What exactly does a compressor do?

Gear
1

I know this might seem like a strange/silly question to most, but I am indeed unsure what exactly a compressor does! And by “does” I mean what it does to the tone, not so much the technology how it does what it does.

I have little problem imagining what a distortion effect does, or even a chorus and a flanger, heck even a noise gate and a fuzz-wah… But, even though it is one of the most common effects, I am still a bit unsure what exactly a compressor does.

So, what does it do to the tone and how is this beneficial (i.e., how do I use it best)?

Thanks to the very knowledgeable gear-heads in here :smile: !

7 Likes
2

Thank you for asking that. I’ve been wondering myself, but was too bashful to ask.

3 Likes
3

There is a somewhat complex physics answer to this question, based on sound wave formats and the audible range we can hear as humans. But in the most simple of explanations here is what it does:

It basically adjust the loudest part of the audio signal and lowers it, and the quietest portion and boosts it. It generates an end result of a more smooth overall signal.

Remember sound is represented as wave form, and in each wave there is a high and a low point. So clipping off a section of the highest point, and the lowest point, your left with the nice solid piece in the middle, balancing out the sound.

I found a simple image of a soundwave, shown below, once you add compression, you see where it strips off the upper and lower portions, basically ‘compressing’ the wave in a more uniform shape, resulting in less high, highs, and low lows.

Hope this helps… I am no expert but hopefully you get the idea of what it does. Where you see this commonly is in podcasts, since people speaking into mics all speak at different tones/volumes, utilizing compression on the mic in a mixer board, will help unify the output to a more stable level for consistent volume.

image

7 Likes
4

Good explanation. I’d say that in terms of sound it basically evens a sound out such that sharp amplitude peaks do not overwhelm lower amplitude sounds. A good example would be slap; there’s a really sharp transient sound when you slap the string, and if that was what you had to adjust your volume to, the ringing of the note after the initial slap would be too quiet. Compression lowers the peak amplitude and raises the part that wasn’t a sharp spike to be a more even overall sound.

6 Likes
5

Thanks, @method72 and @howard - that is kind of what I thought it would do, but wasn’t quite sure. In terms of practical applicability then: is it most important for slap/pop or also for other “techniques” that might cause sharp spikes?? Fingernail scratches perhaps?
And: can you overdo it? What happens if you compress too much?

2 Likes
6

Compressing too much loses tone.

3 Likes
7

too much compression sounds like the tone is crushed, with no dynamic and a very low signal amplitude.

you can use a compressor for everything with a bass. the compressor is the only pedal I always leave turned on (with a very low setting). it makes the sound fuller and more compact.

Also we must say that compression is a pretty subbtle effect, it does not really change the tone but only its dynamics.

5 Likes
8

Here is how it was explained to me…
It magnifies notes you play too quietly and dampens notes you play too loud to smooth out your playing to make you sound more consistent than you actually play.

Is this an accurate way of explaining it?

4 Likes
9

I think that’s one way to describe it, yeah. But I’d say that unless it is cranked up too high, compression is much more about tone in individual notes than it is about making all the notes sound even. In other words, unless you’re using way too much compression, it’s still possible to play notes dynamically and with varying loudness.

What the compressor does is squish amplitudes that are out of range into the range you have it set at, and also lift quieter tones in a note, to even out its attack, sustain and decay.

4 Likes
10

Unfortunately, I think I’m going to have to hear it to really understand. Does anybody want to post some examples?

2 Likes
11

Some good A/B sound comparison in this vid:

4 Likes
12

This reminds me, when I bought my preamp/DI I was seriously considering the TC SpectraDrive instead:

Very clean preamp, little tone coloring itself, with a SpectraComp and TubeDrive built in.

3 Likes
13

This was very helpful, @howard! Thanks! I have now a much better idea of what a compressor can do, and how important it really is!

PS: funny how the subtitle generator is struggling both with the lingo and his Denglish (German-English) :grin:

3 Likes
14

Glen Fricker has a great video on compression that delves into the details. This video is fine, but if you watch his other stuff, be warned that he’s pretty vulgar and likes to make fun of bassists.

How To Use A Compressor–Click Here

4 Likes
15

Great, thanks!

I know the video “just” covers the basics, but I am already almost there where I have to quote Gary Larsen:
image
:grin:

9 Likes
16

My pleasure! I haven’t done it yet but my plan is to put together an effects chain on my B3n that is just:

Compressor
Bass Overdrive
Chorus
Cab sim

and then put the thing in stompbox mode so I can stomp them on and off individually, and have basically all I need.

The only problem is I haven’t found an overdrive setting I like as much as analog overdrives. I can use the overdrive on my Ampeg preamp but it is more about dirt than real drive. I might buy a Behringer BDI-21 just for its drive, because for $35 it sounds great, but I am a little leery of throwing another preamp in there.

Right now my signal path is:

Yamaha TRBX604 -> Zoom B3n -> Ampeg SCR-DI -> Zoom DAI -> Audacity/GarageBand

so in active mode on my bass that ends up being four preamps already (though the DAI is completely neutral.)

3 Likes
17

You mentioned something almost in passing in one of the recent threads, @howard, and that caught my attention (obviously, because I hadn’t given it much thought before).

Can’t find the citation, so I’ll paraphrase: the challenge about taking “your sound” with you when you get new gear. (But, in fact, it might be a more universal challenge…)

Scenario 1: I play at home through my Rumble Studio 40, use oodles of time to get to know all the knobs, presets, effects, amp modelings etc and eventually arrive at something that I find pleasing, and thus declare this particular combination of settings and effects “my sound”.

Scenario 2: I want to try and test a new bass in a shop. Do I bring my Studio 40 as a pre-amp/effects box?? Hardly… So, like you said, @howard, you’d need a pedalboard or multi-effect for this purpose, right!? (In order to bring “your sound” with you and compare how the new bass sounds in this context). No?

Scenario 3: I go to a gig/rehearsal and there is an amp/cabinet there to use. Again, how do I bring “my sound” along?? I guess the Studio 40 is not an option, but again my own pedalboard or multieffect!?

Scenario 4: at a larger gig, there is a PA. What do I do here to bring along and reproduce “my sound”??

Scenario 5: I (at some point in the future) retire my Studio 40 and get a different amp - now what? (That was @howard’s original scenario).

So, it begins to dawn on me that despite my fancy modeling amp, I still need other hardware to make my sound portable. Or??

3 Likes
18

Yeah, this is my thinking. I am actually ampless at the moment - no amp at all. Don’t really miss it TBH. I have some nice studio monitor headphones and three preamps with headphone outs in my signal path.

Most of my gear would fit in a gig bag too. That part is nice. Basically I have two modular components that matter, that I can use with any amp or PA.

@terb is doing something similar with his pedalboard.

Of the scenarios you list, 1/5 and 4 are actually fine. With 1/5 you would just note the effects you use and recreate them with others later (at added expense, later.)

With 4 you would simply have a nice 40W stage monitor with the main volume coming from the house PA. That’s fine. Except you would need to cart your amp to the gig. You might even have an easier time than me because the sound guy might get horrified by the bass guy bringing things with lots of knobs, whereas you would just have an amp :slight_smile:

3 Likes
19

@howard and @joergkutter, after reading through this thread multiple times, I find myself lost in a maze of rabbit holes. So let me throw a shovel in here and help to dig it a little deeper:

Unless you are recording in a well-designed studio, don’t forget to take the acoustics of the venue you are gigging at into account. . . .

That could affect the settings on ALL your equipment. :thinking:

3 Likes
20

Yeah, I guess we can leave that to the sound guy to mess up :scream:

3 Likes