What exactly is "Compression"?

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What exactly is "Compression"?

Post by Ydna » Thu Oct 28, 2010 12:41 am

I've heard the term thrown around a lot, but I've never understood exactly what it means. I hear people talk about microphone compression and speaker compression.

For instance, I did a quick recording, and sent it to a friend, he said it sounded good, except it sounded compressed. In this context, does compression mean the slightly rattling noise the speakers make at times when I play it back?

Then another time, I was talking to my uncle about Marshall's, and he mentioned in a video I showed him, he could hear the microphone compressing.

I did a google search and nothing really came up, so figured I would post it here, in a place where people use this terminology quite a bit.

Thanks ahead of time, Andy.
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Re: What exactly is "Compression"?

Post by demonufo » Thu Oct 28, 2010 3:01 pm

Compression is a kind of limiting which takes squashes the dynamics out.

Imagine amplifying a signal, and limiting the upper sound level, so there aren't any volume peaks, and any quiet troughs either.
That is an exaggeration of compression.
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Re: What exactly is "Compression"?

Post by toner » Thu Oct 28, 2010 4:26 pm

It depends on what type of compression you're talking about. In general, compression refers to limiting the dynamic range of sounds (variance between soft and loud).

A compressor like rack models used in studio or live sound lower the peak audio signals so that the loud portions are decreased. It "smooths out" the sound so there aren't really loud spikes and makes the overall signal more "polished" sounding. 99.99% of all vocals you hear on recordings were compressed and probably 75% of electric guitars also (not with compression pedals but with high-quality units inserted at the mixing console or included in digital hardware/software which compress the microphone's signal). Without compression the quiet portions of a vocal track will get lost in the mix and the loud spots will jump out too much and sound amature. Often the entire mix is compressed or limited during mastering to polish the overall sound. Radio stations heavily compress (squash) their signal and then raise it to get above the noise floor inherent in the broadcasting medium such as FM. Compare a song on the radio with it's CD recording and you'll definitely hear the radio compression.

A simple example of vocal volume loudness from 1-10:
Without compression: soft parts = 2, loud parts = 10
With compression: soft = 4, loud = 7

In my opinion, compression is way overused in most modern recordings. When overused, you lose some of the music's natural dynamics. Compare the overall sound of current rock or country recordings with those from the 70's for example and you'll hear what I mean.

There are other types of compression such as the way tube amps respond when overdriven. Tubes naturally compress when they distort. Speakers can do this also.

Almost all video cameras have built-in limiting to prevent audio from distorting. That's why some loud parts of recordings can sound "mushy" or even quieter than the softer sounds that were recorded (when the limiting wasn't being triggered).

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Re: What exactly is "Compression"?

Post by Guitar-Sam » Thu Sep 08, 2011 6:29 pm

I've been running sound for a few years now and compression eludes me too at times.
For drums a compressor/gate is cool cause you can tighten the drum sound by chopping off the eccess ring creating a tighter sound.I compress the kick about 2.5:1
As far as vocals though I just don't get it.The higher you run it the more bassy and shitty it sounds.I run a compressor on the vocals but really it ain't doing much.I run the threshhold just above 0 the ratio at like 1:1-1.5:1 and a few Db boosted output gain.All it really does is make it slightly louder and slightly fuller.Anymore than that I run into woofy shitty tone that evan the bass control of the channel will not help.I can make it thin but still not get rid of the woolyness.To me bassy uninteligible vocals drive me nutz like nails on a chalk board.
I've read that typical vocal ratios ly between 3:1-6:1 To me it makes no sense as to why you would want to compress that much.
As far as live sound ,to me it seems like compressors get used alot as a crutch,so you don't have to vary gain and slider settings as much.But I don't care cause i meter the lead vocal on just about everysong anyways.And I ride the vocal faders allnight anyways,to keep harmonies blended.
Am I using the compressors wrong or do I just have an ear that dislikes compression or what??
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