Hello everybody! I took a look at SuperSweets Reason FAQ today. Great page!
It looks like there are still a few open questions about compression, so I decided to make another experiment and post my findings here. What came out in the end is an extremely simple explanation. First of all, I converted the experiment into a .rps that you can download here:
Here's a primer how you can grasp compression very quickly: Play the rps and look at the LEDs on the first Mixer at Track 1 and you'll see that the sound gets 1 LED louder every second. Then turn the compressor from "Bypass" to "On" and set the following settings:
Ratio: 127 (16:1, the maximum)
Before you play the song again, remember that the signal that goes into the compressor is still the same, but what comes out now is the processed signal. Play it. The fact that the outcoming signal is now louder is not important. The really special thing is that as soon as the signal reaches 3 yellow LEDs, it stays there. The input signal gets louder, but the output signal stays about the same. This is compression (D'oh!)
What do the knobs do?
THRESH defines how loud the incoming signal has to be that the compression kicks in. Here's a handy table:
01 . . . . . 0
02 . . . . . 0
03 . . . . . 0
04 . . . . . 0
05 . . . . . 8
06 . . . . . 20
07 . . . . . 30
08 . . . . . 40
09 . . . . . 50
10 . . . . . 60
11 . . . . . 60
12 . . . . . 70
13 . . . . . 80
14 . . . . . 90
15 . . . . . 100
16 . . . . . 110
17 . . . . . 120
18 . . . . . 127
19 . . . . . 127
20 . . . . . 127
RATIO: You may have noticed in our experiment that the volume stays at 3 yellow LEDs for some time, but then still gets louder. This is because the Reason compressor doesn't limit the volume absolutely. What it does is rather: After the threshhold point, an additional increase in input volume result in a very small increase in output volume.
With the RATIO knob, you can decide how steeply this increase happens. The increase in our example is the flattest setting (16:1). The steepest setting on the other side is when an certain increase in input volume result in the same increase in output volume (1:1), which is the same thing as using no compression at all.
So what we experience as "compression" is the fact that louder parts of your music are turned down and closer to the soft parts, resulting in a more uniform loudness.
For all my experiments, I've set the parameters "ATTACK" and "RELEASE" to the minimum, so that the changes in amplification and compression happen immediately. This can be changed for certain effects. Let's say that any change in the input can only be of two forms:
1 - the input gets louder
2 - the input gets softer
ATTACK and RELEASE can control how the device reacts in these two cases. ATTACK controls the case of "input getting louder", and RELEASE controls the case of "input getting softer"
ATTACK: When you have a signal of average loudness and suddenly it gets louder, the device would normaly just cut back the signal according to your settings. But maybe you want to preserve a bit of the "punch" in the sudden increase of volume. You want that the signal to be louder for a short moment before it gets back to your specified settings. With the ATTACK parameter, you can decide how long the old compression of the softer part will still be applied until it gets to the new setting. The range of this knob is between 0 and about 0.3 seconds. Most common usage: preserve the "punch" of drums.
RELEASE: After the loud signal everything goes back to average. You want the listener to hear the decrease in loudness, so the old setting for the loud part should still apply for a short time, making the softer part even softer. The range for this know is between 0 and about 3 seconds.
I hope this is of use for some people