Compression when recording

Discussion in 'Recording Gear and Equipment [BG]' started by parrott, Jan 29, 2003.

  1. I need help here.

    I'm learning about recording at college, we've done stuff on mics, on desk settings, and lots more, and now we're onto Compression.

    Thing is, I'm missing why it's done. I've recorded something so far, without compression, and they've sounded good. Yet my teacher was talking as if applying some compression is essential.

    I'm not even sure what compression really does.

    Why is compression used when recording?
    What is it used for?
    What happens if you don't use it?

    Basically, can someone explain compression and its uses from the ground up? Because I am really clueless on the issue.

    Thanks in advance.
  2. PollyBass

    PollyBass ******

    Jun 25, 2001
    Shreveport, LA
    I can tell you a little. Compression, in effect, makes loud quieter, and quieter louder. making whatever your recording sound more "Even". the more you use, the less dynamic the sound is. I use very little in my bands recordings, but if your going for an even, fat sound across the bored, it's very handy.

    A side note, todays cd's are COMPRESSED TO HELL.


    It doesnt have to be just bass, it can be and is used with vocals, guitar, and the finished product.
  3. moley


    Sep 5, 2002
    Hampshire, UK
    Polly is essentially right there.

    A compressor is something that is built into mixing desks, some amps, and also comes in the form of a box you can put audio signal through.

    What it does is, it monitors the volume level of the sound, and if it exceeds a certain level, it brings the level down, and then lets it back up again as the signal gets quieter again. Compressors let you choose what the compression threshold is (the volume level at which the compressor starts reducing the level) - as well as the attack time (how quickly it reduces the level in response to the level going above the threshold), and the release time (how long it takes to bring the level back to normal).

    The result of this is that the loudest parts of the performance are made quieter. This means that the peak level (the volume level at the loudest point) is lower. Since the loudest part is now a bit quieter - you can bring the level of the whole performance up, without causing distortion. If you didn't compress the sound, the volume level of the whole performance could only be *so* loud without causing distortion at the loudest parts. Since, with compression, the loudest parts are now quieter, you can bring the whole level up, making the whole performance louder, without distortion.

    As such, compressors have an output gain control, using which you can set how much louder you want to bring the overall level up by, after compression.

    The result of this is that you get a more even sounding performance (as, like Polly said, the loud bits are quieter, and the quiet bits are louder) - as well as a higher overall level.

    In recording, this really is standard, it's done all the time. It is very often done on individual tracks (e.g. the vocals, the bass etc.) to even out the level on that indivual track - and it is also done on the whole mix. If you recorded vocals, and didn't apply compression in the mix, you'd quite possibly find the vocals would probably be pretty uneven - the quietest bits would be too quiet and get lost, and the loudest bits would be too loud and stick out. So compression takes care of this, making the overall performance at a reasonable level. The trick is, to use just enough compression to achieve this, without going overboard and removing all the natural dynamics from the performance. You still wanna have loud bits and quiet bits, but you want the quiet bits to be loud enough in the mix that they don't get lost, and you don't want the loud bits to stick out too much. As I said, this is done on vocals, and bass, and to some extent on most other instruments, and really does help to control the evenness of sound.

    Compression (or peak limiting - a more severe form of compression) is also used on the final mix, too. Because you're listening to many tracks mixed together, 'random peaks' can be produced - where 2 or more tracks happen to have peaks at the same point, making the overall level louder at that point. Compression is used here to even out the overall level, reducing these peaks, which means you can make the overall mix louder.

    However, nowadays in the pop music industry, there tends to be pressure from the bosses to make CDs as loud as possible - so they hit you right between the eyes when you put them on, and grab your attention. To this end, there can be pressure on the producers to compress pop songs as much as possible, to get them as loud as possible. This can (and has) led to over-compression. This is where the sound has been compressed so much that there's very little dynamic range - and the whole recording sounds very loud. The excessive compression has made the loud bits so much quieter than they were, that they're not so much louder than the quieter bits, which are now very loud. So the overall thing sounds very loud, and in your face. IMHO this is not pleasant. I think it is much better to leave a natural dynamic range and not go too far with compression. But it is something I think producers of pop records don't really want to do (it makes for kinda unmusical results) but tend to be pressured into by label bosses wanting the music to have as much impact as possible.

    So basically - compression really is a good thing, but it can be overused, with not-so-good results.

    Does that help?
  4. VERY BASICALLY...Compression reduces dynamic range. You can decide when the compression will begin to affect a note and the duration of the compression.

    It will make the loudest notes a bit less loud.
    lt will make the softest notes a bit louder.
    It can affect the attack and decay of a note.
    It can appear to add sustain particularly to guitar and bass.
  5. dave64o

    dave64o Talkbass Top 10 all time lowest talent/gear ratio! Gold Supporting Member

    Jun 15, 2000
    Southern NJ
    Here's a linkg to a web site owned by one ofthe regulars at It was written by one of the pros that also regularly posts there. The thing I like about his article is that it contains sound clips to explain the concepts he writes about. He also references another worthwhile article written by another pro who hangs out there as well.

    Moshe Wohl's Article on Compression
  6. Petebass


    Dec 22, 2002
    QLD Australia
    Like any effect it can be over-used. But I can't tell you how namy kick-ass vocal takes I've lost because the singer clipped the input (distorted) and I didn't have a compressor to squash the peaky signal.

    Definitely use it on vocals, everything else is case by case.
  7. Its amazing how much difference a few hours studio time can make.

    I was in there at the weekend with my band, and on Monday for class, and after experimenting with it a bit on a few tracks (mostly vocals, bass and guitar overdubs) it's really making sense to me.

    I'm still not sure about using it to really quieten down loud parts of a song, but using it to lessen pops and stray peaks has made my demo sound soooo much better.

    Next question; how to use it on drums? Surely you can't really, because to catch the actual sound of the drums, you'd need a really fast attack, which (on other instruments) kills some of the treble. And what about release? Would have have that really slow, say on the cymbols, to "smooth" them?

    My teacher mentioned this, he's gonna show us how next week, I just want some more information....
  8. moley


    Sep 5, 2002
    Hampshire, UK
    Yes, you'll definitely want a quick attack time (like 0 :)) for drums. But the thing is, you won't be applying compression (well, not much) to the entire mix. You apply compression to the individual tracks. So for the drum tracks you'll use a compression setting with a fast attack time, and for other tracks you'll have different attack/release times. So your 0 attack time for the drums doesn't affect any of the other instruments.

    The standard thing would be to apply compression to individual tracks as you see fit - and then peak limit the entire mix.
  9. I wasn't worrying about applying it to the whole mix, I tried that with my teacher and it worked fine, so I'm fine with that.
    I also get that one setting will not work for everything - that was one fo the first things my teacher demonstated.
    And I have already used it on individual tracks - bass and some high guitar stuff.

    The problem with wanting to do all the compression in the final mix in the studio I'm using is that there's only 4 compressers, all rack-mounted ones, a Drawmer D-something and a DBX (I think). So if I'm using two for the overall song in the final mixdown, then I've only got two others to use, most likely for bass or voice.

    But with the drums - set the attack to 0? Surely that'll take off a lot of the treble of the drums, esprecially the snare, and the cymbols? And what about the release? You'd want the pretty fast for the snare, to let ghost notes and the rattling of the snares through, yeah? But on the cymbols, you'd want it pretty slow, wouldn't you?

    Gah, it's getting more confusing now that I understand the basics.
  10. moley


    Sep 5, 2002
    Hampshire, UK
    I'm no expert at drum recording, but I'm not aware of a 0 attack time particularly taking off the treble. And yeah, a slow release time for cymbals might be a good plan.

    But, ask your teacher. Being that he's teaching this stuff, I'm sure he knows plenty more than me about this :)
  11. IM(limited)E, having a 0 attack time really kills the treble, it's most noticable on things like vocals, but some of a drum kit is quite trebley....

    Problem is, I only see him for two hours a week (first thing on Monday.... gah) and there's between 6 and 10 people in the class.
    We spend most of our time doing the practical, hands-on stuff, there's very little time for the theory behind it.

    That's why this place is so useful.