BOB DIFAZIO: Hey. Welcome back to Gearwire.Com. Bob DiFazio here, ready to show you another piece of gear, and this piece of gear here is the Pro VLA or V-L-A, whatever you want to call it, "Pro V-L-A" I think would probably be better, and it's made by ART, and it is a two-channel compression box.

And, what I've got right now hooked up is my bass guitar through a preamp which I had just walked you through in previous video, so you can go look up that video, which is for the PreSonus ADL 600, and that preamp is being directly feda into and out of the first channel of this compressor.

Now, what I'd like to do is take a second to make sure it's well understood what in fact a compressor is. A compressor is an automatic attenuation device. That means it is an automatic turner-downer. So, pretend the compressor is my hand, and my hand is on a fader. When I get louder, the compressor turns me down, and then when I stop getting louder it turns me back up again. So, a compressor turns down the loud parts to match the softer parts to achieve dynamic unity so the sound remains at a consistent dynamic, or at least a more consistent dynamic than it did when it came into the box.

So, why compress things? Compress things because people get dynamically out of hand. Okay, here I am playing my bass line [BOB PLAYS A BASS LINE] and then [BOB PLAYS LOUDER], alright, and get out of hand, and the producer says, "That's ridiculous. Can you please turn that down?" Well, am I supposed to sit there with my hand on the fader? Every single time the bass player gets too loud, I'm supposed to turn him down? Well, maybe I have to worry about the snare drum and maybe I have to worry about all these other things. So, a compressor is an automatic fader that you can program to turn your sound down when it gets too loud. So, let's talk about how the compressor is aware of what is too loud, how much it should turn it down, how fast it should turn down the signal, and how fast the signal should return to the level that it was at before the attenuation happened. Got that? Alright.

So, is this the most flexible compressor that there's ever been? No. But does it have the basics that every compressor should have? Yes. Let's start with the most important knob that a single compressor can ever have which is called the threshold. Be advised when I am turning knobs on a compressor, I am not looking at the settings. I don't particularly care what number this knob should happen to fall on. Because I'm using my ears and not numbers, I just need to know what does this knob do, and then after that I can use my ears, not some recipe book that you found online that tells you where the threshold's should be when you're compressing XYZ sound. That's not the good way to go because every sound is different like a little snowflake, alright?

So, the threshold is the point at which compression will begin, and by compression I mean attenuation. When will the compressor do what it does which is turn the signal down. If I have the threshold all the way full right, maximum, that means that I will never get gain reduction, which is attenuation. So, this meter here will show me if I'm achieving any sort of compression. Zero decibels of compression means obviously no change, then I've got -1, -2, -4, -6, -10, -15 decibels of attenuation. So, I'm going to play my bass guitar into this guy. You can see that the output is quite around zero and no matter how hard I play or soft I play, I get no gain reduction whatsoever, nothing happens pretty much no matter what. As I bring the threshold back, eventually I'm going to get to a point where I start to trigger the compression, and this means -- follow me on this -- when I set this threshold, what does that mean? It means this: Any signals that rise above this threshold will be attenuated, so this is the dividing line between not soft or not loud and loud. So, how does the compressor know what is too loud and when should I turn down the signal? The threshold tells this internal circuit anything above this line is too loud; turn that down. Anything below this line is fine; don't mess with it.

So, what I'm going to do is I'm going to play soft, you see no gain reduction. Then I'm going to play loud, and there we've got a lot of gain. If I move this knob so that it's full right, it doesn't matter how loud you play because this device is telling me or I'm telling this device that everything above the threshold should be reduced but the threshold is at its full so nothing can be above the threshold so nothing will happen. So, if your threshold is all the way up, don't expect to hear any difference, okay? So, we'll bring the threshold down to some reasonable point where I start seeing compression or hearing compression. Where is that point you ask? Your ears are supposed to tell you. That's what engineering is all about. It's not about recipes, alright?