What exactly is compression?

[rayc]

SouthSIDE Glen,
Thanks for the download. Compression scares me. I've only used it a couple of time successfully and that was as non destructive software.
My little outboard compressor is almost unused - I look forward to a little more understanding post your tute.
Mind you I also loath most 80's pop & that was professor compressor will fix all land wasn't it?

 

[SouthSIDE Glen]

SouthSIDE Glen,
Thanks for the download. Compression scares me. I've only used it a couple of time successfully and that was as non destructive software.

You're welcome, I hope it helps you out somewhat.

Compression should not be feared, when used properly it is both a necessary and useful tool in the audio engineering toolkit. Unfortunately there are IMHO far too many rookies who not only do not fear compression, they embrace it as the magic box that'll do all their engineering for them and in the process wind up misusing and abusing it. I honestly wish more of them had at least some of your respect for the signal and trepidation over abusing it.

That said, though, don't be afriad to explore it and to use it. Once you learn it properly you'll be putting out better mixes than you are now.

G.

 

[slidey]

best bass sound I ever had was recorded flat & remained flat & also uncompressed

compressors can be the ultimate destroyer in a mix & can also help in good ways BUT it's certainly not to be considered "magic"

IMO one can never know enough about compression or EQ for that matter

 

[MCreel]

Imagine a hand on a volume control and every time there is a loud peak in a track, the hand adjusts the volume to compensate. That's basically what a compressor does. Precise volume attenuation. A volume peak reducer or peak remover (if set as a limiter). A limiter reacts to peaks so fast, they kind of get chopped off.

Depending on how the controls are set, compression can have audible side effects which can be desirable or not so desirable like distortion, pumping, a brickwall sound, etc. When a large amount of compression is applied, the loudest parts of a track are reduced in volume and brought closer to the volume level of the quietest parts of the track so the lower volume parts of the track will seem louder.

The threshold control sets the point at which the compression kicks in. For example, the imaginary hand begins turning down the volume when the track volume reaches -13 db, or -3db, or.........your choice. 0 db being about the loudest useful volume in the digital world.

The ratio control sets the amount of compression to be applied. For example, you set the threshold to -13 db and the ratio to 2:1. When the track volume reaches -13 db, a ratio of 2:1 compression is applied to the signal. 10:1 would be more compression than 2:1.

(think of the threshold as the volume level at which the compression will be applied and the ratio as the amount of compression that will be applied.)

The attack control sets the speed at which the imaginary hand turns down the volume. For example, you want the volume level adjusted very quickly so you set the attack to 2 ms.

The release control sets the speed at which the imaginary hand turns the volume back up after attenuating the volume.

If you can imagine how many different ways the imaginary hand on the volume control can react, then you'll have an idea of what some of the effects of compression sound like.

Good post.....but instead of telling a way to think about the ratios you shoudl explain what the numbers mean. 2:1 means that for every 2 decibels of volume increase (over the threshold number) the compressor will allow 1 decibel to proceed through. Isn't this correct?

 

[apl]

Good post.....but instead of telling a way to think about the ratios you shoudl explain what the numbers mean. 2:1 means that for every 2 decibels of volume increase (over the threshold number) the compressor will allow 1 decibel to proceed through. Isn't this correct?

I don't think so. I think the ratio is based on the linear values, not the dB values.

I may be mistaken.

 

[SouthSIDE Glen]

Good post.....but instead of telling a way to think about the ratios you shoudl explain what the numbers mean. 2:1 means that for every 2 decibels of volume increase (over the threshold number) the compressor will allow 1 decibel to proceed through. Isn't this correct?

I don't think so. I think the ratio is based on the linear values, not the dB values.

I may be mistaken.

dB is just a form of measurement at that point, just a scale that's used. MCreel basically has it right. Compression ratio is just that, its a linear ratio of input value to output value for values above a certain threshold level. As that threshold level is typically measured in decibels, so is the compression ratio.

G.

 

[apl]

dB is just a form of measurement at that point, just a scale that's used. MCreel basically has it right. Compression ratio is just that, its a linear ratio of input value to output value for values above a certain threshold level. As that threshold level is typically measured in decibels, so is the compression ratio.

G.

Yeah, I should have checked. If it's set for 2:1, you get 1 dB out for every 2 dB in above the threshold. I'm gonna have to play with the dB math to see what that's doing in the linear domain.

 

[travelin travis]

Good post.....but instead of telling a way to think about the ratios you shoudl explain what the numbers mean. 2:1 means that for every 2 decibels of volume increase (over the threshold number) the compressor will allow 1 decibel to proceed through. Isn't this correct?

I've read alot of beginner compression articles and most were a little unclear to me when covering threshold and ratio. All anyone really needs to know about the ratio control is that if you turn it up more compression is applied.

 

[MCreel]

I've read alot of beginner compression articles and most were a little unclear to me when covering threshold and ratio. All anyone really needs to know about the ratio control is that if you turn it up more compression is applied.

I think the application and function of a compressor makes it more complicated than boiling it down to simply that statement. But you could be right. I know when I first used a compressor and people said that about the ratios I still thought "but what do the numbers mean?"

You've gotta have a grasp of how those numbers interact to know what its doing to your sound.

 

[SouthSIDE Glen]

I know when I first used a compressor and people said that about the ratios I still thought "but what do the numbers mean?"

You've gotta have a grasp of how those numbers interact to know what its doing to your sound.

That's the catch 22^2 of compressor control. Compression ratio settings have very little meaning unless discussed in tandem with the threshold setting. And the threshold setting is meaningless unless discussed within the context of a particular signal. "It depends upon the track or song" is, quite literally and quite technically, 100% true.

A statement like, "Set your compression to 4:1 for vocals" has as much meaning and accuracy to any random reader that "drive 4 miles east to get to the grocery store" does.

G.

 

[noisewreck]

best bass sound I ever had was recorded flat & remained flat & also uncompressed

I like to use the UAD-1 1176LN on clean synth subbbass. But I use it more for slight distortion than dynamics control (it's kinda hard to have wild dynamic issues when playing a synth, and if you do... sigh... MIDI can be edited much more easily ) So, I hit it pretty hard (usually around 10+dB reduction at either 4:1 or 8:1 ratio) and then adjust with attack and release to get the desired kind of distortion. Has a nice way of bringing the subbass into focus by adding some high frequency content without sounding obviously distorted.

Unfortunately there are IMHO far too many rookies who not only do not fear compression, they embrace it as the magic box that'll do all their engineering for them and in the process wind up misusing and abusing it.

I guess I am one of them... just give me a signal to destroy

 

[RDMSstudio]

Blowin' the myth

I emplore you not to renforce this idea and to disavow it now. There is already an overload of people who think compressors are magic boxes that'll do their engineering for them, we don't need to reenforce this rampant misunderstanding with statements like this.

G.

It's not a rampant misunderstanding, It's an accumulated knowledge of how these things work. Compressors don't do the job for me, I tell them exactly what I want them to do.
If your ears are good enough you can hear how any minute adjustment of any parameter affects not only the volume and clarity, it also changes the relationship of the sounds to each other. Establishing a tighter groove and more interplay between sounds.

Compressors are thought of too often as a fix up for bad levels or clarity.
When you know your stuff, you find they are an amazing creative tool.

How many of you for example realise that the attack setting of a compressor on Bass guitar will not only change the percieved initial sound, it also changes the timing and symbiosis of the part to every other instrument.

Try it, pull up just drums and Bass. Find a compressor setting you like on Bass then change the attack time 1ms at a time. Just listen to the relationship between the drums and Bass. See how the timing between the two shifts subtly. One particular attack time will magically lock the two together.
If you can't hear it you haven't been at the game long enough.

Guess what, the release time has the same impact on timing and groove.

Those that get it, use compressors to make recordings that blow peoples minds.
Those that think compressors are used to fix stuff, go on to complain about their overuse.

Cheating to use compressors this way? I don't think so. Is EQ cheating? Reverb? Delay?

 

[SouthSIDE Glen]

Compressors are thought of too often as a fix up for bad levels or clarity.
When you know your stuff, you find they are an amazing creative tool.

You are absolutely correct on all points.

Which is exactly why compressors should not be touted on this bard as magic boxes. You "know you stuff". You already know how to use compressors correctly.

That's not what I'm talking about.

You're right, 90% of the folks reading your post have absolutely no idea what you're talking about when you refer to using envelope shaping to create a groove. Or, if if they understand the concept, they don't yet have the chops to execute the technique very well.

This 90% are the ones I'm talking about. I'm talking about the person who comes on here asking, "What compression ratio I should use to make my music sound good", or one of the infinite variations thereof. It's these folks who get the gear long before they even know why they have it or how to use it, who are under the impression that they can drop their tracks into the top of a signal chain, push a couple of presets, and have their mix come out the bottom of the chain sounding like Grammy. They think the gear is more-or-less automatic. "I own a compressor, therefore my compression problems will be handled. Just tell me whether I should set it for 'Permanent Press' or 'Delicate' so I can move on to the next step in the signal chain."

That's what I'm talking about when I hear the term "magic box". And that's what I was emploring you not to substantiate.

You have pretty much indirectly refuted it in your reply. Your technique for getting a groove via envelope shaping is a manual feedback technique where one actually has to use equal parts ears, knowledge, creativity, and adaptation to the content to get the desired result. The compressor works wonders on a subtle detail, but it does so only because it has a qualified pilot. The compressor is just the tool that you are skillfully using to manually engineer the content. It contains no magic that you haven't imparted to it via technique.

In fact, in that example, the compressor is not the "magic box"; YOU ARE!

G.

 

[RDMSstudio]

Great response. I stand corrected.

I guess what I was trying to impart upon the padawans is the concept of understanding what compressors are actually capable of, given time and patience.

It's not enough to tell someone a general set of parameters for compression. Understanding WHY is more important.

It's true that it takes quite a long time to have ears attuned to micro adjustment of any audio tool. The road to getting those ears is telling people what to listen for.

Do you remember all those moments when you start hearing detail things for the first time? Wasn't every one of them an amazing revelation to yourself?