Compression

Ok, I'll cut through the technical gobbledygook for ya...

When you have a sound output, you've got a dynamic range. There's the 'peak' (loudest) output, and there's an average output.

What compressors do is reduce the amount of variance between peaks/valleys and the average level - soft sounds get louder, loud sounds get softer... everything comes closer to the average.

Let's say your loudest sound is 80db, and your average sound is 30db. Using 2:1 compression means that for every change of two units in the unaltered sound, the compressor will output only 1 unit of change in the processed sound. Since the difference in the example is 80-30 = 50db, the compressor set at 2:1 will cut that in half, and the peak will be heard at 55db (average + 25). A 5:1 ratio will lower the peak to 40db.

This is a fairly well thought-out article on how and when to use a compressor. It's true that there are a lot of "try it and see" comments, but the philosophy is pretty solid.

Compression - A Simple Explanation

-Laz

This is why I come here, thanks guys.

Kido

I would lightly compress the vocals while tracking, to control transients and get a good level on tape. I would not compress the acoustic while tracking because I think compressed acoustic sounds like crap.

I would track them to two separate tracks (even if you record them at the same time) - this gives you the option to make EQ decisions during mixing.

I would probably use some light limiting on the final mix to make the overall level louder, but not too much because I would want to preserve the dynamic range of the piece.

A compressor is used to compresses the dynamic range of a signal so that quieter bits sound louder. It automatically rides the gain. It increases the volume when things get quiet and lowers the peaks down when they get loud. The goal of the compressor is to achieve a more uniform and consistent signal. Don't get too wild with compressor settings at the input recording stage. Unless thats the effect your looking for. You want the recorded vocal to sound natural, where the compressor just makes it an overall more useful signal.

Once you have your tracks recorded on your computer. The idea is to get the tracks uniform, so you don't have instruments or vocals suddenly dropping out because they went soft on you or became to loud with peaks. The thing is to make all low volume passages have a strong enough level where they won't bring in noise later on and stop the loud peaks from overloading.

The Noise floor threshold, eliminates all of the signal when it dips below the threshold, which is set from say between -50db to -10db, Around -30db is good. If the gate is set too high, then the attack of the vocalists words may be cut off or come in too abruptly.

The Rate, fades out the signal as the gate comes on. This is effective to prevent the gate from chopping off the ends of words. Usually a rate of 1-1.5 sec is good.

The Threshold, is the level at which the compressor kicks in. If you set the threshold to -10, it will leave all of the signal under -10 alone. When the signal exceeds -10 then it starts compressing at the ratio. -10 is an excellent place to start. Although the threshold seems like it is a volume control, it is not. It is telling the compressor at what level compression takes over the signal.

Setting the Ratio: 2:1 is probably the most common setting for a compressor recording or playing back nearly anything. A great starting point. What this means, simply, is that it takes 2 decibels of sound energy to raise the output meter by 1db. You can read the 1st number as the db IN and the second as the db OUT. Again, 2db IN equals 1 db OUT. With 2:1 you simply divide by two.

Setting Attack and Release: These settings can be tricky as they can delay the effect of compression on the attack and make is hold on a bit too long on release if not set properly. Which takes quite a bit of experimentation, you use the fastest attack and enough of a release so the vocal is not boosted as the word trails off.

Setting the output: This is the final adjustment as the signal leaves the compressor. It's sometimes called the make-up gain. They call it that because compression often lowers the overall signal and you may need to boost it back up. Basically you want to optimize this so it does not ever go over 0db. You should see a consistent level on the input meters regardless of how loud the vocalist is singing.

joe

Very thorough Joe thanks.

kido

Your welcome.

I use rack mounted compressors on the preamp side of my guitar. Here's the compressor setting for a preset I call Distortion 2. The Drive..100%, Output..100%, Slope..2:1, Attack..2ms, Release..200ms, then the signal moves to an Expander, Distortion, Exciter, Equalizer, AES (acoustic environment simulator), programed level, another Equalizer, Power amps.

Here's one I call Dream that has a different settings. Drive..78%, Output..94%, Slope..4:1, Attack..4ms, Release..750ms. My rack equipment is connected to a laptop with software that will allow me to adjust the processors in real time. Mostly its spending time experimenting to see what you like and how it sounds. There are few setting like I posted before thats a good starting point to work from.

Acoustic guitars can sound pretty impressive using a compressor on them, like the Boston albums.

Joe