What exactly is compressioon
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InSight-Beats
Guest
Technical version:
In simple terms, a compressor is an automatic volume control. Loud sounds over a certain threshold are reduced in level; quiet sounds are not reduced. In this way it reduces the dynamic range of an audio signal. This may be done for aesthetic reasons, to deal with technical limitations of audio equipment, or to improve audibility of audio in noisy environments.
In a noisy environment background noise can overpower quiet sounds (such as listening to a car stereo while driving). A comfortable listening level for loud sounds makes the quiet sounds inaudible below the noise: A comfortable listening level for quiet sounds makes the loud sounds too loud. To make both the soft and loud parts of a sound audible at the same time, compression is used. Compression reduces the level of the loud sounds, but not the quiet sounds, thus, the level can be raised to a point where the quiet sounds are audible, but without the loud sounds being too loud. Contrast this with the complementary process of an expander, which increases the dynamic range of a signal.[1]
Different compression ratiosA compressor reduces the gain (level) of an audio signal if its amplitude exceeds a threshold. The amount of gain reduction is determined by a ratio. For example, with a ratio of 4:1, when the (time averaged) input level is 4 dB over the threshold, the output signal level will be 1 dB over the threshold. The gain (level) has been reduced by 3 dB. When the input level is 8 dB above the threshold, the output level will be 2 dB; a 6 dB gain reduction.
My version: Makes the lows louder and the peaks softer.
Reason you might use it: For instance, you might have a thick pad that is covering up too much of the spectrum (or more than you want). You would use compression to "tame" it.
In simple terms, a compressor is an automatic volume control. Loud sounds over a certain threshold are reduced in level; quiet sounds are not reduced. In this way it reduces the dynamic range of an audio signal. This may be done for aesthetic reasons, to deal with technical limitations of audio equipment, or to improve audibility of audio in noisy environments.
In a noisy environment background noise can overpower quiet sounds (such as listening to a car stereo while driving). A comfortable listening level for loud sounds makes the quiet sounds inaudible below the noise: A comfortable listening level for quiet sounds makes the loud sounds too loud. To make both the soft and loud parts of a sound audible at the same time, compression is used. Compression reduces the level of the loud sounds, but not the quiet sounds, thus, the level can be raised to a point where the quiet sounds are audible, but without the loud sounds being too loud. Contrast this with the complementary process of an expander, which increases the dynamic range of a signal.[1]
Different compression ratiosA compressor reduces the gain (level) of an audio signal if its amplitude exceeds a threshold. The amount of gain reduction is determined by a ratio. For example, with a ratio of 4:1, when the (time averaged) input level is 4 dB over the threshold, the output signal level will be 1 dB over the threshold. The gain (level) has been reduced by 3 dB. When the input level is 8 dB above the threshold, the output level will be 2 dB; a 6 dB gain reduction.
My version: Makes the lows louder and the peaks softer.
Reason you might use it: For instance, you might have a thick pad that is covering up too much of the spectrum (or more than you want). You would use compression to "tame" it.
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Darkstarr_
Guest
InSight-Beats said:
hhmm imo with that example you're sending him in the wrong direction.
technically if you have a thick pad thats covering up to much of the spectrum you'd use an eq to lower the unwanted frenquencies....
a more common use of compression:
you are recording a singer and he sings some softs parts and also screams pretty loud in some other parts, you'd put a compression on the vocal track to lower the high peaks, have them sitting next to the lower parts and then use the gain to bring up level of the whole track.
so lets say you are looking at the sound wave you can see some low peaks and some high peaks:
2-3-3-3-8-8-9-4-2-3-2-8-9-10-2-3-2...
(picture 1 being the lowest peaks and 10 being the loudest peaks)
First, You'd bring the high peaks down. in this example lets say 3 equals -16dbfs, and 10 is peaking at -6dbfs, you'd set the threshold of the compressor at around -18dbfs, with let's say a ratio of 6:1 (so every 6db, only 1db comes out)
so it becomes:
2-3-3-3-3-3-4-4-2-3-2-3-4-5-2-3-2
then you'd turn the gain up on the compressor to have it at a good loud level, so now the vocal track becomes:
7-8-8-8-8-8-9-9-7-8-7-8-9-10-7-8-7
get it???
tried to explain it quickly, throwed some quick figures, probably missed some parts, someone correct me if i missed something
hackenslash
Replicant
OK. To start with, an analogy. You know that bit in Star Wars episode 1 where Luke, Leia, Han, and Chewy are in the garbage chute and the walls start to close in on them? Same thing, roughly speaking.
Compression is a way to reduce the dynamic range of a wave. If, for instance, you are having some difficulty getting a vocal to sit in the mix properly because there are parts that are a bit too quiet and other parts that are a bit too loud, you would use compression to reduce the difference between the quietest and loudest parts of the signal. In the olden days of 16 bit recording when it was important to get a hot signal, compression was a useful tool to ensure that you could do so without clipping. This was also true in the stone age when we used magnetic tape (look that up, you will be astounded), and in fact the magnetic tape itself was used as a form of compression (some really archaic studios even use this these days). Anyhoo, I digress. The idea of compression is largely that it pushes the transient peaks down towards the RMS (average, although this is a bit misleading. RMS is a way of calculating the mean of a waveform over time, loosely speaking), thereby reducing the difference between peak level and RNS level. A compressor generally includes a make-up gain control so that you can push the peak level back up, bringing the average level (loudness) back up with it.
This is all very well, but far too often it's apparent that peeps don't understand or hear the effects of compression, and drive it too hard, resulting in overcompression, characterised by pumping in the audio. HERE is a truly great example of overcompression. Note the constant pumping in the sound. Not good.
I suspect that what you're really asking is how you should apply it in real terms. This is a question that only you can answer, as it is in many ways an artistic decision. The only time it falls outside the artistic is in cases like the above, in which the producer obviously has no clue about its effects. That anyone could ever think that sounds acceptable is totally beyond me.
Now then! In some forms of music, that pumping can be acceptable in artistic terms, particularly in dance music, where the pumping can actually aid the piece in its energy. I, for one, have never found it pleasant, though, even in that context.
The key to any kind of dynamics processing, AFAIC, is to be subtle. There are members here who would, no doubt, disagree with me. What do I know, after all. I'm just a cheesy rocker. However, in my professional life, I deal with all kinds of music, mostly jazz, reggae and blues, where such things are apparent and unacceptable.
Compression can be used to great effect in taming dynamic range for any part that is proving to be recalcitrant during mixing, but you should be careful to exercise caution and not overdo it.
Some techie stuff.
1) Threshold: This is important, as it defines at what level compression should be applied. Any signal above the threshold will be squashed according to the ratio defined. Setting this too low will lead to pumping
2) Ratio: This defines how hard the compressor should work. This is a bit more difficult to explain in my drunken state, but it works like any other ratio. If your compression ratio is, for example, 2:1, any signal that is 2db over the given threshold will be reduced to 1db over the threshold, giving a gain reduction of 1db.
3) Knee: This is the rate at which the compressor works as it reaches and crosses the threshold. A soft knee will bring the compression in gradually, while a hard knee will bring it in more aggressively as you move up the amplitude range.
4) Attack: This determines how quickly the compressor activates. This is quite important, as this is the factor that most affects transients. Setting a fast attack means that the attack peaks of your audio events will be more affected. Transients are the peaks that make your music breathe, so you need to pay careful attention here. With a very fast attack, the attack phase of your events will be pushed down toward the average level, or RMS, meaning that, although the dynamics will be tamed, the events will be less lively, resulting in dulling of events and loss of transients. Did I already mention that those are the important bits? I think I did...
5) Release: this is fairly self-explanatory. This determines the time between the compressor meeting the last audio event that breaches the threshold and the compressor shutting off.
6) Make up gain: This calculation should be based on your threshold and ratio settings and, more importantly, your ears. For example, if you set your threshold at -10db with a ratio of 2:1 and your level before compression is - 6db, resulting in a 4db gain reduction, you should add 4db of make up gain to bring the peak level of the signal back up to the level it was before you applied compression.
7) train and then trust your ears. They are the most valuable piece of kit in your studio, and can't be vetoed by any piece of kit, or meter.
This is a guide only, and subject to dispute by such audio gods as are to be found in these parts. I would be happy to receive any corrections/clarification as these peeps can give me, but this should about cover it.
****! My post took so long to formulate and type, I was beaten to it! Ah, well. Them's the breaks!
Compression is a way to reduce the dynamic range of a wave. If, for instance, you are having some difficulty getting a vocal to sit in the mix properly because there are parts that are a bit too quiet and other parts that are a bit too loud, you would use compression to reduce the difference between the quietest and loudest parts of the signal. In the olden days of 16 bit recording when it was important to get a hot signal, compression was a useful tool to ensure that you could do so without clipping. This was also true in the stone age when we used magnetic tape (look that up, you will be astounded), and in fact the magnetic tape itself was used as a form of compression (some really archaic studios even use this these days). Anyhoo, I digress. The idea of compression is largely that it pushes the transient peaks down towards the RMS (average, although this is a bit misleading. RMS is a way of calculating the mean of a waveform over time, loosely speaking), thereby reducing the difference between peak level and RNS level. A compressor generally includes a make-up gain control so that you can push the peak level back up, bringing the average level (loudness) back up with it.
This is all very well, but far too often it's apparent that peeps don't understand or hear the effects of compression, and drive it too hard, resulting in overcompression, characterised by pumping in the audio. HERE is a truly great example of overcompression. Note the constant pumping in the sound. Not good.
I suspect that what you're really asking is how you should apply it in real terms. This is a question that only you can answer, as it is in many ways an artistic decision. The only time it falls outside the artistic is in cases like the above, in which the producer obviously has no clue about its effects. That anyone could ever think that sounds acceptable is totally beyond me.
Now then! In some forms of music, that pumping can be acceptable in artistic terms, particularly in dance music, where the pumping can actually aid the piece in its energy. I, for one, have never found it pleasant, though, even in that context.
The key to any kind of dynamics processing, AFAIC, is to be subtle. There are members here who would, no doubt, disagree with me. What do I know, after all. I'm just a cheesy rocker. However, in my professional life, I deal with all kinds of music, mostly jazz, reggae and blues, where such things are apparent and unacceptable.
Compression can be used to great effect in taming dynamic range for any part that is proving to be recalcitrant during mixing, but you should be careful to exercise caution and not overdo it.
Some techie stuff.
1) Threshold: This is important, as it defines at what level compression should be applied. Any signal above the threshold will be squashed according to the ratio defined. Setting this too low will lead to pumping
2) Ratio: This defines how hard the compressor should work. This is a bit more difficult to explain in my drunken state, but it works like any other ratio. If your compression ratio is, for example, 2:1, any signal that is 2db over the given threshold will be reduced to 1db over the threshold, giving a gain reduction of 1db.
3) Knee: This is the rate at which the compressor works as it reaches and crosses the threshold. A soft knee will bring the compression in gradually, while a hard knee will bring it in more aggressively as you move up the amplitude range.
4) Attack: This determines how quickly the compressor activates. This is quite important, as this is the factor that most affects transients. Setting a fast attack means that the attack peaks of your audio events will be more affected. Transients are the peaks that make your music breathe, so you need to pay careful attention here. With a very fast attack, the attack phase of your events will be pushed down toward the average level, or RMS, meaning that, although the dynamics will be tamed, the events will be less lively, resulting in dulling of events and loss of transients. Did I already mention that those are the important bits? I think I did...
5) Release: this is fairly self-explanatory. This determines the time between the compressor meeting the last audio event that breaches the threshold and the compressor shutting off.
6) Make up gain: This calculation should be based on your threshold and ratio settings and, more importantly, your ears. For example, if you set your threshold at -10db with a ratio of 2:1 and your level before compression is - 6db, resulting in a 4db gain reduction, you should add 4db of make up gain to bring the peak level of the signal back up to the level it was before you applied compression.
7) train and then trust your ears. They are the most valuable piece of kit in your studio, and can't be vetoed by any piece of kit, or meter.
This is a guide only, and subject to dispute by such audio gods as are to be found in these parts. I would be happy to receive any corrections/clarification as these peeps can give me, but this should about cover it.
****! My post took so long to formulate and type, I was beaten to it! Ah, well. Them's the breaks!
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Dramatic
Guest
so basically compression is balancing the sound and vocals so that they all sound smoothly when played right?
hackenslash
Replicant
InSight-Beats said:
A bit of misinterpretation there, methinks, unless it is simple misunderstanding. It doesn't make anything louder.
Further, compression has nothing to do with the spectrum. It has only to do with dynamic range, which is not the same thing. In my experience, the best thing to do with a pad that is eating into the mix is to turn it down. My pads never get above 30% of the level of any other signal. Much more than that, and it isn't a pad anymore, but a frontline instrument, regardless of the fact that it's called a pad.
Dramatic said:
I think you posted while I was posting. Read up again. Compression has nothing to do with balance, except in the very braod sense that compression can be used to achieve balance, which is not the same thing.
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Darkstarr_
Guest
^^^Thats a great post hackenslash, well explained
hackenslash
Replicant
Just checking it again, since a slightly earlier post was a bit awry. :O
M
MrHope
Guest
If you use make-up gain after compression, it DOES make the RMS level louder. Some VST compressor-limiters have automatic make-up gain. For example, PeakComp.
The ratio is the mathematical ratio of input gain to output gain. (before the makeup gain stage, which is a separate gain stage).
The ratio is the mathematical ratio of input gain to output gain. (before the makeup gain stage, which is a separate gain stage).
Sanguis Mortuum
New member
sleepy said:
Only if the make-up gain knob on your compressor is broken.
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Darkstarr_
Guest
Sanguis Mortuum said:
No, Sleepy is right.
The act of compressing audio will make the higher level lower, not the other way around.
BUT, one can a/b a compressed audio file vs an uncompressed file and say: "the lower parts sounds louder". Which in a sense is correct.
But technically speaking, A compressor will lower your high peaks and use the make up gain to make the compressed sound (including the "lower" part) louder...
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Sanguis Mortuum
New member
Darkstarr_ said:
Well we're really just arguing symantics here. Of course the act of compressing itself just makes the peaks quieter, but depending on how you set the make up gain it can then also raise the gain so the peaks are the same level and the quieter parts are louder than before. The real definition of a compressor is that it reduces the dynamic range...
D
Darkstarr_
Guest
Sanguis Mortuum said:
You are absolutely correct there,
but personally, if someone asks "what is compression"?
and one responds with:"Makes the lows louder and the peaks softer"
I believe it can be misleading...
cheers man
InSight-Beats said:
It does not make the lows louder.
InSight-Beats said:
A compressor will not do too much to "tame" that. A "thick pad" is generally not particularly dynamic... it pretty much hovers at the same level... no real peaks or anything... not much for a compressor to do.
Plus, a compressor does not deal with "the spectrum"... it sounds like you are describing about something for an EQ/filter.
Sanguis Mortuum said:
Well, it reduces the dynamic range by lowering the peaks. A compressor affects the peaks... it does not touch the lows. It looks for peaks that go above a level you set (threshhold), then it lowers them by whatever amount (ratio) you set.
The fact that you may or may not be able to apply some gain to the compressed signal after the fact has nothing to do with compression itself. (almost every plugin has some sort of gain control integrated into its face, but that does not mean it is part of its actual purpose)
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Sanguis Mortuum
New member
dvyce said:
.......
Sanguis Mortuum said:
The act of 'compression' may not make the quiet bits louder, but 'a compressor' can, with the make-up gain knob.
Pointless argument anyway though...
Sanguis Mortuum said:
It is not semantics.
When the question is "what is compression" the answer does not include "it makes the low parts louder."
The point of the make up gain on compressors that have that control is this: A compressor lowers volume. The gain knob allows you to turn the volume up after it has already been compressed.
It is a very silly argument to say that a compressor lowers highs and raises lows just because there is a gain know there.
That is like saying a lowpass filter cuts frequencies and raises the gain of the frequencies that pass through the filter-- and the reason for saying that being that there is a gain control knob. Than would be equally as incorrect as making that previous statement about compression.
hackenslash
Replicant
Dvyce is correct.