some opening words
there are no stickies about, and quite frankly i can't recall ever seeing any threads about compression in this forum. i thought i'd write up a quick starter's guide to compression. i put "dynamics processing" in the title but we're gonna focus on just compression, which falls in as a subsidiary of the "dynamic processing" subject. the art of compression is the most misunderstood, underrated, most neglected step of the mixing and mastering process, in the history of unprofessional music-making. for the most part, the reason why "underground" producers tend to "forget" to use compression is that they simply don't know what a compressor does. i'm gonna start off by explaining some of the terms you'll encounter if you decide to give it a shot. i have readied two images that i will use to demonstrate, both show a wave and how a compressor affects it. if you don't know what a wave is, you have no business reading this guide in the first place.
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clipping
when a sound signal is amplified to exceed 0dB, your signal is clipped off, which results in a distorted wave. a good way to see what a majorly distorted digital wave sounds like is loading an audio file up in a wave editor like cool edit, increase the volume by 5-10dB and then decrease it by the same amount and play it.
threshold
the threshold determines how loud a signal must be for the compressor to compress it. if you set the threshold level on your compressor to -10dB, the compressor will apply compression to any and every sound in your wave that exceeds the threshold. that is, any sound louder than -10dB is compressed. digital audio levels are often misunderstood. when you work with digital audio, 0dB is the absolute volume, nothing can exceed 0dB. it's like 100%.
ratio
the ratio determines how much compression should be applied to any signal that exceeds the threshold level. a 2:1 ratio means the output signal is reduced to half the input signal.
attack/release
attack and release (or decay) works just like the envelope controls on a synth/sampler. it determines how the compressor will act when a signal exceeds the threshold you've set. a slow attack will allow for some of the signal that exceeds the threshold level to pass through uncompressed before the compressor kicks in. a slow release means the compressor will keep compressing for a while (normally about 0-50ms) after the offending signal has been compressed.
gain
basically a volume controller. the input gain lets you boost the signal before it's compressed. practically, that means your wave will undergo a harder compression as boosting the volume sub-sequently pushes a larger part of the wave above the threshold. the output gain lets you boost the volume of the compressed signal.
soft/hard knee
compression will alter the sound of a wave, and thus also the way it looks in a wave editor. if you look at image number two above, you'll see that my kickdrum wave has a very soft, round shape. basically, this attribute determines how "soft" your compressed signal is gonna sound/look. it actually makes a big difference.
limiter/gate
this has got nothing to do with this guide, but since i'm already covering compression... a compressor falls in under "dynamic processors." why? because it alters the dynamic range of your mix. a limiter and a noise gate are two other devices that also fall in under "dynamic processors." a noise gate is like a reversed compressor. you set a threshold level, but instead of compressing everything that exceeds the threshold, a noise gate eliminates anything that's below the threshold. if you're recording live music with a band playing all at the same time for instance, letting the vocal mic go through a noise gate will eliminate all the background noises from the other instruments that are being played as the vocalist sings. a limiter uses mild distortion to prevent clipping. once a signal exceeds 0dB, the signal is distorted. the limiter uses a gentlier kind of distortion to cut the signal before it starts to clip. in most cases, the distortion caused by the limiter is barely noticable. this, of course, depends on how drastic your settings are. another dynamic processor is a finalizer. finalizers are kind of like a mastering suite preset. it adds a little reverb, and boosts the highs and lows a little. technically useless. most professionals frown upon them even. i don't think i've ever added reverb to an entire track in my life.
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rizzle speaks on compression
so what is compression? when you compress, say, a mix, you lower the volume of sounds that stick out of your mix like a sore thumb, so that you can bring up the overall volume of your mix to make it sound more like a professional commercial album. boosting an uncompressed signal would make parts of the wave (most noticably the kick drum and snare) exceed 0dB, and thus distort the entire wave. additionally, compression adds thump. i don't think i've ever made a set of drums without adding compression to the snare and kick. a long attack which lets the climax of your kick and snare go through uncompressed makes for a very thumpy, snappy sound. i vary my release, but i always use a long attack on my drums, regardless.
compression is not only recommended, but neccesary, if you want the bottom end of your mix to sound good. you may have noticed that whenever you make a beat, some notes in your bassline stick out because they are way louder than the rest. you may have noticed that some times when you're playing your beat in your car or on your computer's speaker setup, that third note on your triangular bass makes your subwoofer go BOOOOOOM!!!!! (just a funny observation; i love the wu-tang clan but a lot of their old tracks have basslines like this. it ruins the track when you bump it on a bassy stereo system) well this is where you use compression to even it out. however, i must warn you - do NOT apply compression to individual instruments in your mix, nor the entire mix, unless you have a good set of monitors in front of you. headphones, in my personal experience, as well as speakers that lack a good bass element, are useless for mixing and mastering in that compression alters the bass a lot, and you won't be able to tell what it actually sounds like. you need to be able to pick up the slightest change in the bass sound in order to mix it right. i don't have top notch studio monitors but mine are "O.K." for now. compressors have a tendency to make basslines sound very growly. they also have a tendency to kill the bottom end. it's like cutting everything between 0-400hz and boosting everything between 400-1,5khz. it sounds like shit. as long as you have studio monitors or a subwoofer you should be okay. it's an ongoing debate whether one should equalize before or after one applies compression. personally, i prefer to start off with compression, then set the stereo image, then equalize, and then amplify and limit it at the end there. if you equalize your bassline before compressing it, boosting 5dB at 150hz, it's still likely the compressor is gonna rob your bass of it's actual lower frequencies. you can equalize your bass, mix, or whatever before you compress it, but it's likely you'll have to re-equalize it afterwards anyway seeing as how the compressor's gonna change how it (the bassline, the mix, the whatever) sounds entirely.
i use compression both when i mix and when i master, although it's a mastering tool really. when i mix i only compress individual instruments, but when i master i apply very mild compression to the entire mix. when you compress an entire mix, you have to be very careful when setting the threshold level. if you set the threshold lower than the kickdrum's peak, the compressor will compress the entire mix whenever the kick drum hits. in the end it'll sound like someone's sliding the mix's main volume fader up and down like a raging madman.
like everything else that's related to making music, the key, of course, is experimenting. hopefully, now you'll have a little bit more clue as to what it is, exactly, that you're doing. i've merely scraped the surface, but if you actually call yourself "a producer" and have ambition that one day you're gonna sell your beats, you owe it to yourself to read up on, and learn how to use a compressor, because your shit will never sound clean, punchy and professional without it. in fact, you don't need a whole bunch of ambition. whether you produce because it's your passion in life, because it's what you want to do when you grow up, or because you're very bored on afternoons, you should check out and read up on compression anyway cause it's gonna improve your stuff.
-------------------
oh, and if i misunderstood something and am wrong, feel free to correct me ;x
there are no stickies about, and quite frankly i can't recall ever seeing any threads about compression in this forum. i thought i'd write up a quick starter's guide to compression. i put "dynamics processing" in the title but we're gonna focus on just compression, which falls in as a subsidiary of the "dynamic processing" subject. the art of compression is the most misunderstood, underrated, most neglected step of the mixing and mastering process, in the history of unprofessional music-making. for the most part, the reason why "underground" producers tend to "forget" to use compression is that they simply don't know what a compressor does. i'm gonna start off by explaining some of the terms you'll encounter if you decide to give it a shot. i have readied two images that i will use to demonstrate, both show a wave and how a compressor affects it. if you don't know what a wave is, you have no business reading this guide in the first place.
-------------------
clipping
when a sound signal is amplified to exceed 0dB, your signal is clipped off, which results in a distorted wave. a good way to see what a majorly distorted digital wave sounds like is loading an audio file up in a wave editor like cool edit, increase the volume by 5-10dB and then decrease it by the same amount and play it.
threshold
the threshold determines how loud a signal must be for the compressor to compress it. if you set the threshold level on your compressor to -10dB, the compressor will apply compression to any and every sound in your wave that exceeds the threshold. that is, any sound louder than -10dB is compressed. digital audio levels are often misunderstood. when you work with digital audio, 0dB is the absolute volume, nothing can exceed 0dB. it's like 100%.
ratio
the ratio determines how much compression should be applied to any signal that exceeds the threshold level. a 2:1 ratio means the output signal is reduced to half the input signal.
attack/release
attack and release (or decay) works just like the envelope controls on a synth/sampler. it determines how the compressor will act when a signal exceeds the threshold you've set. a slow attack will allow for some of the signal that exceeds the threshold level to pass through uncompressed before the compressor kicks in. a slow release means the compressor will keep compressing for a while (normally about 0-50ms) after the offending signal has been compressed.
gain
basically a volume controller. the input gain lets you boost the signal before it's compressed. practically, that means your wave will undergo a harder compression as boosting the volume sub-sequently pushes a larger part of the wave above the threshold. the output gain lets you boost the volume of the compressed signal.
soft/hard knee
compression will alter the sound of a wave, and thus also the way it looks in a wave editor. if you look at image number two above, you'll see that my kickdrum wave has a very soft, round shape. basically, this attribute determines how "soft" your compressed signal is gonna sound/look. it actually makes a big difference.
limiter/gate
this has got nothing to do with this guide, but since i'm already covering compression... a compressor falls in under "dynamic processors." why? because it alters the dynamic range of your mix. a limiter and a noise gate are two other devices that also fall in under "dynamic processors." a noise gate is like a reversed compressor. you set a threshold level, but instead of compressing everything that exceeds the threshold, a noise gate eliminates anything that's below the threshold. if you're recording live music with a band playing all at the same time for instance, letting the vocal mic go through a noise gate will eliminate all the background noises from the other instruments that are being played as the vocalist sings. a limiter uses mild distortion to prevent clipping. once a signal exceeds 0dB, the signal is distorted. the limiter uses a gentlier kind of distortion to cut the signal before it starts to clip. in most cases, the distortion caused by the limiter is barely noticable. this, of course, depends on how drastic your settings are. another dynamic processor is a finalizer. finalizers are kind of like a mastering suite preset. it adds a little reverb, and boosts the highs and lows a little. technically useless. most professionals frown upon them even. i don't think i've ever added reverb to an entire track in my life.
-------------------
rizzle speaks on compression
so what is compression? when you compress, say, a mix, you lower the volume of sounds that stick out of your mix like a sore thumb, so that you can bring up the overall volume of your mix to make it sound more like a professional commercial album. boosting an uncompressed signal would make parts of the wave (most noticably the kick drum and snare) exceed 0dB, and thus distort the entire wave. additionally, compression adds thump. i don't think i've ever made a set of drums without adding compression to the snare and kick. a long attack which lets the climax of your kick and snare go through uncompressed makes for a very thumpy, snappy sound. i vary my release, but i always use a long attack on my drums, regardless.
compression is not only recommended, but neccesary, if you want the bottom end of your mix to sound good. you may have noticed that whenever you make a beat, some notes in your bassline stick out because they are way louder than the rest. you may have noticed that some times when you're playing your beat in your car or on your computer's speaker setup, that third note on your triangular bass makes your subwoofer go BOOOOOOM!!!!! (just a funny observation; i love the wu-tang clan but a lot of their old tracks have basslines like this. it ruins the track when you bump it on a bassy stereo system) well this is where you use compression to even it out. however, i must warn you - do NOT apply compression to individual instruments in your mix, nor the entire mix, unless you have a good set of monitors in front of you. headphones, in my personal experience, as well as speakers that lack a good bass element, are useless for mixing and mastering in that compression alters the bass a lot, and you won't be able to tell what it actually sounds like. you need to be able to pick up the slightest change in the bass sound in order to mix it right. i don't have top notch studio monitors but mine are "O.K." for now. compressors have a tendency to make basslines sound very growly. they also have a tendency to kill the bottom end. it's like cutting everything between 0-400hz and boosting everything between 400-1,5khz. it sounds like shit. as long as you have studio monitors or a subwoofer you should be okay. it's an ongoing debate whether one should equalize before or after one applies compression. personally, i prefer to start off with compression, then set the stereo image, then equalize, and then amplify and limit it at the end there. if you equalize your bassline before compressing it, boosting 5dB at 150hz, it's still likely the compressor is gonna rob your bass of it's actual lower frequencies. you can equalize your bass, mix, or whatever before you compress it, but it's likely you'll have to re-equalize it afterwards anyway seeing as how the compressor's gonna change how it (the bassline, the mix, the whatever) sounds entirely.
i use compression both when i mix and when i master, although it's a mastering tool really. when i mix i only compress individual instruments, but when i master i apply very mild compression to the entire mix. when you compress an entire mix, you have to be very careful when setting the threshold level. if you set the threshold lower than the kickdrum's peak, the compressor will compress the entire mix whenever the kick drum hits. in the end it'll sound like someone's sliding the mix's main volume fader up and down like a raging madman.
like everything else that's related to making music, the key, of course, is experimenting. hopefully, now you'll have a little bit more clue as to what it is, exactly, that you're doing. i've merely scraped the surface, but if you actually call yourself "a producer" and have ambition that one day you're gonna sell your beats, you owe it to yourself to read up on, and learn how to use a compressor, because your shit will never sound clean, punchy and professional without it. in fact, you don't need a whole bunch of ambition. whether you produce because it's your passion in life, because it's what you want to do when you grow up, or because you're very bored on afternoons, you should check out and read up on compression anyway cause it's gonna improve your stuff.
-------------------
oh, and if i misunderstood something and am wrong, feel free to correct me ;x