, no compression) vs. -24db compression with an 8:1 ratio:<\/p>\n\n\n\n<\/audio>0db threshold (no compression)<\/figcaption><\/figure>\n\n\n\n<\/audio>-24db threshold (super duper over compressed)<\/figcaption><\/figure>\n\n\n\nNotice how terrible it sounds. Well, that’s a good example of over-compression, it demonstrates the principle of the threshold, though.<\/p>\n\n\n\n
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What Is Ratio In Compression?<\/h3>\n\n\n\n\nHow much the volume is lowered for the amplitude above the threshold. A 4:1 ratio means for every dB of input, you get 1dB of output<\/p>\n<\/blockquote>\n\n\n\n
Ratio in a DAW compressor is simply how much volume to lower the sound that is over the threshold. The higher the ratio, the more aggressive the compressor. <\/strong><\/p>\n\n\n\n4:1 is kind of at the top end of your day-to-day audio compression. Although you can see really aggressive 10:1 compression (especially with drums), that is getting into the realm of limiting<\/strong>, where you are not really trying to shape the volume curve as much as you’re trying to prevent any sound above a certain threshold. <\/p>\n\n\n\nTry and stick between 2:1 and 4:1 in your compression<\/strong>. Go above intentionally.<\/p>\n\n\n\nLet’s take a look to see what ratio looks like:<\/p>\n\n\n\n <\/picture>How to Understand Ratio in Compression<\/figcaption><\/figure>\n\n\n\nRatio is a bit easier to see and understand in compression. It’s the size of the purple peaks in this diagram. The longer the purple (the more compression), the higher the ratio. <\/strong><\/p>\n\n\n\nLet’s hear the difference between 1:1 ratio (no compression), and 4:1 ratio (mid-level aggressive compression):<\/p>\n\n\n\n<\/audio>1:1 ratio (no compression)<\/figcaption><\/figure>\n\n\n\n<\/audio>4:1 ratio (mid-high compression)<\/figcaption><\/figure>\n\n\n\nAgain, even here the difference is subtle if you’re not used to it, but I’m able to notice a big difference in the “thumpiness” of the bass drum. Also, the hi-hat doesn’t cut through as much as the high transients are being aggressively brought down. <\/p>\n\n\n\n
What Is Attack In A Compressor?<\/h3>\n\n\n\n\nHow long the compressor waits to kick in after the amplitude crosses above the threshold.<\/p>\n<\/blockquote>\n\n\n\n
Attack is usually expressed in milliseconds (ms<\/strong>), or 1 thousandth of a second.<\/p>\n\n\n\nLet’s see if a diagram can help us understand attack:<\/p>\n\n\n\n <\/picture>How to Understand Attack in Compression<\/figcaption><\/figure>\n\n\n\nThis one is a bit hard to see, but I’ve drawn some annotations to make it more clear. The PURPLE represents compression. The WHITE shows what final output signal is after compression<\/strong>. <\/p>\n\n\n\nThe lower the attack, the quicker the compressor kicks in <\/strong>and so more of the signal gets compressed, therefore the taller the purple line (the orange line that I’ve drawn on these shows the height of the purple line).<\/p>\n\n\n\nThus,<\/strong> with 20ms <\/strong>attack, the compressor almost misses the waveform altogether before it goes underneath the threshold. While with 10ms attack, more of the transient is getting through. You’ll notice with 0ms attack the signal stops right at the threshold. <\/p>\n\n\n\nNext, let’s do an audio compressor example of 0ms attack and 10ms attack compression on a bass drum. The difference is very<\/strong> subtle, but if you listen closely you can hear a difference in the transient (the sound at the beginning of the bass drum)<\/p>\n\n\n\n<\/audio>Compressor activated at 0ms Attack<\/figcaption><\/figure>\n\n\n\n<\/audio>Compressor activated at 10ms Attack<\/figcaption><\/figure>\n\n\n\nWhat Is Release In A Compressor?<\/h3>\n\n\n\n\nAfter the compressor is activated, release is how long the compressor waits to turn off after the amplitude crosses below the threshold <\/p>\n<\/blockquote>\n\n\n\n
Release is usually expressed in milliseconds (ms<\/strong>), or 1 thousandth of a second.<\/p>\n\n\n\nLet’s take a look at a diagram that will help us understand release.<\/p>\n\n\n
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<\/picture>How to understand Release in compression<\/figcaption><\/figure><\/div>\n\n\nLook at the picture example above to see how Release works in a compressor. I have 4 different release values (in ms): 2000, 1000, 500, and 250. These are all very high for a compressor. If you notice, though, the blue sloping line represents how long the compressor is ACTIVE<\/strong>. The compressor becomes ACTIVE<\/strong> once the sound goes OVER<\/strong> the THRESHOLD<\/strong> (the horizontal blue line in the picture). <\/p>\n\n\n\n