Need help in understanding 'compressors'

[ankursamtaney]

Hi,
Am looking to understand what a compressor is, what it does, and what difference it makes to a recording.
I record using some rather cheap equipment.. run a Behringer B2-Pro mic into my Line6 Tone Port sound interface, which runs into my Dell notebook.
I don't have any dedicated (hardware) preamps, compressors etc. However, what i do have is the 'gearbox' software that came with the sound interface, which has plug-ins of amps, preamps, effects, etc.
When recording voice / acoustic guitar, i go with the 'Basic Vocal Tone' preset in order for the initial recording to be dry and flat. Under the EQ and the amp / preamp selection area, there's a 'compressor' which has two knobs - 1 for Gain and the other for Threshold. I know what gain means, but what's threshold? When i lower it, the volume and the noise seem to increase ...

Technically, what is the whole 'compressor' affair meant for?

I usually leave it untouched, coz it gives me quality that's acceptable to my amateur ear (with respect to judging recordings), but what can i do with it to improve what I'm recording?


Thanks,
ANkur.

[Edu Cesar]

Hi there! I´m not very experienced in audio recording, but I´ll try to help you with this...

The compressor is one of the most used tools in audio recording. It works (basicly) compressing the louder parts of the audio. The result is less difference between the louder and quieter parts of the track (in other words, less dynamic range).

The threshold knob you see sets at what level the compressor will start to work. So, whenever some part of the audio reaches that level, it get´s compressed.
The gain knob will amplify the whole audio (after compressed), so you can adjust the level of the track (compensating the gain reduction caused by de compressor).

This is a simple explanation about compressor. There are some other parameters like attack and ratio that you´ll see in more sophisticated compressors. I suggest you play with the compressor and try different settings to hear the difference. Then go to google (or even at this forum) and search for more detailed information.

I hope I was able help you (and sorry for any stupid English errors).

[MatsonMusicBox]

I would add that compression and the related limiting (compression with very high compression ratio essentially) and the also related multi-band limiting are often used for 3 things in my experience.

1) on input to control peaks - a vocalist screaming, a loud drum crack, to smooth out overall level in very dynamic input. I suppose 1a) would be to do the same thing after the fact on a track.

2) To get a "compressed" sound. It does get a very distinct sound at certain levels, and sometimes some of this is deisirable. I often compress my Drum sub-buss to get a nice slightly-to mid level compressed sound on them - nice for a lot of rock drums.

3) Multi-band limiting in particular - used as a mastering effect to get final product up to commercial CD levels.

Many other common uses - but these are the main ones I use and typically see.

[Ethan Winer]

Originally Posted by ankursamtaney

Am looking to understand what a compressor is, what it does, and what difference it makes to a recording.

Here you go, short and right to the point:

Compressors and Limiters

--Ethan

[dwood]

Originally Posted by Ethan Winer

Here you go, short and right to the point:

Compressors and Limiters

--Ethan

Thanks Ethan, that's an awesome description. Other compression descriptions have always confused me, but that was to the point.

I've bookmarked your site for the other articles as well. :-)

David

[ankursamtaney]

Many thanks, all you guys!
Ethan - gotta admit, a neat explanatory article you got there!

Have seen all these responses while at work (not in a studio, but in a conventional office! haha).. will be a while before i can play around and try out the stuff you guys have mentioned. However, have a follow-up question to your responses, and in response to Ethan's article too---

So, the compressor compresses sounds that are louder than the threshold / ceiling. In this case, am i supposed to route my mic through the compressor when recording, to limit / compress any sounds / notes that might clip? or the can the compressor also be used in a way to act on a track AFTER it's recorded? And if both can be done.. what's an 'ideal' method and why?

I know (or atleast think) that it's best to record flat and dry, and then apply any EQ or effects like reverb / delay to the track AFTER it's recorded. How should i go about with the compression bit?

Thanks,
Ankur.

[MatsonMusicBox]

Well - if you clip coming in (record the clip) - compressing at that point is not going to get rid of the clip.

You will need an analog compressor before it gets to your interface to level out a vocal line or whatever. My mic chain for example runs from my mic to my preamp to a dbx compressor and then into my interface.

You can certainly apply it after the fact to a track or buss - that can smooth out a level, add it as an effect and help keep the buss from clipping, but it won't help the track itslef if it is already clipped.

HTH!

[brandondrury]

this case, am i supposed to route my mic through the compressor when recording, to limit / compress any sounds / notes that might clip?

There is no "supposed to". You can. It took 7 years of recording before I purchased a hardware compressor. I use it for the color it gives. If I need clean compression I still use plugins.

Clipping is caused by poor gain structure. A hardware compressor will allow you to get a higher average level into the computer, but I'm not sure what good that is in and of itself.

the can the compressor also be used in a way to act on a track AFTER it's recorded?

I do most of my compression during mixing, but with hardware you can do it during tracking too.

And if both can be done.. what's an 'ideal' method and why?

The ideal method is whatever sounds the best. Why? Because that is what the client pays for and what makes the music most effective.

The ONLY reason I see to compress on the way in is to take advantage of specific character that can really only be achieved with hardware. Some compressors just have a sound to them. You'll read about big boys who use the LA-2A or a Tubetech or 1176 fairly subtly because they like the added character.

Brandon

[ankursamtaney]

Thanks a ton for the advice and insights.
Now, I guess I only need to play around and see what i get with each of the permutations. Thankfully, now i know what exactly i should be aiming at when i mess around with each of the knobs or parameters!
Thanks again, guys!

[ankursamtaney]

Umm.. sorry about re-opening this chapter! This time's its not about compressors, but about exactly the opposite.

What do you all do when you want to maintain uniformity in level on the downside? That is, like a compressor helps to prevent overshooting the 'ceiling', anything you can recommend that might help in always remaining above the 'floor'?

I record on old-fashioned Acid Pro 4.0, and usually adjust levels manually at different parts of each track in order to maintain uniformity. I'm sure there'd be automated (and hence, faster and more precise) ways of doing something similar. Any plugins (like the compressor) i could use?

I guess this is really basic stuff that i'm dragging beyond a point of boredom for many of you - but for whatever it's worth, am really grateful for all the advise I'm getting!

Thanks,
Ankur.